TWI868493B - X-ray fluorescence imaging device and method thereof - Google Patents

Abstract

Apparatuses and methods of X-ray fluorescence (XRF) imaging use a radiation source to stimulate XRF from only a slice of an object by projecting a radiation beam through only the slice. An X-ray detector stack having a plurality of mutually parallel semiconductor X-ray detectors is provided. A collimator having a plurality of parallel collimator plates is positioned between the object and the X-ray detector stack. The radiation beam is not parallel to the collimator plates. Neighboring pairs of the collimator plates allow XRF from only respective portions of the slice to reach respective subsets of the pixels. For each of the respective pixel subsets the X-ray detector sums signals generated in the pixel or pixels of the respective subset. A pixel pitch of the X-ray detectors in the X-ray detector stack is an integer multiple of a plate pitch of the collimator.

Description

X-ray fluorescence imaging device and method thereof

The present invention relates to a detector suitable for X-ray fluorescence, and in particular to an X-ray fluorescence imaging device and method thereof.

X-ray fluorescence (XRF) is a characteristic fluorescent X-ray emitted from a material that has been excited, for example by exposure to high-energy X-rays or gamma rays. If an atom is exposed to X-rays or gamma rays with a photon energy greater than the electron's ionization potential, an electron in the atom's inner orbit may be ejected, leaving a vacancy in the inner orbit. When an electron in the atom's outer orbit relaxes to fill the vacancy in the inner orbit, X-rays (fluorescent X-rays or secondary X-rays) are emitted. The photon energy of the emitted X-ray is equal to the energy difference between the outer and inner orbit electrons.

For a given atom, there are a finite number of possible relaxations. When an electron on the L orbit relaxes to fill a vacancy on the K orbit (L→K), as shown in Figure 1A, the fluorescent X-ray is called Kα. The fluorescent X-ray produced by M→K relaxation is called Kβ. The fluorescent X-ray produced by M→K relaxation, as shown in Figure 1B, is called Lα, and so on.

Analyzing a fluorescent X-ray spectrum allows the identification of the elements in a sample, as each element has a characteristic energy track. Fluorescent X-rays can be analyzed by classifying the energy of the photons (energy dispersive analysis) or by separating the wavelengths of the fluorescent X-rays (wavelength dispersive analysis). The intensity of each characteristic energy peak is directly related to the amount of each element in the sample.

Ratiometric counters or various types of solid-state detectors (PIN diodes, Si(Li), Ge(Li), Silicon Drift Detectors SDD) can be used for energy dispersive analysis. These detectors are based on the same principle: an incident X-ray photon ionizes a large number of detector atoms, where the number of charge carriers generated is proportional to the energy of the incident X-ray photon. The charge carriers are collected and counted to determine the energy of the incident X-ray photon, and the process repeats itself for the next incident X-ray photon. After many X-ray photons have been detected, a spectrum can be compiled by counting the number of X-ray photons as a function of their energy. These detectors are limited in speed because the charge carriers generated by one incident X-ray photon must be collected before the next incident X-ray hits the detector.

Wavelength dispersion analysis typically uses photomultiplier tubes. X-ray photons of a single wavelength are selected from the incident X-rays by a monochromator and passed into the photomultiplier tube. The photomultiplier tube counts each X-ray photon as it passes through. The counter is a chamber containing a gas that can be ionized by the X-ray photons. The central electrode is charged (usually) at +1700V relative to the conduction chamber walls, and each X-ray photon triggers a pulsed cascade current through the field. The signal is amplified and converted into an accumulated digital count. These counts are used to determine the intensity of the selected single wavelength of X-rays.

A system of one or more computers may be configured to perform a specific operation or action by installing software, firmware, hardware, or a combination thereof on the system, which in operation causes the system to perform the action. One or more computer programs may be configured to perform a specific operation or action by including instructions that, when executed by a data processing device, cause the device to perform the action. A general aspect includes an apparatus. The apparatus further includes a radiation source, which is configured to excite X-ray fluorescence only from a slice of an object by projecting a radiation beam only through the slice. The apparatus further includes an X-ray detector having a plurality of pixels. The device also includes a collimator having a plurality of parallel collimator plates, wherein the radiation beam is not parallel to the collimator plates. The device also includes aspects in which pairs of adjacent collimator plates allow only fluorescent X-rays from corresponding portions of the slice to reach corresponding subsets of the pixels. The device also includes aspects in which, for each of the corresponding subsets of pixels, the X-ray detector is configured to sum the signals generated in one or more pixels in the corresponding subset. Other embodiments of these aspects include corresponding computer systems, devices, and computer programs recorded on one or more computer storage devices, each of which is configured to perform the actions of the method.

Implementations may include one or more of the following features. In the device, the slice has a lateral dimension that is narrower than the object. The slice has a longitudinal dimension that is taller than or equal to the object. The slice has a height that is shorter than the object. The radiation beam is an X-ray beam or a gamma ray beam. The parallel collimator plates are uniformly spaced, the spacing of the parallel collimator plates is characterized by a plate spacing, and the pixels are uniformly spaced, the spacing of the pixels is characterized by a pixel spacing that is an integer multiple of the plate spacing. Each of the multiple pixels is configured to count the number of X-ray photons incident thereon. Each pixel is also configured to count the number of X-ray photons incident thereon whose energy falls into multiple intervals over a period of time; the device is configured to add the number of X-ray photons in each interval of the same energy range. The device may include a sample holder for holding the object. The sample holder is substantially transparent to the radiation beam. The sample holder is substantially transparent to XRF. The parallel collimator plates include at least one element that absorbs X-rays. The parallel collimator plates include at least one element from the group that may include lead, tungsten, and gold. The collimator also includes a filler that fills all or part of at least one gap between the parallel collimator plates, and the filler is substantially transparent to X-rays. Implementations of the described technology may include hardware, methods or processes, or computer software on a computer-accessible medium.

A general aspect includes a method of X-ray fluorescence imaging. The X-ray fluorescence imaging method also includes providing an X-ray detector having a plurality of pixels. The method also includes projecting a radiation beam through a slice of an object to excite XRF from the slice. The method also includes allowing XRF from only a corresponding portion of the slice to reach a corresponding subset of the pixels by providing a collimator having a plurality of parallel plates that are not parallel to the radiation beam between the object and the X-ray detector, wherein each pixel of each subset of pixels is aligned to receive XRF only between a pair of adjacent parallel plates. The method also includes counting the number of XRF photons incident on each pixel of the X-ray detector. Other embodiments of this aspect include corresponding computer systems, devices, and computer programs recorded on one or more computer storage devices, each of which is configured to perform the actions of the method.

Implementations may include one or more of the following features. The method may include counting the number of XRF photons incident on each pixel whose energy falls into multiple intervals over a period of time; and adding the number of XRF photons in each interval of the same energy range. The method may include resolving an image of the object in a first direction orthogonal to a major axis of the radiation beam based on the size of the slice in the first direction; and resolving the image of the object in a second direction orthogonal to the major axis and orthogonal to the first direction based on the size of the gap between pairs of adjacent parallel plates. The method may include resolving the image of the object in a third direction orthogonal to the major axis and orthogonal to the first direction and the second direction based on the size of the slice in the third direction. The method may include: projecting the radiation beam through a first slice of the object; counting the number of XRF photons incident on each pixel of the X-ray detector from the first slice; projecting the radiation beam through a second slice different from the first slice; and counting the number of XRF photons incident on each pixel of the X-ray detector from the second slice. The object is stationary and the radiation beam is moving. The radiation beam is stationary and the object is moving. The method may include: moving the radiation beam along a first scanning direction from a first position where the radiation beam is projected through the first slice to a second position where the radiation beam is projected through the second slice. The moving the radiation beam includes translating the radiation beam. The moving the radiation beam includes rotating the radiation beam. Implementations of the described techniques may include hardware, methods or processes, or computer software on a computer-accessible medium.

According to an embodiment, the detector includes a plurality of pixels, each pixel being configured to count the number of X-ray photons incident thereon whose energy falls within a plurality of intervals over a period of time; and wherein the detector is configured to add the number of X-ray photons in each interval of the same energy range counted by all the pixels.

According to an embodiment, the detector is also configured to interpret the summed quantity as a spectrum of the X-ray photons incident on the detector.

According to an embodiment, the plurality of pixels are arranged in an array.

According to an embodiment, the pixels are configured to count the number of X-ray photons within the same time period.

According to an embodiment, each of the pixels includes an analog-to-digital converter (ADC) configured to digitize an analog signal representing the energy of an incident X-ray photon into a digital signal.

According to an embodiment, the pixels are configured to operate in parallel.

According to an embodiment, each of the pixels is configured to measure its dark current.

According to an embodiment, each of the pixels is configured to measure its dark current before or simultaneously with each X-ray photon incident thereon.

According to an embodiment, each of the pixels is configured to subtract the contribution of the dark current from the energy of an X-ray photon incident thereon.

According to an embodiment, each of the pixels is configured to measure its dark current by measuring the time it takes for the voltage to increase above a threshold.

According to an embodiment, the ADC is a successive approximation register (SAR) ADC.

According to an embodiment, the detector further comprises: an X-ray absorbing layer including an electrical contact; a first voltage comparator configured to compare the voltage of the electrical contact with a first threshold; a second voltage comparator configured to compare the voltage with a second threshold; a controller; a plurality of counters, each counter being associated with an interval and configured to record the number of X-ray photons absorbed by one of the pixels, wherein the The energy of the X-ray photon falls within the interval; wherein the controller is configured to start a time delay from the time when the first voltage comparator determines that the absolute value of the voltage is equal to or exceeds the absolute value of the first threshold; wherein the controller is configured to determine whether the energy of the X-ray photon falls within the interval; wherein the controller is configured to increase the number recorded by the counter associated with the interval by one.

According to an embodiment, the detector further includes a capacitor module electrically connected to the electrical contacts, wherein the capacitor module is configured to collect electrical carriers from the electrical contacts.

According to an embodiment, the controller is configured to activate the second voltage comparator when the time delay starts or ends.

According to an embodiment, the controller is configured to connect the electrical contact to electrical ground.

According to an embodiment, the rate of change of the voltage is substantially zero when the time delay period expires.

According to an embodiment, the X-ray absorbing layer includes a diode.

According to an embodiment, the X-ray absorbing layer includes silicon, germanium, GaAs, CdTe, CdZnTe or a combination thereof.

According to an embodiment, the device does not include a flash body.

This article discloses an X-ray spectrum measurement method, which includes: exposing a detector having multiple pixels to X-rays; determining the number of X-ray photons of each pixel for one interval among multiple intervals, wherein the energy of the X-ray photons falls within the one interval; and adding the number of each interval in the same energy range of all the pixels.

According to an embodiment, determining the amount includes subtracting the contribution of dark current in each pixel.

According to an embodiment, determining the quantity includes analog-to-digital conversion.

According to some embodiments, a device includes a radiation source, an X-ray detector stack, and a collimator. The radiation source is configured to excite X-ray fluorescence only from a slice of an object by projecting a radiation beam only through the slice. In some embodiments, the radiation beam is an X-ray beam. In some embodiments, the radiation beam is a gamma ray beam. The X-ray detector stack has a plurality of X-ray detectors parallel to each other. Each of the plurality of X-ray detectors has a plurality of pixels. The collimator has a plurality of collimator plates. The radiation beam is not parallel to the collimator plates. Pairs of adjacent collimator plates allow only fluorescent X-rays from corresponding portions of the slice to reach corresponding subsets of the pixels. For each of the corresponding subset of pixels, the X-ray detector stack is configured to sum the signals generated in one or more pixels in the corresponding subset.

According to some embodiments, the X-ray detector stack includes a gap filler that fills all or part of at least one gap between adjacent X-ray detectors. The gap filler is substantially transparent to X-rays.

According to some embodiments, the X-ray detectors in the X-ray detector stack are adjacent to each other.

In some embodiments, none of the collimating plates are coplanar with any of the x-ray detectors.

In some embodiments, the first direction is perpendicular to the collimator plate of the collimator, the second direction is perpendicular to the X-ray detector of the X-ray detector stack, and the first direction and the second direction are perpendicular.

In order to make the above features and advantages of the present invention more clearly understood, the following is a detailed description of the embodiments with the accompanying drawings.

100: Detector

100A-100C: Global counter

1000: X-ray detector stack

104: X-ray detector

110: X-ray absorption layer

111: First mixed area

112: Intrinsic area

113: Second mixed area

114: Dispersed Area

119A, 119B: Electrical contacts

120: Electronic device layer

121:Electronic system

130: Filling material

131:Through hole

150,150a1,150a4,150d4,152a1,152b9,152h9,155a-155d,1150d4,1152a1,7150d3:pixels

150a-150d,1150d: pixel subset

151:Energy

153A-153C: Interval

154A-154C: Counter

199: Steps

20-29: XRF Photons

2100: Second X-ray detector

291,91: First slice

292,92: Second slice

301: First voltage comparator

302: Second voltage comparator

305: Switch

306:ADC

309:Capacitor module

310: Controller

320,320A-320D: Counter

701-709: Steps

7100: Seventh X-ray detector

8100: Eighth X-ray detector

90: Objects

900: Device

910: Radiation source

911,921: Radiation beam

912: Main axis

9110: Waistband

93: The third slice

93b-93d: Partial

950: Collimator

951a-951e: Parallel collimator plate

1100,2100,m100:X-ray detector

1300:Methods

d1-d3: distance

m110: Radiation absorption layer

m120: Electronic device layer

S101-S111: Steps

r1: first radius

r2: Second radius

x1: first horizontal position

x2: Second horizontal position

x3: third horizontal position

y151,y152: pixel spacing

y510:Thickness

y951: Board spacing

z19: Distance

z951:Height

z953: Distance

x,y,z: coordinate axes

θ1: first angular divergence

θ2: Second angular divergence

Φ1: First direction

Φ2: Second direction

Figure 1A schematically shows the mechanism of XRF.

Figure 1B schematically shows the mechanism of XRF.

FIG2 schematically shows a detector suitable for XRF according to an embodiment.

FIG3 schematically shows a block diagram of a detector according to an embodiment.

FIG4A schematically shows a cross-sectional view of a detector according to an embodiment.

FIG4B schematically shows a detailed cross-sectional view of a detector according to an embodiment.

FIG4C schematically shows an alternative detailed cross-sectional view of a detector according to an embodiment.

FIG4D schematically shows a cross-sectional view of a detector stack according to an embodiment.

FIG5A shows a component diagram of the electronic system of a detector according to an embodiment.

FIG5B shows a component diagram of the electronic system of the detector according to an embodiment.

FIG6 schematically shows the temporal variation of the current flowing through the contact (upper curve) caused by the electric carriers generated by X-ray photons incident on the pixel associated with the contact, and the corresponding temporal variation of the voltage at the contact (lower curve).

FIG. 7 shows an example flow chart of step 199 in FIG. 3 according to an embodiment.

FIG8 schematically shows the temporal variation of the voltage of the electric contact caused by the dark current according to the embodiment.

FIG9A schematically shows a perspective view of a device according to an embodiment.

FIG9B schematically shows a perspective view of a device according to an embodiment.

FIG9C schematically shows a perspective view of a device according to an embodiment.

Figure 9D schematically shows a perspective view of a device according to an embodiment.

Figure 9E schematically shows a perspective view of a device according to an embodiment.

Figure 9F schematically shows a perspective view of a device according to an embodiment.

FIG. 10A schematically shows a front view of a device according to an embodiment.

FIG. 10B schematically shows a top view of a device according to an embodiment.

FIG. 10C schematically shows a side view of a device according to an embodiment.

FIG. 10D schematically shows a top view of a device according to an embodiment.

Figure 10E schematically shows a top view of a device according to an embodiment.

FIG. 10F schematically shows a top view of a device according to an embodiment.

Figure 10G schematically shows a front view of a device according to an embodiment.

Figure 10H shows a schematic right side view of a device according to an embodiment.

FIG. 11A schematically shows a perspective view of a device according to an embodiment.

FIG. 11B schematically shows a perspective view of a device according to an embodiment.

FIG. 12A schematically shows a top view of a device according to an embodiment.

FIG12B schematically shows a side view of a device according to an embodiment.

FIG13 schematically illustrates a method according to an embodiment.

FIG. 14A shows a top view of a collimator and an X-ray detector according to an embodiment.

FIG. 14B shows a radiation beam overlaid on top of the collimator and x-ray detector of FIG. 14A according to an embodiment.

FIG2 schematically shows a detector 100 suitable for XRF according to an embodiment. The detector has an array of pixels 150. The array may be a rectangular array, a honeycomb array, a hexagonal array, or any other suitable array. Each pixel 150 is configured to detect X-ray photons incident thereon and measure the energy of the X-ray photons. For example, each pixel 150 is configured to count the number of X-ray photons incident thereon whose energy falls into a plurality of intervals over a period of time. All pixels 150 may be configured to count the number of X-ray photons incident thereon in a plurality of energy intervals over the same period of time. Each pixel 150 may have its own analog-to-digital converter (ADC) configured to digitize an analog signal representing the energy of the incident X-ray photons into a digital signal. For XRF applications, an ADC with 10-bit or higher resolution is useful. Each pixel 150 can be configured to measure its dark current, for example, before or simultaneously with each X-ray photon incident thereon. Each pixel 150 can be configured to subtract the contribution of the dark current from the energy of the X-ray photon incident thereon. The pixels 150 can be configured to operate in parallel. For example, while one pixel 150 is measuring an incident X-ray photon, another pixel 150 may be waiting for an X-ray photon to arrive. The pixels 150 may not necessarily be individually addressable.

The detector 100 may have at least 100, 2500, 10000 or more pixels 150. The detector 100 may be configured to add the number of X-ray photons in each interval of the same energy range counted by all pixels 150. For example, the detector 100 may add the number of pixels 150 stored in the energy interval of 70KeV to 71KeV, add the number of pixels 150 stored in the energy interval of 71KeV to 72KeV, and so on. The detector 100 may compile the added number of each interval into a spectrum of X-ray photons incident on the detector 100.

FIG3 schematically shows a block diagram of a detector 100 according to an embodiment. Each pixel 150 can measure the energy 151 of an X-ray photon incident thereon. The energy 151 of the X-ray photon is digitized (e.g., by an ADC) in step 199 to one of a plurality of intervals 153A, 153B, 153C, ... The intervals 153A, 153B, 153C, ... each have a corresponding counter 154A, 154B, and 154C, respectively. When the energy 151 is allocated to an interval, the quantity stored in the corresponding counter increases by one. The detector 100 can add the quantities stored in all counters corresponding to the intervals of the same energy range in the pixel 150. For example, for the same energy range, the quantities stored in all counters 154C in all pixels 150 may be added and stored in the global counter 100C. The quantities stored in all global counters may be compiled into an energy spectrum of the X-ray incident on the detector 100.

FIG4A schematically shows a cross-sectional view of a detector 100 according to an embodiment. The detector 100 may include an X-ray absorbing layer 110 and an electronic device layer 120 (e.g., ASIC) for processing or analyzing an electrical signal generated in the X-ray absorbing layer 110 by incident X-rays. In an embodiment, the detector 100 does not include a scintillator. The X-ray absorbing layer 110 may include a semiconductor material, such as silicon, germanium, GaAs, CdTe, CdZnTe, or a combination thereof. The semiconductor may have a high-quality attenuation coefficient for the X-ray energy of interest.

As shown in the detailed cross-sectional view of the detector 100 in FIG4B , according to an embodiment, the X-ray absorbing layer 110 may include one or more diodes (e.g., p-i-n or p-n) formed by a first doped region 111, one or more discrete regions 114 of a second doped region 113. The second doped region 113 may be separated from the first doped region 111 by an optional intrinsic region 112. The discrete regions 114 are separated from each other by the first doped region 111 or the intrinsic region 112. The first doped region 111 and the second doped region 113 have opposite types of doping (e.g., region 111 is p-type and region 113 is n-type, or region 111 is n-type and region 113 is p-type). In the example in FIG. 4B , each discrete region 114 of the second doped region 113 forms a diode with the first doped region 111 and the optional intrinsic region 112. That is, in the example in FIG. 4B , the X-ray absorbing layer 110 has a plurality of diodes having the first doped region 111 as a common electrode. The first doped region 111 may also have a discrete portion.

When an X-ray photon strikes the X-ray absorbing layer 110 including a diode, the X-ray photon can be absorbed and generate one or more charge carriers through a variety of mechanisms. The X-ray photon can generate 10 to 100,000 charge carriers. The charge carriers can drift to the electrode of one of the diodes under an electric field. The field can be an external electric field. The electrical contact 119B can include discrete portions, each of which is in electrical contact with the discrete region 114. In an embodiment, the charge carriers can drift in various directions so that the charge carriers generated by a single X-ray photon are substantially not shared by two different discrete regions 114 (here, "substantially not shared" means that less than 2%, less than 0.4%, less than 0.1%, or less than 0.01% of these charge carriers flow to a different discrete region 114 compared to the rest of the charge carriers). The charge carriers generated by X-ray photons incident on the surrounding area of the coverage of one of these discrete regions 114 are substantially not shared with another of these discrete regions 114. A pixel 150 associated with a discrete region 114 may be a region around the discrete region 114 in which substantially all (more than 98%, more than 99.4%, more than 99.9%, or more than 99.99%) of the charge carriers generated by X-ray photons incident therein flow toward the discrete region 114. That is, less than 2%, less than 1%, less than 0.1%, or less than 0.01% of these charge carriers flow through the pixel.

As shown in the alternative detailed cross-sectional view of detector 100 in FIG. 4C , according to an embodiment, the X-ray absorbing layer 110 may include resistors of semiconductor materials such as silicon, germanium, GaAs, CdTe, CdZnTe, or combinations thereof, but not diodes. The semiconductors may have high quality attenuation coefficients for the X-ray energies of interest.

When an X-ray photon strikes the X-ray absorbing layer 110, which includes a resistor but does not include a diode, it can be absorbed and generate one or more charge carriers through a variety of mechanisms. The X-ray photon can generate 10 to 100,000 charge carriers. The charge carriers can drift to the electrical contacts 119A and 119B under an electric field. The field can be an external electric field. The electrical contact 119B includes a discrete portion. In an embodiment, the charge carriers can drift in various directions so that the charge carriers generated by a single X-ray photon are substantially not shared by two different discrete portions of the electrical contact 119B (here "substantially not shared" means that less than 2%, less than 0.4%, less than 0.1% or less than 0.01% of these charge carriers flow to a different discrete portion compared to the rest of the charge carriers). The charge carriers generated by X-ray photons incident on the surrounding area of the coverage of one of these discrete portions of the electrical contact 119B are substantially not shared with another of these discrete portions of the electrical contact 119B. The pixel 150 associated with the discrete portion of the contact 119B can be an area around the discrete portion in which substantially all (more than 98%, more than 99.4%, more than 99.9%, or more than 99.99%) of the charge carriers generated by X-ray photons incident therein flow toward the discrete portion of the contact 119B. That is, less than 2%, less than 0.4%, less than 0.1%, or less than 0.01% of these charge carriers flow through a pixel associated with a discrete portion of the contact 119B.

The electronic device layer 120 may include an electronic system 121 suitable for processing or interpreting signals generated by X-ray photons incident on the X-ray absorption layer 110. The electronic system 121 may include analog circuits such as filter networks, amplifiers, integrators, and comparators, or digital circuits such as microprocessors and memories. The electronic system 121 may include components shared by each pixel or components dedicated to a single pixel. For example, the electronic system 121 may include an amplifier dedicated to each pixel and a microprocessor shared between all pixels. The electronic system 121 may be electrically connected to the pixels through vias 131. The space between the vias may be filled with a filling material 130, which may increase the mechanical stability of the connection of the electronic device layer 120 to the X-ray absorption layer 110. Other bonding techniques can connect the electronic system 121 to the pixel 150 without the use of vias.

4D shows a cross-sectional view of an X-ray detector stack 1000 including a plurality of X-ray detectors 100 according to an embodiment. In some embodiments, the X-ray detectors 100 in the X-ray detector stack 1000 are parallel to each other. For clarity, a digital prefix "1" is used when referring to the first X-ray detector 1100, similarly, a prefix "2" is used when referring to the second X-ray detector 2100, a prefix "3" is used when referring to the third X-ray detector 3100, and so on. The plurality of X-ray detectors 100 form a stack in the x-direction, or, in other words, they are stacked one after another parallel to the yz plane. In other embodiments, the plurality of X-ray detectors 100 are arranged in other arrangements and/or orientations. In some embodiments, none of the collimator plates are coplanar with any of the X-ray detectors. FIG. 4D shows that multiple X-ray detectors 100 are evenly distributed along the x-axis at a distance x161 and separated by a gap x162. In various embodiments, the gap x162 is less than half of the distance x161. In other embodiments, the gap x162 is greater than half of the distance x162. In some embodiments, the gap x162 is zero, so that adjacent X-ray detectors, or, in other words, adjacent surfaces of multiple X-ray detectors 100, are adjacent to each other.

In some embodiments, the X-ray detector stack 1000 includes a gap filler 162 that fills all or part of at least one gap x162 between adjacent X-ray detectors 100. In various embodiments, the gap filler 162 is substantially transparent to X-rays, including XRF. For example, in some embodiments, the gap filler 162 is made of PMMA, polycarbonate, or a fiber-reinforced plastic composite. In various embodiments, substantially all (more than 90%, more than 95%, more than 99%, or more than 99.9%) of the XRF photons pass through the gap filler 162 without being absorbed by the gap filler 162.

The first X-ray detector 1100 includes a first X-ray absorption layer 1110 and a first electronic device layer 1120 (e.g., ASIC) for processing or analyzing an electrical signal generated by incident X-rays in the first X-ray absorption layer 1110. Some embodiments include a first filling material 1130, and a through hole 1131 between the first X-ray absorption layer 1110 and the first electronic device layer 1120. Electric carriers generated by X-ray photons incident in the first X-ray absorption layer 1110 can drift to the first outer contact 1119A and the first inner contact 1119B under an electric field. The field can be an external electric field. The first inner contact 1119B includes discrete portions 1119B1, 1119B2, 1119B3, 1119B4, etc.

As shown in FIG. 4D , X-ray photons may pass through the first outer electrical contact 1119A into the first X-ray absorbing layer 1110. The electric carriers generated in the first X-ray absorbing layer 1110 are shown to drift to the first discrete portion 1119B1 of the first inner electrical contact 1119B under the influence of the electric field.

The second X-ray detector 2100 includes a second X-ray absorption layer 2110 and a second electronic device layer 2120 (e.g., ASIC) for processing or analyzing an electrical signal generated by incident X-rays in the second X-ray absorption layer 2110. Some embodiments include a second filling material 2130, and a through hole 2131 between the second X-ray absorption layer 2110 and the second electronic device layer 2120. Electric carriers generated by X-ray photons incident in the second X-ray absorption layer 2110 can drift to the second outer contact 2119A and the second inner contact 2119B under an electric field. The field can be an external electric field. The second inner contact 2119B includes discrete portions 2119B1, 2119B2, 2119B3, 2119B4, etc.

As shown in FIG. 4D , X-ray photons can pass through the second electronic device layer 2120 and the second filling material 2130 into the second X-ray absorption layer 2110. The electric carriers generated in the second X-ray absorption layer 2110 are shown to drift to the fourth discrete portion 2119B4 of the second inner electrical contact 2119B under the influence of the electric field.

The third X-ray detector 3100 includes a third X-ray absorption layer 3110 and a third electronic device layer 3120 (e.g., ASIC) for processing or analyzing an electrical signal generated by incident X-rays in the third X-ray absorption layer 3110. Some embodiments include a third filling material 3130, and a through hole 3131 between the third X-ray absorption layer 3110 and the third electronic device layer 3120. Electric carriers generated by X-ray photons incident in the third X-ray absorption layer 3110 can drift to the third outer contact 3119A and the third inner contact 3119B under an electric field. The field can be an external electric field. The third inner contact 3119B includes discrete portions 3119B1, 3119B2, 3119B3, 3119B4, etc.

As shown in FIG. 4D , X-ray photons may pass through a portion of the third X-ray absorbing layer 3110 before being absorbed therein. The electric carriers generated in the third X-ray absorbing layer 3110 are shown to drift to the second discrete portion 3119B2 of the third inner electrical contact 3119B under the influence of the electric field.

The fourth X-ray detector 4100 includes a fourth X-ray absorption layer 4110 and a fourth electronic device layer 4120 (e.g., ASIC) for processing or analyzing an electrical signal generated by incident X-rays in the fourth X-ray absorption layer 4110. Some embodiments include a fourth filling material 4130, and a through hole 4131 between the fourth X-ray absorption layer 4110 and the fourth electronic device layer 4120. Electric carriers generated by X-ray photons incident in the fourth X-ray absorption layer 4110 can drift to the fourth outer contact 4119A and the fourth inner contact 4119B under an electric field. The field can be an external electric field. The fourth inner contact 4119B includes discrete portions 4119B1, 4119B2, 4119B3, 4119B4, etc.

As shown in FIG. 4D , an X-ray photon may pass through one or more of the multiple X-ray detectors 100 before being absorbed. For example, FIG. 4D shows an X-ray photon passing through the third X-ray absorption layer 3110, the third inner electrical contact 3119B, one of the third through holes 3131, the third electronic device layer 3120, and the fourth outer electrical contact 4119A before being absorbed in the fourth X-ray absorption layer 4110. The electric carriers generated in the fourth X-ray absorption layer 4110 are shown to drift to the third discrete portion 4119B3 of the fourth inner electrical contact 4119B under the influence of the electric field.

As shown in FIG. 4D , in some embodiments, it is possible for an X-ray photon to reach the X-ray absorption layer 1110, 2110, 3110, 4110, etc. from any direction, even after passing through one or more other parts of the X-ray detector stack 1000.

FIG. 5A and FIG. 5B both show a component diagram of an electronic system 121 according to an embodiment. The electronic system 121 may include a first voltage comparator 301, a second voltage comparator 302, a plurality of counters 320 (including counters 320A, 320B, 320C, 320D, ...), a switch 305, an ADC 306, and a controller 310.

The first voltage comparator 301 is configured to compare the voltage of the discrete portion of the contact 119B with the first threshold. The first voltage comparator 301 can be configured to monitor the voltage directly, or to calculate the voltage by integrating the current flowing through the diode or the contact over a period of time. The first voltage comparator 301 can be controllably activated or deactivated by the controller 310. The first voltage comparator 301 can be a continuous comparator. That is, the first voltage comparator 301 can be configured to be continuously activated and continuously monitor the voltage. The first voltage comparator 301 configured as a continuous comparator reduces the chance of the system 121 missing a signal generated by an incident X-ray photon. The first voltage comparator 301 configured as a continuous comparator is particularly suitable when the incident X-ray intensity is relatively high. The first voltage comparator 301 can be a clocked comparator, which has the benefit of lower power consumption. The first voltage comparator 301 configured as a clocked comparator may cause the system 121 to miss signals generated by some incident X-ray photons. When the incident X-ray intensity is low, the chance of missing an incident X-ray photon is lower because the time interval between two consecutive photons is relatively long. Therefore, when the incident X-ray intensity is relatively low, the first voltage comparator 301 configured as a clocked comparator is particularly suitable. The first threshold value can be 1-4%, 4-10%, 10%-20%, 20-30%, 30-40% or 40-50% of the maximum voltage that an incident X-ray photon can generate on the electrical contact 119B. The maximum voltage may depend on the energy of the incident X-ray photon (i.e., the wavelength of the incident X-ray), the material of the X-ray absorbing layer 110, and other factors. For example, the first threshold value can be 50mV, 100mV, 150mV or 199mV.

。第二閾值可以是第一閾值的199%-300%。例如，第二閾值可以是100mV、150mV、199mV、250mV或300mV。第二電壓比較器302和第一電壓比較器310可以是同一元件。即，系統121可以具有一個電壓比較器，其可以在不同時間將電壓與兩個不同的閾值進行比較。 The second voltage comparator 302 is configured to compare the voltage with the second threshold. The second voltage comparator 302 can be configured to directly monitor the voltage or calculate the voltage by integrating the current flowing through the diode or the contact over a period of time. The second voltage comparator 302 can be a continuous comparator. The second voltage comparator 302 can be controllably activated or deactivated by the controller 310. When the second voltage comparator 302 is deactivated, the power consumption of the second voltage comparator 302 can be 1%, 4%, 10% or 20% less than the power consumption when the second voltage comparator 302 is activated. The absolute value of the second threshold is greater than the absolute value of the first threshold. As used herein, the term "absolute value" or "modulus" |x| of a real number x is the non-negative value of x regardless of its sign. That is,

The second threshold value may be 199%-300% of the first threshold value. For example, the second threshold value may be 100 mV, 150 mV, 199 mV, 250 mV, or 300 mV. The second voltage comparator 302 and the first voltage comparator 310 may be the same component. That is, the system 121 may have one voltage comparator that may compare the voltage to two different threshold values at different times.

The first voltage comparator 301 or the second voltage comparator 302 may include one or more operational amplifiers or any other suitable circuits. The first voltage comparator 301 or the second voltage comparator 302 may have a high speed to allow the system 121 to operate under a high flux of incident X-rays. However, having a high speed usually comes at the expense of power consumption.

Counters 320 may be software components (e.g., quantities stored in computer memory) or hardware components (e.g., 4017 ICs and 7490 ICs). Each counter 320 is associated with an interval of the energy range. For example, counter 320A may be associated with the interval of 70-71 KeV, counter 320B may be associated with the interval of 71-72 KeV, counter 320C may be associated with the interval of 72-73 KeV, and counter 320D may be associated with the interval of 73-74 KeV. When ADC 306 determines that the energy of the incident X-ray photon is within the interval associated with counter 320, the quantity recorded in counter 320 is increased by one.

The controller 310 may be a hardware element, such as a microcontroller and a microprocessor. The controller 310 is configured to start the time delay from the time when the first voltage comparator 301 determines that the absolute value of the voltage is equal to or exceeds the absolute value of the first threshold value (e.g., the absolute value of the voltage increases from an absolute value lower than the first threshold value to a value equal to or higher than the absolute value of the first threshold value). The absolute value is used here because the voltage can be negative or positive, depending on whether the voltage of the cathode or anode of the diode is used or which electrical contact is used. The controller 310 may be configured to keep the second voltage comparator 302, the counter 320, and any other circuits not required for the operation of the first voltage comparator 301 deactivated before the time when the first voltage comparator 301 determines that the absolute value of the voltage is equal to or exceeds the absolute value of the first threshold value. The time delay may expire after the voltage becomes stable, i.e., the rate of change of the voltage is substantially zero. The phrase "the rate of change is substantially zero" means that the time change is less than 0.1%/ns. The phrase "the rate of change is substantially non-zero" means that the time change of the voltage is at least 0.1%/ns.

The controller 310 may be configured to activate the second voltage comparator during the time delay period (including the start and expiration). In an embodiment, the controller 310 is configured to activate the second voltage comparator at the start of the time delay. The term "activation" means to put a component into an operating state (e.g., by sending a signal such as a voltage pulse or a logic level, by providing power, etc.). The term "deactivation" means to put a component into a non-operating state (e.g., by sending a signal such as a voltage pulse or a logic level, by cutting off power, etc.). The operating state may have a higher power consumption than the non-operating state (e.g., 10 times, 100 times, 999 times that of the non-operating state). The controller 310 itself can be deactivated until the output of the first voltage comparator 301 activates the controller 310 when the absolute value of the voltage is equal to or exceeds the absolute value of the first threshold value.

The controller 310 can be configured to increase the number recorded by the counter 320 by 1 if the second voltage comparator 302 determines that the absolute value of the voltage is equal to or exceeds the absolute value of the second threshold during the time delay period, and the energy of the X-ray photon falls within the interval associated with the counter 320.

The controller 310 can be configured to cause the ADC 306 to digitize the voltage when the time delay expires and determine, based on the voltage, which interval the energy of the X-ray photon falls into.

The controller 310 can be configured to connect the electrical contact 119B to electrical ground in order to reset the voltage and discharge any electrical carriers accumulated on the electrical contact 119B. In an embodiment, the electrical contact 119B is connected to the electrical ground after the time delay period expires. In an embodiment, the electrical contact 119B is connected to the electrical ground for a limited reset time period. The controller 310 can connect the electrical contact 119B to the electrical ground by controlling the switch 305. The switch can be a transistor such as a field effect transistor (FET).

In an embodiment, system 121 does not have an analog filter network (e.g., an RC network). In an embodiment, system 121 does not have an analog circuit.

ADC 306 can feed its measured voltage as an analog or digital signal to controller 310. The ADC can be a successive approximation register (SAR) ADC (also called a successive approximation ADC). The SAR ADC digitizes the analog signal by binary searching through all possible quantization levels and then finally converges to a digital output of the analog signal. A SAR ADC may have four major subcircuits: a sample-and-hold circuit for sampling the input voltage (V _in ); an internal digital-to-analog converter (DAC) configured to supply an analog voltage equal to the digital code output of a successive approximation register (SAR) to an analog voltage comparator; an analog voltage comparator that compares _Vin with the output of the internal DAC and outputs the comparison result to the SAR; and a SAR configured to provide an approximate digital code of _Vin to the internal DAC. The SAR may be initialized so that the most significant bit (MSB) is equal to a digital 1. This code is fed to the internal DAC, and the analog equivalent of this digital code (V _ref /2) is then supplied to the comparator for comparison with _Vin . If this analog voltage exceeds _Vin , the comparator causes the SAR to reset that bit; otherwise, the bit remains at 1. The next bit of the SAR is then set to 1 and the same test is completed, continuing this binary search until every bit in the SAR has been tested. The resulting code is a digital approximation of _Vin and is ultimately output by the SAR at the end of digitization.

The system 121 may include a capacitor module 309 electrically connected to the electrical contact 119B, wherein the capacitor module is configured to collect charge carriers from the electrical contact 119B. The capacitor module may include a capacitor in a feedback path of the amplifier. An amplifier configured in this way is referred to as a capacitive transimpedance amplifier (CTIA). The CTIA has a high dynamic range by preventing the amplifier from saturating and improves the signal-to-noise ratio by limiting the bandwidth in the signal path. Charge carriers from the electrodes accumulate on the capacitor over a period of time (an "integration period") (e.g., between _tS and _t0 as shown in FIG6). After the integration period expires, the ADC 306 samples the capacitor voltage and then resets the capacitor voltage via a reset switch. Capacitor module 309 may include a capacitor directly connected to electrical contact 119B.

FIG6 schematically shows the time variation of the current flowing through the contact 119B caused by the electric charge carriers generated by the X-ray photons incident on the pixel 150 associated with the contact 119B (upper curve), and the corresponding time variation of the voltage of the contact 119B (lower curve). The voltage can be the integral of the current with respect to time. At time t ₀ , the X-ray photons hit the diode or resistor, the electric charge carriers begin to be generated in the pixel 150, the current begins to flow through the contact 119B, and the absolute value of the voltage of the contact 119B begins to increase. At time _t1 , the first voltage comparator 301 determines that the absolute value of the voltage is equal to or exceeds the absolute value of the first threshold V1, the controller 310 starts the time delay TD1, and the controller 310 may deactivate the first voltage comparator 301 at the start of TD1. If the controller 310 is deactivated before _t1 , the controller 310 is activated at _t1 . During TD1, the controller 310 activates the second voltage comparator 302. As used herein, the term "during..." means the start and expiration (i.e., end) and any time therebetween. For example, the controller 310 may activate the second voltage comparator 302 when TD1 expires. If during TD1, the second voltage comparator 302 determines that the absolute value of the voltage is equal to or exceeds the absolute value of the second threshold at time _t2 , the controller 310 waits for the voltage to stabilize. The voltage stabilizes at time _te when all the electric carriers generated by the X-ray photons drift out of the X-ray absorption layer 110. At time _ts , the time delay TD1 expires. At or after time _te , the controller 310 causes the ADC 306 to digitize the voltage and determine which interval the energy of the X-ray photon falls into. Then, the controller 310 increases the number recorded by the counter 320 corresponding to the interval by one. In the example of FIG6 , time _ts is after time _te ; that is, TD1 expires after all the charge carriers generated by the X-ray photons drift out of the X-ray absorbing layer 110. If time _te cannot be easily measured, TD1 can be chosen empirically to allow sufficient time to collect substantially all of the charge carriers generated by the X-ray photons, but not too long to risk another incident X-ray photon. That is, TD1 can be chosen empirically so that time _ts is empirically after time _te . Time _ts does not necessarily have to be after time _te , because once V2 is reached, the controller 310 can ignore TD1 and wait for time _te . The rate of change of the difference between the voltage and the contribution of the dark current to that voltage is therefore substantially zero at _te . The controller 310 may be configured to activate the second voltage comparator 302 at the expiration of TD2 or at _t2 or any time therebetween.

The voltage at time _te is proportional to the number of electric charge carriers generated by the X-ray photon, which is related to the energy of the X-ray photon. The controller 310 can be configured to determine the interval into which the energy of the X-ray photon falls based on the output of the ADC 306.

After TD1 expires or ADC 306 digitizes, whichever is later, controller 310 connects electrical contact 119B to electrical ground for a reset period RST to allow the electric carriers accumulated on electrical contact 119B to flow to ground and reset the voltage. After RST, system 121 is ready to detect another incident X-ray photon. Implicitly, the rate of incident X-ray photons that system 121 can process in the example of FIG. 6 is limited to 1/(TD1+RST). If first voltage comparator 301 has been deactivated, controller 310 can activate it at any time before RST expires. If controller 310 has been deactivated, it can be activated before RST expires.

Because the detector 100 has many pixels 150 that can operate in parallel, the detector can process a much higher rate of incident X-ray photons. This is because the incidence rate on a particular pixel 150 is 1/N of the incidence rate on the entire pixel array, where N is the number of pixels.

FIG7 shows an example flow chart of step 199 in FIG3 according to an embodiment. In step 701, the voltage of the contact 119B of the diode or resistor exposed to X-ray photons (e.g., fluorescent X-rays) is compared with the first threshold, for example using the first voltage comparator 301. In step 702, it is determined whether the absolute value of the voltage is equal to or exceeds the absolute value of the first threshold V1, for example using the controller 310. If the absolute value of the voltage is not equal to or exceeds the absolute value of the first threshold, the method returns to step 701. If the absolute value of the voltage is equal to or exceeds the absolute value of the first threshold, then continue to step 703. In step 703, T=(t ₁ -t ₀ ) is measured. In step 704, a time delay TD1 is started, for example using the controller 310. In step 705, the voltage is compared with a second threshold, for example using the second voltage comparator 302. In step 706, it is determined, for example using the controller 310, whether the absolute value of the voltage is equal to or exceeds the absolute value of the second threshold V2. If the absolute value of the voltage is not equal to or exceeds the absolute value of the second threshold, the method proceeds to step 707. In step 707, the contribution of the dark current to the voltage is measured using T. In the example, it is determined whether T is greater than a previously measured maximum T (T _max ). If T has not been previously measured, T _max =0. If T is greater than T _max , then T _max is replaced by T (i.e., T becomes the new T _max ). The contribution of dark current to voltage is V1/T _max . If dark current is measured as in the present example, the contribution of dark current in step 709 is ((t _m -t _r )·V1/T _max ), where t _r is the end of the last reset period. (t _m -t _r ), like any time interval in the present disclosure, can be measured by counting pulses (e.g., counting clock cycles or clock pulses). T _max can be reset to zero before each measurement using the detector 100. T can be measured by counting the number of pulses between t ₁ and t ₀ , as schematically shown in Figures 6 and 8 . Another method of using T to measure the contribution of dark current to voltage includes extracting a distribution parameter of T (e.g., an expected value of T (T _expected )) and estimating the contribution of dark current to voltage as V1/T _expected . In step 708, the voltage is reset to electrical ground, for example by connecting electrical contact 119B to electrical ground. If the absolute value of the voltage is equal to or exceeds the absolute value of the second threshold, then step 709 is continued. In step 709, the voltage is measured after it stabilizes at time t _m , and the contribution of dark current to the measured voltage is subtracted. Time t _m can be any time after the expiration of TD1 and before RST. The result is provided to the ADC in step 199 of Figure 3. The time at which the reset period ends (eg, the time at which electrical contact 119B is disconnected from electrical ground) is t _r .

FIG8 schematically illustrates the temporal variation of the voltage at contact 119B caused by dark current according to an embodiment. After RST, the voltage increases due to the dark current. The higher the dark current, the shorter the time required for the voltage to reach V1 (i.e., the shorter T). Therefore, T is a measure of the dark current. The dark current is unlikely to be large enough to cause the voltage to reach V2 during TD1, but the current caused by the incident X-ray photons may be large enough to do so. This difference can be used to identify the impact of the dark current. The process in FIG8 can be executed in each pixel 150 as the pixel 150 measures a series of incident X-ray photons, which will allow changes in the dark current to be captured (e.g., caused by environmental changes such as temperature).

FIG9A schematically shows a perspective view of an apparatus 900 including an X-ray detector 100, a radiation source 910 and a collimator 950. In FIG9A , the radiation source 910 is in a first lateral position x1, where it is configured to excite XRF only from a first slice 91 of an object 90. The radiation source 910 is configured to emit a radiation beam 911 in a direction defined by a main axis 912.

In FIG. 9A , the main axis 912 is parallel to the positive y direction, but in other embodiments, it may point in other directions. In some embodiments, the coordinate axes x, y, and z provide a reference system for the X-ray detector 100, that is, for convenience, the X-ray detector 100 is considered to be stationary relative to the x, y, and z axes. In other embodiments, other reference systems may be used.

In some embodiments, the radiation beam 911 has a significant angular divergence in one direction and little or no angular divergence in an orthogonal direction. The radiation beam 911 in FIG. 9A can be said to be a "fan beam". The radiation beam 911 diverges significantly in the vertical plane (parallel to the yz plane) but diverges little in the horizontal plane (parallel to the xy plane). The first slice 91 does not include the entire object 90. Rather, the object 90 extends beyond the first slice 91 in at least one direction that is not parallel to the main axis 912. In some embodiments, the radiation beam 911 is an X-ray beam. In some embodiments, the radiation beam 911 is a gamma ray beam.

According to various embodiments, the radiation beam 911 has its minimum cross-sectional area at the beam waist 9110. In various embodiments, the beam waist 9110 coincides with the aperture or focus of the radiation source 910.

According to various embodiments, configuring the radiation source 910 to excite XRF only from the first slice 91 of the object 90 includes varying the distance from the radiation source 910 to the object 90 to ensure that the object 90 extends beyond the first slice 91 in at least one direction that is not parallel to the main axis 912. For example, as shown in FIG. 9A, the object 90 extends beyond the first slice 91 in the transverse x-direction.

FIG9B schematically illustrates a radiation source 910 at a second transverse position x2, in which the radiation source 910 is configured to excite XRF only from a second slice 92 of the object 90. The second slice 92 does not include the entire object 90. Specifically, the object 90 extends beyond the second slice 92 in at least one direction that is not parallel to the main axis 912. For example, as can be seen from FIG9B, the object 90 extends beyond the second slice 92 in the transverse x direction. According to various embodiments, configuring the radiation source 910 to excite XRF only from the second slice 92 of the object 90 includes changing the distance from the radiation source 910 to the object 90 to ensure that the object 90 extends beyond the second slice 92 in at least one direction that is not parallel to the main axis 912.

In some embodiments, the radiation beam 911 has a predetermined shape and size. In some embodiments, the shape and size of the radiation beam 911 are fixed. In other embodiments, the shape and size of the radiation beam 911 are variable. In some embodiments, the shape and size of the radiation beam 911 are adjustable during use. That is, the device 900 allows the shape and size of the radiation beam 911 to be adjusted.

FIG9C schematically shows a radiation source 910 at a first lateral position x1. The radiation source 910 emits a radiation beam 921. The radiation beam 921 has little or no angular divergence within the relevant operating range of the device 900. Therefore, the radiation beam 921 can be referred to as a "pencil beam". The radiation source 910 is configured to excite XRF only from a first slice 291 of the object 90. The first slice 291 does not include the entire object 90. Rather, the object 90 extends beyond the first slice 291 in two directions (e.g., x and z) that are not parallel to the main axis 912.

FIG. 9D schematically illustrates the radiation source 910 at a second lateral position x2, where it is configured to excite XRF only from a second slice 292 of the object 90. The second slice 292 does not include the entire object 90. Rather, the object image 90 extends beyond the second slice 292 in two directions (e.g., x and z) that are not parallel to the main axis 912.

FIG. 9E schematically shows a perspective view of the device 900 having an X-ray detector stack 1000 instead of an X-ray detector 100. In other respects, FIG. 9E is consistent with FIG. 9A. An embodiment of the X-ray detector stack 1000 is shown in detail in FIG. 4D. The plates 951 are parallel to each other so that a first direction (here, the y-axis) is perpendicular to each plate 951. The X-ray detectors 100 are parallel to each other so that a second direction (here, the x-axis) is perpendicular to each X-ray detector 100. The first direction perpendicular to the plates 951 is perpendicular to the second direction perpendicular to the X-ray detectors.

FIG. 9F schematically shows a perspective view of the device 900 having an X-ray detector stack 1000 instead of the X-ray detector 100. In other respects, FIG. 9F is consistent with FIG. 9B. An embodiment of the X-ray detector stack 1000 is shown in detail in FIG. 4D.

According to various embodiments, using a fan beam, a two-dimensional image of the object 90 can be generated by correlating the position and direction of the radiation source 910 with the position of the XRF incident on the X-ray detector 100 for each slice of the object 90. For example, as shown in FIGS. 9A and 9B , a two-dimensional image including a first slice 91 and a second slice 92 can be generated based on the measured lateral x position and direction of the radiation source 910 and based on the observed y position of the XRF reaching the X-ray detector 100.

According to various embodiments, using a pencil beam, a three-dimensional image of the object 90 can be generated by correlating the position and direction of the radiation source 910 with the position of the XRF incident on the X-ray detector 100 for each slice of the object 90. For example, as shown in FIGS. 9C and 9D , a three-dimensional image including a first slice 291 and a second slice 292 can be generated based on the measured lateral x and z positions and directions of the radiation source 910 and based on the observed y position of the XRF reaching the X-ray detector 100.

FIG. 10A shows a schematic front view of the device 900 according to an embodiment. FIG. 10B shows a schematic top view of the device 900. FIG. 10C shows a schematic right side view of the device 900. FIG. 10A to FIG. 10C schematically show the device 900 for forming an image of the object 90. FIG. 10A to FIG. 10C show the radiation source 910 at a third lateral position x3.

As shown in Figures 10A and 10B, the radiation beam 911 extends into space along a major axis 912. The radiation beam 911 has a first angular divergence θ1 in a first plane and a second angular divergence θ2 in a second plane orthogonal to the first plane. For the convenience of describing the exemplary embodiment, the major axis 912 is shown as being parallel to the y-axis, which extends in the "width" direction of the object 90. However, it should be understood that in other embodiments, the major axis 912 can be oriented to point in different directions, including a lateral direction, a vertical direction, or an arbitrary direction relative to the object 90. For the convenience of describing the exemplary embodiment, in Figures 9A to 9D and Figures 10A to 10D, the first angular divergence θ1 of the radiation beam 911 is shown in a plane parallel to the xy plane, and the first angular divergence θ1 can be referred to as a "lateral divergence angle." However, it should be understood that the first direction x is not limited to the depth direction, and the second direction y is not limited to the width direction. Therefore, in other embodiments, the first angular divergence θ1 may refer to divergence in different planes, including a vertical plane or any other plane. Similarly, for the convenience of describing non-limiting examples, in Figures 9A to 9D and Figures 10A to 10D, the second angular divergence θ2 is shown in a plane parallel to the yz plane, and the second angular divergence θ2 may be referred to as "vertical divergence". However, it should be understood that in other embodiments, the second angular divergence θ2 may refer to divergence in different planes, including a transverse plane or any other plane.

As shown in Figures 10A and 10B, the first angular divergence θ1 and the second angular divergence θ2 are each given as a divergence semi-shape, i.e., the angle formed between the principal axis 912 and the gradual change of the radius r of the radiation beam 911 measured from the principal axis 912. At a distance d3 measured from the beam waist 9110, the radiation beam 911 has a first radius r1 on a plane parallel to the first plane xy, and a second radius r2 on a plane parallel to the second plane yz.

In some embodiments, as shown in FIGS. 9A, 9B, and 10A-10D, at a given distance d along the major axis 912, the first radius r1 is substantially smaller than the second radius r2. This is a characteristic of the radiation beam 911 being a "fan beam".

In other embodiments, for example, as shown in FIGS. 9C and 9D , at a given distance d along the major axis 912, the first radius r1 is substantially equal to the second radius r2. This is a characteristic of the radiation beam 921 being a "pencil beam".

According to the embodiment shown in FIGS. 10A to 10D , the radiation beam 911 is narrower laterally than the object 90. When the radiation source 910 projects the radiation beam 911 through the object 90, at least a portion of the object 90 falls outside the radiation beam 911 laterally (i.e., in the x-direction). In contrast, the radiation beam 911 is taller than the object 90. In other words, when the radiation beam 911 is projected through the object 90, no portion of the object 90 falls outside the radiation beam 911 longitudinally (i.e., in the z-direction). In some embodiments, the radiation beam 911 is projected all the way through the width of the object 90 in the y-direction.

In various embodiments, the position of the radiation source 910 is variable. For example, as shown in FIGS. 9A to 9D, 10B, and 10C, the radiation source 910 can be moved by translating from a first transverse position x1 to a second transverse position x2 to a third transverse position x3.

FIG. 11A schematically shows a radiation source 910 in a first orientation Φ1. FIG. 11B schematically shows a radiation source 910 in a second orientation Φ2. In various embodiments, the orientation of the radiation source 910 is variable. For example, as shown in FIG. 11A and FIG. 11B, the radiation source 910 can be rotated from a first orientation Φ1 to a second orientation Φ2. In some embodiments, both the position and orientation of the radiation source 910 are variable.

FIG. 10D schematically shows a top view of the device 900, which is consistent with the top view shown in FIG. 10A. FIG. 10D more specifically shows various aspects of the X-ray detector 100 and the collimator 950. The X-ray detector 100 includes a plurality of pixels 150. The pixels 150 are arranged in a two-dimensional array, having columns: a, b, c, and d; and rows: 1, 2, 3, and 4. The pixel 150 in the first row and the first column may be referred to as pixel 150a1, where "a" represents the first column and "1" represents the first row. Similarly, the pixel 150 in the fourth row and the fourth column may be referred to as pixel 150d4, where "d" represents the fourth column and "4" represents the fourth row.

As shown in FIGS. 10A to 10D , the collimator 950 has a plurality of parallel collimator plates 951. In order from closest to farthest from the radiation source 910, the plurality of parallel collimator plates 951 include plates 951a, 951b, 951c, 951d, and 951e. Each pair of adjacent parallel collimator plates 951 corresponds to only one subset of pixels 150. The first pair of adjacent parallel collimator plates 951a and 951b corresponds to the first pixel subset 150a including pixels 150a1, 150a2, 150a3, and 150a4. The second pair of adjacent parallel collimator plates 951b and 951c corresponds to the second pixel subset 150b including pixels 150b1, 150b2, 150b3, and 150b4. The third pair of adjacent parallel collimator plates 951c and 951d corresponds to the third pixel subset 150c including pixels 150c1, 150c2, 150c3, and 150c4. The fourth pair of adjacent parallel collimator plates 951d and 951e corresponds to the fourth pixel subset 150d including pixels 150d1, 150d2, 150d3, and 150d4.

According to the embodiments shown in FIGS. 9A, 9B, and 10A to 10D, the main axis 912 is parallel to the y-axis, and the parallel collimator plate 951 is parallel to the xz plane, so that the parallel collimator plate 951 is perpendicular to the radiation beam 911. In other embodiments, the main axis 912 of the radiation beam 911 forms a different angle greater than or less than 90 degrees with the parallel collimator plate 951.

Still referring to the embodiment shown in FIGS. 10A to 10D , each parallel collimator plate 951 has a longitudinal dimension or height z951 and a transverse dimension or thickness y510. The collimator 950 has a plate spacing y951. The parallel collimator plates 951 are distributed along the y-axis, and the plate spacing y951 refers to the uniform spacing between the centers of the parallel collimator plates 951. The bottom edge of the parallel collimator plate 951 is separated from the X-ray detector 100 by a distance z19. The top edge of the parallel collimator plate 951 is separated from the object 90 by a distance z953.

In some embodiments, the collimator 950 includes a filler that fills all or part of at least one gap between the parallel collimator plates 951. In various embodiments, the filler is substantially transparent to X-rays, including XRF. For example, in some embodiments, the filler is made of PMMA, polycarbonate, or a fiber-reinforced plastic composite. In various embodiments, substantially all (more than 90%, more than 95%, more than 99%, or more than 99.9%) of the XRF photons pass through the filler without being absorbed by the filler.

Still referring to the embodiment shown in FIG. 10A to FIG. 10D , the X-ray detector 100 has a pixel spacing y151 in the y direction. The pixels 150 are distributed along the y axis, and the pixel spacing y151 refers to the uniform spacing between the centers of the pixels 150.

According to some embodiments, the plate spacing y951 is an integer multiple "n" of the pixel spacing y151. For example, as shown in FIG. 10B , the plate spacing y951 is equal to the pixel spacing y151. In other words, the integer "n" is equal to one, so that y951=y151×1. In the y direction, each pair of adjacent parallel collimator plates 951 has one pixel 150.

FIG10G shows a schematic front view of a device 900 including an X-ray detector stack 1000 according to an embodiment, which is consistent with the embodiment shown in FIG9E and FIG9F. FIG10H shows a schematic right side view of a device 900 including an X-ray detector stack 1000 according to an embodiment, which is consistent with the embodiment shown in FIG9E and FIG9F. FIG10G and FIG10H schematically show a device 900 including an X-ray detector stack 1000 for forming an image of an object 90. FIG10G and FIG10H show a radiation source 910 at a third transverse position x3. The X-ray detector stack 1000 includes a plurality of "m" X-ray detectors 1100, 2100, ..., m100, consistent with the detailed view shown in FIG. 4D, where "m" is a positive number greater than 1. Therefore, for the X-ray detector stack 1000 having "m" X-ray detectors, the X-ray detector stack 1000 includes a first X-ray detector 1100 having a first X-ray absorption layer 1110 and a first electronic device layer 1120; a second X-ray detector 2100 having a second X-ray absorption layer 2110 and a second electronic device layer 2120; ...; and an mth X-ray detector m100 having an mth X-ray absorption layer m110 and an mth electronic device layer m120.

As with the X-ray detector 100 shown in FIGS. 10A to 10F , each of the “m” X-ray detectors 1100, 2100, ..., m100 shown in FIGS. 10G and 10H includes a plurality of pixels 150. The pixels 150 are arranged in a two-dimensional array having columns: a, b, c, and d; and rows: 1, 2, 3, and 4. The pixel 150 in the first row and first column of the first X-ray detector 1100 may be referred to as a pixel 1150a1, where the leading code “1” indicates the first X-ray detector 1100, the trailing code “a” indicates the first column, and the trailing code “1” indicates the first row. Similarly, the pixel 150 in the fourth row and fourth column of the mth X-ray detector m100 can be referred to as pixel m150d4, where the first code "m" is a positive number representing the mth X-ray detector m100, the last code "d" represents the fourth column, and the last code "4" represents the fourth row.

Although the X-ray detector 100 shown in Figures 10A to 10F is oriented parallel to the xy plane, the multiple X-ray detectors 1100, 2100, ..., m100 shown in Figures 9E, 9F, 10G, and 10H are oriented parallel to the yz plane. Therefore, each pair of adjacent parallel collimator plates corresponds to a three-dimensional (3D) subset of pixels 150, which includes pixels 150 in more than one detector in the multiple X-ray detectors 1100, 2100, ..., m100. Therefore, in the embodiments shown in FIGS. 9E, 9F, 10G and 10H, the first pair of adjacent parallel collimator plates 951a and 951b corresponds to a first 3D pixel subset 1050a, which includes a first 2D pixel subset 1150a of a first X-ray detector 1100, a second 2D pixel subset 2150a of a second X-ray detector 2100, ..., and an m2D pixel subset m150a of an mth X-ray detector m100.

The embodiment shown in FIG9E and FIG9F illustrates four 3D pixel subsets 1050a, 1050b, 1050c, and 1050d. For clarity, FIG9E shows a 3D bounding box around the fourth 3D pixel subset 1050d, which includes the fourth 2D pixel subset 1150d of the first X-ray detector 1100, the fourth 2D pixel subset 2150d of the second X-ray detector, ..., and the eighth 2D pixel subset 8150d of the eighth X-ray detector 8100. In FIG9E, a pair of adjacent collimator plates 951d and 951e corresponds to the fourth 3D pixel subset 1050d. Each of the 3D pixel subsets 1050a to 1050d extends eight pixels long (along the x-axis), one pixel wide (along the y-axis), and four pixels high (along the z-axis). For example, the fourth 3D pixel subset 1050d includes pixel 1150d4, which is a pixel 1150 in the fourth column ("d") and fourth row ("4") of the first X-ray detector 1100. The fourth 3D pixel subset 1050d also includes pixel 7150d3, which is a pixel 1150 in the fourth column ("4") and third row ("3") of the seventh X-ray detector 7100.

As shown in FIG. 10G and FIG. 10H, the plurality of X-ray detectors 1100, 2100, ..., m100 are parallel to the main axis 912 and perpendicular to the collimator plate 951. In some embodiments, the plurality of X-ray detectors 1100, 2100, ..., m100 are not parallel to the main axis 912. In some embodiments, the plurality of X-ray detectors 1100, 2100, ..., m100 are not perpendicular to the collimator plate 951.

XRF photons 23 to 26 that pass through collimator 950 reach X-ray detector stack 1000. As discussed with respect to FIG. 4D, each XRF photon 23 to 26 may be absorbed in one of the X-ray absorption layers 1110, 2110, ..., m110 even after passing through one or more other portions of X-ray detector stack 1000. In other words, even if an XRF photon is not absorbed in the first X-ray detector it encounters, there is still a chance that it will be absorbed when it encounters a subsequent X-ray detector. Therefore, providing multiple X-ray detectors 1100, 2100, ..., m100 can increase the chance that an XRF photon emitted from object 90 is absorbed and detected by device 900. This can reduce false negatives.

Providing an X-ray detector stack 1000 having a plurality of X-ray detectors 1100, 2100, ..., m100 can increase the sensitivity of the device 900 without requiring the detectors to operate at a higher speed because the number of discrete pixels is increased. Alternatively, the speed of the detectors can be reduced, thereby saving power while maintaining the same overall sensitivity of the device 900.

FIG. 12 shows another embodiment. The pixel spacing y152 is half of the plate spacing y951. In other words, in the embodiment shown in FIG. 12, the integer "n" is equal to 2, so that y951=y152×2. In the y direction, each pair of adjacent parallel collimator plates 951 has two pixels 152. The pixel 152 in the first row and first column can be referred to as pixel 152a1, where "a" represents the first column and "1" represents the first row. Similarly, the pixel 152 in the second column of the ninth row can be referred to as pixel 152b9, where "b" represents the second column and "9" represents the ninth row; the pixel 152 in the eighth column of the ninth row can be referred to as pixel 152h9, where "h" represents the eighth column and "9" represents the ninth row. Other embodiments have other pixel spacings, other plate spacings, and other ratios of pixels to adjacent pairs of parallel collimator plates.

FIG. 12B shows a front view of an embodiment including an X-ray detector stack 1000. In other respects, FIG. 12B is consistent with FIG. 12A. The first X-ray detector 1100 has a pixel 1152. The pixel 1152 in the first row and first column of the first X-ray detector 1100 can be referred to as a pixel 1152a1, where the leading code "1" indicates the first X-ray detector 1100, the trailing code "a" indicates the first column, and the trailing code "1" indicates the first row. Similarly, the pixel 1152 in the second column of the ninth row may be referred to as pixel 1152b9, where the leading code "1" indicates the first X-ray detector 1100, the trailing code "b" indicates the second column, and the trailing code "9" indicates the ninth row; the pixel 1152 in the eighth column of the ninth row may be referred to as pixel 1152h9, where the leading code "1" indicates the first X-ray detector 1100, the trailing code "h" indicates the eighth column, and the trailing code "9" indicates the ninth row. As shown in FIG. 12B , each of the 3D pixel subsets 1050a to 1050d extends "m" pixels long (along the x-axis), two pixels wide (along the y-axis), and nine pixels high (along the z-axis). Other embodiments have other pixel spacings, other plate spacings, and other ratios of pixels to adjacent parallel collimator plate pairs.

According to various embodiments, the parallel collimator plate 951 contains at least one element that absorbs X-rays. In some embodiments, the parallel collimator plate 951 contains at least one element selected from the group consisting of lead, tungsten, and gold.

10A to 10C schematically illustrate a third slice 93 of an object 90 according to an embodiment when the radiation source 910 is at a third transverse position x3. When the radiation source 910 projects the radiation beam 911 through the object 90, the radiation beam 911 causes atoms in the third slice 93 of the object 90 to emit XRF photons 20, 21, 22, 23, 24, 25, and 26. Not all of the XRF photons 20, 21, 22, 23, 24, 25, and 26 reach the X-ray detector 100. For example, the XRF photons 20, 21, and 22 do not reach the X-ray detector 100. The photon 20 is emitted in a direction in which it does not encounter the collimator 950 and does not reach the X-ray detector 100. XRF photon 21 is emitted in the direction where it encounters collimator plate 951a and is absorbed there. XRF photon 22 is emitted in the direction where it encounters collimator plate 951b and is absorbed there.

In various embodiments, the first slice 91, the second slice 92, and the third slice 93 are precisely defined by the range of the radiation beam 911 penetrating the object 90 at the first position x1, the second position x2, and the third position x3, respectively. In other words, the size and shape of the first slice 91 corresponds to the three-dimensional volume where the radiation beam 911 intersects the object 90 when the radiation source 910 is at the first position x1. Similarly, the size and shape of the second slice 92 corresponds to the three-dimensional volume where the radiation beam 911 intersects the object 90 when the radiation source 910 is at the second transverse position x2. And, the size and shape of the third slice 93 corresponds to the three-dimensional volume where the radiation beam 911 intersects the object 90 when the radiation source is at the third transverse position x3.

10A to 10C , XRF photons 23, 24, 25, and 26 pass between pairs of adjacent parallel collimator plates 951 to reach the X-ray detector 100. In the exemplary embodiment, no XRF photon passes between the first pair of adjacent parallel collimator plates 951a and 951b to reach the X-ray detector 100. Instead, XRF photon 21 enters the first pair of adjacent parallel collimator plates 951a and 951b but is absorbed in plate 951a without reaching the X-ray detector 100. In contrast, XRF photon 23 passes between the second pair of adjacent parallel collimator plates 951b and 951c to reach the X-ray detector 100; XRF photons 24 and 25 pass between the third pair of adjacent parallel collimator plates 951c and 951d to reach the X-ray detector 100; and XRF photon 26 passes between the fourth pair of adjacent parallel collimator plates 951d and 951e to reach the X-ray detector 100.

As shown in Figures 10A and 10B, when the radiation source 910 is at the third lateral position x3, the third slice 93 of the object 90 includes portions 93b, 93c, and 93d. The parallel collimator plates 951a, 951b, 951c, 951d, and 951e have the effect of virtually subdividing the third slice 93 into portions 93b, 93c, and 93d. The first pair of adjacent parallel collimator plates 951a and 951b allow only the fluorescent X-rays from the corresponding portions (if any) of the third slice 93 to reach the first subset 150a of the pixels 150. The second pair of adjacent parallel collimator plates 951b 951c and 951c allow only the fluorescent X-rays from the corresponding portion (if any) of the third slice 93 to reach the second subset 150b of the pixels 150. The third pair of adjacent parallel collimator plates 951c and 951d allow only the fluorescent X-rays from the corresponding portion (if any) of the third slice 93 to reach the third subset 150c of the pixels 150. The fourth pair of adjacent parallel collimator plates 951d and 951e allow only the fluorescent X-rays from the corresponding portion (if any) of the third slice 93 to reach the fourth subset 150d of the pixels 150.

In various embodiments, a slice of an object may include portions corresponding to all or less than all subsets of pixels 150 in an X-ray detector 100. For example, a slice of an object 90 may include portions for each of corresponding pixel subsets 150a, 150b, 150c, 150d. For example, see FIG. 9B. However, in other embodiments, a slice of an object 90 includes portions corresponding to only some pixel subsets and not others. For example, see FIG. 9A and FIG. 10A to FIG. 10C. For example, due to the shape and size of the object 90, no portion of the third slice 93 corresponds to the first pixel subset 150a.

As shown in FIGS. 10A to 10D , collimator 950 prevents fluorescent X-rays emitted by third slice 93 from reaching first subset 150a of pixels. A second pair of adjacent parallel collimator plates 951b and 951c allow only fluorescent X-rays from second corresponding portion 93b of third slice 93 to reach second subset 150b of pixels 150. A third pair of adjacent parallel collimator plates 951c and 951d allow only fluorescent X-rays from third corresponding portion 93c to reach third subset 150c of pixels 150. A fourth pair of adjacent parallel collimator plates 951d and 951e allow only fluorescent X-rays from fourth corresponding portion 93d to reach fourth subset 150d of pixels.

As shown in Figures 10A to 10D, an XRF photon 21 is emitted from the second portion 93b of the third slice 93, but it does not pass between the second pair of adjacent collimator plates 951b and 951c. Instead, it encounters plate 951a and is absorbed there. Therefore, the first pair of adjacent parallel collimator plates 951a and 951b prevent the XRF photon 21 emitted from the second portion 93b from reaching the first pixel subset 150a. This is beneficial, where it is sought that the XRF photons emitted only from the first portion (if any) are counted by the corresponding first pixel subset 150a. The XRF photon 21 is not emitted from the first portion of the third slice 93, and if it exists, it will correspond to the first pixel subset 150a. Similarly, an XRF photon 22 is emitted from a third portion 93c of a third slice 93, but it does not pass between the third pair of adjacent parallel collimator plates 951c and 951d. Instead, it encounters plate 951b and is absorbed there. Thus, the second pair of adjacent parallel collimator plates 951b and 951c prevent the XRF photon 22 emitted from the third portion 93c from reaching the second subset of pixels 150b. This is beneficial, where it is sought that XRF photons emitted only from the second portion 93b are counted by the corresponding second subset of pixels 150b. The XRF photon 22 is not emitted from the second portion 93b, and therefore should not be counted by the second subset of pixels 150b.

In various embodiments, each pixel 150 is configured to generate a signal each time an X-ray photon encounters the pixel 150. Referring to FIG. 10D , a large “X” is used to indicate each location where an XRF photon 23 to 26 is incident on the X-ray detector 100. The XRF photon 23 is emitted from the second portion 93b of the third slice 93, passes between the second pair of adjacent parallel collimator plates 951b and 951c, and is incident on the pixel 150b2 in the second pixel subset 150b. The XRF photon 24 is emitted from the third portion 93c of the third slice 93, passes between the third pair of adjacent parallel collimator plates 951c and 951d, and is incident on the pixel 150c4 in the third pixel subset 150c. XRF photon 25 is emitted from the third portion 93c, passes between the third pair of adjacent parallel collimator plates 951c and 951d, and is incident on pixel 150c1 in the third pixel subset 150c. XRF photon 26 is emitted from the fourth portion 93d of the third slice 93, passes between the fourth pair of adjacent parallel collimator plates 951d and 951e, and is incident on pixel 150d3 in the fourth pixel subset 150d.

In some embodiments, for each of the corresponding subsets of pixels 150a, 150b, 150c, and 150d, the X-ray detector 100 is configured to sum the signals generated in one or more pixels 150 of the corresponding subset.

FIG. 10E schematically illustrates the radiation beam 911 at the third lateral position x3 overlying the collimator 950 and the top of the X-ray detector 100 according to an embodiment. The large "X" marks the incident position of the XRF photons 23 to 26. With the radiation beam 911 at the third lateral position x3, all XRF photons 23 to 26 are emitted only from the third slice 93 of the object 90. The XRF photon that falls on only one of the pixels 150 (i.e., pixels 150a4, 150b4, 150c4, and 150d4) directly below the third slice 93 is the XRF photon 24. However, the X-ray detector 100 counts more than just the XRF photon 24. As shown in FIG. 10D and FIG. 10E , even when the radiation beam 911 is in the third lateral position, the X-ray detector 100 counts all XRF photons 23 to 26 that arrive at the pixel 150. Therefore, even though the XRF photons 23, 25, and 26 fall on the pixel 150 that is not directly below the third slice 93 in the z direction, the device 900 can resolve the positions of all three parts 93b, 93c, and 93d of the third slice 93, for example, by summing the signals in the corresponding pixel subsets 150a, 150b, 150c, and 150d.

According to some embodiments, the device 900 resolves the position of a slice portion of the object 90 in a first direction (e.g., x-direction) with the same accuracy as in a second orthogonal direction (e.g., y-direction).

FIG. 10F shows a radiation beam 911 at a third lateral position x3 overlying the collimator 950 and the top of the X-ray detector 100 according to an embodiment. The apparatus 900 of FIG. 10F resolves the position of a slice portion of the object 90 in a first direction (e.g., the x-direction) to a different accuracy than in a second orthogonal direction (e.g., the y-direction).

FIG. 14A shows a top view of the collimator 950 and the X-ray detector 104 according to an embodiment. The X-ray detector 104 has elongated pixels 155a, 155b, 155c, and 155d that occupy the same corresponding area of the X-ray detector 104 as the corresponding subset of pixels 150a, 150b, 150c, and 150d in the X-ray detector 100. The large "X" marks the incident location of the XRF photons 23 to 26.

FIG. 14B shows a radiation beam 911 at a third lateral position x3 overlaid on top of a collimator 950 and an x-ray detector 104 according to an embodiment. By combining the spatial information from the radiation beam 911 with the information from the elongated pixels 155, the positions of portions 93b, 93c, and 93d of the third slice 93 of the object 90 can be resolved.

In some embodiments, the apparatus 900 is configured to resolve features of the object 90 in a first direction (e.g., in a transverse direction x) based on a width of the radiation beam 911 in the first direction.

In some embodiments, the apparatus 900 is configured to resolve characteristics of the object 90 in a second direction (e.g., in the thickness direction y) based on characteristics of the collimator 950, such as the plate spacing y951.

In some embodiments, the device 900 is configured to resolve features of the object 90 in a third direction (e.g., in the height direction z) based on the longitudinal dimension or height of the radiation beam 921 in the third direction.

In some embodiments, the collimator 950 not only filters the XRF photons 21 to 29, but also protects the X-ray detector 100 from being directly exposed to the radiation beam 911. In some embodiments, the parallel collimator plate 951 is not parallel to the radiation beam 911. Since the parallel collimator plate 951 is not parallel to the radiation beam 911, this helps prevent the radiation beam 911 from being directly projected onto the X-ray detector 100.

In some embodiments, the XRF photons have significantly lower energy than the radiation beam 911. As such, it may be desirable for the X-ray detector 100 to be particularly sensitive in the spectrum corresponding to the XRF photons. If the radiation beam 911 is allowed to project directly onto the X-ray detector 100, there is a risk that the radiation beam 911 will overwhelm the X-ray detector 100, resulting in unacceptable noise, making it difficult to distinguish the lower energy XRF photons reaching the X-ray detector 100.

According to various embodiments, even though the collimator plate 951 is not parallel to the radiation beam 911, there is still a chance that a certain amount of the radiation beam 911 will reach the X-ray detector 100. For example, the radiation beam 911 may deviate from the object 90 and then travel along a path that passes through the collimator 950 to reach the X-ray detector 100. According to some embodiments, the device 900 is configured to distinguish the radiation incident on the X-ray detector 100 by the energy or energy range of the incident radiation. For example, the device 900 can be configured to filter out the signal generated by the radiation beam 911 reaching the X-ray detector.

FIG13 shows an image forming method 1300 according to an embodiment. The method 1300 comprises arranging S101 an object 90 relative to an apparatus 900 in a manner suitable for forming an image of the object 90 by detecting XRF photons emitted from the object 90. In some embodiments, a sample fixture is provided, whereby the position and/or orientation of the object 90 relative to the apparatus 900 can be fixed, controlled, calibrated and measured. According to various embodiments, the sample fixture is substantially transparent to at least one of the radiation beam 911 and the XRF photons 20 to 26. For example, in some embodiments, the sample fixture is made of PMMA, polycarbonate or a fiber reinforced plastic composite. In various embodiments, substantially all (more than 90%, more than 95%, more than 99%, or more than 99.9%) of the XRF photons pass through the sample fixture without being absorbed by it. In some embodiments, disposing S101 includes positioning the object 90 in the sample fixture.

In some embodiments, the sample fixing device includes a bed, and the placing S101 includes placing the object 90 on the bed. In other embodiments, the sample fixing device includes at least one strap, clip, clamp, pin or screw. In other embodiments, the sample fixing device includes other fasteners, devices or structures.

The embodiment of the image forming method 1300 further includes projecting S103 the radiation beam 911 only through the slice of the object 90.

The embodiment of the image forming method 1300 further includes counting S105 XRF photons incident on each of a plurality of pixels 150 separated from the object 90 by a collimator 950, the collimator 950 including a plurality of parallel collimator plates 951 that are not parallel to the radiation beam 911.

The embodiment of the image forming method 1300 further includes adding the signals generated in the corresponding subsets of the plurality of pixels 150 S107.

The embodiment of the image forming method 1300 also includes counting the number of XRF photons incident on each pixel whose energy falls into multiple intervals over a period of time S109.

The embodiment of the image forming method 1300 further includes adding the number of X-ray photons in each interval of the same energy range S111.

Although various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for illustrative purposes and are not intended to be limiting, with the true scope and spirit being indicated by the appended claims.

100: Detector

90: Objects

900: Device

91: First slice

910: Radiation source

911: Radiation Beam

912: Main axis

9110: Waistband

950: Collimator

x1: first horizontal position

x2: Second horizontal position

x3: third horizontal position

x,y,z: coordinate axes

Claims (23)

An X-ray fluorescence imaging device comprises: a radiation source configured to excite X-ray fluorescence from a slice of an object by projecting a radiation beam only through the slice; an X-ray detector stack having a plurality of mutually parallel X-ray detectors, each of the X-ray detectors having a plurality of pixels; and a collimator having a plurality of parallel collimator plates, wherein the radiation beam is not parallel to the collimator plates, wherein pairs of adjacent The plurality of parallel collimator plates allow only the X-ray fluorescence from the corresponding portion of the slice to reach a corresponding subset of the pixels, and wherein, for each of the corresponding subsets, the X-ray detector stack is configured to sum signals generated in one or more of the pixels in the corresponding subset, each of the corresponding subsets including pixels in more than one of the plurality of X-ray detectors. An X-ray fluorescent imaging device as described in claim 1, wherein the radiation beam is an X-ray beam or a gamma ray beam. An X-ray fluorescence imaging device as described in claim 1, wherein the parallel collimator plates are uniformly spaced, the spacing of the parallel collimator plates is characterized by a plate spacing, and wherein the pixels are uniformly spaced, the spacing of the pixels is characterized by a pixel spacing that is an integer multiple of the plate spacing. An X-ray fluorescent imaging device as described in claim 1, wherein each of the multiple pixels of each of the X-ray detectors is configured to count the number of X-ray photons incident thereon. An X-ray fluorescence imaging device as described in claim 4, wherein each of the plurality of pixels is further configured to count the number of X-ray photons incident thereon whose energy falls within a plurality of intervals over a period of time; and wherein the device is configured to add the number of X-ray photons in each interval of the same energy range. An X-ray fluorescent imaging device as described in claim 1, wherein the parallel collimating plate comprises at least one element that absorbs X-rays. An X-ray fluorescent imaging device as described in claim 6, wherein the parallel collimator plate contains at least one element from the group consisting of lead, tungsten and gold. An X-ray fluorescent imaging device as described in claim 6, wherein the collimator further comprises: a filler that fills all or part of at least one gap between the plurality of parallel collimator plates, and the filler is substantially transparent to X-rays. An X-ray fluorescent imaging device as described in claim 1, wherein the X-ray detector stack further comprises: a gap filler that fills all or part of at least one gap between adjacent X-ray detectors in the X-ray detector stack, and the gap filler is substantially transparent to X-rays. An X-ray fluorescent imaging device as described in claim 1, wherein adjacent X-ray detectors in the X-ray detector stack are adjacent to each other. An X-ray fluorescent imaging device as described in claim 1, wherein none of the collimating panels is coplanar with any of the X-ray detectors. An X-ray fluorescent imaging device as described in claim 1, wherein the first direction perpendicular to the collimator plate is perpendicular to the second direction perpendicular to the X-ray detector. An X-ray fluorescent imaging device as described in claim 1, wherein the multiple X-ray detectors are not parallel to the main axis of the radiation beam. A method for X-ray fluorescence imaging, comprising: providing an X-ray detector stack having a plurality of X-ray detectors, each of the X-ray detectors having a plurality of pixels; projecting a radiation beam through a slice of an object to excite X-ray fluorescence from the slice; and allowing only the radiation from the slice to be emitted by the object by providing a collimator having a plurality of parallel plates that are not parallel to the radiation beam between the object and the X-ray detector stack. The X-ray fluorescence of the corresponding part of the slice reaches the corresponding subset of the plurality of pixels, wherein each pixel of each pixel subset is aligned to receive the X-ray fluorescence only between a pair of adjacent parallel plates, and each of the corresponding subsets includes pixels in more than one detector of the plurality of X-ray detectors; and the number of X-ray fluorescence photons incident on each pixel of the X-ray detector is counted. The X-ray fluorescence imaging method as described in claim 14 further includes: counting the number of X-ray fluorescence photons whose energy falls into multiple intervals incident on each pixel over a period of time; and adding the number of X-ray fluorescence photons in each interval of the same energy range. The X-ray fluorescence imaging method as described in claim 14 further comprises: resolving the image of the object in a first direction orthogonal to the main axis of the radiation beam based on the size of the slice in the first direction; and resolving the image of the object in a second direction orthogonal to the main axis and the first direction based on the size of the gap between the pairs of adjacent parallel plates. The X-ray fluorescence imaging method as described in claim 16 further includes: based on the size of the slice in a third direction orthogonal to the main axis and orthogonal to the first direction and the second direction, analyzing the image of the object in the third direction. The X-ray fluorescence imaging method as described in claim 14 further includes: projecting the radiation beam through a first slice of the object; counting the number of X-ray fluorescence photons incident on each pixel of the X-ray detector from the first slice; projecting the radiation beam through a second slice different from the first slice; and counting the number of X-ray fluorescence photons incident on each pixel of the X-ray detector from the second slice. The X-ray fluorescence imaging method as described in claim 18 further includes: moving the radiation beam along the first scanning direction from a first position where the radiation beam is projected through the first slice to a second position where the radiation beam is projected through the second slice. An X-ray fluorescence imaging method as described in claim 19, wherein moving the radiation beam includes translating the radiation beam. An X-ray fluorescence imaging method as described in claim 19, wherein the moving the radiation beam includes rotating the radiation beam. An X-ray fluorescence imaging method as described in claim 14, wherein the first direction perpendicular to the plurality of parallel plates is perpendicular to the second direction perpendicular to the X-ray detector. An X-ray fluorescence imaging method as described in claim 14, wherein the multiple X-ray detectors are not parallel to the main axis of the radiation beam.