CN114795262A - Multisource static CT system for cardiac scanning and imaging method thereof - Google Patents

Abstract

The invention discloses a multisource static CT system facing cardiac scanning, which comprises an X-ray source ring, a detector ring, a Z-direction shielding beam limiter, an X-Y-direction shielding beam limiter and a control unit, wherein the Z-direction shielding beam limiter is used for limiting the width of a Z-direction ray; the X-Y direction shielding beam limiter is arranged below the Z direction shielding beam limiter and is used for limiting the X-Y direction ray width; the control unit is used for realizing the switching between a general scanning mode and a heart scanning mode; in the cardiac scanning mode, the control unit controls the X-Y shield beam limiter to reduce the X-Y beam width of the radiation beam, so that the width of the single radiation beam only covers the cardiac region. The multi-source static CT system and the imaging method thereof provided by the invention can adopt a multi-source parallel exposure mode, and further improve the time resolution of the multi-source static CT system so as to meet the clinical requirement of dynamic scanning of the heart.

Description

Cardiac scanning-oriented multi-source static CT system and its imaging method

technical field

The invention relates to a multi-source static CT system, as well as a corresponding imaging method and an electrocardiographic gate control circuit.

Background technique

Cardiac CT is a non-invasive examination, which can be completed within a few minutes by intravenous injection of contrast agent, and the degree of anastomosis with coronary angiography can reach up to 90%. At present, enhanced cardiac CT examination has been widely used in clinical practice due to its advantages of non-invasiveness, safety, relatively less X-ray radiation, and easy acceptance by patients. When performing a heart scan on a CT scan subject, it is necessary to determine phases (eg, diastole and systole) to perform the CT scan. Under normal circumstances, the relative phase of the diastolic phase used for CT scanning is about 75%, and the relative phase of the systolic phase is about 30%. Also, dual-source CT devices are often used where it is desired to achieve the highest possible temporal resolution in CT scans, eg to generate tomographic images of a beating heart.

In the PCT international application with the international publication number of WO2018/153382, a static real-time CT imaging system and an imaging method thereof adapted to the requirements of a large field of view are disclosed. The static real-time CT imaging system includes a multi-focus ring X-ray source and a ring photon detector; wherein, the multi-focus ring X-ray source is composed of a plurality of scanning X-ray sources arranged in a ring, and the ring photon counting detector is composed of a ring arranged in a ring. It is composed of multiple photon counting detector modules; each scanning X-ray source emits a wide beam of X-rays in turn, and after passing through the measured object, it is projected on the corresponding photon counting detector module, scanning the X-ray source and the corresponding photon counting The non-reverse geometric imaging method is adopted between the detector modules; each photon counting detector module works in an overlapping manner, and the corresponding exposure information is sent to the data acquisition and processing unit, and the real-time image is completed in the data acquisition and processing unit. Reconstruction and visual reproduction. However, this static real-time CT imaging system is not specially developed for cardiac scanning needs, and further improvement is still required in meeting medical clinical needs.

SUMMARY OF THE INVENTION

The primary technical problem to be solved by the present invention is to provide a multi-source static CT system for cardiac scanning.

Another technical problem to be solved by the present invention is to provide an imaging method for cardiac scanning.

Another technical problem to be solved by the present invention is to provide an ECG gating circuit for heart scanning.

In order to achieve the above object, the present invention adopts the following technical scheme:

According to a first aspect of the embodiments of the present invention, a multi-source static CT system for cardiac scanning is provided, including an X-ray source ring, a detector ring, a Z-direction occlusion beam limiter, an X-Y occlusion beam limiter, and a control unit, in,

The Z-direction occlusion beam limiter is used to limit the ray width in the Z-direction;

The X-Y shielding beam limiter is arranged below the Z shielding beam limiter, and the X-Y shielding beam limiter is used to limit the ray width in the X-Y direction;

The control unit is used for switching between the general scanning mode and the cardiac scanning mode;

In the heart scanning mode, the control unit controls the X-Y shielding beam limiter to reduce the ray width of the ray beam in the X-Y direction, so that the width of a single ray beam only covers the heart region.

Preferably, in the heart scanning mode, sequential exposure in which multiple radiation sources are exposed at the same time is adopted.

Preferably, in the general scanning mode, two adjacent exposures are performed by two radiation sources whose detectors corresponding to the two projections do not overlap.

According to a second aspect of the embodiments of the present invention, there is provided a static CT imaging method for cardiac scanning, wherein scanning is performed in a multi-source parallel manner; and the X-ray X-Y width is limited by an X-Y shielding beam limiter , so that the detectors of multiple ray sources do not overlap each other.

Preferably, Idle_A=It, Idle_B=2×Rt+3×It

The exposure time is Rt, the idle time between two exposures is It, the time from the end of the exposure of the first ray source to the start of the exposure of the second ray source is Idle_A, and the afterglow time is Idle_B.

According to a third aspect of the embodiments of the present invention, an ECG gating circuit is provided, including: an acquisition workstation is responsible for analyzing the restoration of the ECG signal; the nvSync node is an electrical node that receives the exposure sequence; the signal of the ECG monitor outputs the ECG The signal is sent to the ifBox circuit board; the ifBox circuit board is responsible for processing the ECG signal to realize the sequential logic relationship in the above sequence diagram; on this circuit board, the ECG signal is simulated and output to the ADC inside the FPGA, which is implemented by the MCU inside the FPGA The ADC samples and encapsulates the ADC sampled data into an energy network protocol and transmits it to the acquisition workstation through the MAC and PHY; the detection processing processes the ECG signal to identify the R wave and output the phase detection pulse synchronously, which is generated by the FPGA internally according to the phase detection pulse. The gated timing waveform of the response.

Preferably, the shoulder area before exposure and the shoulder area after exposure are set to zero, then the C signal is always the exposure area. At this time, D allows the Spot signal pulse output throughout the time of C to realize retrospective ECG image acquisition.

Preferably, the response parameters of the pre-exposure shoulder area and the post-exposure shoulder area are set according to the requirements, then the C signal exposure area shows that there is an exposure allowable time in one heartbeat cycle, and the Spot signal is only allowed in the exposure area at this time. Pulse output to achieve forward-looking ECG image acquisition.

Preferably, the method for realizing the phase detection pulse by the above-mentioned ECG gating circuit includes: the circuit board does not set a special detection processing circuit, but uses the sampling signal of the ADC, and performs the processing on the data of the ADC and the set data threshold by using the sampling signal of the ADC. Compare to identify the R wave and generate a phase detection pulse.

The multi-source static CT system and imaging method for cardiac scanning provided by the present invention adopts the mode of multi-source parallel exposure to further improve the time resolution of the static CT system to cope with the dynamic scanning of the heart. At the same time, the present invention also designs an exposure timing sequence, which lowers the requirements for the afterglow performance of the scintillator material of the entire ring detector, thereby reducing the cost of the detector.

Description of drawings

1A is a schematic diagram of FOV projection in a general scanning mode;

FIG. 1B is a schematic diagram of FOV projection in heart scan mode;

Fig. 2 is the schematic diagram of six-source parallel exposure timing;

Fig. 3 is the effect diagram of Z direction blocking beam limiter, X-Y direction blocking beam limiter and comprehensive blocking;

Fig. 4 is the functional structure of the beam limiter control board;

Fig. 5 is the timing sequence of the ECG gating circuit;

Figure 6 is an ECG gating circuit;

FIG. 7 is a schematic diagram of exposure timing.

Detailed ways

The technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

On the basis of the existing static real-time CT imaging system, the present invention designs a beam limiter structure with a variable field of view. The structure provides two kinds of ray constraints, one for constraining the X-ray beam with a large range, and the other for constraining the X-ray beam. The range is small, and the normal FOV and the cardiac FOV are satisfied in the two cases, respectively.

In FIGS. 1A and 1B , a standard FOV projection and a cardiac FOV projection are illustrated by taking an X-ray projection as an example, respectively. Among them, the cardiac FOV projection is smaller than the standard FOV projection. It can be seen that the number of detectors used for X-ray projection under the X-ray beam constraint of the cardiac FOV is relatively reduced.

Aiming at this characteristic, a working mode of parallel exposure of multiple ray sources is designed. In an embodiment of the present invention, in this mode, there are 6 ray sources exposed at the same time at the same time. It should be noted that the 6 ray sources are only for illustration. In other embodiments, the number of ray sources may be 3, 4, 8, 12, etc., which is not specifically limited.

As shown in FIG. 2 , in an embodiment of the present invention, the ray sources are divided into 6 groups, and each group has N ray sources. At a certain moment, the first numbered ray sources of the 6 groups are exposed at the same time, after the exposure, the second numbered ray sources of the 6 groups are exposed at the same time, and so on in turn, until the Nth ray source of each group is exposed. Done, this is a cycle. According to the needs of the scanning length of the system, the number of the cycles is controlled to realize the scanning of the patient.

2. Beam limiter structure and control description:

The present invention also provides a beam limiter structure for realizing the above-mentioned X-ray width variation. As shown in Figure 3, the beam limiter is divided into upper and lower layers. The first layer is the Z-direction blocking beam limiter, which is a fixed structure. The size of the ray passing window is determined according to the geometric relationship of the system. The second layer is the X-Y shielding beam limiter, which is composed of two shielding tungsten sheets and a transmission structure. Through the transmission structure, the physical position of the two tungsten sheets can be adjusted, so that the rays passing through the window change, so as to obtain X-rays of different sizes through the window. After the two beam limiters are assembled together, a comprehensive X-ray beam limiting effect is obtained, in which the rays pass through window 2 to fit the standard FOV, and the rays pass through window 1 to fit the cardiac FOV.

Correspondingly, the beam limiter device is equipped with a control board, and Figure 4 shows the functional structure of the control board. The control board consists of a controller, communication interface, drive circuit and feedback circuit. The communication interface communicates with the central controller in the existing multi-source static CT system, so as to obtain the instruction of switching the field of view of the beam limiter. The controller adopts the mechanical communication protocol to generate a control signal to drive the transmission mechanism of the beam limiter through the drive circuit, so that the position of the beam limiter in the X-Y direction changes to realize the switching command of the beam limiter field of view. At the same time, the feedback circuit feeds back the state of the transmission structure to the controller, and the controller obtains the state of the transmission mechanism and determines whether the vision switching command is completed.

3. ECG synchronization

In order to further improve the temporal resolution and better capture images of the dynamic heart, an ECG gated circuit timing sequence is designed, which integrates real-time ECG analog signals and image exposure information, which is not only suitable for retrospective ECG image acquisition, but also suitable for Prospective ECG image acquisition.

As shown in Figure 5. In Figure 5, A represents a normal ECG signal, and B represents a phase detection signal for the ECG signal, which detects the position of the R wave overshoot of the ECG signal, and generates a square wave signal at this position. According to the square wave signal, data such as the heartbeat cycle can be obtained. Then, a heartbeat cycle is divided into an exposure area, a pre-exposure shoulder area, and a post-exposure shoulder area, as shown in Figure C. The exposure action is triggered only in the exposure area, and the Spot signal is generated, as shown in D in the figure.

Therefore, under this model, by setting the length of the exposure area of C, the shoulder area before exposure and the length of the shoulder area after exposure, the ECG gate signal, that is, the waveform of D, can be realized. If the pre-exposure shoulder area and the post-exposure shoulder area are set to zero, the C signal is always the exposure area. At this time, D allows the Spot signal pulse output throughout the time of C, which corresponds to retrospective ECG image acquisition. If the response parameters of the shoulder area before exposure and the shoulder area after exposure are set according to the requirements, the C signal exposure area shows that there is an exposure allowable time in one heartbeat cycle, and the Spot signal pulse output is only allowed in the exposure area at this time. This situation corresponds to prospective ECG image acquisition.

According to this idea, an ECG gating circuit is specially designed in the present invention, and its circuit principle is shown in FIG. 6 . In Figure 6, the acquisition workstation is responsible for analyzing the restoration of the ECG signal. The nvSync node is the electrical node that receives the exposure timing. The signal of the ECG monitor outputs the ECG signal to the ifBox circuit board. The ifBox circuit board is responsible for processing the ECG signal to realize the sequential logic relationship in the above sequence diagram. In this circuit board, the ECG signal is simulated and output to the ADC inside the FPGA. The MCU inside the FPGA implements ADC sampling and encapsulates the ADC sampling data into an energy network protocol and transmits it to the acquisition workstation through MAC and PHY. The detection processing processes the ECG signal to identify the R wave and output the phase detection pulse synchronously, and the FPGA generates the corresponding gated timing waveform according to the phase detection pulse.

There is another way to realize the phase detection pulse. In this way, the circuit board does not set a special detection processing circuit, but uses the sampling signal of the ADC to identify the data by comparing the ADC data with the set data threshold. The R wave is generated and the phase detection pulse is generated.

Fourth, reduce the timing of detector afterglow requirements

In the existing static CT exposure sequence, the ray sources perform the exposure action in turn. Taking FIG. 7 as an example, according to the symbols in the figure, the conventional static CT exposure sequence is: ray source #1-1 → ray source #1 -2→...→ray source#1-N→ray source#2-1→...ray source#2-N→ray source#3-1→...ray source#3-N→ray source#1- 1→..., expose all radiation sources sequentially. In this mode, two adjacent ray sources are exposed sequentially, and the detectors corresponding to the projections of the two ray sources have overlapping parts. Therefore, from the end of the exposure of the first ray source to the start of the exposure of the second ray source. A period of time (defined as Idle_A) that determines the afterglow parameters of the detector scintillator material.

In the present invention, a new exposure sequence is defined, which requires that two adjacent exposures are not completed by two adjacent ray sources, but by two ray sources whose detectors corresponding to the two projections do not overlap. . As shown in Figure 7, the exposure sequence in the optimal case is: ray source #1-1 → ray source #2-1 → ray source #3-1 → ray source #1-2 →... ray source #1- N→ray source #2-N→ray source #3-N→ray source #1-1→..., complete all the radiation sources in turn exposure. Correspondingly, the afterglow time of the detector scintillator material is determined from the end of the first projection exposure to the beginning of the fourth projection exposure (defined as Idle_B).

If the exposure time is defined as Rt and the idle time between two exposures is It, then, Idle_A=It, Idle_B=2×Rt+3×It, thus effectively reducing the afterglow time requirement of the detector. For example: Rt=It=1ms, then Idle_A=1ms, Idle_B=5ms, the afterglow requirement of the detector is extended from 1ms to 5ms, thereby reducing the performance requirements of the detector scintillation material and contributing to the reduction of the detector cost.

To sum up, the key point of the present invention is to design a working mode in which multiple radiation sources are exposed at the same time, thereby improving the time resolution of static CT scanning.

In cooperation with it, a beam limiter with adjustable field of view in the XY direction is designed. In the working mode for simultaneous exposure of multiple sources, the size of the field of view of the beam limiter can be adjusted to reduce the size of the beam limiter to ensure simultaneous exposure of multiple sources. , no overlapping of FOV projections occurs.

In cooperation with it, in the mode of multi-source simultaneous exposure, an implementation method of ECG gating is designed for cardiac scanning, which synchronously integrates real-time simulated ECG signals and exposure information, and can realize prospective and retrospective cardiac scanning. Electric gating function.

At the same time, an alternate exposure sequence is applied, which prolongs the time interval for the same detector segment to be projected, reduces the requirements for the afterglow performance of the detector, and thus reduces the cost space of the detector.

The heart scanning-oriented multi-source static CT system and the imaging method thereof provided by the present invention have been described in detail above. For those of ordinary skill in the art, any obvious changes made to the present invention without departing from the essential content of the present invention will constitute an infringement of the patent right of the present invention, and will bear corresponding legal responsibilities.

Claims (10)

1. a multi-source static CT system oriented to cardiac scanning, is characterized in that comprising X-ray source ring, detector ring, Z to shield beam limiter, X-Y to shield beam limiter and control unit, wherein, The Z-direction occlusion beam limiter is used to limit the ray width in the Z-direction; The X-Y shielding beam limiter is arranged below the Z shielding beam limiter, and the X-Y shielding beam limiter is used to limit the ray width in the X-Y direction; The control unit is used for switching between the general scanning mode and the cardiac scanning mode; In the heart scanning mode, the control unit controls the X-Y shielding beam limiter to reduce the ray width of the ray beam in the X-Y direction, so that the width of a single ray beam only covers the heart region. 2. The multi-source static CT system of claim 1, wherein: In the heart scan mode, sequential exposure in which multiple radiation sources are exposed at the same time is used. 3. The multi-source static CT system of claim 1, wherein: In the general scan mode, two adjacent exposures are made by two radiation sources whose detectors corresponding to the two projections do not overlap. 4. A multi-source static CT imaging method oriented to cardiac scanning, implemented based on the multi-source static CT system according to any one of claims 1 to 3, characterized in that it comprises the following steps: Two adjacent exposures are not completed by two adjacent ray sources, but by two ray sources whose detectors corresponding to the two projections do not overlap. 5. The multi-source static CT imaging method according to claim 4, wherein: Scanning is carried out in a multi-source parallel manner; and the X-Y direction width of the X-ray is limited by the X-Y direction shielding beam limiter, so that the detectors of multiple ray sources do not overlap each other. 6. The multi-source static CT imaging method according to claim 4, wherein: Idle_A=It, Idle_B=2×Rt+3×It The exposure time is Rt, the idle time between two exposures is It, the time from the end of the exposure of the first ray source to the start of the exposure of the second ray source is Idle_A, and the afterglow time is Idle_B. 7. An ECG gating circuit, used in the multi-source static CT system according to any one of claims 1 to 3, characterized in that it comprises: The acquisition workstation is responsible for analyzing the restoration of the ECG signal; the nvSync node is the electrical node that receives the exposure sequence; the signal of the ECG monitor outputs the ECG signal to the ifBox circuit board; the ifBox circuit board is responsible for processing the ECG signal to realize the above sequence diagram. On the circuit board, the analog processing of the ECG signal is output to the ADC inside the FPGA, and the MCU inside the FPGA implements ADC sampling and encapsulates the ADC sampling data into an energy network protocol and transmits it to the acquisition workstation through MAC and PHY. ; The detection processing processes the ECG signal to identify the R wave and output the phase detection pulse synchronously, and the FPGA generates the gated timing waveform of the response according to the phase detection pulse. 8. ECG gating circuit as claimed in claim 7, is characterized in that: Set the pre-exposure shoulder area and the post-exposure shoulder area to zero, then the C signal is always the exposure area. At this time, D allows the Spot signal pulse output during the entire C time to realize retrospective ECG image acquisition. 9. ECG gating circuit as claimed in claim 7, is characterized in that: Set the response parameters of the shoulder area before exposure and the shoulder area after exposure according to the requirements, then the C signal exposure area shows that there is an exposure allowable time in one heartbeat cycle. At this time, the D signal pulse output is only allowed in the exposure area to achieve forward-looking. ECG image acquisition. 10. The electrocardiographic gating circuit according to claim 7, wherein the method for realizing the phase detection pulse comprises: no special detection and processing circuit is provided on the circuit board, but the sampling signal of the ADC is used, and the data of the ADC is Compare with the set data threshold to identify the R wave and generate the phase detection pulse.

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