WO2014171833A9

WO2014171833A9 - X-ray device, mask and method for taking an x-ray image

Info

Publication number: WO2014171833A9
Application number: PCT/NL2014/050254
Authority: WO
Inventors: Reinier Cornelis HOOGEVEEN
Original assignee: GENTLECEPH BV
Current assignee: GENTLECEPH BV
Priority date: 2013-04-18
Filing date: 2014-04-18
Publication date: 2014-12-11
Anticipated expiration: 2015-10-18
Also published as: WO2014171833A1; EP2986227A1; NL2010770C2

Abstract

The invention relates to an x-ray device and method for taking an x-ray image of a skull of a person using a cephalostat. The cephalostat (104) comprises a first fixating organ (111) and a second fixating organ(112) for fixating ahead of the person at opposite sides of the head such that a sagital plane is transverse to a direction of an x-ray beam (101A) originating from an x-ray source(101). According to the invention,an outer contour of a shielded area (SA) is defined. The defined shielded area (SA) prevents a head from x-ray radiation and leaves landmarks for diagnostics accessible. The shielded area is valid for a large variety of individuals. Frequent adjustments to a shielding mask are no longer necessary for each individual. The shielded area is obtained by implementing a mask (150, 1) at the cephalostat for blocking a part of the x-ray beam.

Description

Title: X-ray device, mask and method for taking an X-ray image The present invention relates to an x-ray device for taking an x-ray image of a head of a person in a sagittal plane. Taking X-ray images is an important tool for obtaining diagnostic information. In the field of obtaining diagnostic information, it is common to refer to said sagittal plane, which is a plane parallel to the sagittal suture and divides the human body into left and right portions, a coronal plane, which is, also called a frontal plane, which divides the body into back and front portions and a transverse plane, also known as cross- section, which divides the body into cranial (head) and caudal (tail) portions.

The x-ray device comprises an x-ray source for producing an x-ray beam. The x-ray beam is extending in an x-ray direction. The x-ray device comprises an x-ray detector for receiving an incoming x-ray beam originating from the x-ray source.

The x-ray device further comprises a cephalostat. A cephalostat is a device for fixating the head of the person in a defined manner so as to ensure that the x-ray image taken is best for the purpose intended by the clinician. It also helps to ensure reproducibility, for example in case the x-ray image has to be compared with another x-ray image taken earlier or later, e.g. during growth or after surgery. The cephalostat is arranged for fixating a head of a person with respect to the x-ray device, such that the sagittal plane of the head is transverse to the direction of the x-ray beam. The cephalostat is situated between the x-ray source and the x-ray detector. The cephalostat comprises a first fixating organ and a second fixating organ. Each fixating organ comprises a tip to be located at an opening of an external auditory canal of the head of the person for fixating the head with respect to the x-ray device. The tip of the fixating organ is also called an ear plug. The first fixating organ is situated between the second fixating organ and the x-ray source.

Exposure to x-rays is deemed undesirable and the dose received by a person should be as low as reasonably achievable (ALARA principle). To this end, the x-ray device comprises a mask to provide a shielded area positioned in a plane extending in parallel with the sagittal plane and crossing the centre of the tip of the first organ. An origin of a coordinate system in the plane of the shielded area is defined by a point at the centre of the tip. The coordinate system has a Y-axis in parallel with the coronal plane and extending towards the top of the head of the person. The coordinate system has an X-axis in parallel with the transversal plane and extending towards the face of the person.

From DE10.2004.002.000 a mask is know which is connectable to a first fixating organ, such that the mask is positioned at a close distance from a head of a patient. The mask is panel shaped and has an outer contour which is designed to precisely shield a skull of the patient. The mask shields a region of the skull which should not be imaged for the purposes of an x-ray diagnostic. The mask is connectable by bolts, magnetic means etc. to the first fixating organ to be able to adjust the position of the mask. The position of the mask should be adjusted to compensate for different head sizes of a variety of patients. The mask is adjustable in a cranial-caudal direction and a dorsal-ventral direction. An adjustment of the mask is in particular needed for children, because children have a considerable smaller head size than adults. The mask should shield different head sizes. Head sizes are different, due to the growth of the head that occurs from a child to a grown-up. If a mask is of the wrong size or non-accurately positioned, either there is more exposure than necessary or one or more landmarks (diagnostically relevant structures) are hidden.

A problem to this known mask is that in practise the frequently needed adjustment of the mask for each individual patient is often ignored. In practise, the adjustment of the mask is considered laborious and causes undesired delays during a treatment of a patient. As a result, the mask is often not optimally positioned for each individual patient. Evidently, without a correct adjustment of the mask, patients are exposed to a higher dose of x-rays than necessary which is undesired.

The general object of the present invention is to at least partially eliminate the above mentioned problem and/or to provide a usable alternative. More specific, it is an object of the invention to reduce the x-ray dose received by people whose x-ray images are taken when taking an x-ray image using a cephalostat while at the same time reducing a risk of hiding a landmark for diagnostic information.

According to the invention, this object is achieved by providing an x-ray device according to claim 1.

According to the invention, the x-ray device comprises a predefined shielded area. The shielded area has an outer contour including a predefined lower contour line. The lower contour line is positioned in at least three range intervals:

A first interval extends in X direction in a range of -39 mm≤ X < 5 mm, wherein the lower contour line has a Y coordinate defined by Y|_0Wer contour line = (39/44) *X + 31 ± n mm, wherein n= 6.

A second interval extends in X direction in a range of

5 mm≤ X < 39 mm, wherein the lower contour line has a Y coordinate defined by Y|_0Wer contour line = (1/34)*X + 35 ± n mm, wherein n= 6.

A third interval extends in X direction in a range of

39 mm≤ X < 62 mm, wherein the lower contour line has a Y coordinate defined by Y|_0Wer contour line = (1/2)*X + 17 ± n mm, wherein n= 6. The range interval of 39 mm≤ X < 62 mm is preferably part of an extended range interval of 39 mm≤ X < 65 mm with Yower contour line being

(1/2)*X + 17 ± n mm. The predefined shielded area is a result of an investigation which has established that it is possible to define boundaries of an area to be shielded which area suits to protect a high variety of head sizes and shapes from undesired x-ray radiation, without at the same time shielding parts that include cephalometric landmarks and without hampering the general overview of a skull. The investigation will be explained later in further detail with reference to the drawings. The predefined shielded area is valid to a high variety of patients which differ in age and ethnicity. Advantageously, a single mask can be mounted at a fixed position in the x-ray device to shield the predefined shielded area. Alternatively, the x-ray device can be programmed to refrain from radiating the predefined shielded area. As the shielded area 'fits for all', it is no longer necessary to frequently adjust the position of the mask for each individual patient. Fits for all is quoted, because in exceptional cases it still might be necessary to adjust the mask. However, in most cases, the position of the mask needs no adjustment to be in correspondence with a particular head size of a patient from whom an image is taken by using the x-ray device. Tests have revealed that it is possible to cover 99% of a large group of patients by a single mask.

The n-value defines a bandwidth for the Y coordinate. Several factors which influence an obtained outline of the outer contour of an irradiated area in a midsagittal plane of a person are taken into account by determining the n-value. A factor which is taken into account for determining the n-value regards a difference in distances from an x-ray source to a cephalostat or detector in different types of x-ray devices. Generally, an x-ray source is a point-source which is a source of radiation which emits x-ray radiation from a point location. Such radiation slightly diverges about a certain distance away from the point location. A difference in a relative placement of a mask, cephalostat and detector with respect to the x-ray source within a first or second type of x-ray device will than result in a slightly different irradiated area. The determined n-value compensates for differences caused by this factor. Another factor which is taken into account relates to a difference in different x-ray devices in diversity of x-ray radiation. Another factor which is taken into account relates to an acceptable slightly inclined positioning of a mask or a head of a person with respect to a cephalostat.

In an embodiment of the x-ray device according to the invention, the shielded area has a lower contour line comprising said Y coordinate, wherein n=4. The n-value defines a bandwidth for the Y coordinate. An n-value of 4 defines a more narrow bandwidth. This combines an improved combination of a reduced risk of covering landmarks while limiting unnecessary exposure to x-ray radiation.

In an embodiment of the x-ray device according to the invention, the shielded area comprises a fourth interval defining a frontmost part of the shielded area, said interval being for 49 mm≤ Yf_r0ntedge < 63 mm where the X is (6/14)*Y_frontedge ⁺ 44 ± n mm with n being 6 mm. This results in a mask with an improved capability to leave landmarks in that area exposed irrespective of skull size while limiting unnecessary exposure to x-ray radiation.

In an embodiment of the x-ray device according to the invention, the shielded area comprises a fifth interval defining a second frontmost part of the shielded area, said interval being for 63 mm≤ Y_fr0nt contour line < 78 mm where the X is (-8/15)*Y_front contour line + 104 ± n mm with n being 6 mm. This exposes a further landmark useful for clinical purposes with limited unnecessary exposure of people having relatively large skulls.

In an embodiment of the x-ray device according to the invention, the outer contour of the shielded area comprises an upper contour line having a Y coordinate Y_upPer contour line of at least 65 mm.

In an embodiment of the x-ray device according to the invention, the mask comprises regions of different opaqueness. The mask comprise areas of different opaqueness, be it in the form of a gradient or stepwise. This allows for a window for showing landmarks on the image that may be of high contrast such that they can be easily discerned even with a reduced dose of radiation. Given the high contrast that the posterior calvarium landmarks display on x-ray images, the windows may be semi-opaque, transmitting for example only 30% of the radiation. This reduces the radiation dose. Masks having a suitable limited transparency can be made by choosing the thickness of the blocking material and/or type of blocking material used. In particular, the mask comprises a first region and a second region, wherein the second region is capable of allowing 3-55% of the X-ray radiation to pass whereas the first region allows a passage of at most 40% of the X-ray radiation received by the mask and blocks at least 20% points of the X-ray radiation more than the second region. Thus, the second region provides a window for showing a landmark of the head on the image that is of high contrast (such as the front or top of the skull) such that it can be easily discerned even with a reduced dose of radiation. This allows for a further reduction of radiation exposure.

In an embodiment of the x-ray device according to the invention, the mask is connectable to the first fixating organ, such that a lower edge of said mask is positioned within said range intervals of the shielded area. The lower edge of the mask is shaped according to the definition of the lower contour line of the shielded area. The mask blocks incoming x-ray radiation such that the predefined shielded area is shielded. The mask is connected to the first fixating organ at a predetermined position. Once the mask is in the correct position, no further adjustments are necessary before taking x-ray images for a large group of persons. Advantageously, the mounted single mask provides a valid protection for a high variety of head shapes without a necessity for further positional adjustments. Tests have revealed that 99% of a large group of persons can be diagnosed by applying a single mask at a fixed position. Because the fixating organs of the cephalostat fixate the head in a pre-defined manner, i.e. with reference to the external auditory canals, the position of the mask with respect to the head is accurately known. It has been found that a mask having a lower edge as defined above is suitable for a wide variety of skull sizes/ages with little risk of obstructing important landmarks with excellent reduction of unnecessary exposure of the subjects to x- ray radiation. In other words, the mask can be used to block parts of the head and/or neck that are not of interest to the clinician with little risk that still some part that was of interest is shielded from radiation even if the shadow cast by the mask is very close to the location of the reference point or landmark. The term blocked means that the mask will attenuate the x- ray dose received by the mask by at least 40%. The attenuation achieved by the mask is preferably at least 80%. The mask contains for example a slab of lead. Depending on the x- ray source, it may not expose the whole (upper) part of the skull and in such a case the mask doesn't have to cover the upper part of the skull either.

In an embodiment of the x-ray device according to the invention, the mask is connectable to the cephalostat at a location in between the first fixating organ and the x-ray source. Preferably, the mask is connectable to the cephalostat at a location close to the first fixating organ which advantageously provide a more sharp projection of the shielded area. In particular, the mask is connectable at a location of at most 50 mm, more in particular at most 30 mm away from the first fixating organ.

In an alternative embodiment of the x-ray device according to the invention, the x-ray device comprises a shield for shielding an incoming x-ray beam. The shield is positioned in between the first fixating organ of the cephalostat and the x-ray source. The shield comprises a slit which extends in a y-direction in parallel with the Y-axis of the defined shielded area to allow a portion of the incoming x-ray beam to pass the mask. The slit is movable by a shield drive in a x-direction in parallel with the X-axis for scanning a region of the sagittal plane behind the mask. A mask is connected to the shield. The mask is movably connected to the shield to cover a length portion of the slit, such that a passage of the incoming x-ray beam through the slit is controlled by the mask. Due to the presence of the mask, the slit has a variable slit length. The x-ray device comprises control electronics which are programmed to move the mask by a mask drive with respect to the slit in dependence of a x-position of the slit.

Herewith, the shielded area is advantageously incorporated in the control electronics of the x-ray device. The x-ray device is programmed and controlled to radiate an area outside the predefined shielded area. Advantageously, the programming of the shielded area in the control electronics allows a quick change to the outer contour of the shielded area if desired for specific cases. The outer contour can be easily adapted by changing a setting of the control electronics to comply with occasional requirements to provide diagnostic information about certain landmarks. Another advantage may be that by adjusting the outer contour in the control electronics, the outer contour may be defined more precisely, for example by setting the n-value at n=2.

According to an embodiment, the cephalostat comprises a moveable slit and a moveable detector, the mask being between the head and the moveable slit when the x-ray image is taken. This mask is capable of shielding a significant part of the x-ray beam from reaching parts of the head that are not of interest for orthodontic applications, thus significantly reducing the x-ray dose received by the person.

In an embodiment of the x-ray device according to the invention, the x-ray detector comprises an electronic detector, an x-ray film or a photostimulable phosphorplate (PSP; a plate that is scanned after exposure).

Further, the invention relates a mask for shielding an incoming x-ray beam. The mask is manually connectable to the cephalostat, preferably to a first fixating organ of a

cephalostat of an x-ray device, such that the mask shields the defined shielded area according to the invention. The mask includes a lower edge comprising range intervals with for -39 mm≤ X < 5 mm, Y|_0Wer contour line is (39/44)*X + 31 ± n mm;

for 5 mm≤ X < 39 mm, Y|_0Wer contour line is (1/34)*X + 35 ± n mm;

for 39 mm≤ X < 62 mm, Y|_0Wer contour line is (1/2)*X + 17 ± n mm;

where n is 6 mm.

Advantageously, the mask can be used to revise an existing x-ray device. The existing x-ray device can be adapted by installing the mask to implement the predefined shielded area in the x-ray device. The mask is preferably mounted to the first fixating organ of the existing x-ray device. Advantageously, the mask can be mounted at a fixed position. Due to the defined lower edge of the mask, it is not necessary to frequently carry out adjustment operations to re-position the mask with respect to a head of an individual person.

In an embodiment of the mask according to the invention, the mask comprises an upper edge Y_upPer edge which is at least 65mm in said intervals. Advantageously, the shielded area in between the lower edge and the upper edge is sufficient large to protect a variety of head sizes of different individuals against undesired x-ray radiation.

In an embodiment of the mask according to the invention, the mask comprises a mounting kit including an adapter for mounting the mask to the first fixating organ.

Preferably, the mask is mechanically attached e.g. by bolts or a clamp, to the first fixating organ. Generally, the first fixating organ comprises a strut. The mask may be mounted to the strut. Preferably, the mask is positioned in a first step in a rough position with respect to the first fixating organ. Subsequently, the rough position of the mask is fine tuned in a second step. The adapter comprises an alignment tool for fine tuning and positioning the mask with respect to the defined shielded area. The alignment tool is connectable to the mask at a predetermined position and orientation. The alignment tool comprises an alignment member to be aligned with the tips of the fixating points. By aligning the alignment member with the first and second fixating organs, the alignment tool is brought together with the connected mask in the correct position and correct orientation to provide the defined shielded area in the x-ray device. Advantageously, the presence of the mounting kit provides a simple and reliable alignment procedure to get the mask in a correct position with respect to the cephalostat.

In an embodiment of the mask according to the invention, the mask comprises a first fixating organ. The mask may be pre-assembled with the first fixating organ. The mask may be connected to a strut of the first fixating organ by a mechanical connection, like a screw or snap connection. Preferably, the mask is integrally formed with a strut of the first fixating organ, such that the mask and strut are a one piece item. The pre-assembled mask has a fixed position with respect to the first fixating organ. The pre-assembly of the mask and first fixating organ can be supplied to a user of an x-ray device. Advantageously, the pre- assembly can be installed in the cephalostat such that a mask for shielding the predefined shielded area is quick and easy positioned at a right position.

Further the invention relates to a method for taking an x-ray image of a portion of a head of a person involving the use of an x-ray device according to the invention and/or the mask according to the invention. In particular, the invention relates to a method for revising an existing x-ray device by installing a mask according to the invention for providing the predefined shielded area. Preferably, in a step of the method, the mask according to the invention is mounted to a first fixating organ of a cephalostat.

In an embodiment of the method according to the invention, the method comprises a step of aligning the mask in a line with respective tips of a first and second fixating organ of the cephalostat. The mask can be manually aligned by a person. Preferably, the mask comprises an alignment member which should be aligned with the tips of the first and second fixating organ during an alignment procedure. Preferably, the alignment member is provided by an alignment tool which is releasably connectable to the mask. The person can manually position the mask to bring the alignment member in line with the tips of the fixating organs. After the alignment of the mask, the imaging of persons can begin and no further adjustments in position of the mask might be necessary to take x-ray images of a large group of individuals. After carrying out the alignment steps, the alignment tool can be removed.

In an embodiment of the method according to the invention, the method comprises a step of verifying an obtained position of the mask. The step of verifying the position of the mask is performed by taking an x-ray image without a person being situated in the cephalostat. The taken x-ray image will show the respective tips of the first and second fixating organ and the alignment member. An operator of the x-ray device may judge the outcome of the verifying step. A deviation from a predefined concentricity of the tips and the alignment member may lead to a rejection. Preferably, the x-ray device comprises software which is programmed to judge the taken x-ray image to provide an approval or rejection at the end of the verifying step.

The invention will be explained in more detail with reference to the appended drawings. The drawings show a practical embodiment according to the invention, which may not be interpreted as limiting the scope of the invention. Specific features may also be considered apart from the shown embodiment and may be taken into account in a broader context as a delimiting feature, not only for the shown embodiment but as a common feature for all embodiments falling within the scope of the appended claims, in which:

Fig. 1A shows a front view of an x-ray device comprising a cephalostat including a mask mounted to a first fixating organ;

Fig. 1 B shows a perspective view of a cephalostat including a mask mounted to a movable shield with a slit;

Fig. 2 shows a sagittal view through a head of a person which view includes cephalometric landmarks;

Fig. 3 shows a defined shielded area of the head of Fig. 2 which shielded area provides a reduction of exposure to x-ray radiation for a variety of head sizes and exposes the cephalometric landmarks for in particular taking orthodontic x-ray images; and

Fig. 4A and 4B show in a perspective view a mask according to the invention having a lower edge in correspondence with a lower contour line of a defined shielded area and an alignment tool for positioning and mounting the mask to a cephalostat at a fixed position. Fig. 1A shows a front view of an x-ray device 100 for taking an x-ray image of a head of a person in a sagittal plane. Fig. 1 B shows a perspective view of the cephalostat 104.

The x-ray device 100 comprises an x-ray source 101 , a moveable x-ray detector 102, a moveable shield with a slit 103, also simply called a movable slit, capable of moving in synchronisation with the moveable x-ray detector 102 and a cephalostat 104 between the x- ray source 101 and the x-ray detector 102. The x-ray source 101 , the x-ray detector 102 and the cephalostat 104 are all mounted on a yoke 105 that can be moved up and down with respect to a support 106 using a control unit 107 to accommodate for the length of a person for whom it is desired that an x-ray image (cephalogram) is to be taken. A framework 1051 is connected to the end of the yoke 105 for holding the cephalostat 104.

The x-ray source 101 is arranged for producing an x-ray beam 101 A. The x-ray beam extends in a z-direction towards the x-ray detector 102. The x-ray beam 101A extends in an x-ray beam direction normal to a sagittal plane of the person. The x-ray source 101 is positioned at a distance of about 1 ,50 m from detector 102. Most types of existing x-ray devices comprise an x-ray source 101 which is positioned at a distance of about 1 , 10-1 ,70 m from a detector 102.

The x-ray detector 102 is arranged for receiving and detecting an incoming x-ray beam. The x-ray detector 102 is an electronic detector comprising an array of sensors for detecting the incoming x-ray beam. The x-ray detector 102 is linearly movable, which is here in a x-direction.

The shield 103 is positioned in between the x-ray source 101 and the cephalostat 104. The shield 103 is arranged for shielding a first portion of an incoming x-ray beam. The shield 103 comprises a slit to allow a second portion of the incoming x-ray beam to pass the shield. Here, the slit extends in in a slit direction which is here a y-direction. The slit of the shield 103 is positioned opposite the array of sensors of the x-ray detector 102. By linearly moving the shield 103 by a shield drive and the x-ray detector 102 in a direction transverse to the slit direction an x-ray scan can be made.

The cephalostat 104 comprises a first fixating organ 1 1 1 and a second fixating organ

1 12, both in the form of legs or struts 1 1 1 L, 1 12R and each comprising a tip 1 13L, 1 13R. As further shown in Fig. 1 B, the first fixating organ 1 1 1 has a strut 1 11 L. The strut has a longitudinal body. The strut extends in a downwards, in particular vertical, direction. The strut has a proximal end which is connected to the framework 1051 at the end of the yoke 105 of the x-ray device 1. The strut has a distal end which is provided with a tip 1 13 formed as a left earplug 1 13L of a pair of earplugs, the second fixating organ 1 12 is positioned opposite the first fixating organ 1 11. The second fixating organ 1 12 has a similar structure as the first fixating organ 1 1 1 including a strut 112R and has a distal end provided with a right earplug 1 13R of the pair of earplugs. The tips 1 13, also called ear plugs, are to be received in the opening of the external auditory canals of a person. By positioning the left and right ear plugs 1 13L, 113R at the external openings of the auditory canals, a person's head can be positioned in between the first and second fixating organ 1 1 1 , 1 12 in a defined manner to diagnose a skull of the person. This contributes to achieving a defined position of the head of the person. For taking an image, the person is instructed to look straight forward in x-direction. The skull is diagnosed in a sagittal plane, in particular a midsagittal plane. An imaginary line extending from the tip 113L of the first fixating organ 1 1 1 to the tip 113R of the second fixating organ 112 is orthogonal to the sagittal plane. The imaginary line extends in parallel with an incoming x-ray beam originating from an x-ray source.

To make an x-ray cephalogram, the x-ray source 101 sends an x-ray beam 101 A towards the head of the person. The moveable x-ray detector 102 and the moveable slit 103 are, for example, both oriented vertically and are moved horizontally along the sides of the head. Thus a scan is created. In the illustrated embodiment, the slit 103 is oriented vertically.

As shown in Figure 1A, the first fixating organ 1 1 1 is provided with a mask 150, also called an anatomic cranial collimator. The mask is illustrated in further detail in Figure 4A and 4B. The mask 150 is arranged for blocking a x-ray radiation to obtain a shielded area SA in the sagittal plane. To block radiation, the mask may for example comprise a layer of lead for blocking x-ray radiation. The mask 150 may also comprise a heavy metal embedded in a matrix, such as a barium salt embedded in plastic. Such a mask 150 is capable of shielding a part of the head and reducing the dose of x-ray radiation received by the person.

The mask 150 is panel shaped. The outer contour of the mask 150 defines the outer contour of the shielded area SA in a plane in parallel with the sagittal plane of a head of a person oriented by the cephalostat 104. According to the invention, the outer contour of the shielded area SA is accurately defined to obtain a shielded area SA which protects a large group of individuals against x-ray radiation while at the same time leaving relevant landmarks for cephalometric diagnostics open for detection. Since, the shielded area SA is designed to protect a variety of persons, it is not necessary to frequently adjust a position of the mask 150 with respect to the first fixating organ 1 1 1. It is not necessary to each time tune the mask to an individual head size. The mask 150 can be mounted to the first fixating organ 1 1 1 at a fixed position for a group of persons.

Fig. 1 B shows an alternative embodiment for achieving the shielded area SA. The shield including the slit 103 comprises a mask 151. The mask 151 is movable connected to the shield 103. The mask 151 is movable by a mask drive with respect to the slit, such that a portion of the slit can be covered by the mask 151. Here, the mask 151 is movable in the slit direction (y-direction) with respect to the slit to cover a predetermined upper portion of the slit in dependence of a position of the shield 103. The x-ray device comprises control electronics which are programmed to control a movement of the mask 151. Herewith, the amount of x-ray beams 101 A which pass through the shield 103 can be controlled by the control electronics, such that an area outside the programmed shielded area SA is radiated.

In the following, with reference to figure 2, it is first explained how the outer contour of the shielded area SA in the sagittal plane is determined. Thereafter, with reference to figure 3, the outer contour of the shielded area SA is presented in further detail.

Figure 2 shows a schematic view of a skull in the sagittal plane in which the skull is provided with landmarks which represent points of interest for diagnostic information. This schematic view was drafted to investigate whether it would be possible to provide a single mask to obtain reduced exposure to x-ray radiation but still showing important landmarks for orthodontic purposes, even for various head sizes and shapes. More specifically, the schematic view was used to investigate whether it would be possible to not prevent the area of the head above the skull base from radiation without shielding parts that have

cephalometric landmarks and without hampering the general overview of the face. In the investigation, cephalograms of one hundred subjects of various age and etnicity were analyzed. A so called 'landmark free area' (LFA) was defined inside the calvarium above the skull base (delimited by + signs in Fig. 2). Ten points located on the boundary of this LFA were plotted on these hundred cephalograms and the X and Y coordinates of these points of the viewing area (rectangle in Fig. 2) were recorded. The averaged coordinates of these points were plotted. The standard deviations of these coordinates were calculated. A line was drawn inside these plotted averaged coordinates at a distance of one standard deviation of 8 points. At the remaining two points a distance of two standard deviations was used. This was around the border points anterior clinoid and posterior clinoid. The reason that a bigger distance was kept around these points is because of the important landmark Sella that is situated close to those two points. If this point is not on the cephalogram due to the shielding, the cephalogram has lost a lot of diagnostic value and in fact may well have to be retaken. By clearing the two clinoid points by two standard deviations, the chance that these two points are blocked by the shield is 2,5%, the point Sella which again in the order of another standard deviations further away has an even remoter chance to not be displayed due to the shielding. For landmarks designated with a plus symbol, arcuate lines are an indication of the boundary of the two standard deviations position.

As a result, Fig. 2 shows a number of landmarks that may be of interest to a clinician, in which:

A. A point

B. B point

C. Sella

D. Nasion

E. Orbitale

F. Anterior Nasal Spine

G. Upper Incisor Apex

H. Upper Incisor edge

I. Lower Incisor edge

J. Lower Incisor Apex

K. Pogonion

L. Gnathion M. Menton

N. Gonion

O. Articulare

P. Condylion

Q. Basion

R. Pterygoid point

S. Posterior Nasal Spine

T. Porion. Figure 3 shows in a schematic view the outer contour of the shielded area SA in the sagittal plane. The shielded area SA is positioned in a plane running in parallel with the sagittal plane. The plane of the shielded area SA crosses a centre of the tip 1 13 of the first fixating organ 1 1 1. The centre of the tip 113 defines an origin of a coordinate system in the plane of the shielded area SA. The origin is defined by the centre of the earplug 1 13 of the first fixating organ 1 1 1. The coordinate system has a Y-axis which extends in parallel with the coronal plane and extends towards a top of the head of the person and a X-axis extending in parallel with the transversal plane towards the face of the person.

The shielded area SA has an outer contour including a lower contour line. The lower contour line is positioned in an adjacent first, second and third interval 1 , 2, 3 extending in x- direction. The first interval extends about a range of -39 mm≤ X < 5 mm, wherein the lower contour line has an Y coordinate of Ylower contour (39/44)*X + 31 ± n mm. The second interval extends about a range of 5 mm≤ X < 39 mm, wherein the lower contour line has a Y coordinate of Ylower edge is (1/34)*X + 35 ± n mm. The third interval extends about a range of 39 mm≤ X < 62 mm, wherein the lower contour line has a Y coordinate of Ylower edge is (1/2)*X + 17 ± n mm. the N-value indicates a range Y direction of ±6 mm, preferably ±4 mm.

The mask 150 used in the method according to the present invention comprises a lower edge comprising the following intervals, with a Ylower edge value within a range determined by n:

1 : for -39 mm≤ X < 5 mm, Ylower edge is (39/44)*X + 31 ± n mm;

2: for 5 mm≤ X < 39 mm, Ylower edge is (1/34)*X + 35 ± n mm; and

3: for 39 mm≤ X < 62 mm, Ylower edge is (1/2)*X + 17 ± n mm,

where n is 6 mm.

In addition to the diagnostically irrelevant LFA, the posterior calvarium is deemed to be of no or little importance for orthodontic diagnostics. Many cephalometric x-ray machines do not record this area, others record them only when the dimensions of the head are small enough to fit on the image. This makes it justified to shield the back of the head completely exposing only two small areas that make it possible to reconstruct the form of the back of the head. The shielded area SA as shown in Fig. 3 may correspond to an outer contour of a mask 150 and may have two optional windows 301 for this. To provide access to other landmarks, use may be made of the one or more windows 301.

For the frontside of the head, landmarks may be exposed while avoiding excess unnecessary exposure to x-rays by a fourth and fifth range:

4: 49 mm≤ Yfront edge < 63 mm where the X is (6/14)*Yfront edge + 44 ± n mm with n being 6 mm; and

5: 63 mm≤ Yfront edge < 78 mm where the X is (-8/15)*Yfront edge + 104 ± n mm with n being 6 mm,

where n is 6 mm.

While taking a cephalometric X-ray, the patients head is fixed in a cephalostat with two fixating organs 1 1 1 , 1 12, each provided with an earplugs 1 13. These earplugs 1 13 show on the image as two rings (because of the divergent nature of the x-ray beam and the different distance to the x-ray source), one from the left side of the patient and one from the right side. These two rings are displayed on the image closely over each other. Because the cephalostat 104 is statically connected with the rest of the X-ray device 100 (the x-ray source 101 and the x-ray detector 102) the rings of the earplugs 1 13 are displayed always on the same position on the image. This is why we can use the relation of the image of the earplugs 113 to the LFA to transfer this to the position of a mask 150 that can be mounted onto the first fixating organ 1 1 1 which closest to the x-ray source 101 in relation to the earplugs 1 13 of the cephalostat 104.

Figure 4A and 4B show the mask 150 in further detail in a perspective view. The mask 150 is connectable to a cephalostat 104. The cephalostat 104 is arranged to fixate a person's head to be diagnosed in a defined manner with respect to an incoming x-ray beam. A configuration of the cephalostat 104 is shown in Fig. 1 B.

The mask 150 is panel shaped. The panel shaped mask 150 is oriented in parallel with the sagittal plane. The mask 150 has an outer edge which is in correspondence with a predefined outer contour of a shielded area SA, as shown in figure 3. The outer edge of the mask 150 has a lower edge 155 which has a shape which is defined by the definition of the lower contour line of the shielded area SA. The mask 150is positioned at a fixed position with respect to the cephalostat 104, such that the position of the lower edge 155 of the mask 150 corresponds with the lower contour line of the defined shielded area SA.

The tip 113L of the first fixating organ 1 1 1 of the cephalostat 104 provides a reference point in the sagittal plane for positioning the mask 150.

Figure 4A shows a mounting kit 160 including at least one bolt 164, an adapter

161 , 162 and an alignment tool 161 which can be used for positioning the mask 150 with respect to the left tip 1 13L in a calibrating method. The adapter is arranged for mounting the mask 150 to the strut 11 1 L of the first fixating organ 1 1 1. The adapter comprises a first adapter part 161 and a second adapter part 162 which are clampable to each other. The adapter is clampable to the strut 1 1 1 L. The adapter has a recess which fits to the strut 1 1 1 L. As shown, at least one filler plate can be used to adapt the adapter to a particular type of a cephalostat 104.

The mask 150 is mounted to the adapter. In the shown embodiment, the mask 150 has two through holes. Two bolts 164 can be used to mount the mask 150 to the adapter and at the same time clamp the adapter to the strut. The mounting kit 160 may include a fastening tool 167 to fasten the bolts 164. Another way of fastening the mask 150 to the adapter may be to snap the mask 150 to the adapter.

Before definitively fastening the mask 150 to the cephalostat 104, the mask is aligned. An alignment tool 166 can be used to accurately position the mask 150 with respect to the cephalostat 104. The shown alignment tool 166 is plate shaped. The alignment tool 166 is connectable to the mask 150 at a predetermined position.

The alignment tool 166 has a marking 1660 to place the alignment tool 166 at the predetermined position with respect to the mask 150. Here, the alignment tool 166 is provided with two holes which fit to a first and second head of a first and second bolt 164, which were used to clamp the mask 150 to the adapter. The two holes provide said marking 1660 to the alignment tool 166. The two holes can be placed about the bolt heads 164 for orienting the alignment tool 166 with respect to the mask 150.

Further, the alignment tool 166 comprises an alignment member 1661 to align the mask 150 with respect to the cephalostat 104, in particular with respect to the left and right tip 113 of the fixating organs 1 1 1 , 1 12. The alignment member 1661 is shaped by a through hole in the plate shaped tool. As shown in figure 4B, the alignment member 1661 can be manually aligned by an operator with respect to the first and second fixating organ 1 1 1 , 1 12 by looking through the hole of the alignment member 1661 towards the tips of the fixating organs 1 1 1 , 1 12 and shifting the alignment tool 166 together with the mask 150 until the alignment member 1661 and the tips of the fixating organs are placed in a straight line. After carrying out the step of aligning the mask 150 with respect to the cephalostat 104, the mask 150 can be definitively fastened to the first fixating organ 1 1 1.

Preferably, a next step of verifying the obtained position of the mask 150 is carried out in a method of calibrating the mask 150. The step of verifying the position of the mask 150 is performed by taking an x-ray image without a person situated in the cephalostat 104. Preferably, the first and second fixating organs 1 1 1 , 1 12 are spaced apart at a distance of about 15 cm during the verifying step. A length dimension of an instruction manual for calibrating the cephalostat 104 is preferably used to check the distance in between the first and second fixating organs. Preferably, the alignment tool 160 comprising the alignment member 1661 is further used as a verifying tool in the verifying step. The alignment tool 160 is connected to the mask 150 at the predetermined position during the verifying step. After taking the x-ray image, a check is made to establish whether or not the alignment member is depicted concentric with the tips of the fixating organs at the x-ray image. The check can be integrated in a software program and be carried out by the control electronics of the x-ray device. Alternatively, the check can be carried out by a person. The verifying step of the method for calibrating the mask of the x-ray device can result in an approval to start using the x-ray device or a warning to re-align the mask with respect to the cephalostat.

In general, the x-ray source, the cephalostat and the detector will be part of a single device, although it is feasible that the x-ray source, x-ray detector and cephalostat are separate devices mounted in a room at fixed locations relative to one another.

Generally spoken, the invention can be easily carried out using existing cephalostats which merely have to be provided with a mask suitable for that cephalostat, preferably by taking the shape of first fixating organ into account to securely fix the mask at the correct position (height). The mask 150, 151 does not need to shield parts of the skull outside the bundle area (rectangle in Fig. 2 and 3).

The invention is further defined by the following clauses: 1. A method of taking an X-ray image of a portion of a head of a person using a cephalostat (104), said method involving the use of

- an x-ray source (101) producing an x-ray beam,

- an x-ray detector (102) detecting x-ray radiation, and

- a cephalostat (104), said cephalostat (104) being present between the x-ray source (101) and the x-ray detector (102)

where the cephalostat (104) comprises

- a first fixating organ (1 11) comprising a tip (1 13), and

- a second fixating organ (1 12) comprising a tip (1 13),

said fixating organs (11 1 , 1 12) fixate the head of the person at opposite sides of the head with the tips (113) located at the opening of the external auditory canals of the head such that the sagital plane of the head is transverse to the direction of the x-ray beam, the first fixating organ (1 1 1) being between the second fixating organ (1 12) and the x-ray source (101);

the first fixating organ (1 1 1) comprises a mask (150) running parallel to the sagittal plane of the head for shielding part of the head and/or neck, and part of the x-ray radiation is prevented by the mask (150) from reaching the x-ray detector (102), characterized in that a point in a plane of the mask (150) where a line from the centre of the tip (1 13) of the first fixating organ (1 1 1) to the x-ray source (101) at the point where x-rays emanate crosses said plane of the mask (150) defines the origin of a coordinate system parallel to the sagittal plane of the head of the person, the coordinate system having a Y-axis parallel to the coronal plane running towards the top of the head of the person and an X-axis running parallel to the transversal plane towards the face of the person, wherein the mask (150) has a lower edge comprising range intervals with

for -39 mm≤ X < 5 mm, Ylower edge is (39/44)*X + 31 ± n mm;

for 5 mm≤ X < 39 mm, Ylower edge is (1/34)*X + 35 ± n mm;

for 39 mm≤ X < 62 mm, Ylower edge is (1/2)*X + 17 ± n mm;

where n is 6 mm,

and in these intervals the upper edge of the mask Yupper edge is at least 65 mm.

2. The method according to clause 1 , wherein the mask comprises a fourth interval defining a frontmost part of the mask, said interval being for 49 mm≤ Yfront edge < 63 mm where the X is (6/14)*Yfront edge + 44 ± n mm with n being 6 mm.

3. The method according to clause 2, wherein the mask comprises a fifth interval defining a second frontmost part of the mask, said interval being for 63 mm≤ Yfront edge < 78 mm where the X is (-8/15)*Yfront edge + 104 ± n mm with n being 6 mm.

4. The method according to any of the preceding clauses, wherein n = 4 mm.

5. The method according to any of the preceding clauses, wherein the cephalostat (104) comprises a moveable slit (103) and a moveable detector (102), the mask (150) being between the head and the moveable slit (103) when the x-ray image is taken.

6. The method according to any of the preceding clauses, wherein the mask (150) comprises a first region and a second region, the second region capable of allowing 3-55% of the x-ray radiation to pass whereas the first region allows passage of at most 40% of the x-ray radiation received by the mask (150) and blocking at least 20% points of the x-ray radiation more than the second region.

7. An x-ray device (100) comprising

- an x-ray source (101) capable of producing an x-ray beam,

- an x-ray detector (102), and

- a cephalostat (104), said cephalostat (104) being present between the x-ray source (101) and the x-ray detector (102) where the cephalostat (1 04) comprises a first fixating organ (1 1 1 ) and a second fixating organ (1 12) , said fixating organs (1 1 1 , 1 12) being suitable for fixating a head of a person at opposite sides of the head such that the sagital plane of the head is transverse to the direction of the x-ray beam, the first fixating organ (1 1 1 ) being between the second fixating organ (1 12) and the x-ray source (1 01 ) , characterized in that the first fixating organ (1 1 1 ) has a mask (1 50) for shielding part of the head and/or neck, said mask (1 50) being a mask having a lower edge comprising range intervals

for -39 mm≤ X < 5 mm, Y|_0Wer edge is (39/44)*X + 31 ± n mm;

for 5 mm≤ X < 39 mm, Y|_0Wer edge is (1/34)*X + 35 ± n mm;

for 39 mm≤ X < 62 mm, Yiower edge is (1/2)*X + 1 7 ± n mm;

where n is 6 mm,

and in these intervals the upper edge of the mask Y_Up_Per edge is at least 65 mm.

The invention is disclosed with reference to embodiments of the x-ray device, mask and method according to the invention. Reference is expressly made to the fact that, after reading the description, a person skilled in the art may wish to make changes or adaptations that are possible from a technical viewpoint, but that said changes or adaptations do not fall outside the scope of protection of the invention as defined in the attached claims. The person skilled in the art must understand that it is possible to make various adaptations from a technical viewpoint and to replace elements with equivalents without thereby departing from the essence of the invention. It is in particular possible to make changes, which fall within the definition according to the attached claims, with respect to the illustrated embodiments which do not depart from the essence of the invention and thus remain within the teaching of the invention. The invention is therefore not restricted to the illustrated and described embodiments, but the scope of protection of the invention will cover all embodiments which fall within the definition of the attached claims.

Thus, the invention provides an x-ray device, mask and a method for taking an x-ray image of a skull of a person using a cephalostat. An outer contour of a shielded area (SA) is defined which prevents a head from x-ray radiation and leaves landmarks for diagnostics accessible. The shielded area is valid for a large variety of individuals. Frequent adjustments to a shielding mask are no longer necessary for each individual. The shielded area is obtained by implementing a mask at the cephalostat for blocking a part of the x-ray beam.

Claims

1 . An x-ray device (1 00) for taking an x-ray image of a head of a person in a sagittal plane comprising

- an x-ray source (1 01 ) for producing an x-ray beam in an x-ray beam direction;

- an x-ray detector (102) for receiving an incoming x-ray beam; and

- a cephalostat (1 04) for fixating a head of a person, such that the sagittal plane of the head is transverse to the direction of the x-ray beam, said cephalostat (1 04) being situated between the x-ray source (1 01 ) and the x-ray detector (102), in which said cephalostat (1 04) comprises a first fixating organ (1 1 1 ) and a second fixating organ (1 12) each having a tip (1 1 3) to be located at an opening of an external auditory canal of the head of the person for fixating the head with respect to the x-ray device (1 00) , in which the first fixating organ (1 1 1 ) is situated between the second fixating organ (1 12) and the x-ray source (101 )

, in which the x-ray device (1 00) comprises a mask (150, 1 51 ) to provide a shielded area (SA) which shielded area (SA) is positioned in a plane running in parallel with the sagittal plane and crossing a centre of the tip (1 1 3) of the first organ (1 1 1 ), in which an origin of a coordinate system in the plane of the shielded area is defined by a point at the centre of the tip (1 1 3), the coordinate system having a Y-axis in parallel with the coronal plane running towards a top of the head of the person and an X-axis running in parallel with the transversal plane towards a face of the person

, characterized in that the shielded area (SA) has an outer contour including a lower contour line positioned in range intervals:

for -39 mm≤ X < 5 mm, Y|_0Wer contour line is (39/44)*X + 31 ± n mm;

for 5 mm≤ X < 39 mm, Y|_0Wer contour line is (1/34)*X + 35 ± n mm;

for 39 mm≤ X < 62 mm, Y|_0Wer contour line is (1/2)*X + 1 7 ± n mm;

where n is 6 mm.

2. X-ray device (100) according to claim 1 , wherein the shielded area comprises a fourth interval defining a frontmost part of the shielded area, said interval being for 49 mm≤ Yfront contour line < 63 mm where the X is (6/14)*Y_front edge ⁺ 44 ± n mm with n being 6 mm.

3. X-ray device (1 00) according to claim 1 or 2, wherein the shielded area comprises a fifth interval defining a second frontmost part of the shielded area, said interval being for 63 mm≤ Yfront contour line < 78 mm where the X is (-8/1 5) *Y_front concur line + 1 04 ± n mm with n being 6 mm.

4. X-ray device (100) according to any of the claims 1-3, wherein the outer contour of the shielded area comprises an upper contour line Y_upPer contour line is at least 65 mm.

5. X-ray device (100) according to any of the claims 1-4, wherein the mask (150, 151) comprises regions (301) of different opaqueness.

6. X-ray device (100) according to claim 5, wherein the mask (150, 151) comprises a first region and a second region, the second region capable of allowing 3-55% of the X-ray radiation to pass whereas the first region allows passage of at most 40% of the X-ray radiation received by the mask and blocking at least 20% points of the X-ray radiation more than the second region.

7. X-ray device (100) according to any of the preceding claims, wherein the mask (150) is connectable to the first fixating organ (1 1 1), such that a lower edge of said mask (150) is positioned within said range intervals of the shielded area (SA).

8. X-ray device (100) according to any of the claims 1-6, wherein the x-ray device (100) comprises a shield for shielding an incoming x-ray beam, in which the shield is positioned in between the first fixating organ (1 11) of the cephalostat (104) and the x-ray source (101), in which the shield comprises a slit (103) extending in a slit-direction which is preferably in parallel with the Y-axis of the defined shielded area (SA) to allow a portion of the incoming x- ray beam to pass the shield, and in which the slit (103) is movable by a shield drive in a direction transverse to the slit-direction which is preferably in parallel with the X-axis for scanning a region of the sagittal plane behind the shield, wherein the mask (151) is movably connected to the shield to cover a length portion of the slit (103), such that a passage of the incoming x-ray beam through the slit (103) is controlled by the mask (151), wherein the x-ray device comprises control electronics which are programmed to move the mask (151) with respect to the slit (103) in dependence of a linear position of the slit (103).

9. Mask (150) for shielding an incoming x-ray beam which mask is manually

connectable to a cephalostat, preferably to a first fixating organ (1 1 1) of the cephalostat (104), of an x-ray device (100) according to any of the preceding claims, such that the mask (150) shields the defined shielded area, wherein the mask (150) includes a lower edge comprising range intervals with

for -39 mm≤ X < 5 mm, Yower contour line is (39/44)*X + 31 ± n mm;

for 5 mm≤ X < 39 mm, Y|_0Wer contour line is (1/34)*X + 35 ± n mm;

for 39 mm≤ X < 62 mm, Yower contour line is (1/2)*X + 17 ± n mm; where n is 6 mm.

10. Mask according to claim 9, wherein an upper edge of the mask Y_Up_Per e_dge is at least 65mm in these intervals.

1 1. Mask according to any of the claims 9 or 10 comprising a mounting kit (160) including an adapter for mounting the mask to the first fixating organ (1 11), in which the adapter comprises an alignment tool (166) for positioning the mask (150) with respect to the defined shielded area (SA), wherein the alignment tool comprises a marking (1660) to connect the mask at a predetermined position and wherein the alignment tool comprises a alignment member (1661) to be aligned with cephalostat 104, in particular with the tips (1 13L, 1 13R) of the fixating points (11 1 , 1 12).

12. Mask according to any of the claims 9 or 10 comprising a first fixating organ (11 1) including a strut ( 1 1 1 L) , wherein the mask is connected to the strut at a fixed position.

13. Method for taking an x-ray image of a portion of a head of a person involving the use of an x-ray device according to any of the claims 1-8 and/or the mask (150) according to any of the claims 9-12.

14. Method according to claim 13, wherein the method comprises a step of mounting a mask (150) to a cephalostat (104), in particular to a first fixating organ (1 1 1) of a cephalostat (104).

15. Method according to claim 14, wherein the method comprises a step of aligning the mask (150) in a line with tips (113) of a first and second fixating organ (1 1 1 , 1 12) of a cephalostat (104).