X-ray imaging device

Abstract

To provide an X-ray imaging device that has resolution characteristics capable of sufficiently visualizing bone trabeculae, respiratory bronchioles, alveolar ducts, etc., and also has excellent signal-to-noise ratio (SNR). [Solution] The X-ray imaging apparatus of the present invention includes an X-ray irradiation unit including an X-ray tube for irradiating a subject with X-rays, an X-ray detection unit including an X-ray detector positioned opposite the X-ray tube with the subject in between for detecting transmitted X-rays from the subject, a pedestal on which the subject is placed, a rotation mechanism having a ring-shaped frame configured to rotate around the pedestal, and a control unit that controls the rotation of the ring-shaped frame and the irradiation of X-rays from the X-ray tube. The X-ray irradiation unit and the X-ray detection unit are attached to the ring-shaped frame, and the X-ray tube is positioned outside the ring-shaped frame.

Description

[Technical Field]

[0001] This invention relates to an X-ray imaging device, such as an X-ray computed tomography (X-ray) scanner, used in medical applications. [Background technology]

[0002] X-ray imaging devices, such as X-ray diagnostic equipment and X-ray computed tomography (CT) equipment, are widely used in medical imaging and medical diagnosis. Currently, the highest-resolution X-ray CT scanners used for medical purposes include device A, which is equipped with a detector element measuring 0.25 mm in size, and device B, which has a 0.6 mm detector element with a comb-shaped filter placed on top to reduce the aperture width to approximately 0.3 mm. In recent years, development has also progressed on devices equipped with detector elements measuring approximately 0.1 mm in size in order to achieve even higher resolution X-ray detectors.

[0003] Thus, while miniaturization of detector elements is leading to higher resolution X-ray detectors, the actual resolution of the obtained X-ray images is far from 0.1 mm. For example, a research report on a CT scanner equipped with an X-ray detection element of 0.25 mm reported that the measurement error for a simulated tracheal wall of 0.5 mm was 20%, and the measurement error for a lumen size of 0.8 mm was about 50%, demonstrating the limitations of the resolution characteristics for fine structures in existing X-ray CT scanners.

[0004] The inventors evaluated the resolution and noise characteristics of the two devices, A and B, using their respective indicators, MTF (modulation transfer function) and NPS (noise power spectrum). As a result, it was found that, at contrast levels such as CT angiography, the signal-to-noise ratio (SNR) is insufficient within the normally conceivable dose range, and that approximately nine times the dose is required to depict a resolution of about half the size of conventional images at the same level as conventional images. In other words, from the standpoint of radiation exposure and the performance limits of the X-ray tube, realizing ultra-high-resolution CT is difficult. Therefore, the subjects that can be adequately depicted are limited to the lungs and bones, which have contrast levels of 1000 HU (Hunsfield units) to 2000 HU, where high SNRs are easily obtained. Consequently, the current resolution is insufficient to adequately depict trabeculae (size: 0.15 mm), respiratory bronchioles (size: 0.3 mm), alveolar ducts (size: 0.1 mm), etc.

[0005] One possible reason for insufficient resolution is that factors causing blurring of the X-ray image exist during the X-ray image formation process, resulting in a blurred and non-sharp X-ray image. For example, during imaging with an X-ray CT scanner, vibration and deflection of the X-ray detector due to rotation can cause blurring of the X-ray image. X-ray rotational imaging devices are known that correct the coordinate position of measurement data due to such X-ray detector vibration to obtain high-quality images with high contrast and resolution in difference images, projection images, and reconstructed images (for example, Patent Document 1). However, even after correcting the coordinate position to account for X-ray detector vibration, the resolution of the resulting X-ray images was far below 0.1 mm, which was insufficient for adequately visualizing bone trabeculae, respiratory bronchioles, alveolar ducts, etc. [Prior art documents] [Non-patent literature]

[0006] [Patent Document 1] Japanese Patent Publication No. 2002-291726 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The object of the present invention is to provide an X-ray imaging device that has resolution characteristics capable of sufficiently visualizing bone trabeculae, respiratory bronchioles, alveolar ducts, etc., and also has excellent signal-to-noise ratio (SNR). [Means for solving the problem]

[0008] These objectives are achieved by the present invention as described in (1) to (12) below. (1) An X-ray irradiation unit including an X-ray tube for irradiating the subject with X-rays, An X-ray detection unit is positioned opposite the X-ray tube with the subject in between, and includes an X-ray detector that detects transmitted X-rays from the subject. A rotating mechanism comprising a rotating body configured to rotate around the subject, The system includes a control unit that controls the rotation of the rotating body and the irradiation of X-rays from the X-ray tube, The X-ray irradiation unit and the X-ray detection unit are attached to the rotating body, An X-ray imaging apparatus characterized in that, when the distance from the focal point of the X-ray tube to the center of rotation of the rotating body is X (mm), and the distance from the center of rotation to the detection surface of the X-ray detector is Y (mm), the ratio X:Y is 9:1 to 7:3.

[0009] (2) The X-ray imaging apparatus described in (1) above, wherein the rotating body is a ring-shaped frame. (3) The X-ray irradiation unit further comprises a first mounting member for fixing to the ring-shaped frame, The X-ray imaging apparatus according to (2) above, wherein the X-ray tube is attached to the first mounting member so as to be located on the outside of the ring-shaped frame.

[0010] (4) The X-ray detection unit further has a second mounting member for fixing to the ring-shaped frame, The X-ray imaging apparatus according to (2) or (3) above, wherein the X-ray detector is attached to the second attachment member so as to be located inside the ring-shaped frame.

[0011] (5) The X-ray imaging apparatus according to (3) above, wherein the X-ray tube is movably attached to the first attachment member. (6) The X-ray imaging apparatus according to (4) above, wherein the X-ray detector is movably attached to the second attachment member.

[0012] (7) When the size of the focal spot of the X-ray tube is F (mm), the distance from the focal spot of the X-ray tube to the rotation center of the rotating body is X (mm), and the distance from the rotation center to the detection surface of the X-ray detector is Y (mm), the penumbra P due to the focal spot at the rotation center represented by the following formula (1) is 0.1 to 0.25 mm. The X-ray imaging apparatus according to any one of (1) to (3) above. [Formula 1] P = F × Y / (X + Y) …(1)

[0013] (8) The X-ray imaging apparatus according to (7) above, wherein the size of the focal spot of the X-ray tube is 0.6 to 1.0 mm. (9) The X-ray imaging apparatus according to any one of (1) to (3) above, wherein the distance Y (mm) from the rotation center of the rotating body to the detection surface of the X-ray detector is 70 to 140 mm. (10) The X-ray imaging apparatus according to any one of (1) to (3) above, further comprising a pedestal disposed between the X-ray tube and the X-ray detector, on which the subject is placed.

[0014] (11) The subject is the head of the subject including the dentition of the subject, The control unit controls the rotating body to rotate half a turn while maintaining the state in which the X-ray detector is close to the dentition of the subject. The X-ray imaging apparatus according to any one of (1) to (3) above.

[0015] (12) The X-ray imaging apparatus according to (11) above, wherein the control unit controls the rotating body to rotate by (180+α) degrees when the fan angle of the X-ray tube is α (degrees). [Effects of the Invention]

[0016] In typical X-ray imaging devices, the X-ray tube and X-ray detector are positioned so as to overlap with the ring-shaped frame in a plan view of the ring-shaped frame, or inside the ring-shaped frame. Therefore, the distance from the X-ray tube to the rotation center of the ring-shaped frame is approximately equal to the distance from the rotation center of the ring-shaped frame to the X-ray detector. In contrast, according to the present invention, by positioning the X-ray tube outside the ring-shaped frame, the distance from the X-ray tube to the rotation center of the ring-shaped frame becomes longer than the distance from the rotation center to the X-ray detector. With this configuration, the penumbra caused by the focal point of the X-ray tube at the rotation center of the ring-shaped frame can be reduced, thereby suppressing blurring associated with the penumbra in the formed X-ray image. As a result, it is possible to provide an X-ray imaging device that has resolution characteristics capable of sufficiently depicting bone trabeculae, respiratory bronchioles, alveolar ducts, periodontal tissue, etc., and also has an excellent signal-to-noise ratio (SNR). [Brief explanation of the drawing]

[0017] [Figure 1] Figure 1 is a front view of an X-ray imaging apparatus (excluding the base) according to a first embodiment of the present invention. [Figure 2] Figure 2 is a perspective view of an X-ray imaging apparatus according to a first embodiment of the present invention. [Figure 3] Figure 3(a) is a schematic diagram of the configuration of a typical X-ray imaging device (X-ray CT scanner) used for medical purposes, and Figure 3(b) is a schematic diagram of the configuration of an X-ray imaging device according to the first embodiment of the present invention. [Figure 4] Figure 4 is a graph showing the relationship between spatial frequency (cycles / mm) and MTF in the X-ray imaging apparatus shown in Figures 3(a) and (b). [Figure 5]Figure 5 is a graph showing the relationship between spatial frequency (cycles / mm) and SNR2 in the X-ray imaging apparatus shown in Figures 3(a) and (b). [Figure 6] Figure 6 is a graph showing the SNR2 magnification of the X-ray imaging device shown in Figure 3(b) relative to the X-ray imaging device shown in Figure 3(a), calculated from the graph shown in Figure 5. [Figure 7] Figure 7 is a schematic diagram of the configuration of an X-ray imaging apparatus according to a second embodiment of the present invention. [Figure 8] Figure 8 is a schematic diagram of the configuration of an X-ray imaging apparatus according to a third embodiment of the present invention. [Figure 9] Figure 9 is a diagram illustrating the configuration of a rotating mechanism provided in an X-ray imaging apparatus according to a fourth embodiment of the present invention, where Figure 9(a) is a schematic diagram of the rotating mechanism viewed from the front, and Figure 9(b) is a schematic diagram of the rotating mechanism shown in Figure 9(a) viewed from the side. [Figure 10] Figure 10 is a schematic diagram illustrating the state of X-ray imaging of a subject's dentition using an X-ray imaging device (dental X-ray imaging device) according to the fifth embodiment of the present invention, where Figure 10(a) shows the state at the start of scanning, Figure 10(b) shows the state during scanning, and Figure 10(c) shows the state at the end of scanning. [Figure 11] Figure 11 shows X-ray images obtained by imaging a subject (a human foot phantom) using the X-ray imaging apparatus of the examples and comparative examples. [Figure 12] Figure 12 shows X-ray images obtained by imaging the subject (dental phantom) using the X-ray imaging apparatus of the examples and comparative examples. [Modes for carrying out the invention]

[0018] The X-ray imaging apparatus of the present invention comprises an X-ray irradiation unit, an X-ray detection unit, a rotation mechanism equipped with a rotating body configured to rotate around a subject, and a control unit. The X-ray imaging apparatus of the present invention will be described in detail below based on preferred embodiments shown in the accompanying drawings.

[0019] <First Embodiment> Figure 1 is a front view of an X-ray imaging apparatus (excluding the base) according to a first embodiment of the present invention. Figure 2 is a perspective view of an X-ray imaging apparatus according to a first embodiment of the present invention.

[0020] As shown in Figures 1 and 2, the X-ray imaging apparatus 100 of this embodiment includes an X-ray irradiation unit 1 including an X-ray tube 11, an X-ray detection unit 2 including an X-ray detector 21 positioned opposite the X-ray tube 11 with the subject O in between, a base 3 positioned between the X-ray tube 11 and the X-ray detector 21, a rotation mechanism 4 equipped with a ring-shaped frame 41 as a rotating body configured to rotate around the base 3, and a control unit 5. In this X-ray imaging apparatus 100, the subject O is placed on the base 3 (see Figure 2), X-rays are irradiated onto the subject O from the X-ray tube 11, and the X-ray detector 21 detects the transmitted X-rays from the subject O. Examples of the subject O include the limbs (hands, feet), head, chest, and abdomen of the human body. In particular, the X-ray imaging apparatus 100 of this embodiment is suitable for imaging the fine structure (trabeculae) of the limbs (hands, feet).

[0021] (X-ray irradiation section) The X-ray irradiation unit 1 includes an X-ray tube 11, a high-voltage generator 12, a collimator 13, and a first mounting member 14. The X-ray tube 11 irradiates the subject O with X-rays. The X-ray tube 11 is not particularly limited, but a rotating anode type X-ray tube that rotates the target to disperse heat can be used. Furthermore, reducing the size of the focal spot of the X-ray tube 11 reduces the penumbra caused by the focal spot of the X-ray tube 11, as described later, and is effective in increasing resolution. However, it is preferable not to reduce the size of the focal spot of the X-ray tube 11 too much. From the above viewpoint, the size of the focal spot of the X-ray tube 11 is preferably about 0.6 to 1.0 mm, and more preferably about 0.7 to 0.9 mm. If the size of the focal spot is within the above range, the penumbra caused by the focal spot of the X-ray tube 11 can be sufficiently reduced. In addition, sufficient X-ray output can be obtained, resulting in a high SNR and a reduction in scan time.

[0022] The high-voltage generator 12 is wired to the X-ray tube 11 and is supplied with power from an external power source (not shown). Under the control of the control unit 5, the high-voltage generator 12 supplies filament current to the cathode (filament) inside the X-ray tube 11 and also supplies (applies) a high voltage between the cathode and the anode (target). The collimator 13 is positioned on the subject O side of the X-ray tube 11 and is positioned to focus the X-ray beam of X-rays irradiated from the X-ray tube 11 to match the size of the X-ray detector 21.

[0023] The first mounting member 14 has the function of attaching the X-ray tube 11, high-voltage generator 12, and collimator 13 to the ring-shaped frame 41. The first mounting member 14 is fixed to the ring-shaped frame 41 at one end (lower side in the figure). The first mounting member 14 is a plate-like structure with a roughly rectangular shape, with two corners on the other end (upper side in the figure) cut out. The shape of the first mounting member 14 is not limited to the shape shown in Figure 1; any shape that allows the X-ray tube 11 to be positioned outside the ring-shaped frame 41 is acceptable. The first mounting member 14 may also be circular, elliptical, polygonal, trapezoidal, or other shapes. The X-ray tube 11 is mounted to the center of the other end of the first mounting member 14, the collimator 13 is mounted to the center of one end, and the high-voltage generator 12 is mounted to the side of the X-ray tube 11 and the collimator 13. The high-voltage generator 12 may also be mounted to the second mounting member 23, which will be described later.

[0024] In this embodiment, the X-ray tube 11 is attached to the other end of the first mounting member 14, so that the X-ray tube 11 is positioned outside the ring-shaped frame 41. By positioning the X-ray tube 11 outside the ring-shaped frame 41, the distance from the X-ray tube 11 to the rotation center C of the ring-shaped frame 41 becomes longer than the distance from the rotation center C to the X-ray detector 21. With this configuration, the penumbra P caused by the focal point of the X-ray tube 11 at the rotation center C of the ring-shaped frame 41 can be reduced (the penumbra P will be described later). Therefore, blurring associated with the penumbra P in the formed X-ray image can be suppressed. As a result, an X-ray imaging device can be provided that has resolution characteristics capable of sufficiently depicting fine structures such as bone trabeculae, respiratory bronchioles, alveolar ducts, and periodontal tissue, as well as having excellent SNR.

[0025] The distance X (mm) from the focal point of the X-ray tube 11 to the rotation center C of the ring-shaped frame 41 is preferably about 300 to 1400 mm, and more preferably about 400 to 1000 mm. If the distance X is within the above range, the distance from the focal point of the X-ray tube 11 to the rotation center C will be sufficiently longer than the distance from the rotation center C to the detection surface of the X-ray detector 21. Therefore, the ratio of the distance from the center of the subject O to the detection surface of the X-ray detector 21 to the distance from the focal point of the X-ray tube 11 to the detection surface of the X-ray detector 21, i.e., the magnification of the subject O, becomes smaller. As the magnification of the subject O decreases, the penumbra P becomes smaller, blurring in the X-ray image is suppressed, resulting in a sharper image and improved resolution. As a result, an X-ray imaging device with resolution characteristics capable of sufficiently depicting fine structures can be provided.

[0026] Furthermore, the distance from the focal point of the X-ray tube 11 to the outer surface of the ring-shaped frame 41 is preferably about 50 to 600 mm, and more preferably about 100 to 400 mm. If the distance from the focal point of the X-ray tube 11 to the outer surface of the ring-shaped frame 41 is within the above range, the centrifugal force generated by the rotation of the X-ray tube 11 can be suppressed, the load on the first mounting member 14 can be reduced, and the X-ray imaging device 100 can be used more safely. In addition, the overall size of the X-ray imaging device 100 can be sufficiently reduced.

[0027] (X-ray detection unit) The X-ray detection unit 2 includes an X-ray detector 21, a data acquisition system 22, and a second mounting member 23. The X-ray detector 21 is positioned opposite the X-ray tube 11, with the subject O in between, and detects the transmitted X-rays from the subject O. Such an X-ray detector 21 is constructed by arranging multiple detector elements in a two-dimensional manner. More specifically, multiple detector elements are arranged in a two-dimensional array to constitute the X-ray detector 21. Examples of X-ray detectors 21 include digital X-ray detectors such as indirect conversion type FPDs (Flat Panel Detectors) and direct conversion type FPDs.

[0028] An indirect conversion type FPD consists of a detector element formed from a phosphor such as thallium-activated cesium iodide (CsI:Tl), amorphous silicon, or a two-dimensional optical sensor such as CMOS. Although the specific configuration is not shown in the diagram, in an indirect conversion type FPD, the intensity of X-rays incident on the detector element (X-ray signal) is converted into the intensity of light (optical signal) by the phosphor. This optical signal is converted into a charge signal by a photodiode, and then detected as a voltage or current value.

[0029] Furthermore, direct conversion type FPDs have a detector element in which a voltage is applied to amorphous selenium (a-Se), which is a phosphor. In direct conversion type FPDs, X-ray images are formed in the same way as indirect conversion type FPDs described above, except that the X-ray signal incident on the detector element is directly converted into negative and positive charge signals using a-Se to which a voltage is applied.

[0030] The size of the detector elements constituting the X-ray detector 21 is advantageous for achieving high resolution as it is smaller, and is preferably 0.3 mm or less, more preferably 0.2 mm or less, and even more preferably 0.1 mm or less.

[0031] The voltage or current signal generated by the X-ray detector 21 is digitized within the X-ray detector 21 by an A / D (Analogue Digital) converter (not shown) and supplied to the data processing system 22. The data processing system 22 is wired to the X-ray detector 21 and is powered by an external power supply (not shown). The data processing system 22 includes a processing unit, a memory device, a transmitter, and a control device (none of which are shown). The data processing system 22 performs calculations on the supplied digital signal and transmits it to an image processing device (computer) via the transmitter, forming a two-dimensional image (X-ray image).

[0032] The second mounting member 23 has the function of attaching the X-ray detector 21 and the data processing system 22 to the ring-shaped frame 41. The second mounting member 23 is fixed to the ring-shaped frame 41 at one end (lower side in the figure) from its center. The shape of the second mounting member 23 is a plate-like shape forming a roughly rectangular shape with two corners cut out on the other end (upper side in the figure). The shape of the second mounting member 24 is not limited to the shape shown in Figure 1, and may be various shapes such as circular, elliptical, polygonal, or trapezoidal. An X-ray detector 21 is attached to the center of the other end of the second mounting member 23, and a data processing system 22 is attached to one end.

[0033] In this embodiment, the X-ray detector 21 is attached to the other end of the second mounting member 23, so that the X-ray detector 21 is positioned inside the ring-shaped frame 41. By positioning the X-ray detector 21 inside the ring-shaped frame 41, the distance from the rotation center C of the ring-shaped frame 41 to the X-ray detector 21 is shortened compared to when the X-ray detector 21 is positioned on the ring-shaped frame 41. With this configuration, the penumbra P formed by the focal point of the X-ray tube 11 at the rotation center C of the ring-shaped frame 41 can be made smaller. Therefore, blurring associated with the penumbra P in the formed X-ray image can be suppressed more effectively. As a result, it becomes possible to more clearly visualize fine structures such as bone trabeculae, respiratory bronchioles, alveolar ducts, and periodontal tissue.

[0034] The distance Y (mm) from the rotation center C of the ring-shaped frame 41 to the detection surface of the X-ray detector 21 is preferably about 50 to 300 mm, more preferably about 60 to 200 mm, and even more preferably about 70 to 140 mm. If the distance Y is within the above range, the distance from the rotation center C to the detection surface of the X-ray detector 21 becomes sufficiently shorter than the distance from the focal point of the X-ray tube 11 to the rotation center C. As a result, the magnification of the subject O becomes smaller. With a smaller magnification of the subject O, the penumbra P becomes smaller, blurring in the X-ray image is suppressed, resulting in a sharper image and improved resolution characteristics. As a result, an X-ray imaging device with resolution characteristics that can more sufficiently depict fine structures can be provided. In addition, if the distance is within the above range, the separation state between the X-ray detector 21 and the subject O is reliably ensured when the X-ray detector 21 rotates, and the X-ray imaging device 100 can be used more safely.

[0035] In this embodiment, the X-ray detector 21 is located inside the ring-shaped frame 41, but it may also be located on or outside the ring-shaped frame 41.

[0036] (pedestal) As shown in Figure 2, the base 3 has the function of placing the subject O on it. The base 3 is made of a long, flat plate. This base 3 is placed between the X-ray tube 11 and the X-ray detector 21. The base 3 is positioned so that the subject O placed on the base 3 is located at the rotation center C of the ring-shaped frame 41. The width of the base 3 can be adjusted as appropriate depending on the size of the subject to be placed on it. Specifically, when the subject is a limb (arm (from arm to hand) or leg (from knee to toe)), the width of the base 3 is preferably 100 to 200 mm, and more preferably 70 to 150 mm. When the subject is a chest or abdomen, the width of the base 3 is preferably 250 to 300 mm. When the subject is a head, the width of the base 3 is preferably 100 to 200 mm.

[0037] (Rotation mechanism) The rotating mechanism 4 includes a ring-shaped frame 41 and a drive motor 42. The ring-shaped frame 41 is composed of a ring-shaped frame and is configured to rotate around the base 3. As the ring-shaped frame 41 rotates, the X-ray irradiation unit 1 and the X-ray detection unit 2 rotate around the base 3 (the subject). At this time, X-rays are irradiated from the X-ray tube 21, and the X-ray detector 21 detects the X-rays that have passed through the subject O, thereby enabling the acquisition of a tomographic image of the subject O. The direction of rotation of the ring-shaped frame 41 is not particularly limited and may rotate clockwise or counterclockwise.

[0038] The inner diameter of the ring-shaped frame 41 can be appropriately changed depending on the size of the subject placed on the base 3. Specifically, when the limbs (arms, legs) are used as the subject, the inner diameter of the ring-shaped frame 41 is preferably about 400 to 800 mm, and more preferably about 500 to 600 mm. When the chest or abdomen is used as the subject, the inner diameter of the ring-shaped frame 41 is preferably about 600 to 700 mm. When the head is used as the subject, the inner diameter of the ring-shaped frame 41 is preferably about 400 to 700 mm.

[0039] The drive motor 42 is powered by an external power source (not shown) and rotates the ring-shaped frame 41 around the base 3 under the control of a control device provided by the data processing system 22. As such a drive motor 42, for example, a stepping motor can be used, from the viewpoint of being able to precisely control its position and speed.

[0040] (Control Unit) The control unit 5 controls the X-ray irradiation from the X-ray tube 11 (supply of filament current and high voltage from the high-voltage generator 12 to the X-ray tube 11) based on instructions from the user. More specifically, the control unit 5 controls the high-voltage generator 12 to change the interval between X-ray irradiations from the X-ray tube 11, the irradiation time per irradiation, the magnitude of the voltage applied to the X-ray tube, etc. The control unit 5 is wired and connected to the high-voltage generator 12. In the X-ray imaging apparatus 100 of this embodiment, the control unit 5 is attached to the first mounting member 14.

[0041] (Frame) Furthermore, the X-ray imaging device 100 also has a frame 70 that houses the X-ray irradiation unit 1, the X-ray detection unit 2, the base 3, the rotation mechanism 4, and the control unit 5. Each side of the frame 70 is composed of metal columns or beams. The frame 70 also includes support sections 71 made of metal plates that protrude inward from a pair of columns on the front side in Figure 1. The ring-shaped frame 41 is rotatably supported within the frame 70 by these support sections 71.

[0042] In the X-ray imaging apparatus 100 of this embodiment, as described above, the X-ray tube 11 is positioned outside the ring-shaped frame 41. Therefore, the distance from the X-ray tube 11 to the rotation center C of the ring-shaped frame 41 is longer than the distance from the rotation center C to the X-ray detector 21, thereby reducing the penumbra P caused by the focus of the X-ray tube 11 at the rotation center C of the ring-shaped frame 41.

[0043] Here, we will explain the penumbra P formed by the focal point of the X-ray tube 11 at the rotation center C of the ring-shaped frame 41 in the configurations of a general X-ray imaging device (X-ray CT device) used for medical purposes and an X-ray imaging device according to the first embodiment of the present invention.

[0044] Figure 3(a) is a schematic diagram of the configuration of a typical X-ray imaging device (X-ray CT scanner) used for medical purposes, and Figure 3(b) is a schematic diagram of the configuration of an X-ray imaging device according to the first embodiment of the present invention. The term "penumbra" refers to a physical property related to the size of the X-ray tube's focal point and the ratio of the distance from the center of the subject to the detection surface of the X-ray detector to the distance from the focal point of the X-ray tube to the detection surface of the X-ray detector. In other words, it is related to the magnification of the subject and indicates the degree of blurring that occurs in the X-ray image. A large penumbra results in a blurred, unsharp X-ray image, reducing the resolution. Conversely, a small penumbra suppresses the blurring in the resulting X-ray image, resulting in a sharper image and improving the resolution.

[0045] Furthermore, the X-ray imaging apparatus used, as shown in Figures 3(a) and 3(b), was an X-ray imaging apparatus with the following conditions. (X-ray imaging device shown in Figure 3(a)) X-ray tube focal spot size: 0.8 mm Detector element aperture size (detector element size): 0.1 mm Distance from the X-ray tube (focal point) to the center of rotation: 500 mm Distance from X-ray tube (focus) to X-ray detector: 900 mm (X-ray imaging device in Figure 3(b)) X-ray tube focal spot size: 0.8 mm Detector element aperture size (detector element size): 0.1 mm Distance from the X-ray tube (focal point) to the center of rotation: 450 mm Distance from X-ray tube (focus) to X-ray detector: 550 mm

[0046] Here, if we let F (mm) be the size of the focal point of the X-ray tube 11, X (mm) be the distance from the X-ray tube 11 to the rotation center C of the ring-shaped frame 41, and Y (mm) be the distance from the rotation center C to the X-ray detector 21, then the penumbra P due to the focal point of the X-ray tube 11 at the rotation center C is expressed by the following equation (1). [Formula 1] P = F × Y / (X + Y) …(1)

[0047] In typical X-ray imaging devices used for medical purposes, the X-ray tube 11 and X-ray detector 21 are positioned so as to overlap with the ring-shaped frame 41 in a plan view of the ring-shaped frame 41, or inside the ring-shaped frame 41, as shown in Figure 3(a). Therefore, the distance (X) from the X-ray tube 11 to the rotation center C of the ring-shaped frame 41 and the distance (Y) from the rotation center C of the ring-shaped frame 41 to the X-ray detector 21 are approximately equal. Consequently, the penumbra P (blur size) expressed by the above equation (1) is close to F / 2 (= F × Y / (Y + Y)).

[0048] Reducing the focal size F of the X-ray tube 11 is effective in reducing the penumbra and improving resolution. However, from the perspective of allowing sufficient current to flow through the X-ray tube and obtaining sufficient X-ray output, the focal size F of the X-ray tube 11 is often around 0.6 to 1.0 mm. As a result, in typical X-ray imaging devices, the penumbra P is around 0.3 to 0.5 mm, making it impossible to obtain sharp images of fine structures such as trabeculae (size: 0.15 mm), respiratory bronchioles (size: 0.3 mm), and alveolar ducts (size: 0.1 mm).

[0049] On the other hand, in the X-ray imaging apparatus 100 of this embodiment, the distance (X) from the focal point of the X-ray tube 11 to the rotation center C of the ring-shaped frame 41 is longer than the distance (Y) from the rotation center C to the detection surface of the X-ray detector 21, so that the penumbra P becomes sufficiently smaller than F / 2. As a result, blurring of the formed X-ray image can be suppressed, and an X-ray imaging apparatus with resolution characteristics that can sufficiently depict fine structures such as bone trabeculae, respiratory bronchioles, alveolar ducts, and periodontal tissue can be provided.

[0050] Furthermore, in the X-ray imaging apparatus 100 of this embodiment, since the X-ray detector 21 is positioned inside the ring-shaped frame 41, the distance (Y) from the rotation center C to the detection surface of the X-ray detector 21 is short. As a result, the ratio of distance (X) to distance (Y) becomes larger, and the penumbra P formed by the focus of the X-ray tube 11 at the rotation center C of the ring-shaped frame 41 can be made significantly smaller.

[0051] Furthermore, the X-ray imaging apparatus 100 of this embodiment exhibits superior signal-to-noise ratio (SNR) in the high spatial frequency range compared to general X-ray imaging apparatuses used for medical purposes. Figure 4 is a graph showing the relationship between spatial frequency (cycles / mm) and MTF in the X-ray imaging apparatus shown in Figures 3(a) and (b). Figure 5 shows the relationship between spatial frequency (cycles / mm) and SNR in the X-ray imaging apparatus shown in Figures 3(a) and (b). 2 This graph shows the relationship. Figure 6 shows the SNR of the X-ray imaging device shown in Figure 3(b) relative to the X-ray imaging device shown in Figure 3(a), calculated from the graph shown in Figure 5. 2 This is a graph showing the magnification.

[0052] SNR of X-ray imaging device (SNR 2 (u)) is expressed by the following equation (2), using MTF(u) (modulation transfer function), which is an indicator of resolution, and NPS(u) (noise power spectrum), which is an indicator of noise. Note that SNR 2 (u), MTF(u), and NPS(u) are all functions of spatial frequency (u). [Formula 2] SNR 2 (u) = MTF 2 (u) / NPS(u) …(2)

[0053] Furthermore, in Figures 4 to 6, the spatial frequency (cycles / mm) on the horizontal axis is related to the resolution, and the SNR of a spatial frequency of 1 cycle / mm 2 This is the SNR at a resolution of approximately 0.5 mm. 2is also the case that the SNR at a spatial frequency of 2 cycles / mm 2 is the SNR at a resolution of about 0.25 mm 2 The SNR at a spatial frequency of 3 cycles / mm 2 is the SNR at a resolution of about 0.17 mm 2 The SNR at a spatial frequency of 4 cycles / mm 2 is the SNR at a resolution of about 0.125 mm 2 The SNR at a spatial frequency of 5 cycles / mm 2 is the SNR at a resolution of about 0.1 mm 2 is as follows

[0054] As shown in FIG. 4, in the X-ray imaging apparatus shown in FIG. 3(a), since the penumbra P cannot be reduced, as the spatial frequency increases, the MTF(u) rapidly decreases. Therefore, at a relatively low spatial frequency (about 2.3 cycles / mm), the MTF(u) approaches zero. As a result, as shown in FIG. 5, the SNR 2 also approaches zero. On the other hand, in the X-ray imaging apparatus 100 of the present embodiment (FIG. 3(b)), since the penumbra P is very small, even when the spatial frequency increases, the MTF(u) decreases gently. Also, although the value of NPS changes in inverse proportion to the square of the X-ray focus-detector distance, it is offset by a coefficient determined by the magnification factor, and the value of NPS is the same between the X-ray imaging apparatus of FIG. 3(a) and the X-ray imaging apparatus 100. Therefore, even at a relatively high spatial frequency, the MTF(u) is significantly high, so the SNR 2 increases accordingly (see FIGS. 4 and 5).

[0055] Therefore, the X-ray imaging apparatus 100 of the present embodiment has an excellent SNR at a high spatial frequency (high resolution) compared to a general X-ray imaging apparatus. Also, as shown in FIG. 6, the SNR of the X-ray imaging apparatus 100 of the present embodiment (FIG. 3(b)) with respect to the X-ray imaging apparatus shown in FIG. 3(a) 2The magnification increases rapidly as the spatial frequency increases. Specifically, at a spatial frequency of approximately 2.6 cycles / mm, the SNR of the X-ray imaging apparatus 100 of this embodiment (Figure 3(b)) compared to the X-ray imaging apparatus shown in Figure 3(a) 2 The magnification will be around 100 times.

[0056] In the X-ray imaging apparatus 100 of this embodiment, when the distance from the focal point of the X-ray tube 11 to the rotation center C of the ring-shaped frame 41 is X (mm), and the distance from the rotation center C to the detection surface of the X-ray detector 21 is Y (mm), the ratio X:Y is 9:1 to 7:3. Furthermore, the ratio X:Y is preferably 8.8:1.2 to 7.2:2.8, and more preferably 8.5:1.5 to 7.5:2.5.

[0057] When the ratio X:Y is within the above range, the distance from the focal point of the X-ray tube 11 to the rotation center C becomes sufficiently longer than the distance from the rotation center C to the detection surface of the X-ray detector 21. Therefore, the ratio of the distance from the center of the subject O to the detection surface of the X-ray detector 21 to the distance from the focal point of the X-ray tube 11 to the detection surface of the X-ray detector 21, i.e., the magnification of the subject O, becomes small (see equation (1) above). As the magnification of the subject O becomes small, the penumbra P becomes very small, suppressing blurring in the formed X-ray image and resulting in a sharp image. Also, because the penumbra P is very small, the MTF(u) can be increased to a certain extent even at high spatial frequencies. Therefore, even at relatively high spatial frequencies (3 cycles / mm or more) with a resolution of 0.17 mm or less, where a sufficient SNR could not be obtained conventionally, a sufficiently good SNR can be obtained (see equation (2) above, Figures 4 and 5). As a result, it is possible to provide an X-ray imaging device that has resolution characteristics that enable more adequate visualization of fine structures such as bone trabeculae, respiratory bronchioles, alveolar ducts, and periodontal tissues, while exhibiting particularly excellent signal-to-noise ratio (SNR) in the high spatial frequency range.

[0058] Furthermore, the penumbra P represented by formula (1) above is preferably about 0.1 to 0.25 mm, and more preferably about 0.12 to 0.20 mm. When the penumbra P is a very small value within the above range, blurring in the formed X-ray image is suppressed, and a sharper image can be obtained.

[0059] In the X-ray imaging apparatus 100 of this embodiment described above, the X-ray detector 21 is located inside the ring-shaped frame 41, but it can also be positioned so as to overlap with the ring-shaped frame 41 in a plan view of the ring-shaped frame 41.

[0060] <Second Embodiment> Figure 7 is a schematic diagram of the configuration of an X-ray imaging apparatus according to a second embodiment of the present invention. The following description will focus on the differences between the X-ray imaging apparatus of the second embodiment and the X-ray imaging apparatus of the first embodiment, and will omit explanations of similar matters.

[0061] In this embodiment, the configuration of the X-ray irradiation unit 1 and the X-ray detection unit 2 is different, but otherwise it is the same as the X-ray imaging apparatus of the first embodiment described above. As shown in Figure 7, the X-ray irradiation unit 1 is equipped with a first moving mechanism 15 for moving the X-ray tube 11. This first moving mechanism 15 is attached to a first mounting member 14. The first moving mechanism 15 comprises a slide portion 16 to which the X-ray tube 11 is attached, a pair of guide portions 17 arranged parallel to each other, and a fixing portion (not shown).

[0062] The slide portion 16 is configured to be movable along the guide portion 17. The slide portion 16 has a roughly rectangular plate shape. Both sides of the slide portion 16 are slidably inserted into a pair of guide portions 17. The X-ray tube 11 is mounted approximately in the center of the slide portion 16, and by sliding the slide portion 16 along the guide portion 17, the X-ray tube 11 can be moved vertically in the first mounting member 14 in Figure 7. Each of the pair of guide portions 17 extends vertically from the first mounting member 14 and has the function of guiding the movement of the slide portion 16. The pair of guide portions 17 are mounted approximately in the center of the first mounting member 14, spaced apart so that the slide portion 16 is inserted between them. The sliding portion 16 slides along the guide portion 17 and is fixed to the guide portion 17 by the fixing portion at the desired position.

[0063] In this embodiment, the operation of the first moving mechanism 15 (sliding of the slide portion 16) allows the X-ray tube 11 to be moved closer to or further away from the rotation center C of the ring-shaped frame 41. That is, in this embodiment, the position of the X-ray tube 11 can be adjusted by sliding the slide portion 16 along the guide portion 17 and fixing it at the desired position with the fixing portion. In an X-ray imaging apparatus 100 with this configuration, the ratio X:Y of the distance X from the X-ray tube 11 to the rotation center C of the ring-shaped frame 41 and the distance Y from the rotation center C to the X-ray detector 21 can be freely adjusted according to the size of the subject and the desired resolution. Furthermore, the slide portion 16 can also be automatically slid by the control unit 5. In this case, the control unit 5 controls the vertical movement of the slide portion 16 based on the size of the subject O detected by a detection unit (not shown) and the distance (X) stored in the memory unit. This makes it easy to position the X-ray tube 11 in an appropriate location so that a high-resolution X-ray image can be obtained.

[0064] Furthermore, in this embodiment, as shown in Figure 7, the X-ray detection unit 2 is equipped with a second moving mechanism 24 for moving the X-ray detector 21, and this moving mechanism 24 is attached to the second mounting member 23. The second moving mechanism 24 includes a slide portion 25 to which the X-ray detector 21 is attached, a pair of guide portions 26 arranged parallel to each other, and a fixing portion (not shown).

[0065] The slide portion 25 is configured to be movable along the guide portion 26. The slide portion 25 has a roughly rectangular plate shape. Both sides of the slide portion 25 are slidably inserted into the pair of guide portions 26. The X-ray detector 21 is attached to the upper end of the slide portion 25, and by sliding the slide portion 25 along the guide portion 26, the X-ray detector 21 can be moved vertically in the second mounting member 23 in Figure 7. Each of the pair of guide portions 26 extends vertically from the second mounting member 23 and has the function of guiding the movement of the slide portion 25. The pair of guide portions 26 are mounted approximately in the center of the second mounting member 23, spaced apart so that the slide portion 25 is inserted between them. The sliding portion 25 slides along the guide portion 26 and is fixed to the guide portion 26 by the fixing portion at the desired position.

[0066] Similar to the first moving mechanism 15 described above, the operation of the second moving mechanism 24 (sliding of the slide portion 25) allows the X-ray detector 21 to be moved closer to or further away from the rotation center C of the ring-shaped frame 41. In other words, in this embodiment, the position of the X-ray detector 21 can be adjusted by sliding the slide portion 25 along the guide portion 26 and fixing it at the desired position with the fixing portion. In an X-ray imaging device 100 with this configuration, the ratio X:Y can be adjusted more freely to match the size of the subject and the desired resolution. Furthermore, the slide portion 25 can also be automatically slid by the control unit 5. In this case, the control unit 5 controls the vertical movement of the slide portion 25 based on the size of the subject O detected by a detection unit (not shown) and the distance (Y) stored in the memory unit. This makes it easy to position the X-ray detector 21 in an appropriate location so that a high-resolution X-ray image can be obtained.

[0067] In particular, when the chest or abdomen is used as the subject O, the width of the base 3 needs to be larger than when the limbs are used as the subject O. In this case, it is necessary to ensure a sufficient distance between the base 3 and the X-ray detector so that the rotating X-ray detector 21 does not interfere with the base 3 and the subject O. In such cases, the desired ratio X:Y can be satisfied by adjusting the position of the X-ray detector 21 so that it is away from the rotation center C of the ring-shaped frame 41, and by adjusting the position of the X-ray tube 11 so that it is away from the rotation center C of the ring-shaped frame 41.

[0068] Furthermore, in cases where the subject is small, such as a fingertip, the desired ratio X:Y can be satisfied by adjusting the position of the X-ray detector 21 so that it is close to the rotation center C of the ring-shaped frame 41, and by adjusting the position of the X-ray tube 11 so that it is close to the rotation center C of the ring-shaped frame 41. In the above description, a configuration was described in which the first moving mechanism 15 and the second moving mechanism 24 are provided so that the position of either the X-ray tube 11 or the X-ray detector 21 can be adjusted. However, it is also possible to provide only one of the first moving mechanism 15 and the second moving mechanism 24 so that the position of either the X-ray tube 11 or the X-ray detector 21 can be adjusted.

[0069] The X-ray imaging apparatus of this second embodiment also produces the same functions and effects as the X-ray imaging apparatus of the first embodiment.

[0070] <Third Embodiment> Figure 8 is a schematic diagram of the configuration of an X-ray imaging apparatus according to a third embodiment of the present invention. The following description focuses on the differences between the X-ray imaging apparatus of the third embodiment and the X-ray imaging apparatus of the first and second embodiments, and similar matters will be omitted from the explanation.

[0071] In this embodiment, the X-ray imaging apparatus is the same as that of the first embodiment described above, except that the X-ray tube 11 of the X-ray irradiation unit 1 is located inside the ring-shaped frame 41.

[0072] In this embodiment, as shown in Figure 8, the X-ray tube 11 is fixed to the inside of the ring-shaped frame 41 via the first mounting portion 41. The X-ray irradiation unit 1 is the same as in the first and second embodiments described above, except that the position in which the first mounting member 14 is fixed to the ring-shaped frame 41 is different.

[0073] Furthermore, in this embodiment, since the X-ray tube 11 is positioned inside the ring-shaped frame 41, it is preferable to use a ring-shaped frame 41 having a larger inner diameter than the ring-shaped frame 41 used in the first embodiment described above. For example, when the limbs (arms, legs) are used as the subject, it is preferable that the inner diameter of the ring-shaped frame 41 be about 800 to 1500 mm, and more preferably about 800 to 1200 mm.

[0074] Similar to the first embodiment described above, when the ratio X:Y is within the above range, the distance from the focal point of the X-ray tube 11 to the rotation center C becomes sufficiently longer than the distance from the rotation center C to the detection surface of the X-ray detector 21. Therefore, even if the X-ray tube 11 is arranged inside the ring-shaped frame 41, as in this embodiment, the same effects and advantages as the X-ray imaging apparatus 100 of the first embodiment described above can be obtained.

[0075] <Fourth Embodiment> Figure 9 is a diagram illustrating the configuration of a rotating mechanism provided in an X-ray imaging apparatus according to a fourth embodiment of the present invention, where Figure 9(a) is a schematic diagram of the rotating mechanism viewed from the front, and Figure 9(b) is a schematic diagram of the rotating mechanism shown in Figure 9(a) viewed from the side. The following description focuses on the differences between the X-ray imaging apparatus of the fourth embodiment and the X-ray imaging apparatus of the first to third embodiments, and similar matters will be omitted from the explanation.

[0076] In this embodiment, the configuration is the same as the first embodiment described above, except for the difference in the rotation mechanism. The overlapping parts are omitted. Instead of the ring-shaped frame 41, an arm 43 is used as the rotating body of the aforementioned rotation mechanism 4. Although Figure 9 shows a configuration in which the arm 43 rotates clockwise, the configuration is not limited to this, and the arm 43 may rotate counterclockwise. The rotating mechanism 4 of this embodiment includes an arm 43 and a drive motor 44 that drives (rotates) the arm 43.

[0077] The arm 43 is made of a long, flat plate and is configured to rotate on the upper part of the base 3. The arm 43 has an X-ray irradiation unit 1 and an X-ray detection unit 2 attached to both ends. As the arm 43 rotates, the X-ray irradiation unit 1 and the X-ray detection unit 2 rotate around the base 3 (the subject). At this time, X-rays are irradiated from the X-ray tube 21, and the X-ray detector 21 detects the X-rays that have passed through the subject O, thereby enabling the acquisition of a tomographic image of the subject O.

[0078] The length of the arm 43 can be appropriately changed depending on the size of the subject placed on the base 3. Specifically, when the limbs (arms and legs) are used as the subject, the length of the arm 43 is preferably about 400 to 800 mm, and more preferably about 500 to 700 mm. When the chest or abdomen is used as the subject, the length of the arm 43 is preferably about 700 to 1000 mm. When the head is used as the subject, the length of the arm 43 is preferably about 400 to 700 mm.

[0079] In this embodiment, the X-ray irradiation unit 1 has a rod-shaped first mounting member 14, and the X-ray detection unit 2 has a rod-shaped second mounting member 23. The first mounting member 14 has a base end that is fixed to one end of the arm 43 and a tip to which the X-ray tube 11 is attached. The second mounting member 23 has a base end that is fixed to the other end of the arm 43 and a tip to which the X-ray detector 21 is attached. Although not shown in the diagram, the high-voltage generator 12 and collimator 13 of the X-ray irradiation unit 1 are located on one end of the arm 43. Also, although not shown in the diagram, the data acquisition system 22 of the X-ray detection unit 2 is located on the other end of the arm 43.

[0080] The drive motor 44 is powered by an external power source (not shown) and rotates the arm 43 on the top of the base 3 under the control of a control device provided by the data processing system 22. A motor similar to the drive motor 42 described above can be used for this drive motor 44; for example, a stepping motor can be used. The drive motor 44 is fixed to a frame (not shown). As the drive motor 44 rotates, the arm 43 rotates around the upper part of the base 3 relative to this frame.

[0081] Similar to the first embodiment described above, when the ratio X:Y is within the above range, the distance from the focal point of the X-ray tube 11 to the rotation center C becomes sufficiently longer than the distance from the rotation center C to the detection surface of the X-ray detector 21. Therefore, the same effects and advantages as the X-ray imaging apparatus 100 of the first embodiment described above can be obtained.

[0082] Furthermore, by using the arm 43 instead of the ring-shaped frame 41, the weight of the rotation mechanism 4 can be reduced. In addition, when not in operation, the X-ray imaging device 100 of this embodiment has a smaller installation area compared to the X-ray imaging device 100 using the ring-shaped frame 41. Therefore, the storage space for the X-ray imaging device 100 can be reduced.

[0083] Furthermore, the first mounting member 14 and the second mounting member 23 may each be configured to be movable in the longitudinal direction of the arm 43. If the first mounting member 14 and the second mounting member 23 are movable in the longitudinal direction of the arm 43, the ratio X:Y of the distance X from the X-ray tube 11 to the rotation center C of the ring-shaped frame 41 and the distance Y from the rotation center C to the X-ray detector 21 can be freely adjusted according to the size of the subject and the desired resolution.

[0084] <Fifth Embodiment> Figure 10 is a schematic diagram illustrating the state of X-ray imaging of a subject's dentition using an X-ray imaging device (dental X-ray imaging device) according to the fifth embodiment of the present invention, where Figure 10(a) shows the state at the start of scanning, Figure 10(b) shows the state during scanning, and Figure 10(c) shows the state at the end of scanning. The following description will focus on the differences between the X-ray imaging apparatus of the fifth embodiment and the X-ray imaging apparatus of the first to fourth embodiments, and will omit explanations of similar matters.

[0085] In this embodiment, we will describe a case in which the X-ray imaging device 100 of the first embodiment described above is used as a dental X-ray imaging device to image the head of a subject O, including the dentition O1. In the X-ray imaging apparatus 100 of each embodiment described above, the X-ray irradiation unit 1 and the X-ray detection unit 2 are configured to rotate 1 full turn around the base 3 as the ring-shaped frame 41 rotates. In contrast, in the X-ray imaging apparatus 100 of this embodiment, it is preferable that the rotation of the ring-shaped frame 41 is restricted, so that the X-ray irradiation unit 1 and the X-ray detection unit 2 rotate approximately half a turn around the base 3. The following describes X-ray imaging of the subject's head, including the dentition, using the X-ray imaging device 100 of this embodiment.

[0086] Figure 10(a) shows the state at the start of scanning by the X-ray imaging device 100. In this embodiment, the subject's head is positioned so that the center of the subject's dental arch O1 is located at the rotation center C of the ring-shaped frame 41. In the configuration of Figure 10, the base 3 is not used, but the base 3 can be used to support the subject's occipital region O2 to prevent the subject's head from moving during scanning.

[0087] The initial position of the X-ray irradiation unit 1 is set considering the fan angle (opening): α degrees, which depends on the size of the focal point of the X-ray tube 11. Specifically, in Figure 10(b), a straight line passing through the rotation center C and parallel to the detection surface of the X-ray detector 21 is defined as line L. The X-ray irradiation unit 1 is positioned in a counterclockwise direction of line L such that the angle between the line connecting the focal point of the X-ray tube 11 and the rotation center C and line L is α / 2 degrees. When the fan angle is 10 degrees, the initial positions of the X-ray irradiation unit 1 and the X-ray detection unit 2 are set to a position rotated 5 degrees counterclockwise from line L.

[0088] During scanning by the X-ray imaging device 100, as shown in Figure 10(b), the X-ray irradiation unit 1 and the X-ray detection unit 2 rotate clockwise to acquire a tomographic image of the dentition O1. Subsequently, as shown in Figure 10(c), the scan by the X-ray imaging device 100 ends when the X-ray irradiation unit 1 reaches a position rotated α / 2 degrees clockwise from the straight line L. If the fan angle is 10 degrees, the scan ends when the X-ray irradiation unit 1 is rotated 5 degrees clockwise from the straight line L.

[0089] Therefore, in this embodiment, the control unit 5 controls the rotation of the ring-shaped frame 41 so that the X-ray irradiation unit 1 and the X-ray detection unit 2 rotate clockwise by (180 + α) (= α / 2 + 180 + α / 2) degrees. This scanning method, which involves approximately half a rotation (190 degrees when α = 10 degrees), is called the half-scan method.

[0090] As shown in Figures 10(a) to 10(c), X-ray imaging by the X-ray imaging device 100 is performed with the X-ray detector 21 always in close proximity to the dentition O1 of the subject O. Furthermore, since the control unit 5 restricts the rotation of the X-ray detector 21 toward the occipital region O2 of the subject O, the X-ray detector 21 can be positioned close to the rotation center C.

[0091] Conventional dental X-ray imaging systems are configured so that the X-ray tube and X-ray detector rotate 360 ​​degrees around the patient's head. In such dental X-ray imaging systems, if the X-ray detector is configured to rotate closer to the patient's dentition in order to reduce the penumbra caused by the focus of the X-ray tube, the X-ray detector will collide with the back of the patient's head during rotation. Therefore, it is necessary to set a large rotation radius for the X-ray detector to prevent it from colliding with the back of the patient's head during rotation. However, in such a configuration, the X-ray detector detects X-rays at a position far from the patient's dentition, so the penumbra caused by the focus of the X-ray tube cannot be reduced, resulting in a blurred X-ray image and reduced resolution. Furthermore, with such a configuration, it is not possible to achieve a sufficiently high signal-to-noise ratio (SNR) in the high spatial frequency range.

[0092] On the other hand, in the X-ray imaging apparatus 100 of this embodiment, since X-ray imaging is performed using the half-scan method, the X-ray detector 21 can be positioned near the rotation center C of the ring-shaped frame 41, that is, close to the dentition O1 of the subject O. Therefore, as described above, the distance from the focal point of the X-ray tube 11 to the rotation center C is sufficiently longer than the distance from the rotation center C to the detection surface of the X-ray detector 21. As a result, the same effects and advantages as those of the X-ray imaging apparatus 100 of the first embodiment described above can be obtained. Furthermore, even if the X-ray imaging apparatus 100 of the second to fourth embodiments described above is used instead of the X-ray imaging apparatus 100 of the first embodiment, the above-mentioned effects and advantages can be obtained by performing X-ray imaging using the half-scan method. Although Figure 10 shows a configuration in which the ring-shaped frame 41 rotates clockwise, the positions of the X-ray irradiation unit 1 and the X-ray detector 2 may be swapped so that the ring-shaped frame 41 rotates counterclockwise.

[0093] Although the X-ray imaging apparatus of the present invention has been described above based on the illustrated embodiment, the present invention is not limited thereto, and each component can be replaced with any component capable of performing a similar function, or components of any configuration can be added. [Examples]

[0094] Next, the X-ray images captured using the X-ray imaging apparatus of the present invention will be described based on the following specific examples.

[0095] (Examples) An X-ray imaging apparatus, as shown in Figure 3(b), that satisfies the aforementioned conditions was prepared. (Comparative example) An X-ray imaging apparatus, as shown in Figure 3(a), that satisfies the aforementioned conditions was prepared.

[0096] [X-ray image evaluation (foot phantom)] X-ray imaging was performed on a human foot phantom (corresponding to the heel to toe area of ​​the human body) using the X-ray imaging apparatus of the example (Figure 3(b)) and comparative example (Figure 3(a)), and the obtained X-ray images were evaluated. The X-ray irradiation conditions for the X-ray tube were: tube voltage: 80kV, tube current (filament current): 7mA, and irradiation time: 5000msec. The results are shown in Figure 11.

[0097] [X-ray image evaluation (dental phantom)] Using the X-ray imaging apparatuses of the Example (Figure 3(b)) and Comparative Example (Figure 3(a)), X-ray imaging of dental phantoms was performed using the half-scan method from the scan start position shown in Figure 10(a) to the scan end position shown in Figure 10(c), and the obtained X-ray images were evaluated. The X-ray irradiation conditions for the X-ray tube were: tube voltage: 80kV, tube current (filament current): 7mA, and irradiation time: 5000msec. The results are shown in Figure 12.

[0098] Figure 11 shows X-ray images obtained by imaging a subject (a human foot phantom) using the X-ray imaging devices of the examples and comparative examples. Figure 12 shows X-ray images obtained by imaging a subject (a dental phantom) using the X-ray imaging devices of the examples and comparative examples.

[0099] As shown in Figure 11, when using the X-ray imaging device of the example for a human foot phantom, almost no blurring was observed, and an X-ray image clearly depicting the bone trabeculae (size: 0.15 mm) was obtained. On the other hand, when using the X-ray imaging device of the comparative example, a blurry and unsharp X-ray image was formed, and the bone trabeculae were not clearly depicted. Furthermore, as shown in Figure 12, even with dental phantoms, using the X-ray imaging device of the example, blurring was almost completely absent, and X-ray images clearly depicting periodontal tissues such as alveolar bone and dental pulp were obtained. On the other hand, when using the X-ray imaging device of the comparative example, blurry and unsharp X-ray images were formed, and periodontal tissues such as alveolar bone and dental pulp were not clearly depicted. [Industrial applicability]

[0100] According to the present invention, by positioning the X-ray tube outside the ring-shaped frame, the distance from the X-ray tube to the rotation center of the ring-shaped frame becomes longer than the distance from the rotation center to the X-ray detector. In this configuration, the penumbra caused by the focal point of the X-ray tube at the rotation center of the ring-shaped frame can be reduced, thereby suppressing blurring associated with the penumbra in the formed X-ray image. As a result, an X-ray imaging device can be provided that has resolution characteristics capable of sufficiently depicting bone trabeculae, respiratory bronchioles, alveolar ducts, periodontal tissue, etc., and also has an excellent signal-to-noise ratio (SNR). Therefore, the present invention has industrial applicability. [Explanation of symbols]

[0101] 1...X-ray irradiation section 11...X-ray tube 12… High-voltage generator 13...Collimator 14…First mounting member 15…First moving mechanism 16...Slide section 17… Guide Section 2...X-ray detection unit 21...X-ray detector 22...Data Processing System 23…Second mounting member 24...Second mobility mechanism 25...Slide part 26… Guide Section 3…Pedestal 4…Rotation mechanism 41... Ring-shaped frame 42…Drive motor 43... Arm 44…Drive motor 5…Drive unit 70…Frame body 71...Support part 100...X-ray imaging device O...Subject (test subject) O1...dentition O2…occiput C... Center of rotation of the ring-shaped frame L…straight line

Claims

1. An X-ray irradiation unit including an X-ray tube for irradiating the subject with X-rays, An X-ray detection unit is positioned opposite the X-ray tube with the subject in between, and includes an X-ray detector that detects transmitted X-rays from the subject. A rotating mechanism comprising a rotating body configured to rotate around the subject, The system includes a control unit that controls the rotation of the rotating body and the irradiation of X-rays from the X-ray tube, The X-ray irradiation unit and the X-ray detection unit are attached to the rotating body. An X-ray imaging apparatus characterized in that, when the distance from the focal point of the X-ray tube to the center of rotation of the rotating body is X (mm), and the distance from the center of rotation to the detection surface of the X-ray detector is Y (mm), the ratio X:Y is 9:1 to 7:

3.

2. The X-ray imaging apparatus according to claim 1, wherein the rotating body is a ring-shaped frame.

3. The X-ray irradiation unit further includes a first mounting member for fixing to the ring-shaped frame, The X-ray imaging apparatus according to claim 2, wherein the X-ray tube is attached to the first mounting member so as to be located on the outside of the ring-shaped frame.

4. The X-ray detection unit further includes a second mounting member for fixing to the ring-shaped frame, The X-ray imaging apparatus according to claim 2 or 3, wherein the X-ray detector is mounted on the second mounting member so as to be located inside the ring-shaped frame.

5. The X-ray imaging apparatus according to claim 3, wherein the X-ray tube is movably mounted to the first mounting member.

6. The X-ray imaging apparatus according to claim 4, wherein the X-ray detector is movably mounted on the second mounting member.

7. An X-ray imaging apparatus according to any one of claims 1 to 3, wherein, when the size of the focal point of the X-ray tube is F (mm), the distance from the focal point of the X-ray tube to the center of rotation of the rotating body is X (mm), and the distance from the center of rotation to the detection surface of the X-ray detector is Y (mm), the penumbra P at the center of rotation due to the focal point, as expressed by the following formula (1), is 0.1 to 0.25 mm. [Formula 1] P=F×Y / (X+Y)…(1)

8. The X-ray imaging apparatus according to claim 7, wherein the size of the focal point of the X-ray tube is 0.6 to 1.0 mm.

9. The X-ray imaging apparatus according to any one of claims 1 to 3, wherein the distance Y (mm) from the rotation center of the rotating body to the detection surface of the X-ray detector is 70 to 140 mm.

10. The X-ray imaging apparatus according to any one of claims 1 to 3, further comprising a base disposed between the X-ray tube and the X-ray detector on which the subject is placed.

11. The subject is the head including the teeth of the subject, The X-ray imaging apparatus according to any one of claims 1 to 3, wherein the control unit controls the rotating body to rotate half a turn while maintaining the state in which the X-ray detector is close to the teeth of the subject.

12. The X-ray imaging apparatus according to claim 11, wherein, when the fan angle of the X-ray tube is α (degrees), the control unit controls the rotating body to rotate by (180 + α) degrees.

Images