JP6132477B2 - Medical diagnostic imaging equipment - Google Patents

Description

Embodiments of the present invention relates to a medical image diagnostic equipment with improved diagnostic accuracy of the head test, for example, detecting the radiation (gamma rays) emitted from a radioactive isotope substance is administered to the subject by the radiation detector In particular, the present invention relates to a single-photon emission computed tomography (SPECT) apparatus that reconstructs an image based on detection data, and more particularly to a fan beam SPECT apparatus that obtains detection data using a fan beam collimator. Alternatively, the present invention relates to a medical image diagnostic apparatus provided with an X-ray CT apparatus and a SPECT apparatus.

  Conventionally, in order to inspect the head of a subject such as a patient, the radiation (gamma rays) emitted from a radioisotope (hereinafter referred to as RI) administered to the subject is collimated into a fan beam and collimated. SPECT apparatuses that detect fan beam-like radiation and collect fan beam projection data are used.

  There are various SPECT devices, such as a method of rotating a single gamma camera 360 degrees, a method of providing a plurality of sets of radiation detection units (gamma cameras), and rotating a predetermined angle. A gamma ray emitted from the tomographic plane is detected to obtain projection data in a specific direction, and a data group for reconstructing the RI distribution image is obtained. As a head SPECT device including a plurality of sets of gamma cameras, for example, a SPECT device described in Patent Document 1 or a three-detector type GCA-9300A series SPECT device manufactured by Toshiba is known.

  The head SPECT apparatus is provided with a hole into which the head of the subject can be inserted into the gantry, and a plurality of gamma cameras including a collimator and a detector around the hole inside the gantry. In addition, the subject is placed on the top plate of the bed apparatus so that the head of the subject can be taken in and out of the hole provided in the gantry.

  By the way, when the head is inserted into the hole, the patient feels terror when he sees the rotating gamma camera, especially for the elderly, when the comma camera rotates slightly in front of him Will lead to a decrease in inspection accuracy. For this reason, a head cover is attached around the hole to prevent the gamma camera from being seen from the subject, thereby reducing fear.

  However, when the head cover is attached, a subject with a short neck may hit the head cover with a shoulder, and the head may not enter the back of the hole. When the head does not enter the back, for example, the cerebellum is missing from the field of view and the information of the cerebellum is not entered, which has a problem that the diagnosis itself is affected.

JP-A-3-67194

Problems to be Solved by the Invention is that the entire cerebellum also included head, to provide a medical image diagnostic equipment examined to allow without causing vision chipping.

A medical image diagnostic apparatus according to an embodiment includes a bed on which a subject is placed, a collimator that collimates radiation emitted from a radioisotope administered to the subject in a fan beam shape, and the collimated fan beam The collimator has a slant hole structure inclined with respect to the detection surface of the detector and a fan beam structure in a direction perpendicular to the body axis of the subject. And a radiation detection unit in which the focal length of the fan beam gradually decreases from the first position in the body axis direction to the second position, and the slant hole of the collimator is orthogonal to the body axis. As described above, the angle adjustment unit that tilts the radiation detection unit with respect to the body axis of the subject, and the position adjustment that sets the position of the radiation detection unit with respect to the subject A gantry having a hole into which the subject is inserted, and the radiation detector disposed around the hole, and a head of the subject that is fitted in the hole of the gantry and placed on the bed A first accommodating portion having a first diameter for accommodating the portion, and the first accommodating portion connected to the first accommodating portion, so as to accommodate a portion from the head of the subject to the shoulder, than the first diameter. A cylindrical head cover including a second accommodating portion having a space with a large second diameter .

1 is a side view showing a medical image diagnostic apparatus according to an embodiment. 1 is a front view showing a medical image diagnostic apparatus according to an embodiment. Explanatory drawing which shows the structure of the radiation detection part provided in the medical image diagnostic apparatus which concerns on one Embodiment. The side view which shows the structure of the radiation detection part and head cover in one Embodiment. The front view which shows the structure of the collimator of the radiation detection part in one Embodiment. The perspective view which shows the head cover in one Embodiment. The side view which shows the modification of the head cover in one Embodiment. 1 is a system configuration diagram of a medical image diagnostic apparatus according to an embodiment. The flowchart which shows the operation | movement of the data processing of the medical image diagnostic apparatus which concerns on one Embodiment. The conceptual diagram of the fan parallel conversion in one Embodiment. Explanatory drawing which shows an example of the fan parallel conversion process in one Embodiment. The perspective view which shows the medical image diagnostic apparatus which concerns on 2nd Embodiment.

  Hereinafter, a medical image diagnostic apparatus according to an embodiment will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected about the same location.

(First embodiment)
FIG. 1 is a side view illustrating a medical image diagnostic apparatus according to an embodiment, for example, a SPECT (Single-Photon Emission Computed Tomography) apparatus. FIG. 2 is a front view of the SPECT apparatus. In the following description, the SPECT apparatus will be described as an example, but the SPECT / CT apparatus including the X-ray CT apparatus and the SPECT apparatus is not limited to the SPECT apparatus.

  As shown in FIGS. 1 and 2, a medical image diagnostic apparatus (SPECT apparatus) 10 includes a gantry 11, a bed 12, and a computer (described later). The gantry 11 has a hole 15 into which the head of the subject 14 placed on the top plate 13 of the bed 12 can be inserted, and a plurality of (for example, three) radiation detectors including a collimator and a detector are included in the gantry 11. Part (to be described later).

  A subject 14 is placed on the top plate 13 of the bed 12 so that the head can be taken in and out of the hole 15. A head cover 16 is attached to the hole 15. The effective field of view of the SPECT image in diagnosis is determined by the diameter R and depth L of the hole 15 and is R × L. A headrest 17 is provided at the bottom of the hole 15.

  FIG. 3 is an explanatory diagram showing the configuration of the radiation detection unit provided in the gantry 11. As shown in FIG. 3, first, second, and third radiation detection units (gamma cameras) 21, 22, and 23 are arranged in the gantry 11. The gamma cameras 21, 22, and 23 are configured by collimators 211, 221, and 231, and scintillation cameras 212, 222, and 232 that are detectors that convert radiation (gamma rays) into light and detect the light around the hole 15. They are arranged every 120 degrees so as to form a triangle.

  In general, the SPECT apparatus uses a fan beam collimator or a parallel beam collimator to collect gamma rays emitted from the subject 14 in the same direction. For example, when the diagnostic site is small like the head, data is collected using a fan beam collimator to enlarge the effective visual field of the head and improve the resolution. When the diagnosis site is a heart or the like, data may be collected by simultaneously using a fan beam collimator and a parallel beam collimator.

  The detectors 212, 222, and 232 detect collimated fan beam-like gamma rays and create fan beam projection data including a plurality of projection data.

  The gamma cameras 21, 22, and 23 are attached to a rotating frame provided inside the gantry 11, and the rotation angle of the gamma cameras 21, 22, and 23 is controlled by driving the rotating frame with a motor. Note that the number of gamma cameras is not limited to three, and two gamma cameras may be arranged facing each other.

  FIG. 4 is a side view showing the configuration of the gamma cameras 21, 22 and 23 and the head cover 16. Since the gamma cameras 21, 22, and 23 have the same configuration, the first gamma camera 21 will be described as a representative. In FIG. 4, the gamma camera 21 rotates around the subject 14, the state above the subject 14 is indicated by a solid line, and the state below the subject 14 is indicated by a dotted line.

  The gamma camera 21 is tilted with respect to the body axis X around a fulcrum 24 provided at the center of the gamma camera 21, for example, by a tilt mechanism (angle adjustment unit) that tilts the angle with respect to the body axis X of the subject 14. Can be inclined. The collimator 211 has a slant hole structure in the body axis direction and a fan beam structure in a direction perpendicular to the body axis.

  That is, the collimator 211 has a slant hole structure in which parallel holes are inclined by a predetermined angle α with respect to an axis Q orthogonal to the detection surface of the detector 212. Further, as shown in FIG. 5, the collimator 211 has a fan beam structure in a direction perpendicular to the body axis. The focal length of the fan beam is gradually increased in the direction of the cerebellum to prevent truncation.

  5A shows the fan beam structure of the collimator 211 on the inlet side of the hole 15 (first position A in FIG. 4), and FIG. 5B shows the rear side (second position B in FIG. 4). 2 shows the fan beam structure of the collimator 211 at 1. In FIGS. 5A and 5B, W1 and W2 indicate effective visual fields when a SPECT image is reconstructed from projection data when the fan beam collimator 211 is used, and F indicates a virtual focus of the fan beam. Show.

  As shown in FIGS. 5A and 5B, the collimator 211 changes the focal length of the fan beam from the first position (cerebellar part) in the body axis X direction to the second position (the top of the head). By gradually shortening, truncation can be prevented and a high-field head fan beam SPECT inspection can be performed. Note that the gamma camera 21 using the collimator 211 having the slant hole structure and the fan beam structure in which the virtual focus F gradually changes is also a general-purpose 1-detector 2-detector-type SPECT apparatus that does not use the head cover 16. It is valid.

  As can be seen from FIGS. 4 and 5, since the top of the patient is close to the gamma camera 21 and the focal length of the fan beam of the collimator 211 is short, the resolution of the cerebrum is ensured. Further, the fan beam shape of the collimator 211 has a focal length that gradually increases from near the top of the head to the cerebellum, so that the resolution near the cerebellum is somewhat reduced, but can be within the effective visual field. It is effective because the resolution of the cerebrum is maintained clinically and the visual field of the entire brain is covered.

  Next, the configuration of the head cover 16 will be described. As shown in FIG. 4, the head cover 16 has a cylindrical portion 18 that fits into a hole 15 (FIG. 1) into which the head H of the subject 14 is inserted, and a part of the inlet portion of the cylindrical portion 18 (subject 14) (space where 14 shoulder tips hit) is wide. FIG. 6 is a perspective view of the head cover 16, and is provided with a cylindrical portion 18 that accommodates the head of the subject 14 and a space 19 that can accommodate a portion from the head of the subject 14 to the shoulder. The inlet portion of the cylindrical portion 18 has a flange 20 that is fixed to the outer wall surface of the gantry 11. The cylindrical portion 18 is inserted into the hole 15, and the ridge portion 20 is fixed to the outer wall surface of the gantry 11. 11 is integrated.

  FIG. 7 is a side view showing a modified example of the head cover 16, and has a truncated cone shape in which the end portion in the back direction of the cylindrical portion 18 is gradually narrowed. Also in the head cover 16 of FIG. 7, a part of the entrance portion of the cylindrical portion 18 is wide, and has a space 19 in which the shoulder of the subject 14 can be put, so that the visual field for the subject 14 is widened. Can do.

  Next, data collection and image processing by the SPECT apparatus 10 in the first embodiment will be described.

  FIG. 8 is a system configuration diagram of the SPECT apparatus 10. In FIG. 8, the gantry 11 includes a radiation detection unit (gamma camera) 21. In FIG. 8, only the gamma camera 21 is shown for the sake of convenience. However, as shown in FIG. 3, it may be provided with three gamma cameras 21, 22, 23, or two or four. That's all. The gamma camera 21 includes a fan beam collimator 211 and a detector 221, and the fan beam collimator 211 is provided on the surface facing the subject 14.

  The gamma camera 21 detects gamma rays emitted from the RI distributed in the subject 14 and can rotate 360 degrees around the subject 14. When the subject 14 is imaged, the gamma camera 21 detects gamma rays from a 360 degree direction while rotating around the subject 14. The collimator 211 has a slant hole structure in the body axis direction and a fan beam structure in a direction perpendicular to the body axis, and the focal length of the fan beam is changed from the first position in the body axis X direction to the second position. It gradually shortens toward the position.

  Further, a SPECT data collection unit 31 is connected to the gamma camera 21, and projection data acquired by the gamma camera 21 is collected by the SPECT data collection unit 31. The SPECT data collection unit 31 is connected to the bus line 32, and the bus line includes a preprocessing unit 33, a fan / parallel conversion unit 34, a reconstruction unit 35, a cross-section conversion unit 36, an image display unit 37, and an image storage unit 39. And the system controller 39 are connected.

  The fan beam projection data collected by the SPECT data collection unit 31 is sent to the preprocessing unit 33, performs preprocessing for improving the image quality of the captured image, and sends the preprocessed data to the fan / parallel conversion unit 34. The fan / parallel converter 34 performs fan / parallel conversion on the fan beam projection data preprocessed by the preprocessing unit 33 to generate parallel beam projection data, and writes the parallel beam projection data in the image memory.

  That is, the fan-parallel conversion converts the fan beam projection data detected using the collimator 221 into data substantially the same as the parallel projection data detected using the parallel beam collimator. The reconstruction unit 35 reconstructs an image using the parallel beam projection data written in the image memory of the fan / parallel conversion unit 34, for example, a three-dimensional reconstruction image showing an RI density distribution tomogram in the subject. Create data.

  Further, the reconstruction unit 35 may employ a method of reconstructing using the fan beam projection data as it is (direct method reconstruction). That is, the collected fan beam projection data can be taken out as it is (after being pre-processed as necessary), and reconstruction processing can be performed by a direct method reconstruction algorithm to obtain reconstruction data. Fan-parallel conversion and direct method reconstruction are well-known techniques.

  The cross-section conversion unit 36 generates, for example, an axial image, a sagittal image, and a coronal image obtained by performing cross-section conversion from the three-dimensional reconstruction image data generated by the reconstruction unit 35. The image display unit 37 displays the image whose cross section is converted by the cross section conversion unit 36 on the display screen. The image storage unit 38 stores the three-dimensional reconstructed image data created by the reconstruction unit 35 and each image data that has undergone cross-section conversion by the cross-section conversion unit 36.

  The system controller 39 is a computer including a CPU, a RAM, a ROM, and the like, and controls each part of the SPECT apparatus 10. The system controller 39 controls the tilt mechanism (angle adjustment unit) of the gamma cameras 21, 22, and 23 to change the tilt angle. Further, the bed 12 is controlled to adjust the height of the top plate 13, or the position of the top plate 13 is moved along the body axis direction (X) of the subject 14 so that the position of the gantry 11 relative to the subject 14 is relative. Adjust to. Therefore, the system controller 39 also functions as a position adjustment unit.

  Next, the outline of the data processing operation by the SPECT apparatus 10 will be described with reference to the flowchart of FIG. In step S1 of FIG. 9, the subject 14 is placed on the top plate 13 of the SPECT apparatus 10 (or SPECT / CT apparatus).

  Step S2 shows the adjustment operation of the gamma camera 21, and first the collimator 211 is attached. The collimator 211 includes a plurality of slant holes having different angles, and any one of them can be selected and mounted in accordance with the subject or examination. A head cover 16 is attached. Next, the inclination angle of the detector 212 is set. That is, when the head H of the subject 14 is put into the hole 15, the tilt angle of the gamma camera 21 is set and positioned so that the slant hole of the collimator 211 is at an angle orthogonal to the body axis X of the subject 14. (See FIG. 4).

  Next, the head H of the subject 14 (patient) laid on the top plate 13 of the bed 12 is placed in the head cover 16. At this time, the shoulder tip is slightly inserted into the space 19 of the head cover 16 to determine the position of the patient. After positioning the patient in this way, the head fan beam SPECT data is collected by the SPECT data collecting unit 31.

  Step S3 shows a process step in the data processing unit. The data processing unit includes a preprocessing unit 33, a fan / parallel conversion unit 34, a reconstruction unit 35, and a cross-section conversion unit 36. After preprocessing, the data processing unit performs fan / parallel conversion and reconstructs the parallel-converted image (parallel). Reconfigure). Or you may reconfigure | reconstruct by a direct method, without performing fan parallel conversion.

  In order to perform fan-parallel conversion and reconstruction, since the focal length and rotation radius of the fan beam in each slice direction are known, processing is performed by performing fan-parallel conversion and parallel reconstruction in consideration thereof. Alternatively, it is processed by direct method reconstruction.

Here, fan-parallel conversion and parallel reconstruction will be described. Hereinafter, the projection data collected by the fan beam collimator 211 is referred to as fan beam data, and the projection data collected by the parallel beam collimator is referred to as parallel beam data. The collected fan beam data is converted into parallel beam data by fan-parallel conversion and used as projection data for reconstruction.
FIG. 10 is a conceptual diagram of fan-parallel conversion. Fan-beam data as shown in FIG. 10A is fan-parallel converted to obtain parallel beam data as shown in FIG. Then, the reconstruction unit 35 reconstructs the parallel beam projection data and creates reconstructed image data.

  In the fan-parallel conversion, first, sinogram data is created for all slices. Next, since the focal length of the fan beam data in the body axis direction varies depending on the slice position, fan-parallel conversion is performed at different focal lengths for each slice, and the sinogram data is rearranged into two-dimensional projection data. Then, the projection data is enlarged so that the actual pixel lengths in the body axis direction (X axis) and the direction perpendicular to the body axis (Y axis) are the same. The parallel reconstruction is the same as the normal parallel SPECT acquisition data reconstruction method.

  FIG. 11 shows a sinogram obtained by two-dimensionally developing projection data collected using the gamma camera 211 in the θ direction and the X direction, and fan-parallel conversion is performed by using fan beam sinograms (a) and (b) as parallel beam sinograms. Convert to (c). That is, the fan-parallel conversion is performed by interpolating data between fan beam data f collected in an oblique lattice shape as shown in FIG. To parallel beam data p. Also, as shown in FIG. 11 (b), data is interpolated between the fan beam data f collected in an oblique lattice shape, and parallel beam data p arranged in a lattice shape as shown in FIG. 11 (c). Convert to

  FIG. 11A shows a fan beam sinogram based on projection data collected by a collimator 211 having a long focal length as shown in FIG. 5A, for example. FIG. 10B shows a fan beam sinogram based on projection data collected by the collimator 211 having a short focal length as shown in FIG.

  As described with reference to FIGS. 4 and 5, the focal length of the fan beam of the collimator 211 is long in the portion corresponding to the cerebellum of the patient, and gradually decreases toward the tip (cerebrum) of the head. The fan-parallel conversion process (how to interpolate) is also gradually changed from the cerebellum to the top of the head.

  On the other hand, in the direct method reconstruction, the fan beam projection data is directly reconstructed without using fan-parallel conversion to generate reconstructed image data. That is, in direct method reconstruction, first, sinogram data is created for all slices. Next, two-dimensional direct reconstruction is performed at different focal lengths for each slice, so that the actual pixel lengths in the body axis direction (X axis) and the direction perpendicular to the body axis (Y axis) are the same. Dimensional reconstruction data is interpolated and expanded in the body axis direction.

  Also in this case, the focal length of the fan beam of the collimator 211 is long in the portion corresponding to the patient's cerebellum, and gradually decreases toward the tip of the head (cerebrum). It gradually changes from the cerebellum to the top of the head.

  Considering the distance from the virtual focus to the detector, including the slant hole inclination of the collimator 211, and the fact that the slant hole is inclined, the image is enlarged in the body axis direction. Correction is necessary so that the actual pixel lengths in the direction (X axis) and the direction perpendicular to the body axis (Y axis) are the same.

  According to the first embodiment, the collimator 211 has a slant hole structure in the body axis direction, a fan beam structure in a direction perpendicular to the body axis, and the focal length of the fan beam is compared with the detector 212. By gradually increasing the length according to the distance from the specimen (for example, from the top of the head toward the cerebellum), examination including the cerebellum can be performed and truncation can be prevented. In addition, since the head cover 16 is attached, an empty space is generated near the patient's line of sight, so there is less fear than collecting with a parallel collimator, reducing the patient's load at the time of the examination, and reducing the patient's body movement. Can also be reduced.

(Second Embodiment)
FIG. 12 is a perspective view showing a two-detector type SPECT apparatus 40 which is a medical image diagnostic apparatus according to the second embodiment and has a radiation detection unit outside the gantry. In this embodiment, a head cover is unnecessary.

  In FIG. 12, the rotating plate 42 of the gantry 41 is provided with arms 43 and 44. The arms 43 and 44 are provided with first and second radiation detection units (gamma cameras) 45 and 46, respectively, and a subject (not shown). And the detection surfaces are supported so as to face each other. By rotating the rotating plate 42, the gamma cameras 45 and 46 can rotate around the subject. A collimator 47 is provided on the gamma ray incident side of the two gamma cameras 45 and 46. In FIG. 12, the collimator 47 is shown only for the gamma cameras 45 and 46.

  The gamma cameras 45 and 46 are provided with a scintillation camera (not shown) that is a detector that detects gamma rays by converting them into light facing the collimator 47. The gamma cameras 45 and 46 can tilt the angle with respect to the body axis of the subject. For example, the gamma cameras 45 and 46 are centered on fulcrums 48 and 49 provided at the center of the gamma cameras 45 and 46 with respect to the body axis. Can be tilted. The collimator 47 has a slant hole structure in the body axis direction as shown in FIG. 4, and has a fan beam structure in the direction perpendicular to the body axis, as shown in FIG. .

  A subject can be inserted into the hole 50 of the gantry 41, and the head can be inserted between the gamma cameras 45 and 46. Further, truncation is prevented by gradually increasing the focal length of the fan beam of the collimator 47 in the direction of the cerebellum.

  The gantry 41 moves on the rails 52 and 53 provided along the body axis of the subject, thereby moving in parallel (in the direction of the arrow X) with respect to the body axis of the subject, and adjusting the position of the gamma camera. The arms 43 and 44 are attached to the rotary plate 42 so as to be slidable in the vertical direction (Y direction) so that the gamma cameras 45 and 46 can approach and separate from the subject independently.

  The SPECT device 40 shown in FIG. 12 can tilt the gamma cameras 45 and 46 with respect to the body axis around the fulcrums 48 and 49. An example of the tilted state is indicated by a dotted line. When collecting SPECT data, the collimator 47 is first attached to the gamma cameras 45 and 46. The collimator 47 includes a plurality of slant holes having different angles, and any one of them can be selected and mounted in accordance with the subject or examination.

  Next, the inclination angle of the detectors of the gamma cameras 45 and 46 is set. That is, when the head of the subject is put between the gamma cameras 45 and 46, the inclination angle of the gamma cameras 45 and 46 is set so that the slant hole of the collimator 47 becomes an angle orthogonal to the body axis X of the subject. Set. The subject (patient) is placed on the bed and positioned, and then the head fan beam SPECT is collected.

  The collected data is subjected to fan-parallel conversion, and the parallel-converted image is reconstructed (parallel reconstruction). Alternatively, reconstruction is performed by a direct method without performing fan-parallel conversion.

  As described above, in the two-detector type SPECT apparatus 40 in which the gamma camera is outside the gantry, the collimator has a slant hole structure in the body axis direction and a fan beam structure in a direction perpendicular to the body axis. In addition, by gradually increasing the focal length of the fan beam in the direction of the cerebellum, examination including the cerebellum can be performed and truncation can be prevented. In the configuration of FIG. 12, the SPECT apparatus 40 including two gamma cameras has been described. However, any SPECT apparatus including one or a plurality of, that is, at least one gamma camera may be used.

  According to the embodiment of the present invention, it is possible to inspect the head including the cerebellum and provide a medical image diagnostic apparatus that prevents truncation.

  As mentioned above, although several embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the invention described in the claims and equivalents thereof as well as included in the scope and gist of the invention.

10, 40 ... Medical diagnostic imaging device (SPECT device)
DESCRIPTION OF SYMBOLS 11, 41 ... Stand 12 ... Bed 13 ... Top plate 14 ... Subject 15 ... Hole 16 ... Head cover 18 ... Tube part 19 ... Space 21, 22, 23, 45, 46 ... Radiation detection part (gamma camera)
211, 221, 231, 47 ... collimators 212, 222, 232 ... detector 31 ... SPECT data collection unit 32 ... bus line 33 ... pre-processing unit 34 ... fan / parallel conversion unit 35 ... reconstruction unit 36 ... cross-section conversion unit 37 ... Image display unit 38 ... Image storage unit 39 ... System controller

Claims (6)

A bed on which the subject is placed;
A collimator that collimates the radiation emitted from the radioisotope administered to the subject in a fan beam shape, and a detector that detects the collimated fan beam radiation, the collimator comprising the detector And a fan beam structure in a direction perpendicular to the body axis of the subject, from a first position toward the second position in the body axis direction. A radiation detector that gradually shortens the focal length of the fan beam;
An angle adjustment unit for inclining the radiation detection unit with respect to the body axis of the subject so that a slant hole of the collimator is orthogonal to the body axis;
A position adjustment unit for setting the position of the radiation detection unit with respect to the subject;
A pedestal having a hole into which the subject is inserted, and the radiation detector disposed around the hole;
A first accommodating part having a first diameter for accommodating the head of the subject placed in the hole of the gantry and placed on the bed; and connected to the first accommodating part; A cylindrical head cover including a second accommodating portion having a space with a second diameter larger than the first diameter in order to accommodate a portion from the head of the subject to the shoulder;
A medical image diagnostic apparatus comprising:   When the radiation detection unit inspects the head of the subject, the position adjustment unit is configured so that the first position is near the cerebellum and the second position is near the top of the head. The medical image diagnostic apparatus according to claim 1, wherein the detection unit is positioned.   The medical image diagnostic apparatus according to claim 1, wherein the radiation detection unit is rotatably disposed around the hole in the gantry.   2. The medical image according to claim 1, wherein the diameter of the head cover gradually decreases from an end portion of the second housing portion on the bed side toward an end portion of the first housing portion on the opposite side to the bed. 3. Diagnostic device. A fan-parallel conversion unit that performs interpolation processing on the fan beam projection data collected by the radiation detection unit and converts the data into substantially the same data as the parallel projection data detected using a parallel beam collimator,
A reconstruction unit that reconstructs an image based on parallel beam projection data obtained by the fan-parallel conversion unit, and
2. The medical image diagnosis according to claim 1, wherein the fan-parallel converter changes the interpolation processing in accordance with the focal length of the fan beam gradually decreasing from the first position toward the second position. apparatus. A reconstruction unit that creates reconstruction image data by direct method reconstruction of fan beam projection data collected by the radiation detection unit;
2. The medical image according to claim 1, wherein the reconstruction unit changes a direct method reconstruction algorithm in accordance with a gradually decreasing focal length of the fan beam from the first position toward the second position. Diagnostic device.

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