JP2022037495A - X-ray ct apparatus, image processing method and program - Google Patents

Abstract

To improve the image quality of an image obtained with expansion of an FOV.SOLUTION: An X-ray CT apparatus according to an embodiment comprises: an imaging system; a rotary frame; a first acquisition unit; a second acquisition unit; and a reconstruction processing unit. The imaging system comprises: an X-ray tube; and an X-ray detector which detects the X-ray emitted from the X-ray tube and passing through a subject. The rotary frame supports the imaging system so as to be rotatable around the subject. The first acquisition unit acquires first projection data indicating a detection result of the X-ray detector by rotating the rotary frame in such a state where the imaging system is in the first arrangement. The second acquisition unit acquires second projection data including the detection result of the subject that is not included in the first projection data in such a state that the imaging system is in the second arrangement that is relatively moved in the in-plane direction horizontal to the rotary surface of the rotary frame with respect to the subject. The reconstruction processing unit executes reconstruction processing on the basis of the first projection data and the second projection data.SELECTED DRAWING: Figure 1

Description

The embodiments disclosed in the present specification and the like relate to an X-ray CT apparatus, an image processing method, and a program.

Conventionally, in an X-ray CT apparatus, an FOV (Fields of View), which is an imaging range, is set by an operator or the like when photographing a subject. Further, conventionally, the boundary position between the region of the subject existing outside the FOV and another region (air) is estimated from the tendency of the count value in the FOV obtained by imaging, and the count value up to the boundary is estimated. A technique (also referred to as FOV expansion correction, eFOV, etc.) for pseudo-expanding the FOV by predicting the decay curve has been proposed.

However, in the conventional technique, the boundary position with the air outside the FOV is derived by estimation, so that it may be different from the actual boundary position. Therefore, if the FOV is expanded based on an erroneous boundary position, the image quality of the image obtained by reconstruction or the like may deteriorate.

Japanese Unexamined Patent Publication No. 2014-35208

One of the problems to be solved by the embodiments disclosed in the present specification and the like is to improve the image quality of the image obtained by expanding the FOV. However, the problems solved by the embodiments disclosed in the present specification and the like are not limited to the above problems. The problem corresponding to each effect by each configuration shown in the embodiment described later can be positioned as another problem solved by the embodiment disclosed in the present specification.

The X-ray CT apparatus according to the embodiment includes a photographing system, a rotating frame, a first acquisition unit, a second acquisition unit, and a reconstruction processing unit. The imaging system includes an X-ray tube and an X-ray detector that detects X-rays irradiated from the X-ray tube and transmitted through the subject. The rotating frame rotatably supports the imaging system around the subject. The first acquisition unit acquires the first projection data showing the detection result of the X-ray detector by rotating the rotation frame with the photographing system in the first arrangement. The second acquisition unit is used for the first projection data in a state in which the imaging system is relatively moved in the in-plane direction horizontal to the rotation surface of the rotation frame with respect to the subject. The second projection data including the detection result of the subject which is not included is acquired. The reconstruction processing unit executes the reconstruction processing based on the first projection data and the second projection data.

FIG. 1 is a diagram showing a configuration example of an X-ray CT apparatus according to the first embodiment. FIG. 2 is a diagram for explaining an operation example of the moving mechanism according to the first embodiment. FIG. 3 is a diagram for explaining another operation example of the moving mechanism according to the first embodiment. FIG. 4 is a diagram showing an example of projection data according to the first embodiment. FIG. 5 is a diagram showing an example of the counting result according to the first embodiment. FIG. 6 is a diagram for explaining an example of the conversion process executed by the extended function of the first embodiment. FIG. 7 is a partially enlarged view of the vicinity of the right end portion of the subject shown in FIG. FIG. 8 is a diagram schematically showing an example of the reconstructed image according to the first embodiment. FIG. 9 is a diagram showing an example of projection data corrected by the conversion function of the first embodiment. FIG. 10 is a flowchart showing an example of processing performed by the X-ray CT apparatus of the first embodiment. FIG. 11 is a diagram showing a configuration example of the X-ray CT apparatus according to the second embodiment.

Hereinafter, embodiments of the X-ray CT apparatus will be described in detail with reference to the drawings. Further, the X-ray CT apparatus according to the present application is not limited to the embodiments shown below. Further, the embodiment can be combined with other embodiments or conventional techniques as long as the contents do not conflict with each other. Further, in the following description, common reference numerals will be given to similar components, and duplicate description will be omitted.

Further, the X-ray CT apparatus described in the following embodiment is an apparatus capable of performing photon counting CT. That is, the X-ray CT apparatus described in the following embodiment counts the X-rays that have passed through the subject using a photon counting type X-ray detector (photon counting type detector), thereby counting the X-ray CT image. It is a device that can reconstruct data. Further, in the following embodiments, the scan performed by the X-ray CT apparatus (hereinafter, also referred to as “photographing”) means a conventional scan or a helical scan.

[First Embodiment]
FIG. 1 is a diagram showing a configuration example of an X-ray CT apparatus according to the first embodiment. As shown in FIG. 1, the X-ray CT device 1 according to the present embodiment includes a gantry device 10, a bed device 30, and a console device 40.

Here, in FIG. 1, the longitudinal direction of the rotation axis of the rotation frame 13 in the non-tilt state or the top plate 33 of the bed device 30 is the Z-axis direction. Further, the axial direction orthogonal to the Z-axis direction and horizontal to the floor surface is defined as the X-axis direction. Further, the axial direction orthogonal to the Z-axis direction and perpendicular to the floor surface is defined as the Y-axis direction. Note that FIG. 1 is a drawing of the gantry device 10 from a plurality of directions for the sake of explanation, and shows a case where the X-ray CT device 1 has one gantry device 10.

The gantry device 10 includes an X-ray tube 11, an X-ray detector 12, a rotating frame 13, an X-ray high voltage device 14, a control device 15, a wedge 16, a collimator 17, and a DAS (Data Acquisition System). Has 18 and.

The X-ray tube 11 is a vacuum tube having a cathode (filament) that generates thermions and an anode (target) that receives the collision of thermions and generates X-rays. The X-ray tube 11 generates X-rays to irradiate the subject P by irradiating thermions from the cathode toward the anode by applying a high voltage from the X-ray high voltage device 14.

The X-ray detector 12 is a photon counting type detector, and outputs a signal capable of measuring the energy value of the X-ray photon each time an X-ray photon is incident. The X-ray photon is, for example, an X-ray photon irradiated from the X-ray tube 11 and transmitted through the subject P. The X-ray detector 12 has a plurality of detection elements that output one pulse of an electric signal (analog signal) each time an X-ray photon is incident. By counting the number of electric signals (pulses), it is possible to count the number of X-ray photons incident on each detection element (count number). Further, by performing arithmetic processing on this signal, it is possible to measure the energy value of the X-ray photon that caused the output of the signal. For example, the X-ray detector 12 is a surface detector in which detection elements are arranged in N rows in the channel direction (X-axis direction in FIG. 1) and M rows in the slice direction (Z-axis direction in FIG. 1). ..

The above-mentioned detection element is composed of, for example, a scintillator and an optical sensor such as a photomultiplier tube. In such a case, the X-ray detector 12 is an indirect conversion type detector that converts the incident X-ray photon into scintillator light by a scintillator and converts the scintillator light into an electric signal by an optical sensor such as a photomultiplier tube. Further, in the above-mentioned detection element, for example, an electrode is arranged on a semiconductor detection element such as CdTe (cadmium telluride) or CdZnTe (cadmium zinc telluride). In such a case, the X-ray detector 12 becomes a direct conversion type detector that directly converts the incident X-ray photon into an electric signal.

The X-ray detector 12 has a plurality of the above-mentioned detection element and an ASIC (Application Specific Integrated Circuit) connected to the detection element and counting X-ray photons detected by the detection element. The ASIC discriminates the individual charges output by the detection element to count the number of X-ray photons incident on the detection element. Further, the ASIC measures the energy of the counted X-ray photons by performing arithmetic processing based on the magnitude of each electric charge. Further, the ASIC outputs the counting result of the X-ray photon as digital data to the DAS18.

The rotating frame 13 supports the X-ray tube 11 and the X-ray detector 12 facing each other, and the control device 15 rotates the X-ray tube 11 and the X-ray detector 12 around the top plate 33 (subject P). It is an annular frame to make. For example, the rotating frame 13 is a casting made of aluminum. Further, the rotating frame 13 supports an X-ray high voltage device 14, a wedge 16, and a collimator 17 in addition to the X-ray tube 11 and the X-ray detector 12. Further, the rotating frame 13 can further support a DAS 18 or the like or various configurations (not shown).

The wedge 16 is a filter for adjusting the X-ray dose emitted from the X-ray tube 11. Specifically, the wedge 16 transmits and attenuates the X-rays emitted from the X-ray tube 11 so that the X-rays emitted from the X-ray tube 11 to the subject P have a predetermined distribution. It is a filter to do. For example, the wedge 16 is a wedge filter or a bow-tie filter, which is a filter obtained by processing aluminum or the like so as to have a predetermined target angle and a predetermined thickness.

The collimator 17 is a lead plate or the like for narrowing the irradiation range of X-rays transmitted through the wedge 16, and a slit is formed by a combination of a plurality of lead plates or the like. The collimator 17 is an example of an X-ray diaphragm unit. Further, in FIG. 1, a case where the wedge 16 is arranged between the X-ray tube 11 and the collimator 17 is shown, but there is a case where the collimator 17 is arranged between the X-ray tube 11 and the wedge 16. May be good. In this case, the wedge 16 is irradiated from the X-ray tube 11 and transmits and attenuates the X-ray whose irradiation range is limited by the collimator 17.

The X-ray high-voltage device 14 has an electric circuit such as a transformer and a rectifier, and has a high-voltage generator that generates a high voltage applied to the X-ray tube 11 and an X-ray that is generated by the X-ray tube 11. It has an X-ray control device that controls the output voltage according to the above. The high voltage generator may be a transformer type or an inverter type. The X-ray high voltage device 14 may be provided on the rotating frame 13 or on a fixed frame (not shown).

The control device 15 has a processing circuit having a CPU (Central Processing Unit) and the like, and a drive mechanism such as a motor and an actuator. The control device 15 receives an input signal from the input interface 43 and controls the operation of the gantry device 10 and the bed device 30. The control device 15 may be provided in the gantry device 10 or in the console device 40.

For example, the control device 15 controls the rotation of the rotating frame 13, the tilting operation of the gantry device 10, and the like. As an example, the control device 15 rotates the rotating frame 13 about an axis parallel to the X-axis direction based on the input tilt angle (tilt angle) information as a control for tilting the gantry device 10.

Further, in the X-ray CT apparatus 1 of the present embodiment, an imaging system 19 composed of an X-ray tube 11, an X-ray detector 12, a wedge 16, a collimator, etc., and a sleeper device 30 (top plate 33) are provided. It is equipped with a mechanism for changing the relative placement position (hereinafter, also referred to as a movement mechanism). The control device 15 changes the arrangement relationship between the photographing system 19 and the bed device 30 by controlling the operation of the moving mechanism.

FIG. 2 is a diagram for explaining an operation example of the moving mechanism. FIG. 2 shows the arrangement positions of the X-ray tube 11 and the X-ray detector 12 among the parts constituting the photographing system 19 for the sake of simplification of the description. The X-ray tube 11 irradiates X-rays at a fan angle of 2θ according to the FOV. Further, the X-ray detector 12 is arranged so as to face the X-ray tube 11 at a position sandwiching the top plate 33, and detects X-ray photons transmitted through the subject P on the top plate 33.

Under the control of the control device 15, the moving mechanism moves the photographing system 19 relative to the sleeper device 30 in the in-plane direction of the rotating surface of the rotating frame 13 or in a direction orthogonal to the rotating surface. Here, the plane formed by the X-axis and the Y-axis corresponds to the rotating plane of the rotating frame 13, and the directions of the X-axis and the Y-axis correspond to the in-plane direction horizontal to the rotating plane. Further, the Z-axis direction corresponds to an out-of-plane direction orthogonal to the rotation plane of the rotation frame 13. For example, as shown in FIG. 2, the movement mechanism moves the photographing system 19 (X-ray tube 11, X-ray detector 12) arranged at the default position A1 relative to the movement amount M1 minutes in the X-axis direction. By doing so, the photographing system 19 is arranged at the position A2 indicated by the broken line.

The configuration of the moving mechanism is not particularly limited, and various configurations can be adopted. For example, the moving mechanism may have a configuration in which the arrangement position of the rotating frame 13 in the gantry device 10 can be moved in the X-axis or Y-axis direction. In this case, as shown in FIG. 2, for example, the moving mechanism moves the arrangement position of the rotating frame 13 in the X direction to change the relative position of the photographing system 19 with respect to the bed device 30 (top plate 33) from the position A1. Move to position A2.

Further, the moving mechanism may have a configuration in which the arrangement position of the photographing system 19 on the rotating frame 13 can be moved in the X-axis or Y-axis direction. In this case, as shown in FIG. 2, for example, the moving mechanism moves the arrangement position of the photographing system 19 on the rotating frame 13 in the X direction, so that the position of the photographing system 19 relative to the bed device 30 (top plate 33) is relative to the bed device 30 (top plate 33). Is moved from position A1 to position A2. Further, in this case, the moving mechanism may be in the form of moving either the X-ray tube 11 or the X-ray detector 12 constituting the photographing system 19. It should be noted that the moving mechanism moves the other elements constituting the photographing system 19 in association with the movement of the X-ray tube 11 and the X-ray detector 12.

Further, as shown in FIG. 3, the moving mechanism may have a configuration in which the arrangement position of the top plate 33 with respect to the photographing system 19 (X-ray tube 11, X-ray detector 12) can be moved. Here, FIG. 3 is a diagram for explaining another operation example of the moving mechanism.

In FIG. 3, the moving mechanism moves the arrangement position of the top plate 33 with respect to the photographing system 19 in either the X-axis direction or the Y-axis direction under the control of the control device 15. For example, the moving mechanism moves the top plate 33 in the X-axis direction by the amount of movement M1 to arrange the top plate 33 at the position indicated by the broken line. As a result, the moving mechanism can move the relative position of the photographing system 19 with respect to the bed device 30 (top plate 33) from the position A1 to the position A2.

Due to the operation of the moving mechanism described above, the range of the subject P imaged by the photographing system 19, that is, the FOV, changes with the movement of the photographing system 19 or the top plate 33. In this embodiment, a configuration in which the arrangement position of the photographing system 19 can be moved will be described.

Returning to FIG. 1, the DAS 18 generates detection data based on the counting result input from the X-ray detector 12. The detection data is, for example, a synogram. The synogram is data in which the results of counting processing incident on each detection element at each position of the X-ray tube 11 (hereinafter, also referred to as a view angle) are arranged. The synogram is data in which the results of counting processing are arranged in a two-dimensional Cartesian coordinate system centered on the view direction and the channel direction. The DAS 18 generates a synogram, for example, in units of columns in the slice direction in the X-ray detector 12. Here, the result of the counting process is the data to which the number of X-ray photons is assigned to each energy bin. For example, the DAS 18 counts photons (X-ray photons) derived from X-rays irradiated from the X-ray tube 11 and transmitted through the subject P, and discriminates the energy of the counted X-ray photons from the result of the counting process. do. The DAS 18 transfers the generated detection data to the console device 40. DAS18 is realized by, for example, a processor.

The data generated by the DAS 18 is transmitted from a transmitter having a light emitting diode (LED) provided in the rotating frame 13 to a non-rotating portion (for example, a fixed frame not shown) of the gantry device 10 by optical communication. It is transmitted to a receiver having a photodiode provided and transferred to the console device 40. Here, the non-rotating portion is, for example, a fixed frame that rotatably supports the rotating frame 13. The method of transmitting data from the rotating frame 13 to the non-rotating portion of the gantry device 10 is not limited to optical communication, and any non-contact data transmission method may be adopted, and the contact-type data transmission method may be used. You may adopt it.

The bed device 30 is a device for placing and moving the subject P to be imaged, and has a base 31, a bed drive device 32, a top plate 33, and a support frame 34. The base 31 is a housing that supports the support frame 34 so as to be movable in the vertical direction. The bed drive device 32 is a drive mechanism for moving the top plate 33 on which the subject P is placed in the long axis direction (Z-axis direction) of the top plate 33, and includes a motor, an actuator, and the like. The top plate 33 provided on the upper surface of the support frame 34 is a plate on which the subject P is placed. In addition to the top plate 33, the bed drive device 32 may move the support frame 34 in the long axis direction of the top plate 33. Further, the sleeper drive device 32 may move the top plate 33 in the short axis direction (X-axis direction) or the vertical direction (Z-axis direction) of the top plate 33. In this case, the sleeper drive device 32 functions as an example of the above-mentioned moving mechanism.

The console device 40 includes a memory 41, a display 42, an input interface 43, and a processing circuit 44. Although the console device 40 will be described as a separate body from the gantry device 10, the gantry device 10 may include a part of each component of the console device 40 or the console device 40.

The memory 41 is realized by, for example, a RAM (Random Access Memory), a semiconductor memory element such as a flash memory, a hard disk, an optical disk, or the like. The memory 41 stores, for example, detection data and CT image data. Further, for example, the memory 41 stores a program for the circuit included in the X-ray CT apparatus 1 to realize its function.

The display 42 displays various information. For example, the display 42 displays various images generated by the processing circuit 44, and displays a GUI (Graphical User Interface) for receiving various operations from the operator. In addition, the display 42 displays information regarding the waiting time for shooting. Information on the waiting time for shooting will be described in detail later. For example, the display 42 is a liquid crystal display or a CRT (Cathode Ray Tube) display. The display 42 may be a desktop type, or may be configured by a tablet terminal or the like capable of wireless communication with the console device 40 main body. The display 42 is an example of a display unit.

The input interface 43 receives various input operations from the operator, converts the received input operations into electric signals, and outputs the received input operations to the processing circuit 44. Further, for example, the input interface 43 includes conditions for an X-ray irradiation region, scan conditions, reconstruction conditions when reconstructing CT image data, image processing conditions when generating a post-processed image from CT image data, and the like. The input operation of is accepted from the operator. In the following, the X-ray irradiation area set by the operator is also referred to as a reference FOV.

For example, the input interface 43 includes a mouse, a keyboard, a trackball, a switch, a button, a joystick, a touch pad for performing an input operation by touching an operation surface, a touch screen in which a display screen and a touch pad are integrated, and an optical sensor. It is realized by the non-contact input circuit, voice input circuit, etc. used. The input interface 43 may be provided on the gantry device 10. Further, the input interface 43 may be configured by a tablet terminal or the like capable of wireless communication with the console device 40 main body. Further, the input interface 43 is not limited to the one provided with physical operation parts such as a mouse and a keyboard. For example, an electric signal processing circuit that receives an electric signal corresponding to an input operation from an external input device provided separately from the console device 40 and outputs the electric signal to the processing circuit 44 is also an example of the input interface 43. included.

The processing circuit 44 controls the operation of the entire X-ray CT apparatus 1. For example, the processing circuit 44 executes a control function 441, a preprocessing function 442, a determination function 443, an extended function 444, a conversion function 445, a reconstruction processing function 446, and an image processing function 447. Here, the control function 441 is an example of the first acquisition unit. The determination function 443, the extension function 444, and the conversion function 445 are examples of the second acquisition unit. Further, the determination function 443 is an example of a specific unit. The conversion function 445 is an example of a conversion unit. Further, the reconstruction processing function 446 is an example of the reconstruction processing unit.

For example, each of the control function 441, the preprocessing function 442, the determination function 443, the extended function 444, the conversion function 445, the reconstruction processing function 446, and the image processing function 447, which are the components of the processing circuit 44 shown in FIG. The processing function is recorded in the memory 41 in the form of a program that can be executed by a computer. The processing circuit 44 is, for example, a processor, and realizes a function corresponding to each read program by reading and executing each program from the memory 41. In other words, the processing circuit 44 in the state where each program is read out has each function shown in the processing circuit 44 of FIG.

In FIG. 1, each processing function of the control function 441, the preprocessing function 442, the determination function 443, the extended function 444, the conversion function 445, the reconstruction processing function 446, and the image processing function 447 is a single processing circuit 44. Although the case realized by the above is shown, the embodiment is not limited to this. For example, the processing circuit 44 may be configured by combining a plurality of independent processors, and each processor may execute each program to realize each processing function. Further, each processing function of the processing circuit 44 may be appropriately distributed or integrated into a single or a plurality of processing circuits.

The control function 441 controls various processes based on the input operation received from the operator via the input interface 43. Specifically, the control function 441 controls the scan performed by the gantry device 10. Further, the control function 441 sets a reference FOV which is an X-ray irradiation region by receiving an input operation of the X-ray irradiation region from the operator.

Further, the control function 441 controls the collection process of the counting result in the gantry device 10 by controlling the operations of the X-ray detector 12, the X-ray high voltage device 14, the control device 15, the DAS 18, and the sleeper drive device 32. .. As an example, the control function 441 controls the collection process of projection data in the positioning scan for collecting the positioning image (scano image) and the shooting (main scan) for collecting the image used for diagnosis.

Further, the control function 441 controls the display 42 to display various image data stored in the memory 41, information related to shooting, and the like.

The preprocessing function 442 generates data obtained by subjecting the detection data output from the DAS 18 to preprocessing such as logarithmic conversion processing, offset correction processing, sensitivity correction processing between channels, and beam hardening correction. In the following, the data before preprocessing (detection data) and the data after preprocessing are collectively referred to as projection data.

The determination function 443 determines whether or not the subject P exists in a region outside the reference FOV based on the counting result of the X-ray detector 12 obtained by photographing the reference FOV and the projection data. Specifically, the determination function 443 determines whether or not the subject P exists outside the reference FOV based on each of the counting results obtained by photographing at a plurality of angles and the projection data as the rotation frame 13 rotates. judge. Hereinafter, an operation example of the determination function 443 will be described with reference to FIG.

FIG. 4 is a diagram showing an example of projection data. Here, FIG. 4 shows an example of a synogram obtained by shooting with a series of viewing angles. The horizontal axis means the position of the channel (channel position), and the vertical axis means the view angle.

As described above, the imaging by the X-ray CT apparatus 1 is performed while the rotating frame 13 rotates around the subject P. Therefore, the locus drawn on the synogram by the X-ray photon transmitted through each part of the subject P is a sine curve. In other words, the synogram is composed of a plurality of different sine curves superimposed. On the other hand, as shown in the sites B1 to B6, for example, the defective site where the curve of the sine curve is interrupted is a so-called truncation in which a part of the subject P deviates from the reference FOV during imaging with a series of view angles. It is a truncation part that shows the state.

The determination function 443 determines that the subject P is present in a region outside the reference FOV when a defect site is detected in the curve based on the curve shape of the synogram. Then, the determination function 443 specifies the direction of the channel in which the defective portion is detected (hereinafter, also referred to as an expansion direction) and the range of the view angle in which the defective portion is detected (hereinafter, also referred to as an expansion angle). Here, the expansion direction corresponds to the direction in which the portion of the subject P that could not be captured by the imaging of the first arrangement position (for example, the position A1 in FIG. 2) exists. Further, the extended angle corresponds to an angle at which the site (part) of the subject P could not be captured in the imaging of the first arrangement position (for example, the position A1 in FIG. 2).

The determination function 443 may be configured to derive the number of channels (hereinafter, also referred to as a movement amount) necessary for smoothly connecting the curves of the synogram by estimating the curve shape of the defective portion. Here, the amount of movement is the amount of movement of the imaging system 19 to a position where the portion of the subject that could not be captured by imaging at the first arrangement position (for example, position A1 in FIG. 2) can be imaged. handle.

The extended function 444 controls the movement mechanism when the determination function 443 determines that the subject P exists in a region outside the reference FOV, and moves the relative positional relationship between the photographing system 19 and the top plate 33. By doing so, the image of the area outside the reference FOV is executed.

Specifically, the extended function 444 cooperates with the control function 441 to perform shooting at the specified extended angle in a state where the shooting system 19 is moved in the extended direction specified by the determination function 443. Here, the moving direction of the photographing system 19 with respect to the top plate 33 is the channel direction in which the defective portion is present in the synogram. The movement amount in the expansion direction may be a predetermined movement amount or a movement amount derived by the determination function 443.

Hereinafter, an operation example of the extended function 444 will be described with reference to FIGS. 2 and 5. Here, FIGS. 5 (a) and 5 (b) are diagrams showing an example of the counting result.

As shown in FIG. 2, when the photographing system 19 (X-ray tube 11, X-ray detector 12) is in the default position A1, when the subject P on the top plate 33 is photographed at a certain view angle, the subject is photographed. A part of P (right end) may deviate from the range of the fan beam. In this case, since the portion deviated from the fan beam is a region outside the reference FOV, it cannot be captured by the reference FOV.

In this case, as shown in FIG. 5A, the count result of the X-ray detector 12 is in a state where the count value is interrupted at the channel position CH1 corresponding to the right end of the projection path of the projection data. Here, the horizontal axis means the channel position of the X-ray detector 12, and the vertical axis means the count value of the X-ray photon. Further, in this case, in the synogram generated from the counting result of the X-ray detector 12, as described above, a defective portion is generated at the view angle of FIG.

Conventionally, the boundary position between the region of the subject P existing outside the FOV and another region (air) is estimated from the tendency of the count value in the FOV obtained by imaging, and the count value up to the boundary is estimated. By predicting the decay curve, the FOV is quasi-extended.

However, with this method, for example, as shown in FIG. 2, when a highly absorbent substance Pa such as a lesion is present in a region outside the reference FOV of the subject P, this highly absorbent substance Pa cannot be captured. Therefore, it is not possible to reproduce an image that reflects the presence of the highly absorbent substance Pa. Further, since the boundary position between the subject P and the air existing outside the FOV is derived by estimation, it may be different from the actual boundary position. Therefore, if the projection data is generated based on the wrong boundary position, the image quality of the image obtained by the reconstruction may be deteriorated.

On the other hand, in the extended function 444 of the present embodiment, when the subject P is present in a region outside the reference FOV, the photographing system 19 is moved in the extended direction in which the subject P is present (for example, the direction of the movement amount M1 in FIG. 2). Then, the photograph is taken at the extended angle where the defect site is generated. As a result, the portion of the subject P existing in the region outside the reference FOV falls within the range of the reference FOV (fan beam) that has changed with the movement of the photographing system 19. Further, since the boundary position between the region of the subject P and the other region (air) can be captured with the movement of the photographing system 19, the actual boundary position can be specified.

Further, in this case, the counting result obtained by shooting at the position after the movement (for example, the position A2 in FIG. 2) and the counting result obtained by shooting at the position before the movement (for example, the position A1 in FIG. 2). Is integrated by the conversion function 445 described later, and the integrated result is in the state shown in FIG. 5 (b).

In FIG. 5B, the counting result obtained by photographing the position A2 is shown by a broken line. Here, the channel position CH2 means the boundary position between the subject P and the air, and is specified from the counting result after the movement. Further, among the counting results of the position A2, the mountain portion of the curve shown by the broken line represents the counting result of the highly absorbent substance Pa. That is, by moving the photographing system 19, the highly absorbent substance Pa existing outside the reference FOV can be captured in the photographing at the position A1. Hereinafter, the counting result and the projection data obtained by the processing (extended processing) of the extended function 444 are also referred to as additional projection data.

When there are defective parts on both sides in the channel direction as in the parts B1 to B6 of the synogram described with reference to FIG. 4, it is necessary to move the photographing system 19 on both sides in the channel direction. In this case, the extended function 444 causes the shooting of the region outside the reference FOV to be executed while alternately switching the channel direction for moving the shooting system 19.

For example, the extended function 444 may be in a form in which shooting is performed while switching the channel direction for each of the parts B1 to B6.

Further, for example, the expansion function 444 is moved in the direction of one channel, the expansion angles of the defect portions existing in the channel direction are collectively photographed, and then moved in the direction of the other channel, and the defects existing in the channel direction are present. The expansion angles of the parts may be photographed together. In this way, additional projection data can be efficiently acquired by shooting in one channel direction at a time.

Further, the extended function 444 controls the collimator 17 when moving the photographing system 19 to narrow down the irradiation range so that the range photographed by the reference FOV before the movement is not irradiated with X-rays. May be good. Specifically, the extended function 444 adjusts the aperture of the collimator 17 so that the range of the reference FOV expanded by the movement of the photographing system 19 is irradiated with X-rays. As a result, the dose of X-rays irradiated to the subject P can be suppressed, so that safety can be improved.

Returning to FIG. 1, the conversion function 445 obtained the additional projection data by shooting before moving by cooperating with the preprocessing function 442 when the additional projection data was obtained by the expansion processing of the expansion function 444. Perform conversion processing for integration into projection data.

The conversion processing method is not particularly limited, and various methods can be used. Hereinafter, two methods will be described as processing examples of the conversion processing.

First, a first method of conversion processing will be described with reference to FIG. FIG. 6 is a diagram for explaining an example of the conversion process executed by the extended function 444. Note that FIG. 6 shows the positional relationship between each position (A1, A2) of the photographing system 19 (X-ray tube 11) before and after the movement and the subject P (top plate 33) described with reference to FIG. ..

Further, in FIG. 6, the distance (distance between the focal point and the center of rotation) from the focal point of the X-ray tube 11 to the center of rotation of the rotating frame 13 is L. Further, it is assumed that the X-ray tube 11 irradiates X-rays with a fan beam at a fan angle of 2θ, and projection data (additional projection data) has already been acquired at positions A1 and A2.

First, the conversion function 445 expands the projection path (fan angle) when the projection data is obtained by shooting at position A1 to the position of the projection path when additional projection data is obtained by shooting at position A2. Then, the additional projection data is converted into the geometry (geometry of the reconstruction system) when the projection data is reconstructed. Here, the geometry of the reconstruction system is the geometrical arrangement of the X-ray tube 11, the X-ray detector 12, and the subject P, that is, the relative positional relationship.

For example, regarding the position x1 in the subject P through which the projection path of the additional projection data (hereinafter referred to as the additional projection path) is transmitted, the position x1 represents the positional relationship in the channel direction (X-axis direction) with respect to the position A1. It can be described by the following equation (1). Here, φ is the angle between the central ray of the fan beam emitted from the position A2 and the additional projection path transmitted through the position x1. In FIG. 6, the additional projection path is shown by a broken line.
x1 = M1 + L × tanφ ... (1)

Further, it is assumed that the fan angle of the projection data is virtually expanded and the projection path is moved to a position through which the position x1 is transmitted. At this time, the positional relationship of the position x1 in the channel direction (X-axis direction) can be described by the following equation (2). Here, α is the fan angle for the expansion. In FIG. 6, the projection path of the projection data is shown by a solid line, and the projection path of the projection data based on the virtually enlarged fan angle is shown by a alternate long and short dash line.
x1 = L × tan (θ + α)… (2)

Based on the above equations (1) and (2), the conversion function 445 expands the counting result at the position x1 of the additional projection data to the area outside the basic FOV by virtually expanding the fan angle, and the position of the projection data. The conversion process of converting to the counting result at x1 is executed. Then, the conversion function 445 generates the corrected projection data in which the additional projection data is converted into the reconstructed geometry by executing the above conversion process for each position obtained by the additional projection data. This makes it possible to generate an image such as a synogram from the projection data and the additional projection data.

Next, a second method of conversion processing will be described with reference to FIGS. 6, 7, and 8. Here, FIG. 7 is a partially enlarged view around the right end portion (position X1) of the subject P shown in FIG. Further, FIG. 8 is a diagram schematically showing an example of the reconstructed image. Note that FIG. 7 is a partially enlarged view around the position X1 shown in FIG.

The outer shape of the reconstructed image obtained from the projection data will have an outer shape corresponding to the subject P. For example, as shown in FIG. 8, the reconstructed image generated from the projection data obtained by photographing from the position A1 in FIG. 6 has the same shape (elliptical shape) as the outer shape of the subject P. .. However, the portion outside the basic FOV (right end portion) appears in a defective state as shown in the right end portion of FIG.

Therefore, the extended function 444 estimates the entire outer shape C1 of the subject P from the reconstructed image, and identifies the region where the defect exists (hereinafter, the defective region). Next, as shown in FIG. 7, the extended function 444 expands to a region outside the basic FOV by expanding the path length La of the additional projection path (broken line) that passes through each position (position x1) of the defective region and the fan angle. The path length Lb of the projection path (dashed line) that passes through the position x1 is calculated.

Next, the extended function 444 corrects the measurement result by multiplying the measurement result of the position x1 in the additional projection data by the weight of Lb / La. Then, the conversion function 445 generates the corrected projection data converted into the geometry of the reconstruction system by executing the conversion process of the first method described above.

When the second method is used, the weight according to the angle difference between the projection path and the additional projection path is reflected in the measured value of the additional projection data based on the outer shape of the subject P estimated from the reconstructed image. Can be done. Therefore, as compared with the case where the first method is used, it is possible to improve the accuracy when converting to the geometry of the reconstruction system.

By the expansion process of the expansion function 444 described above, for example, additional projection data of the portions B1 to B6 of the synogram shown in FIG. 4 can be obtained. Further, by the conversion process of the conversion function 445 described above, the additional projection data obtained by the expansion process can be integrated into the projection data related to the synogram of FIG.

As a result, it is possible to generate a synogram in which the curved shapes of the portions B1 to B6 are complemented, as shown in FIG. 9, from the projected data after integration. By performing reconstruction using such a synogram, CT image data reflecting a portion of the subject P existing outside the reference FOV can be generated. Note that FIG. 9 is a diagram showing an example of projection data corrected by the conversion function 445.

Returning to FIG. 1, the reconstruction processing function 446 uses a filter correction back projection method, a successive approximation reconstruction method, or the like with respect to the projection data generated by the preprocessing function 442 or the projection data generated by the extension function 444. CT image data is generated by performing the reconstruction process. The reconstruction processing function 446 stores the reconstructed CT image data in the memory 41.

Here, the projection data generated from the counting result obtained by the photon counting CT includes information on the energy of the X-ray attenuated by passing through the subject P. Therefore, the reconstruction processing function 446 can, for example, reconstruct the CT image data of a specific energy component. Further, the reconstruction processing function 446 can, for example, reconstruct the CT image data of each of the plurality of energy components.

Further, the reconstruction processing function 446 assigns, for example, a color tone corresponding to the energy component to each pixel of the CT image data of each energy component, and superimposes a plurality of CT image data color-coded according to the energy component. Can be generated. Further, the reconstruction processing function 446 can generate image data that enables identification of the substance, for example, by utilizing the K absorption edge peculiar to the substance. Examples of other image data generated by the reconstruction processing function 446 include monochromatic X-ray image data, density image data, effective atomic number image data, and the like.

The image processing function 447 uses a known method to process CT image data generated by the reconstruction processing function 446 based on an input operation received from the operator via the input interface 43, such as a tomographic image of an arbitrary cross section or rendering processing. Convert to image data such as a three-dimensional image. The image processing function 447 stores the converted image data in the memory 41.

The configuration of the X-ray CT apparatus 1 has been described above. Under such a configuration, the X-ray CT apparatus 1 makes it possible to efficiently advance the imaging of the site of the subject P existing outside the reference FOV.

It should be noted that the extended function 444 can be arbitrarily set regardless of the timing at which the extended process is started. For example, the execution timing of the extended process may be incorporated into the imaging protocol that defines a series of steps and settings related to imaging of the subject P. Here, the imaging protocol is a set of imaging parameters used when the X-ray CT apparatus 1 photographs the subject P, for example, the timing of performing the positioning scan and the main scan, the X-ray irradiation amount, and the like. Includes shooting parameters such as shooting time. An example incorporated into the shooting protocol will be described below.

First, the first shooting protocol will be described. The first imaging protocol stipulates that first a "positioning scan" be performed with the reference FOV, then a "positioning scan" with the reference FOV moved by extended processing, and finally a "main scan" with the reference FOV. Is.

In this case, the determination function 443 determines whether or not the site of the subject P exists outside the reference FOV based on the projection data (synogram) obtained in the first positioning scan. When the site of the subject P exists outside the reference FOV, the determination function 443 specifies an expansion direction or the like for moving the imaging system 19.

Subsequently, the extended function 444 moves the photographing system 19 in the specified extended direction in the second positioning scan. The extended function 444 then causes a second positioning scan to be performed. In such a positioning scan, shooting is performed at a series of view angles including an extended angle. That is, in the second positioning scan, the portion of the subject P that could not be captured in the first positioning scan can be photographed.

Then, when the main scan is executed based on the scan result of the first positioning scan, the conversion function 445 uses the additional projection data obtained in the second positioning scan to obtain the synogram obtained in the main scan. The defect site is corrected and the corrected synogram is generated. As a result, the reconstruction processing function 446 can generate CT image data in which the portion of the subject P existing outside the reference FOV is reflected.

Next, the second photographing protocol will be described. The second imaging protocol is first "positioning scan" with the reference FOV, then "main scan" with the reference FOV, then scanning with the reference FOV moved by extended processing (hereinafter also referred to as extended scan), and finally. It stipulates that the "conversion process" is performed using the projection data obtained by the main scan and the additional projection data obtained by the extended scan.

In this case, the determination function 443 determines whether or not the site of the subject P exists outside the reference FOV based on the projection data (synogram) obtained in the first positioning scan or the next main scan. When the site of the subject P exists outside the reference FOV, the determination function 443 specifies the expansion direction, the expansion angle, and the like.

Subsequently, the extended function 444 moves the photographing system 19 in each of the specified extended directions in the next extended scan. The extended function 444 then shoots at the specified extended angle. This makes it possible to photograph the part of the subject P that could not be captured by the positioning scan and the main scan. The extended scan may be performed with an X dose equivalent to that of the positioning scan, or may be performed with an X dose equivalent to that of the main scan.

Subsequently, the conversion function 445 collaborates with the preprocessing function 442 and the like, and uses the additional projection data obtained in the extended scan to correct the defective part of the synogram obtained in the main scan, and the corrected synogram. To generate. As a result, the reconstruction processing function 446 can generate CT image data in which the portion of the subject P existing outside the reference FOV is reflected.

Next, the third photographing protocol will be described. The third imaging protocol stipulates that a "positioning scan" is first performed on the reference FOV, then an "extended scan", and finally a "main scan" is performed on the reference FOV.

In this case, the determination function 443 determines whether or not the site of the subject P exists outside the reference FOV based on the projection data (synogram) obtained in the first positioning scan. When the site of the subject P exists outside the reference FOV, the determination function 443 specifies the expansion direction, the expansion angle, and the like.

Subsequently, the extended function 444 moves the photographing system 19 in each of the specified extended directions in the next extended scan. The extended function 444 then shoots at the specified extended angle. This makes it possible to photograph the part of the subject P that could not be captured by the positioning scan.

Then, when the main scan is executed based on the scan result of the positioning scan, the conversion function 445 uses the additional projection data obtained in the extended scan to correct the defective part of the synogram obtained in the main scan. Generate a corrected synogram. As a result, the reconstruction processing function 446 can generate CT image data in which the portion of the subject P existing outside the reference FOV is reflected.

In the above-mentioned photographing protocol, the extended function 444 is in a form of automatically executing the extended process, but the present invention is not limited to this, and the extended function 444 may be executed in response to an input instruction of the operator. For example, when the second protocol is used among the above-mentioned first to third imaging protocols, the operator confirms the CT image data obtained in the second step (main scan) via the display 42. After that, if necessary, it may be configured to indicate whether or not to execute the extended scan via the input interface.

Further, in the above example, the determination function 443 specifies the expansion direction, the expansion angle, the movement amount, and the like from the projection data (synogram), so that the movement direction, the view angle, and the movement amount of the photographing system 19 during the expansion processing are specified. However, the form is not limited to this, and the form in which these information are input by the operator may be used. For example, the operator. Based on the synogram obtained by the positioning scan or the main scan, and the CT image data, the moving direction, the view angle, and the moving amount of the photographing system 19 at the time of the expansion processing may be instructed via the input interface. In this case, the extended function 444 executes the extended process under the instructed conditions.

Next, an operation example of the X-ray CT apparatus 1 will be described with reference to FIG. FIG. 10 is a flowchart showing an example of processing performed by the X-ray CT apparatus 1. The flowchart of FIG. 10 shows the flow of processing based on the above-mentioned first photographing protocol.

First, when the reference FOV is set by the input operation via the input interface (step S11), the control function 441 executes the positioning scan with the set reference FOV (step S12).

Subsequently, the determination function 443 determines whether or not a part of the subject P is present outside the reference FOV based on the projection data obtained by the positioning scan in step S12 (step S13). Specifically, it is determined whether or not a defect site is present in the projection data (synogram).

Here, when the defect site does not exist, the determination function 443 determines that the subject P is contained in the reference FOV (step S13; No). In this case, the control function 441 executes the main scan at the reference FOV based on the scan result of the positioning scan in step S12 (step S14), and proceeds to step S20.

On the other hand, when the defect site is present, the determination function 443 determines that a part of the subject P is present outside the reference FOV (step S13; Yes). Next, the determination function 443 specifies the view angle (expansion angle) and the channel direction (expansion direction) of the defect site where a part of the subject P is assumed to be present (step S15). note that. The determination function 443 may specify the number of channels corresponding to the movement amount of the photographing system 19.

Subsequently, the extended function 444 moves the photographing system 19 by a predetermined amount in the specified channel direction (extended direction) (step S16). The extended function 444 then cooperates with the control function 441 to perform a second positioning scan (step S17). In step S18, an extended scan may be performed in which only the extended angle specified in step S15 is photographed. In this case, this process corresponds to the operation specified by the above-mentioned third imaging protocol.

Subsequently, the control function 441 executes the main scan based on the scan result of the positioning scan in step S12 (step S18). Next, the conversion function 445 converts the additional projection data obtained in the positioning scan in step S17 into the coordinate system of the projection data obtained in the main scan in step S19, and generates corrected projection data (step S19). ).

Subsequently, the reconstruction processing function 446 generates CT image data by executing the reconstruction processing of the projection data generated in the main scan of step S14 or the corrected projection data generated in step S19 (). Step S20). Then, when the CT image data is converted into image data, the image processing function 447 outputs the image data to the display 42 or the memory 41 (step S21), and ends this processing.

As described above, in the X-ray CT apparatus 1 according to the present embodiment, the photographing system 19 is arranged at the first arrangement position (for example, the position A1), and the first projection data (projection data) is acquired. The second projection data including the detection result of the subject not included in the first projection data by arranging the photographing system 19 at the second arrangement position (for example, position A2) moved with respect to the subject P. Get (additional projection data). Then, the X-ray CT apparatus 1 executes the reconstruction process based on the first projection data and the second projection data, and outputs the process result.

As a result, according to the X-ray CT apparatus 1, it is possible to obtain the counting result of the region of the subject P that could not be captured by the imaging of the first placement position due to the movement to the second placement position. At the same time, it is possible to reliably capture the boundary position between the region of the subject P and another region. Therefore, according to the X-ray CT apparatus 1, the image quality of the image obtained by reconstruction or the like can be improved even when the reference FOV is expanded by the expansion function 444 and the conversion function 445.

In the above-described embodiment, the extended function 444 is configured to move the arrangement position of the photographing system 19 with respect to the subject P in the channel direction (X-axis direction in FIG. 1) of the X-ray detector 12. Not limited to this, it may be moved in another direction such as the vertical direction (Y-axis direction in FIG. 1). In this case as well, the conversion function 445 converts the additional projection data obtained in the post-movement shooting into the geometry of the projection data obtained in the pre-movement shooting and integrates them, thereby having the same effect as that of the embodiment of fulfillment. Can be played.

Further, in the above-described embodiment, the extended function 444 is configured to move the arrangement position of the photographing system 19, but the present invention is not limited to this, and the extension function 444 may be configured to move the arrangement position of the top plate 33 (subject P). .. In this case as well, the conversion function 445 converts the additional projection data obtained in the post-movement shooting into the geometry of the projection data obtained in the pre-movement shooting and integrates them, thereby having the same effect as that of the embodiment of fulfillment. Can be played.

[Second Embodiment]
In the first embodiment described above, the imaging system 19 (or the top plate 33) is moved in the channel direction to photograph the portion of the subject P existing outside the basic FOV, whereby the subject P and the air are photographed. I explained the form of photographing the boundary part of. In the second embodiment, a configuration separately provided with a camera for photographing the boundary portion between the subject P and the air will be described. The same elements as those in the first embodiment described above are designated by the same reference numerals, and the description thereof will be omitted.

FIG. 11 is a diagram showing a configuration example of the X-ray CT apparatus according to the second embodiment. As shown in FIG. 11, the X-ray CT apparatus 1 of the second embodiment further includes a camera 20 in the gantry apparatus 10.

The camera 20 is an example of a photographing unit provided with an imaging element such as a CCD (Charge Coupled Device) or a CMOS (Complementary MOS). The camera 20 is supported by a rotating frame 13, and the shooting direction is directed toward the center of rotation. That is, the camera 20 is provided at a position where the subject P placed on the top plate 33 can be photographed. The angle of view of the camera 20 is preferably such that at least the entire area of the top plate 33 in the X-axis direction can be photographed. The image data taken by the camera 20 (hereinafter, also referred to as a camera image) is output to the control device 15 via the DAS 18 or the like.

The processing circuit 44 according to the second embodiment has, for example, a specific function 448 and an estimation function 449 in addition to the above-mentioned control function 441, preprocessing function 442, determination function 443, reconstruction processing function 446, and image processing function 447. Further prepare. Here, the control function 441 is an example of the acquisition unit. The specific function 448 is an example of a specific unit. Further, the estimation function 449 is an example of an estimation unit.

The specific function 448 specifies the boundary position between the subject P and the air based on the camera image taken by the camera 20. For example, the specific function 448 identifies the boundary position between the subject P and the air from the camera image by using a known technique such as edge detection. Further, the specific function 448 specifies the channel position corresponding to the boundary position by converting the specified boundary position into the geometry of the reconstruction system of the projection data.

It is assumed that the coordinate system of the camera image captured by the camera 20 and the coordinate system of the photographing system 19 are aligned in advance. For example, when the camera 20 is installed, the position of the shooting range (and the shooting center thereof) of the camera 20 may be aligned with the coordinate system of the X-ray CT apparatus 1. This makes it possible to specify the channel position corresponding to the boundary position from the camera image.

For example, to explain with reference to FIG. 5B, the specific function 448 specifies the channel position CH2 corresponding to the boundary position between the subject P and the air from the camera image taken by the camera 20. In the following, among the projection paths of the projection data, the channel position (CH1) closest to the channel position (CH2) specified by the specific function 448 is also referred to as a channel end of the projection data. Further, the channel position specified by the specific function 448 is also simply referred to as a boundary position.

The estimation function 449 executes a process of correcting the projection data based on the projection data of the subject P photographed by the reference FOV and the boundary position (channel position) specified by the specific function 448. Specifically, the estimation function 449 estimates the trajectory of the projection data from the channel end of the projection data to the boundary position specified by the specific function 448, and adds the estimation result to the projection data as additional projection data. To execute. Specifically, the estimation function 449 estimates the attenuation locus from the channel end of the projection data to the boundary position where the count value is zero.

Here, the method for estimating the attenuation miracle is not particularly limited, and a known technique may be used. For example, the estimation function 449 may estimate the attenuation locus to the boundary position based on the tendency of the change of the projection data around the channel end. Then, the reconstruction processing function 446 reconstructs the projection data corrected by the estimation function 449 to generate CT image data as in the first embodiment.

The timing at which the specific function 448 specifies the boundary position is not particularly limited. For example, the specific function 448 may be in a form of specifying the boundary position when it is determined by the determination function 443 that a part of the subject P exists outside the reference FOV. Further, the specific function 448 may be in a form of specifying the boundary position in response to an input instruction from the operator. Further, the specific function 448 may be in a form of specifying the boundary position in the default state.

By the way, unlike the additional projection data described in the first embodiment, the additional projection data estimated by the estimation function 449 does not reflect the state of the subject P in the body. However, since the additional projection data according to the second embodiment is derived based on the boundary position specified by the actual measurement, the subject P and the air are compared with the configuration in which the boundary position itself is estimated. You can capture the boundaries more accurately.

Therefore, in the X-ray CT apparatus 1 according to the second embodiment, even when the subject P exists outside the reference FOV, the projection data is corrected by the above-mentioned method, and the image is taken. The image quality of the obtained image can be improved.

In each of the above-described embodiments, an example in which the functional configuration included in the X-ray CT apparatus 1 is realized by the processing circuit 44 has been described, but the embodiment is not limited to this. For example, the functional configuration in the specification may be hardware alone or a mixture of hardware and software to realize the same function.

Further, the term "processor" used in the above description means, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), an integrated circuit for a specific application (ASIC), or a programmable logic device. (For example, a circuit such as a simple programmable logic device (SPLD), a complex programmable logic device (CPLD), and a field programmable gate array (FPGA)) is meant. When the processor is, for example, a CPU, the processor realizes a function by reading and executing a program stored in a storage circuit. On the other hand, when the processor is, for example, an ASIC, the function is directly incorporated as a logic circuit in the circuit of the processor instead of storing the program in the storage circuit. It should be noted that each processor of the present embodiment is not limited to the case where each processor is configured as a single circuit, and a plurality of independent circuits may be combined to form one processor to realize its function. good. Further, a plurality of components in each figure may be integrated into one processor to realize the function.

Here, the program executed by the processor is provided by being incorporated in a ROM (Read Only Memory), a storage circuit, or the like in advance. This program is a file in a format that can be installed or executed on these devices, such as CD (Compact Disk) -ROM, FD (Flexible Disk), CD-R (Recordable), DVD (Digital Versatile Disk), etc. It may be recorded and provided on a computer-readable storage medium. Further, this program may be stored on a computer connected to a network such as the Internet, and may be provided or distributed by being downloaded via the network. For example, this program is composed of modules including each of the above-mentioned functional parts. As actual hardware, the CPU reads a program from a storage medium such as a ROM and executes the program, so that each module is loaded on the main storage device and generated on the main storage device.

According to at least one embodiment described above, the image quality of the image obtained by expanding the FOV can be improved.

Although some embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other embodiments, and various omissions, replacements, changes, and combinations of embodiments can be made without departing from the gist of the invention. These embodiments and variations thereof are included in the scope of the invention described in the claims and the equivalent scope thereof, as are included in the scope and gist of the invention.

1 X-ray CT device 10 Mount device 11 X-ray tube 12 X-ray detector 13 Rotating frame 14 X-ray high voltage device 15 Control device 16 Wedge 17 Collimator 18 DAS
19 Shooting system 20 Camera 30 Bed device 33 Top plate 40 Console device 441 Control function 442 Pre-processing function 443 Judgment function 445 Conversion function 446 Reconstruction processing function 447 Image processing function 448 Specific function 449 Estimating function

Claims (13)

An imaging system having an X-ray tube and an X-ray detector that detects X-rays irradiated from the X-ray tube and transmitted through the subject, and
A rotating frame that rotatably supports the imaging system around the subject,
A first acquisition unit that acquires first projection data indicating the detection result of the X-ray detector by rotating the rotation frame with the photographing system in the first arrangement.
The subject is not included in the first projection data in a state where the photographing system is relatively moved in the in-plane direction horizontal to the rotating surface of the rotating frame with respect to the subject. A second acquisition unit that acquires the second projection data including the detection result, and
A reconstruction processing unit that executes reconstruction processing based on the first projection data and the second projection data, and
X-ray CT apparatus. By moving one or both of the X-ray tube and the X-ray detector in the in-plane direction, the arrangement of the imaging system with respect to the subject is moved from the first arrangement to the second arrangement. The X-ray CT apparatus according to claim 1, further comprising a moving mechanism. A moving mechanism for moving the arrangement of the subject with respect to the imaging system from the first arrangement to the second arrangement is further provided by moving the bed on which the subject is placed in the in-plane direction. The X-ray CT apparatus according to claim 1. The first aspect of the present invention further comprises a moving mechanism for moving the arrangement of the imaging system with respect to the subject from the first arrangement to the second arrangement by moving the rotating frame in the in-plane direction. X-ray CT device. Further provided with a specific portion that identifies the direction in which the site of the subject, which could not be captured in the imaging of the first arrangement, is present based on the first projection data.
The X-ray CT apparatus according to any one of claims 2 to 4, wherein the moving mechanism relatively moves the photographing system in the direction specified by the specific unit. Based on the first projection data, the specific unit identifies an imaging angle at which the site of the subject could not be captured in the imaging of the first arrangement.
The X-ray CT apparatus according to claim 5, wherein the second acquisition unit is used to image the subject at an imaging angle specified by the specific unit. Based on the first projection data, the specific unit identifies the amount of movement of the part of the subject that could not be captured in the imaging of the first arrangement to a position where imaging is possible.
The X-ray CT apparatus according to claim 5, wherein the moving mechanism relatively moves the photographing system by the amount of movement specified by the specific unit. The photographing system further has an X-ray diaphragm portion that narrows the irradiation range of X-rays emitted from the X-ray tube.
The second acquisition unit is the X-ray diaphragm so that the portion corresponding to the detection result of the subject included in the first projection data is not included in the irradiation range in the imaging of the second arrangement. The X-ray CT apparatus according to any one of claims 1 to 7, which controls a unit. A conversion unit that converts the coordinate system of the second projection data into the coordinate system of the first projection data and integrates the first projection data and the second projection data is further provided.
The X-ray CT apparatus according to any one of claims 1 to 8, wherein the reconstruction processing unit executes a reconstruction processing based on the projection data integrated by the conversion unit. An imaging system having an X-ray tube and an X-ray detector that detects X-rays irradiated from the X-ray tube and transmitted through the subject, and
A rotating frame that rotatably supports the imaging system around the subject,
A first acquisition unit that acquires first projection data indicating the detection result of the X-ray detector by rotating the rotation frame with the photographing system in the first arrangement.
The photographing system is relatively moved in the out-of-plane direction perpendicular to the rotating surface of the rotating frame with respect to the subject, and the subject is not included in the first projection data. A second acquisition unit that acquires the second projection data including the detection result, and
A reconstruction processing unit that executes reconstruction processing based on the first projection data and the second projection data, and
X-ray CT apparatus. An imaging system having an X-ray tube and an X-ray detector that detects X-rays irradiated from the X-ray tube and transmitted through the subject, and
An imaging unit that photographs the subject and
A rotating frame that rotatably supports the imaging system and the imaging unit around the subject, and
An acquisition unit that acquires projection data indicating the detection result of the X-ray detector, and
Based on the image taken by the imaging unit, a specific unit that specifies the boundary position between the area of the subject and another area, and a specific unit.
An estimation unit that estimates the detection result of the part of the subject that is not included in the projection data from the detection result of the subject included in the projection data based on the boundary position specified by the specific unit.
A reconstruction processing unit that executes reconstruction processing based on the projection data and the estimation result of the estimation unit, and
X-ray CT apparatus. An imaging system having an X-ray tube and an X-ray detector that detects X-rays irradiated from the X-ray tube and transmitted through the subject, and a rotating frame that rotatably supports the imaging system around the subject. It is an image processing method of projection data obtained by an X-ray CT apparatus provided with.
By rotating the rotating frame with the photographing system in the first arrangement, the first projection data showing the detection result of the X-ray detector is acquired.
The photographing system is relatively moved in the in-plane direction horizontal to the rotating surface of the rotating frame with respect to the subject, and the subject is not included in the first projection data. Acquire the second projection data including the detection result,
The reconstruction process is executed based on the first projection data and the second projection data.
Image processing methods that include. An imaging system having an X-ray tube and an X-ray detector that detects X-rays irradiated from the X-ray tube and transmitted through the subject, and a rotating frame that rotatably supports the imaging system around the subject. A computer that processes projection data obtained by an X-ray CT apparatus equipped with
A first acquisition unit that acquires first projection data indicating the detection result of the X-ray detector by rotating the rotation frame with the photographing system in the first arrangement.
The photographing system is relatively moved in the in-plane direction horizontal to the rotating surface of the rotating frame with respect to the subject, and the subject is not included in the first projection data. A second acquisition unit that acquires the second projection data including the detection result, and
A reconstruction processing unit that executes reconstruction processing based on the first projection data and the second projection data, and
A program to make it work.

Images