JP2018082994A - X-ray CT apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray CT apparatus capable of suppressing an exposure dose on a subject, while generating a positioning image with high resolution.SOLUTION: An X-ray CT apparatus according to one embodiment of the present invention, comprises: a gantry in which an X-ray source for generating X rays and an X-ray detector for detecting X rays transmitted through a subject are respectively arranged in both sides of an opening; a driving unit for changing the relative position between the gantry and the subject; and a scan control unit for controlling the X-ray source and the drive unit in such a manner that positioning photographing is performed using pulsed X rays while the relative position is changed along the body axis with the X-ray source fixed in position. The scan control unit, upon performing the positioning photographing with the relative position being changed along the body axis, controls the X-ray source and the drive unit so as to project pulsed X rays when the relative position is moved in the body axis direction by a predetermined distance shorter than a slice width from the reference projection position after projecting pulsed X rays, and repeats these projection operations.SELECTED DRAWING: Figure 3

Description

  Embodiments described herein relate generally to an X-ray CT apparatus.

  When a subject is imaged by an X-ray CT (Computed Tomography) apparatus, a positioning image (scan image) may be obtained in advance by performing positioning imaging. The positioning image is generated based on projection data obtained by fixing the X-ray tube at a predetermined position and irradiating the subject with X-rays while changing the relative position between the subject and the X-ray tube. By using the positioning image, the positioning of the slice position for the main scan and the setting of the imaging conditions can be performed more accurately.

  On the other hand, as an X-ray detector of an X-ray CT apparatus, a two-dimensional array type detector in which a plurality of rows of X-ray detection elements having a plurality of channels in the channel direction are arranged in the slice direction (z direction) has recently been used. Has come to be. However, even when this type of two-dimensional array type detector is used, at the time of capturing a positioning image, a plurality of detection element arrays that are continuous in the slice direction are often bundled and used as one slice width. . For this reason, the resolution of the positioning image is significantly lower than that of the main scan image. Further, in positioning imaging, imaging is often performed while irradiating X-rays continuously in time. In this case, since the positioning imaging tends to take a long time, the tube current is lower than that of the main scan, but the exposure dose of the subject increases.

JP 2003-175029 A

  The problem to be solved by the present invention is to provide an X-ray CT apparatus capable of suppressing the exposure dose of a subject and generating a positioning image with high resolution.

  In order to solve the above-described problem, an X-ray CT apparatus according to an embodiment of the present invention includes an X-ray source that generates X-rays and a row of X-ray detection elements having a plurality of channels in the channel direction. A plurality of rows arranged in the body axis direction of the subject orthogonal to the X-ray detector for detecting the X-rays transmitted through the subject, a gantry provided with an opening therebetween, the gantry and the subject Positioning imaging using pulsed X-rays while changing the relative position along the body axis direction with the drive unit for changing the relative position to the specimen and the X-ray source fixed at a predetermined position A scan control unit that controls the X-ray source and the drive unit, and the scan control unit performs the positioning imaging while changing the relative position along the body axis direction. After irradiating pulsed X-rays The X-ray source and the drive unit are controlled so that pulse X-ray irradiation is repeated when the relative position moves in the body axis direction by a predetermined distance shorter than the slice width from the reference irradiation position. is there.

1 is a block diagram showing an example of an X-ray CT apparatus according to an embodiment of the present invention. The figure for demonstrating the positional relationship of an X-ray tube and an X-ray detector, and the rotation center of an X-ray tube. The schematic block diagram which shows the example of an implementation | achievement function by the processor of a processing circuit. (A) is explanatory drawing which shows an example of slice width (DELTA) a in a rotation center plane, (b) is explanatory drawing which shows an example of slice width (DELTA) b in the light-receiving surface of an X-ray detection element. The figure for demonstrating the definition of the slice width and X-ray beam width in a rotation center plane. The figure for demonstrating the method to image | photograph a scanogram by irradiating a pulse X-ray for every X-ray beam width. The figure for demonstrating the scanogram imaging method which irradiates a pulse X-ray also when moving the distance of the half of slice width (DELTA) a in addition to the case shown in FIG. The flowchart which shows an example of the procedure at the time of producing | generating the positioning image with high resolution, suppressing the exposure dose of a subject by the processing circuit of an X-ray CT apparatus. For changing the relative position between the X-ray tube and the subject, a scan image capturing method for performing pulse X-ray irradiation at a position shifted by a predetermined interpolation width in the channel direction immediately after pulse X-ray irradiation is described. Figure. The figure for demonstrating the scanogram imaging method in case the interpolation width of a scanning direction is a half of slice width, and the interpolation width of a channel direction is a half of the center-to-center distance between the detection elements along a channel direction. The figure for demonstrating the scanogram imaging method in case the interpolation width of a scanning direction is 1/3 of a slice width, and the interpolation width of a channel direction is 1/3 of the center-center distance between the detection elements along a channel direction. .

  Embodiments of an X-ray CT apparatus according to the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing an example of an X-ray CT apparatus 10 according to an embodiment of the present invention.

  In the X-ray CT apparatus, an X-ray tube and a detector are integrated into a rotation / rotation (rotate / rotate) type in which the periphery of the subject is rotated, and a large number of detection elements are arranged in an annular shape. There are various types such as a fixed / rotation (STATIONION / ROTATE) type in which only the tube rotates around the subject, and a type in which the position of the X-ray source is electronically moved on the target by deflecting the electron beam. However, the configuration shown in the present embodiment is applicable to any type. The type using an electron beam can be applied by appropriately replacing the X-ray tube with an X-ray source. In this embodiment, an example in which the X-ray CT apparatus 10 is a rotation / rotation (ROTATE) type in which the X-ray tube and the X-ray detector are integrated and rotates around the subject O has been described.

  In recent years, the so-called multi-tube type X-ray CT apparatus in which a plurality of pairs of X-ray tubes and X-ray detectors are mounted on a rotating ring has been commercialized, and the development of peripheral technologies has been advanced. The X-ray CT apparatus 10 according to the present embodiment is applicable to either a single tube type or a multi-tube type. Here, an example where the X-ray CT apparatus 10 is a single-tube type will be described.

  As shown in FIG. 1, the X-ray CT apparatus 10 includes a gantry 11, a bed apparatus 12, and a console 13.

  The gantry 11 includes a fixed gantry 21 and a rotary gantry 22. The fixed base 21 is fixed to an installation surface such as a floor surface, and includes a base control circuit 26, a data transmission device 27, and a drive circuit 28. The rotating gantry 22 integrally holds an X-ray tube 31, a diaphragm 32, an X-ray detector 33, and a DAS (Data Acquisition System) 34, and rotates around an opening in a central portion. In the present embodiment, the direction parallel to the rotation center axis of the rotary mount 22 is defined as the z-axis direction, the normal direction of the installation surface is defined as the y-axis direction, and the direction parallel to the installation surface is defined as the x-axis direction (FIG. 1). reference).

  The X-ray tube 31 is controlled by the gantry control circuit 26 and is supplied with a high voltage generated by a high voltage power source (not shown) of the fixed gantry 21 via, for example, a slip ring. Note that the high-voltage power supply may be provided on the rotary mount 22.

  X-rays generated by the X-ray tube 31 are irradiated toward the subject O as fan beam X-rays or cone beam X-rays.

  The diaphragm 32 is formed of, for example, a wedge filter, and is controlled by the gantry control circuit 26 to set an irradiation range of at least one of the X-ray slice direction (z direction and column direction) and the channel direction irradiated from the X-ray tube 31. adjust.

  The X-ray detector 33 includes a plurality of X-ray detection elements (charge storage elements). The X-ray detection element (radiation detection element) detects X-rays that are irradiated from the X-ray tube 31 and transmitted through the subject O. The X-ray tube 31 and the X-ray detector 33 are supported by the rotating gantry 22 so as to face each other with the subject O placed on the bed apparatus 12 therebetween.

  As the X-ray detector 33, a so-called two-dimensional array type (multi-slice type) having a plurality of columns such as 320 columns in the slice direction and a plurality of X-ray detection elements in the channel direction can be used. In the case of the multi-slice type, it is possible to use a plurality of rows of X-ray detection elements having a plurality of channels in the channel direction arranged in the slice direction (z direction). In the case of a two-dimensional array type, the X-ray detector 33 can be configured by a plurality of X-ray detection elements that are densely distributed in both the slice direction (z direction) and the channel direction.

  In the following description, the X-ray detector 33 has a plurality of rows of X-ray detection elements having a plurality of channels in the channel direction in the body axis direction (slice direction, z direction) of the subject O perpendicular to the channel direction. An example in the case of being configured is shown. The X-ray CT apparatus 10 according to the present embodiment uses, for example, data of part of elements in 320 columns in the channel direction (for example, 8 columns, 4 columns, etc.) in positioning imaging (scano imaging).

  The DAS 34 receives an analog signal output from a plurality of X-ray detection elements constituting the X-ray detector 33, and performs processing such as current-voltage conversion, amplification, analog-digital conversion (AD conversion) on the signal. The DAS 34 generates transmission data using these processed signals, and transmits the transmission data to the console 13 via the data transmission device 27. The console 13 performs a reconstruction process based on the projection data included in the transmission data, and generates a reconstructed image.

  FIG. 2 is a diagram for explaining the positional relationship between the X-ray tube 31 and the X-ray detector 33 and the rotation center of the X-ray tube 31.

  The rotary base 22 holds the X-ray tube 31, the diaphragm 32, the X-ray detector 33, and the DAS 34 as one body, and is supported by the fixed base 21. By rotating the rotating gantry 22 under the control of the gantry control circuit 26, the X-ray tube 31, the diaphragm 32, the X-ray detector 33, and the DAS 34 are integrally rotated around the rotation center of the X-ray tube 31. Rotate around the subject O. Further, the rotary mount 22 may be configured to be tiltable with respect to the fixed mount 21. Information on the current rotational speed of the rotary gantry 22, tilt operation, and information on the current tilt angle are given to the console 13 via the gantry control circuit 26.

  The bed apparatus 12 includes a base 36 installed on an installation surface such as a floor surface, a top plate 37 supported by the base 36, and a top plate driving device 38.

  The top plate 37 is configured such that the subject O can be placed thereon. The top plate drive device 38 is controlled by the drive circuit 28 to move the top plate 37 up and down in the y-axis direction (vertical direction). In addition, the top plate driving device 38 is controlled by the drive circuit 28 to move the top plate 37 along the z-axis direction (longitudinal direction of the top plate 37) to the X-ray irradiation field at the opening of the central portion of the rotary mount 22. Transport. Further, the top plate driving device 38 is controlled by the drive circuit 28 to move the top plate 37 in the x-axis direction (the lateral direction of the top plate 37). Further, the top plate driving device 38 is controlled by the drive circuit 28 and can rotate (slew) the top plate 37 about the xyz axes. Information on the movement of the top board 37 (movement speed and direction) and information on the current position are given to the console 13 via the top board driving device 38 and the driving circuit 28.

  The gantry control circuit 26 includes at least a processor and a storage circuit. The gantry control circuit 26 is controlled by the console 13 and controls the gantry 11 according to a program stored in the storage circuit, thereby executing X-ray CT imaging of the subject O.

  Although FIG. 1 shows an example in which the gantry control circuit 26 and the console 13 are connected by wire, the gantry control circuit 26 and the console 13 may be connected via a network so that data can be transmitted and received.

  The data transmission device 27 performs parallel / serial conversion, electrical / optical / electrical conversion, and serial / parallel conversion on the transmission data output from the DAS 34. The data transmission device 27 includes, for example, a parallel / serial converter, an electrical / optical / electrical converter, and a serial / parallel converter (not shown). The transmission data of a plurality of channels output from the DAS 34 is converted into time-sequential one-channel data by a parallel / serial converter provided on the rotary mount 22, and optical communication using the electrical / optical / electrical converter, etc. Is supplied to the serial / parallel converter provided on the fixed base 21.

  Subsequently, the one-channel transmission data is returned to a plurality of channels of transmission data by the serial / parallel converter. The projection data of a plurality of channels obtained in time series is stored in the console 13 as incidental information including arrangement position information and rotation angle information of the radiation detection elements in the channel direction and position information (imaging position) of the projection data in the slice direction. .

  The data transmission method by the data transmission device 27 may be another method as long as data transmission between the DAS 34 provided on the rotating gantry 22 and the gantry control circuit 26 provided on the fixed gantry 21 is possible. For example, a device such as a slip ring may be used for data transmission by the data transmission device 27, or a non-contact transmission method may be used.

  The drive circuit 28 includes at least a processor and a storage circuit. The drive circuit 28 is controlled by the console 13 and controls the top board drive device 38 according to the program stored in the storage circuit, for example, between the X-ray tube 31 and the subject O fixed at a predetermined position in scanography. The relative position is changed by moving the top plate 37 at a constant speed, for example. In addition, when the gantry 11 is configured to be movable in the z-axis direction along a rail (not shown) provided on the installation surface, the drive circuit 28 and the X-ray tube 31 fixed to a predetermined position in scanography are covered. The relative position to the specimen O is changed by moving the gantry 11 along the rail in the z-axis direction at a constant speed. Further, the drive circuit 28 may change the relative position of the X-ray tube 31 and the subject O by moving both the top plate 37 and the gantry 11.

  On the other hand, the console 13 of the X-ray CT apparatus 10 is configured by, for example, a general personal computer or workstation, and has an input circuit 41, a display 42, a storage circuit 43, and a processing circuit 44. Note that the console 13 does not have to be provided independently, and a part of the configuration 41-44 of the console 13 may be provided dispersed on the gantry 11.

  The input circuit 41 includes a general input device such as a trackball, a switch button, a mouse, a keyboard, or a numeric keypad, and outputs an operation input signal corresponding to a user operation to the processing circuit 44. For example, the user can set scan imaging conditions via the input circuit 41. In the present embodiment, it is assumed that the imaging conditions include information on a part to be imaged. Part or all of the imaging conditions may be set via the input circuit 41 or may be acquired via a network.

  The display 42 is configured by a general display output device such as a liquid crystal display or an OLED (Organic Light Emitting Diode) display, and displays a real-time reconstructed image or the like under the control of the processing circuit 44.

  The storage circuit 43 includes a recording medium readable by a processor, such as a magnetic or optical recording medium or a semiconductor memory. Some or all of the programs and data in these recording media may be downloaded by communication via an electronic network. The storage circuit 43 stores, for example, projection data transmitted from the DAS 34, a scano image generated by the processing circuit 44, and the like.

  The processing circuit 44 is a processor that executes a process of generating a positioning image with high resolution while suppressing the exposure dose of the subject O by reading and executing the program stored in the storage circuit 43.

  FIG. 3 is a schematic block diagram showing an example of functions realized by the processor of the processing circuit 44. As shown in FIG. 3, the processor of the processing circuit 44 realizes at least an X-ray control function 50, a condition acquisition function 51, a scan control function 52, and an image generation function 53. Each of these functions is stored in the storage circuit 43 in the form of a program.

  The X-ray control function 50 is controlled by the scan control function 52 to output an X-ray control signal, and supplies a tube current and a tube voltage from the high voltage power source to the X-ray tube 31 at a predetermined timing via the gantry control circuit 26. Let

  The condition acquisition function 51 acquires the imaging condition if the imaging condition is set when the start of scano imaging is instructed by the user via the input circuit 41.

  The scan control function 52 is positioned using pulsed X-rays while changing the relative position between the X-ray tube 31 and the subject O along the body axis direction with the X-ray tube 31 fixed at a predetermined position. The X-ray tube 31 is controlled via the X-ray control function 50 and the drive circuit 28 is controlled so as to perform imaging. Specifically, the scan control function 52 first outputs pulse X-rays at the reference irradiation position when performing positioning imaging while changing the relative position between the X-ray tube 31 and the subject O along the body axis direction. After the irradiation, the X-ray tube 31 and the drive circuit 28 are controlled so that the pulse X-ray is repeatedly irradiated when the relative position moves in the body axis direction by a predetermined distance shorter than the slice width from the reference irradiation position. . Further, the scan control function 52 may irradiate pulse X-rays by moving in the channel direction without waiting for movement in the slice direction.

  FIG. 4A is an explanatory diagram showing an example of the slice width Δa on the rotation center plane, and FIG. 4B is an explanatory diagram showing an example of the slice width Δb on the light receiving surface of the X-ray detection element. FIG. 4 shows an example in which eight rows of detection elements are used in scano imaging. FIG. 5 is a diagram for explaining the definition of the slice width and the X-ray beam width in the rotation center plane.

  As described above, the scan control function 52 repeats the pulse X-ray irradiation again when the relative position moves in the body axis direction by a predetermined distance shorter than the slice width from the reference irradiation position. FIG. 4 shows an example where the predetermined distance shorter than the slice width is half the slice width. The scan control function 52 may track the change in the relative position between the X-ray tube 31 and the subject O on the rotation center plane (see FIG. 4A) or may track on the light receiving surface of the detection element. Good (see FIG. 4B).

  When tracking the change in the relative position on the rotation center plane, and performing X-ray irradiation when moving half the slice width Δa in a plane passing through the rotation center of the X-ray tube 31 and orthogonal to the X-ray irradiation axis, The X-ray beam at the center of rotation can be accurately shifted by a desired distance. In the following description, an example in which a change in relative position between the X-ray tube 31 and the subject O is tracked on the rotation center plane will be described.

  Conventionally, in scanography, for example, four detector element rows of 0.5 mm are used together to continuously irradiate X-rays with a thick slice width such as 2 mm width. The scan image has a lower resolution than the main scan image that is captured.

  Therefore, as shown in FIGS. 4 and 5, the X-ray CT apparatus 10 according to the present embodiment has, for example, eight rows without bunching a slice width of 0.5 mm obtained for each detection element row of 0.5 mm. Use a thin slice width, such as use. For this reason, an image having a higher resolution than that of a conventional scano image can be obtained.

  FIG. 6 is a diagram for explaining a method for capturing a scanogram by irradiating pulsed X-rays for each X-ray beam width. FIG. 7 is a diagram for explaining a scanogram imaging method for irradiating pulse X-rays even when moving by a half of the slice width Δa in addition to the case shown in FIG. FIGS. 6 and 7 show an example in which scan imaging is performed using four 0.5 mm detector element arrays.

  As shown in FIG. 6, the resolution of the scanogram can be increased by using a thin slice width. Also, as shown in FIG. 7, when shooting is performed even when moving a predetermined distance shorter than the slice width, an image with higher resolution can be obtained by further dividing the thin slice width of 0.5 mm.

  The image generation function 53 generates an image every time pulse X-rays are irradiated and displays the image on the display 42.

  Next, an example of the operation of the X-ray CT apparatus 10 according to the present embodiment will be described.

  FIG. 8 is a flowchart showing an example of a procedure for generating a high-resolution positioning image while suppressing the exposure dose of the subject O by the processing circuit 44 of the X-ray CT apparatus 10. In FIG. 8, reference numerals with numbers added to S indicate steps in the flowchart. This procedure starts when scan start imaging is instructed.

  First, in step S1, the condition acquisition function 51 acquires scanning conditions for scanography. The imaging conditions include information on the part to be imaged. It should be noted that this step S1 is omitted when the shooting conditions are not set.

  Next, in step S <b> 2, the scan control function 52 sets a required resolution based on the information on the imaging target part included in the imaging conditions. Step S2 may be omitted.

  For example, when a part such as the head that requires detailed observation is an object to be imaged, the image is often used after being magnified at a high magnification. In the case of such a region to be imaged, it is preferable to set a required resolution high and to narrow the interpolation width (increase the number of divisions) in subsequent steps S3 and S4. On the other hand, if it is a site that can be roughly observed such as the abdomen, the required resolution may be set low.

  In addition, when a required resolution is set in step S2, an allowable noise of the scanogram image may be set according to this resolution. Specifically, when the required resolution is set, the scan control function 52 may set the tube current of the X-ray tube 31 according to this resolution.

  Next, in step S3, the scan control function 52 sets an interpolation width in the slice direction (see FIG. 7). For example, the interpolation width may be a value obtained by dividing the slice width by a positive integer.

  Next, in step S4, the scan control function 52 sets an interpolation width in the channel direction. The interpolation width may be a value obtained by dividing the center-to-center distance between detection elements along the channel direction by a positive integer.

  Note that step S4 may be omitted. On the other hand, in the case where the relative position between the X-ray tube 31 and the subject O is not constantly changed, and imaging may be performed by so-called step-and-shoot, it is moved in the slice direction after the pulse X-ray irradiation. Alternatively, the pulse X-ray irradiation may be performed by moving the interpolation width only in the channel direction.

  FIG. 9 shows a scan image obtained when pulse X-ray irradiation is performed at a position shifted by a predetermined interpolation width in the channel direction immediately after pulse X-ray irradiation when the relative position between the X-ray tube 31 and the subject O is changed. It is a figure for demonstrating a method.

  Even when the relative position between the X-ray tube 31 and the subject O is constantly changed, the scan control function 52 immediately follows the pulse X-ray irradiation at the reference irradiation position without waiting for the movement in the slice direction. Further, pulse X-ray irradiation may be performed by moving the irradiation position by an interpolation width in the channel direction.

  In this case, the relative position of the X-ray tube 31 and the subject O slightly moves in the slice direction while moving the irradiation position in the channel direction by the interpolation width. Therefore, in this case, for example, a method capable of changing the irradiation position in the channel direction at high speed, such as moving the focal position of the X-ray by the FFS method (Flying Focal Spot method), may be adopted. If the focal position of the X-ray is moved by the FFS method immediately after the pulse X-ray irradiation at the reference irradiation position, the reference irradiation position and the reference irradiation position in the slicing direction are clearly seen by comparing the first and second times in FIG. Pulse X-ray irradiation can be performed by moving the irradiation position by an interpolation width in the channel direction at substantially the same position.

  Further, the method shown in FIG. 9 in which the focal position of the X-ray is moved by the FFS method immediately after the pulse X-ray irradiation at the reference irradiation position may be combined with the interpolation method in the slice direction shown in FIG. . In this case, first, pulse X-ray irradiation is performed at the reference irradiation position (see the first time in FIG. 9), and the X-ray focal position is immediately moved by the FFS method to perform pulse X-ray irradiation (see the second time in FIG. 9). . Subsequently, pulse X-ray irradiation is performed when moving a predetermined distance shorter than the slice width (see the second time in FIG. 7), and the X-ray focal position is immediately moved again by the FFS method to perform pulse X-ray irradiation. When the relative position moves in the body axis direction by the slice width from the reference irradiation position, pulse X-ray irradiation may be performed (see the third time in FIG. 7).

  FIG. 10 is a diagram for explaining a scanogram imaging method when the interpolation width in the scan direction is half of the slice width and the interpolation width in the channel direction is half of the center-to-center distance between detection elements along the channel direction. is there. FIG. 11 shows a scanogram imaging method when the interpolation width in the scan direction is 1/3 of the slice width and the interpolation width in the channel direction is 1/3 of the center-to-center distance between the detection elements along the channel direction. It is a figure for demonstrating.

  As shown in FIGS. 10 and 11, when the relative position between the X-ray tube 31 and the subject O is moved at an interpolation width in the slice direction while continuously changing the relative position of the subject O, for example, at a constant speed, the channel direction is set. Alternatively, pulse X-rays may be irradiated by moving the relative position of the X-ray tube 31 and the subject O in the channel direction by the interpolation width. As a method of moving the relative position of the X-ray tube 31 and the subject O in the channel direction, for example, a method of moving the X-ray focal position by the FFS method, a method of moving the top plate 37 in the x-axis direction, or the like. Conceivable. Further, the interpolation width in the slice direction is only required to be shorter than the slice width, and is not limited to the width obtained by dividing the slice width by a positive integer. That is, pulse X-ray irradiation is performed at one or a plurality of interpolation positions that are separated from the reference irradiation position by a distance shorter than the slice width, and when the relative position moves in the body axis direction from the reference irradiation position by the slice width. Irradiation may be performed (see the third time in FIG. 7). Similarly, the interpolation width in the channel direction is not limited to a value obtained by dividing the center-to-center distance between detection elements along the channel direction by a positive integer.

  Next, in step S5, the scan control function 52 performs imaging by irradiating pulse X-rays at the reference irradiation position with the imaging start position as the reference irradiation position.

  Next, in step S6, when the scan control function 52 moves by the interpolation width set in the slice direction, imaging is performed by irradiating pulse X-rays. At this time, when the interpolation width is set in the channel direction, the scan control function 52 performs imaging by changing the relative positional relationship in the channel direction. Note that the scan control function 52 continues to change the relative positional relationship between the X-ray tube 31 and the subject O even during imaging.

  Next, in step S7, the image generation function 53 generates an image based on the projection data obtained by the pulse X-ray irradiation.

  Next, in step S8, the scan control function 52 sets the tube current in the next pulse X-ray irradiation according to the numerical value relating to the image quality of the generated image. As the numerical value related to the image quality, a value obtained by evaluating the noise of the image as a standard deviation value, a value obtained by evaluating the resolution of the image by spatial frequency analysis using Fourier transform, or the like can be used.

  If imaging has not been completed at all interpolation positions within the slice width (NO in step S9), the process returns to step S6. On the other hand, in the case where imaging has been completed at all interpolation positions within the slice width (YES in step S9), the scan control function 52 determines whether imaging of the entire imaging range of scano imaging has been completed.

  If the scan of the entire scan range has not yet been completed (NO in step S10), the scan control function 52 detects the X-ray beam width (for example, 0.5 mm slice width from the previous reference position) in step S11. Pulse X-ray imaging is performed with the position where the relative position has moved in the slicing direction as a new reference irradiation position by 4 mm in the case of 8 instrument rows, and the process returns to step S6. At this time, if the relative position is moved in the channel direction, pulse X-ray imaging is performed using the position where the movement amount in the channel direction is returned to zero as a new reference irradiation position.

  On the other hand, when the scan of the entire scan range is completed (YES in step S10), the series of procedures ends.

  With the above procedure, it is possible to generate a positioning image with high resolution while suppressing the exposure dose of the subject O.

  According to at least one embodiment described above, since pulse X-ray imaging can be performed with a thin slice width and imaging can be performed at an interpolation position in the slice direction, the exposure of the subject O is higher than when continuous X-ray imaging is performed. The dose can be suppressed and a positioning image with high resolution can be generated.

  Note that pulse X-ray irradiation may be performed only when moving to a new reference irradiation position (step S11), and continuous X-ray irradiation may be performed from the reference irradiation position to imaging at the last interpolation position within the same slice width. Even in this case, it is possible to sufficiently reduce the hiber dose of the subject as compared with the case where the continuous X-ray irradiation is continuously performed.

  The scan control function 52 of the processing circuit 44 in the present embodiment is an example of a scan control unit in the claims. The drive circuit 28 in the present embodiment is an example of a drive unit in the claims.

  In the above embodiment, the term “processor” means, for example, a dedicated or general-purpose CPU (Central Processing Unit), GPU (Graphics Processing Unit), or an application specific integrated circuit (ASIC). It shall mean a circuit such as a programmable logic device (for example, a simple programmable logic device (SPLD), a complex programmable logic device (CPLD), and an FPGA). The processor implements various functions by reading and executing a program stored in the storage medium.

  In the above embodiment, an example in which a single processor of a processing circuit realizes each function has been described. However, a processing circuit is configured by combining a plurality of independent processors, and each processor realizes each function. Also good. Further, when a plurality of processors are provided, the storage medium for storing the program may be provided for each processor individually, or one storage medium stores the programs corresponding to the functions of all the processors in a lump. Also good.

  In addition, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel 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 scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 10 ... X-ray CT apparatus 11 ... Mount 31 ... X-ray tube 33 ... X-ray detector 52 ... Scan control function

Claims (9)

An X-ray source for generating X-rays and a row of X-ray detection elements having a plurality of channels in the channel direction are arranged in a plurality of rows in the body axis direction of the subject orthogonal to the channel direction and pass through the subject. An X-ray detector for detecting X-rays, and a gantry provided across an opening;
A drive unit for changing a relative position between the gantry and the subject;
With the X-ray source fixed at a predetermined position, the X-ray source and the drive unit are controlled so as to perform positioning imaging using pulsed X-rays while changing the relative position along the body axis direction. A scanning control unit,
With
The scan control unit
When performing the positioning imaging while changing the relative position along the body axis direction, after irradiating pulse X-rays, the relative position is a predetermined distance shorter than the slice width from the reference irradiation position. Controlling the X-ray source and the driving unit so as to repeat irradiation with pulse X-rays when moving in a direction;
X-ray CT system. The predetermined distance shorter than the slice width is a distance obtained by dividing the slice width by a predetermined positive integer.
The X-ray CT apparatus according to claim 1. The scan control unit
When performing the positioning imaging while changing the relative position along the body axis direction, pulse X-rays are irradiated when the relative position moves in the body axis direction from the reference irradiation position by the predetermined distance. And controlling the X-ray source and the driving unit so as to repeat irradiation with pulse X-rays when the relative position moves in the body axis direction by the slice width from the reference irradiation position.
The X-ray CT apparatus according to claim 1. The scan control unit
When performing the positioning imaging while changing the relative position along the body axis direction, the relative position is set to the body axis immediately after irradiating pulsed X-rays or at a predetermined distance from the reference irradiation position. When moving in the direction, pulse X-rays are emitted by moving the relative position in the channel direction by a second predetermined distance shorter than the center-to-center distance along the channel direction between the X-ray detection elements. Repeat that,
The X-ray CT apparatus according to claim 1. The scan control unit
When the relative position is moved in the body axis direction by the slice width from the reference irradiation position, the movement of the relative position in the channel direction is returned to zero and the pulse X-ray is irradiated.
The X-ray CT apparatus according to claim 4. The scan control unit
Changing the relative position in the channel direction by moving the focal position of the X-rays in the channel direction by the second predetermined distance;
The X-ray CT apparatus according to claim 4 or 5. The predetermined distance is a distance in a plane that passes through the rotation center of the X-ray source and is orthogonal to the irradiation axis of the X-ray, or a distance on a light receiving surface of the X-ray detection element.
The X-ray CT apparatus according to claim 1. The scan control unit
In accordance with the numerical value related to the image quality of the image generated every time the pulse X-ray is irradiated, the tube current when the next pulse X-ray is irradiated is set.
The X-ray CT apparatus according to claim 1. The scan control unit
Setting the predetermined distance based on information of the imaging target part included in the imaging conditions of the positioning imaging;
The X-ray CT apparatus according to claim 1.

Images