JP2010284303A - X-ray ct apparatus, and control program for generating image data - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a dose in CT radiographing by selectively collecting projection data necessary for generating image data. <P>SOLUTION: The collection area calculating part 11 of an X-ray CT apparatus 100 calculates the collection area of the projection data necessary in generating respective pieces of image data of slice cross sections which are arranged at prescribed interval in a body axial direction, on the basis of a radiographing condition which is set before the CT radiographing of a subject 150, where a helical scan system is applied. When the width of the collection area of the projection data in the body axial direction is smaller than the interval of the image data, an X-ray generating part 2 and a projection data collecting part 3 intermittently perform X-ray irradiation, while rotating at high speed in the circumference of the subject 150 moving at a prescribed speed in the body axial direction together with a top plate 8, and then, selectively collect the projection data in the collection area of the projection data. An image data generating part 4 performs the reconstitution processing of the obtained projection data to generate the image data in the respective slice cross sections. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an X-ray CT apparatus and an image data generation control program, and in particular, an X-ray CT apparatus and image data capable of collecting image data in a plurality of slice sections of a subject in a short time by a helical scan method. The present invention relates to a generation control program.

  The X-ray CT apparatus irradiates the subject with X-rays while rotating the X-ray tube and the X-ray detector at high speed around the subject, and reconstructs projection data collected from a plurality of directions. This is an image diagnostic apparatus for generating in-vivo image data. In the early X-ray CT apparatus, since it took a relatively long time to collect projection data and generate image data, for example, projection data in a plurality of slice sections set in the body axis direction is collected sequentially. When a plurality of image data is generated, “breath-holding” for a predetermined period is applied to the subject every time the projection data of the slice cross section is collected in order to prevent image quality deterioration due to respiratory movement of the examination target region. This “breath-holding” was a great burden on the subject.

  In order to solve such problems, in recent years, the top plate on which the subject is placed is moved in the body axis direction while the X-ray tube and the X-ray detector are continuously rotated around the subject at a high speed. Thus, a so-called helical scan method has been developed in which the X-ray tube and the X-ray detector are moved in a spiral manner with respect to the subject (for example, see Patent Document 1). The development of this helical scan system and the high speed / high performance of the X-ray detector and reconstruction processing unit have made it possible to collect high-quality image data that is less affected by respiratory movement in a short time. For this reason, the examination efficiency has been dramatically improved, and the load on the subject in the examination has been greatly reduced.

JP 59-1111738 A

  The helical scan X-ray CT apparatus described in Patent Document 1 described above makes it possible to collect a plurality of image data in the body axis direction in a very short time. However, for example, when a predetermined number of image data is collected at a relatively coarse image data interval for a wide area of a subject, such as in a group examination, for areas where projection data collection is unnecessary. However, since the same X-ray irradiation is continuously performed, the subject is irradiated with more X-rays than necessary.

  The present invention has been made in view of the above-described problems, and an object thereof is necessary for generating image data in each slice cross section set in advance at predetermined intervals in CT imaging to which the helical scan method is applied. When the collection area width of the projection data is smaller than the image data interval (that is, the slice section interval), only the projection data necessary for generating the image data is selectively collected by intermittently irradiating the subject with X-rays. An object of the present invention is to provide an X-ray CT apparatus and an image data generation control program capable of reducing the X-ray exposure dose to the subject.

  In order to solve the above-mentioned problem, an X-ray CT apparatus according to the present invention according to claim 1 is arranged on the subject while rotating the X-ray tube and the X-ray detector at high speed around the subject moving in the body axis direction. In a helical scan type X-ray CT apparatus that generates a plurality of image data in the body axis direction based on projection data obtained by irradiating X-rays, imaging including an interval of the image data in the body axis direction An imaging condition setting means for setting a condition, a collection area calculation means for calculating a collection area for projection data necessary for generating the image data based on the imaging condition, and an imaging condition and a collection area for the projection data Irradiation condition setting means for setting X-ray irradiation conditions, X-ray generation means having the X-ray tube for irradiating the subject with X-rays based on the X-ray irradiation conditions, and transmission through the subject X A projection data collecting means having the X-ray detector for detecting projection and collecting projection data; and an image data generating means for processing the projection data to generate image data, and calculating by the collection area calculating means When the acquisition area width in the body axis direction of the projection data necessary for generating each of the image data is smaller than the interval of the image data, the irradiation condition setting means The X-ray irradiation conditions that enable the selective collection of projection data in the projection data collection region are set by intermittently performing the beam irradiation.

  According to a sixth aspect of the present invention, there is provided a control program for generating image data according to the present invention, wherein X-rays are emitted to the subject while rotating the X-ray tube and the X-ray detector at high speed around the subject moving in the body axis direction. For the helical scan X-ray CT apparatus that generates a plurality of image data in the body axis direction based on the projection data obtained by irradiation, imaging conditions including the interval of the image data in the body axis direction are set. Each of the imaging condition setting function, a collection area calculation function for calculating a collection area of projection data necessary for generating the image data based on the imaging condition, and the image data calculated by the collection area calculation function. A comparison function for comparing the collection area width of the projection data necessary for generation in the body axis direction and the interval between the image data, a comparison result of the comparison function, the imaging condition, and the previous X-ray irradiation conditions in a low-dose imaging mode that enables selective collection of projection data in the projection data collection region by intermittently performing X-ray irradiation on the subject based on the projection data collection region An irradiation condition setting function for setting the X-ray, an X-ray generation function for irradiating the subject with X-rays based on the X-ray irradiation condition, and detecting X-rays transmitted through the subject and collecting projection data A projection data collection function and an image data generation function for processing the projection data to generate image data are executed.

  According to the present invention, in the case of CT imaging to which the helical scan method is applied, when the projection data collection area width required for generating image data in each slice cross-section set in advance at a predetermined interval is smaller than the image data interval, It is possible to reduce the amount of X-ray exposure to the subject by intermittently performing X-ray irradiation on the sample and selectively collecting only the projection data necessary for generating the image data. Therefore, safe helical scan X-ray CT imaging can be performed.

1 is a block diagram showing the overall configuration of an X-ray CT apparatus in an embodiment of the present invention. The figure which shows the specific example of the image data collection conditions in the Example. The figure which shows typically the X-ray irradiation conditions of the low exposure dose imaging mode set in the Example. The figure which shows typically the X-ray irradiation conditions of the normal imaging | photography mode set in the Example. 6 is a flowchart showing a procedure for collecting image data in the embodiment.

  Embodiments of the present invention will be described below with reference to the drawings.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  In this embodiment, when generating each image data of slice sections arranged at predetermined intervals in the body axis direction based on the imaging conditions set prior to CT imaging of the subject to which the helical scan method is applied. The necessary projection data collection area is calculated. When the projection data collection area width in the body axis direction is smaller than the image data interval, the X-ray tube and the X-ray detector are rotated at high speed around the subject moving at a predetermined speed in the body axis direction together with the top plate. While the X-ray irradiation is intermittently performed, the projection data in the projection data collection area is selectively collected, and the projection data collected from the projection data collection area is reconstructed to reduce the exposure dose in the slice cross section. Image data in shooting mode is generated.

  In the embodiment of the present invention described below, projection data in a plurality of projection data collection areas set in the body axis direction using an X-ray detector in which a plurality of X-ray detection elements are arranged in a one-dimensional manner is used. Although the case of collecting will be described, the above-mentioned projection data may be collected using a two-dimensionally arranged X-ray detector.

(Device configuration)
FIG. 1 is a block diagram showing the overall configuration of the X-ray CT apparatus according to the present embodiment. The X-ray CT apparatus 100 includes imaging mode selection information and imaging conditions supplied from an input unit 10 described later, An irradiation condition setting unit 1 that sets an X-ray irradiation condition and generates an irradiation control signal based on information on a projection data collection region supplied from the collection region calculation unit 11, and an irradiation supplied from the irradiation condition setting unit 1 An X-ray generation unit 2 that irradiates the subject 150 with X-rays according to the control signal, a projection data collection unit 3 that detects X-rays transmitted through the subject 150 and collects projection data, and a projection data collection unit 3 An image data generation unit 4 that processes the collected projection data to generate image data, and a display unit 5 that displays the image data generated by the image data generation unit 4 are provided.

  In addition, the X-ray CT apparatus 100 includes a gantry rotating unit 6 on which a part of the X-ray generating unit 2 and the projection data collecting unit 3 are mounted and rotating at a predetermined speed around the subject 150, and an upper surface of a bed (not shown). A top plate 8 that is slidably mounted on the subject 150 and moves the diagnosis target portion in the body axis direction at a predetermined speed, and the top plate 8 is moved based on the imaging conditions supplied from the input unit 10. A moving mechanism unit 9 that rotates the gantry rotating unit 6 at a high speed is provided, an input unit 10 that selects a shooting mode, sets shooting conditions, inputs various command signals, and the like, and shooting conditions supplied from the input unit 10 Are provided with a collection area calculation unit 11 that calculates a collection area of projection data based on the above, and a system control unit 12 that comprehensively controls each unit described above.

  Note that the imaging conditions set in the input unit 10 include an image data collection condition and an image reconstruction condition. As image data collection conditions, the imaging position (the position of the slice cross section where the image data is generated), the image data interval, the number of image data, the image data thickness, the tube voltage and the tube current, the rotation speed of the gantry rotating unit 6, the sky The moving speed of the plate 8 is included, and the reconstruction conditions include a reconstruction method, a reconstruction area size, a reconstruction matrix size, and the like.

  FIG. 2 shows the above-described image data collection conditions, and an image having an image data thickness Iw at each of the imaging positions z1 to zN set at the image data interval Δd in the body axis direction (z direction) of the subject 150. When generating the data S1 to SN, the photographing positions z1 to zN, the image data interval Δd, the number of image data N, the image data thickness Iw, and the like are set in the input unit 10.

  In addition, areas A1 to AN indicated by solid lines in FIG. 2 indicate projection data collection areas in the low exposure dose imaging mode calculated by the acquisition area calculation unit 11, and an area B0 indicated by a broken line indicates the normal imaging mode. The projection data collection area is shown. Then, the projection data collection areas A1 to AN in the low exposure dose imaging mode having the collection area width Δh where the projection data necessary for generating the image data S1 to SN is collected and the normal imaging mode having the collection area width ΔH are collected. The projection data collection area B0 is calculated based on the above-described image data collection conditions supplied from the input unit 10.

  Next, the configuration and function of each of the units included in the X-ray CT apparatus 100 will be described in more detail.

  The irradiation condition setting unit 1 shown in FIG. 1 is supplied from the input unit 10 via the system control unit 12 and the imaging mode selection signal and image data collection conditions and from the collection region calculation unit 11 via the system control unit 12. X-ray irradiation conditions are set based on the calculation result of the projection data collection area, and an irradiation control signal generated based on the X-ray irradiation conditions is supplied to the X-ray generation unit 2. For example, when the low exposure dose imaging mode is selected in the input unit 10, the irradiation condition setting unit 1 receives the calculation result of the projection data collection region supplied from the collection region calculation unit 11, and the projection data collection region Based on the information, X-ray irradiation conditions in the low exposure dose imaging mode are set.

  FIG. 3 schematically shows the X-ray irradiation conditions in the low exposure dose imaging mode set based on the above-described projection data collection area. However, in FIG. 3, the X-ray tube 21 of the X-ray generation unit 2 and the X-ray detector 31 of the projection data collection unit 3 which will be described later are shown in the body axis direction (z direction) of the subject 150 in order to simplify the description. However, in reality, X-ray irradiation is performed on a predetermined region of the subject 150 by moving a not-shown top plate on which the subject 150 is placed in the body axis direction (−z direction). Done.

  That is, by moving the X-ray tube 21 and the X-ray detector 31 relative to the subject 150 in the z direction, an image having the image data thickness Iw at the imaging positions z1 to zN set at the image data interval Δd. When generating the data S1 to SN, the projection data collection area [zn1−zn2] (zn1 = zn−Δh / 2, zn2 = zn + Δh /) necessary for generating the image data S1 to SN as shown in FIG. 2 and n = 1 to N) are supplied from the collection area calculation unit 11 via the system control unit 12.

  The irradiation condition setting unit 1 then transmits the information on the projection data collection region supplied from the collection region calculation unit 11 and the body axis direction (−z direction) of the top 8 supplied from the input unit 10 as the image data collection condition. 3) based on the movement speed Vt (relative movement speed with respect to the body axis direction (z direction) of the X-ray tube 21 and the X-ray detector 31 in FIG. 3). An irradiation period [tn1-tn2] (n = 1 to N) is set. However, tn1 and tn2 are times when the X-ray tube 21 and the X-ray detector 31 having the moving speed Vt pass zn1 and zn2 in FIG. 3A, and the irradiation interval Δτh at the imaging position Zn is Δτh = tn2−tn1 = Δh / Vt, and the irradiation repetition period Δτd is determined by Δτd = Δd / Vt. Note that the tube voltage and tube current in the low exposure dose imaging mode in the irradiation period [tn1-tn2] (n = 1 to N) are set according to the image data collection conditions supplied from the input unit 10.

  On the other hand, when the normal imaging mode is selected in the input unit 10, the irradiation condition setting unit 1 receives the calculation result of the projection data collection area supplied from the collection area calculation unit 11, and based on the projection data collection area Sets the X-ray irradiation conditions in the normal imaging mode.

  FIG. 4 schematically shows the X-ray irradiation conditions in the normal imaging mode set based on the above-described projection data collection area. In this case as well, the X-ray generator 2 is used for the sake of simplicity. The X-ray tube 21 and the X-ray detector 31 of the projection data acquisition unit 3 are relatively moved at the speed Vt in the body axis direction (z direction) of the subject 150, and in the projection data acquisition region B0 in the normal imaging mode. It shows a case where image data S1 to SN at the photographing positions z1 to zN are generated using the collected projection data.

  In this case, the projection data collection area [z01−z02] (z01 = z11 = z1−Δh / 2, z02 = zN2 =) in the normal photographing mode necessary for generating the image data S1 to SN as shown in FIG. Information on zN + Δh / 2) is supplied from the collection area calculation unit 11 via the system control unit 12. Then, the irradiation condition setting unit 1 is based on the above-described projection data collection region supplied from the collection region calculation unit 11 and the moving speed Vt of the top 8 supplied from the input unit 10 as shown in FIG. An X-ray irradiation period [t01-t02] is set.

  However, t01 and t02 are times when the X-ray tube 21 and the X-ray detector 31 having the moving speed Vt relative to the subject 150 pass z01 and z02 in FIG. ΔτH is determined by ΔτH = t02−t01 = ΔH / Vt. Further, the tube voltage and tube current in the normal imaging mode in the irradiation period [t01-t02] are set according to the image data collection conditions supplied from the input unit 10. The tube voltage and tube current in the normal imaging mode and the tube voltage and tube current in the low exposure dose imaging mode may be set equal, but may be set independently.

  Next, the irradiation condition setting unit 1 generates an irradiation control signal for the low exposure dose imaging mode or the normal imaging mode based on the above-described X-ray irradiation conditions, and supplies the irradiation control signal to the high voltage generator 22 of the X-ray generation unit 2. Controls the irradiation intensity and irradiation timing of X-rays irradiated from the X-ray tube 21 to the subject 150.

  Returning to FIG. 1, the X-ray generator 2 generates an X-ray tube 21 that irradiates the subject 150 with X-rays and a high voltage that is applied between the anode and the cathode of the X-ray tube 21. The gantry rotating unit 6 is provided with the generator 22, the X-ray diaphragm 23 for controlling the irradiation range of the X-rays emitted from the X-ray tube 21 to the subject 150, and the high voltage generated by the high voltage generator 22. Further, a slip ring 24 for supplying to the X-ray tube 21 is provided.

  The X-ray tube 21 is a vacuum tube that generates X-rays, and collides electrons accelerated by a high voltage supplied from a high voltage generator 22 according to irradiation control signals in the low exposure dose imaging mode and the normal imaging mode with a tungsten target. X-rays are emitted. The X-ray diaphragm 23 is provided between the X-ray tube 21 and the subject 150, and has a function of narrowing the X-rays emitted from the X-ray tube 21 to a predetermined irradiation range and an X-ray irradiation intensity distribution on the subject 150. Has a function to set. For example, the X-ray beam emitted from the X-ray tube 21 is shaped into a cone beam-like or fan-beam-like X-ray beam corresponding to the imaging region.

  On the other hand, the projection data acquisition unit 3 detects an X-ray detector 31 that detects X-rays that have passed through the subject 150 and a plurality of channels of detection signals (projection data) output from the X-ray detector 31. A data acquisition unit (hereinafter referred to as a DAS (Data Acquisition System) unit) 32 that performs voltage conversion and A / D conversion, and parallel / serial conversion, electrical / optical / electrical conversion, and output signal of the DAS unit 32 A data transmission circuit 33 that performs serial / parallel conversion is provided.

  The X-ray detector 31 of the projection data collection unit 3 includes, for example, a plurality of X-ray detection elements (not shown) arranged one-dimensionally. Each of the X-ray detection elements converts, for example, X-rays into light. It consists of a scintillator and a photodiode that converts light into an electrical signal. These X-ray detection elements are attached to the gantry rotating unit 6 along an arc centered on the focal point of the X-ray tube 21.

  On the other hand, the DAS unit 32 performs current / voltage conversion and A / D conversion on the projection data supplied from the X-ray detector 31. The data transmission circuit 33 includes a parallel / serial converter, an electrical / optical / electrical converter, and a serial / parallel converter (not shown). The projection data output from the DAS unit 32 is attached to the gantry rotating unit 6. The serial / parallel converter is converted into time-series projection data of one channel in the parallel / serial converter and is attached to the gantry fixing unit 7 by optical communication using the electric / optical / electric converter. To be supplied.

  Next, in the serial / parallel converter, the projection data of one channel is returned to the projection data of a plurality of channels and stored in the projection data storage unit 41 of the image data generation unit 4. This data transmission method is another method as long as signal transmission between the projection data collection unit 3 provided in the gantry rotating unit 6 and the image data generation unit 4 provided outside the gantry fixing unit 7 is possible. For example, a device such as the slip ring described above may be used.

  The X-ray tube 21 and the X-ray diaphragm 23 of the X-ray generation unit 2 and the above-described projection data collection unit 3 are mounted on the gantry rotation unit 6 so as to face each other with the subject 150 interposed therebetween, and the movement mechanism unit 9 Thus, high speed rotation is performed at, for example, 1 rotation / second to 2 rotations / second, with an axis parallel to the body axis direction (z direction) of the subject 150 as a rotation center.

  Next, the image data generation unit 4 includes a projection data storage unit 41 and a reconstruction processing unit 42, and the projection data collection areas [z11-z12] to [zN1-] collected by CT imaging in the low exposure dose imaging mode. zN2] projection data or projection data in the projection data collection area [z01-z02] collected in CT imaging in the normal imaging mode has a function of generating image data by reconstructing the projection data.

  That is, in the projection data storage unit 41, a low dose imaging mode collected by a helical scan method that simultaneously performs high-speed rotation of the gantry rotating unit 6 and movement of the top plate 8 in the body axis direction around the subject 150. Projection data in the normal photographing mode or rotation angle information of the gantry rotating unit 6 and position information of the top plate 8 are stored as supplementary information.

  On the other hand, the reconstruction processing unit 42 includes an arithmetic circuit and a program storage circuit (not shown) in which various reconstruction processing programs necessary for image reconstruction are stored in advance. The arithmetic circuit receives image data thickness Iw and image reconstruction condition information of the image data collection condition supplied from the input unit 10 via the system control unit 12, and performs reconstruction processing corresponding to the image reconstruction condition A program is read from the program storage circuit. Then, the projection data read from the projection data storage unit 41 is reconstructed using the reconstruction processing program, so that the image data S1 to SN of the low exposure dose imaging mode or the normal imaging mode having the image data thickness Iw are obtained. Generate.

  The display unit 5 includes a display data generation unit 51 and a monitor 52. The display data generation unit 51 converts the image data S1 to SN of the low exposure dose imaging mode or the normal imaging mode generated by the image data generation unit 4 into a predetermined display format, generates display data, and displays the display data on the monitor 52. .

  Next, the moving mechanism unit 9 includes a top / pedestal moving mechanism unit 91 and a mechanism control unit 92. The top plate / base movement mechanism 91 applies the base rotation part 6 on which the X-ray tube 21 and the X-ray detector 31 are mounted according to the base rotation control signal and the top movement control signal supplied from the mechanism controller 92 to the subject. The object is rotated at a high speed at a speed Vr around 150, and the top 8 is slid in the body axis direction of the subject 150 at a speed Vt.

  On the other hand, the mechanism control unit 92 includes a control circuit (not shown) and a movement condition storage circuit, and the movement condition storage circuit includes image data collection conditions for the normal imaging mode and the low dose imaging mode set by the input unit 10. The rotational speed Vr of the gantry rotating unit 6 and the moving speed Vt of the top plate 8 are stored. The control circuit generates a gantry rotation control signal and a top plate movement control signal based on the movement information read from the movement condition storage circuit, and uses the obtained control signals as a top plate / gantry moving mechanism. By supplying to the unit 91, the gantry rotating unit 6 is rotated and the top plate 8 is moved in the low exposure dose imaging mode or the normal imaging mode.

  The input unit 10 includes input devices such as a display panel, a keyboard, various switches, and a mouse, and forms an interactive interface when used in combination with the display unit 5. Then, an imaging condition setting function 101 for setting imaging conditions such as image data collection conditions and reconstruction conditions in the normal imaging mode and the low exposure imaging mode, and an imaging mode selection function 102 for selecting the normal imaging mode or the low exposure imaging mode. Furthermore, input of subject information, setting of image data display conditions, input of various command signals, and the like are performed using the above-described display panel and input device.

  On the other hand, the collection area calculation unit 11 includes the number N of image data, the image data interval Δd, the photographing positions z1 to zN, the image data thickness Iw, the top of the image data collection condition supplied from the input unit 10 via the system control unit 12. Based on the moving speed Vt of the plate 8 and the rotational speed Vr of the gantry rotating unit 6, the projection data collection area [zn1-zn2] having the collection area width Δh necessary for generating the image data S1 to SN is obtained. ] (N = 1 to N) and the projection data collection area [z01-z02] in the normal imaging mode having the collection area width ΔH.

  The system control unit 12 includes the irradiation condition control unit 1, the projection data collection unit 3, the image data generation unit 4, and the movement mechanism unit 9 based on the above-described input information, setting information, and selection information supplied from the input unit 10. The units are collectively controlled to generate and display image data in the low exposure dose imaging mode and the normal imaging mode.

  Further, it has a function of comparing the collection area width Δh in the low exposure dose imaging mode supplied from the collection area calculation unit 11 and the image data interval Δd of the image data collection conditions supplied from the input unit 10.

(Image data collection procedure)
Next, the image data collection procedure in this embodiment will be described with reference to the flowchart of FIG.

  The operator of the X-ray CT apparatus 100 inputs subject information at the input unit 10 prior to the collection of image data, and further, image data collection conditions in the low exposure dose imaging mode and the normal imaging mode (that is, the imaging positions z1 to zN, image data interval Δd, number of image data N, image data thickness Iw, tube voltage and tube current, rotation speed Vr of gantry rotating unit 6, moving speed Vt of top plate 8) and image reconstruction conditions (that is, reconstruction) Shooting conditions such as a method, a reconstruction area size, and a reconstruction matrix size) are set. The set imaging conditions are supplied to the irradiation condition setting unit 1, the image data generation unit 4, the movement mechanism unit 9, and the collection area calculation unit 11 via the system control unit 12 (step S1 in FIG. 5). ).

  When the setting of the imaging conditions in the input unit 10 is completed, the operator places the subject 150 on the top 8 and the first imaging position (z = z1) is placed in the imaging field of the gantry rotating unit 6. The top plate 8 is moved in the body axis direction.

  On the other hand, the collection area calculation unit 11 includes the number N of image data, the image data interval Δd, the imaging positions z1 to zN, the image data thickness Iw, the sky, and the image data collection conditions supplied from the input unit 10 via the system control unit 12. Projection data collection area [zn1-zn2] (n = 1) in the low exposure dose imaging mode required when generating the image data S1 to SN based on the moving speed Vt of the plate 8 and the rotational speed Vr of the gantry rotating unit 6 To N), the collection area width Δh, the projection data collection area [z01-z02] and the collection area width ΔH in the normal imaging mode, and the calculation result of the collection area width Δh is supplied to the system control unit 12 (FIG. 5). Step S2).

  The system control unit 12 that has received the calculation result of the collection region width Δh in the low exposure dose imaging mode from the collection region calculation unit 11 determines the image data interval Δd already supplied from the input unit 10 and the above-described collection region width Δh. Compare. When Δd> Δh, the comparison result is displayed on the display panel of the input unit 10 or the monitor 52 of the display unit 5 (step S3 in FIG. 5). Either the low exposure dose imaging mode or the normal imaging mode is selected (step S4 in FIG. 5).

  In the above-described step S4, when the low exposure dose imaging mode is selected, the irradiation condition setting unit 1 that has received the low exposure dose imaging mode selection information via the system control unit 12 receives the input unit 10 in the above step 1. The irradiation period [tn1-tn2] based on the top plate moving speed Vt supplied from the image data collection condition and the projection data collection area [zn1-zn2] (n = 1 to N) supplied from the collection area calculation unit 11 The X-ray irradiation conditions in the low exposure dose imaging mode in which intermittent X-ray irradiation is performed at (n = 1 to N) are set (step S5 in FIG. 5). Then, an irradiation control signal is generated based on the X-ray irradiation conditions and supplied to the high voltage generator 22 of the X-ray generator 2.

  On the other hand, the system control unit 12 that has received the selection information for the low exposure dose imaging mode from the input unit 10 supplies a movement instruction signal to the mechanism control unit 92 of the movement mechanism unit 9, and the movement that has received this movement instruction signal. The mechanism control unit 92 generates a gantry rotation control signal and a top plate movement control signal based on the gantry rotation speed Vr and the top plate movement speed Vt supplied from the input unit 10 in step S1 described above. Then, by supplying these control signals to the top board / base movement mechanism 91, the base rotation part 6 and the top board 8 are moved in a predetermined direction at a predetermined speed.

  On the other hand, the high voltage generator 22 of the X-ray generation unit 2 to which the irradiation control signal for the low exposure dose imaging mode is supplied from the irradiation condition setting unit 1 indicates the power (tube voltage and tube current) necessary for X-ray irradiation. The X-ray tube 21 supplied in the irradiation period [tn1-tn2] (n = 1 to N) shown in FIG. 3 and supplied with this power irradiates the subject 150 with X-rays.

  X-rays irradiated from the X-ray tube 21 and transmitted through the subject 150 are detected by the X-ray detector 31 of the projection data collection unit 3. That is, the X-ray transmitted through the subject 150 is converted into a charge (current) signal proportional to the transmitted dose in the X-ray detector 31, and this current signal is supplied to the DAS unit 32 for current / voltage conversion and A / D conversion is performed to generate projection data.

  This projection data is sent to the transmission unit of the data transmission circuit 33 attached to the gantry rotating unit 6 and converted into an optical signal, and is sent to the reception unit of the data transmission circuit 33 attached to the gantry fixing unit 7 via the air. Received. The received projection data is stored in the projection data storage unit 41 of the image data generation unit 4 together with the position information of the top plate 8 and the rotation angle information of the gantry rotation unit 6 which are the accompanying information. That is, the projection data storage unit 41 stores the projection data collected in each of the irradiation periods [tn1-tn2] (n = 1 to N) (step S6 in FIG. 5).

  On the other hand, the reconstruction processing unit 42 of the image data generation unit 4 receives the projection data read from the projection data storage unit 41 from the input unit 10 via the system control unit 12 and the image data thickness Iw of the image data collection condition. Reconstruction processing is performed based on the image reconstruction condition, and image data S1 to SN in the low exposure dose imaging mode having the image data thickness Iw are generated. That is, the image data S1 to SN at the photographing positions z1 to zN are in the projection data collection area [zn1-zn2] (n = 1 to N) collected in the irradiation period [tn1-tn2] (n = 1 to N). It is generated by reconstructing the projection data (step S9 in FIG. 5).

  Then, the display data generation unit 51 of the display unit 5 converts the image data S1 to SN of the low exposure dose imaging mode supplied from the reconstruction processing unit 42 of the image data generation unit 4 into a predetermined display format, and monitors 52 (Step S10 in FIG. 5).

  On the other hand, when the normal shooting mode is selected in step S4 described above, the irradiation condition setting unit 1 that has received the selection information of the normal shooting mode via the system control unit 12 is supplied from the input unit 10 in step 1 described above. The continuous X-ray irradiation in the irradiation period [t01-t02] based on the top plate moving speed Vt under the image data collection conditions and the calculation result of the projection data collection area [z01-z02] supplied from the collection area calculation unit 11 The X-ray irradiation conditions in the normal imaging mode for performing are set (step S7 in FIG. 5). Then, an irradiation control signal is generated based on the X-ray irradiation conditions and supplied to the high voltage generator 22 of the X-ray generator 2.

  On the other hand, the system control unit 12 that has received the selection information of the normal photographing mode from the input unit 10 supplies a movement instruction signal to the mechanism control unit 92 of the movement mechanism unit 9 and receives the movement instruction signal. The unit 92 generates a gantry rotation control signal and a top plate movement control signal based on the gantry rotation speed Vr and the top plate movement speed Vt supplied from the input unit 10 in step S1 described above. Then, by supplying these control signals to the top board / base movement mechanism 91, the base rotation part 6 and the top board 8 are moved in a predetermined direction at a predetermined speed.

  On the other hand, the high voltage generator 22 of the X-ray generator 2 to which the irradiation control signal in the normal imaging mode is supplied from the irradiation condition setting unit 1 shows the power (tube voltage and tube current) necessary for X-ray irradiation in FIG. The X-ray tube 21 supplied during the irradiation period [t01-t02] shown and receiving this power supply irradiates the subject 150 with X-rays. The projection data collected in the irradiation period [t01-t02] by the same procedure as in step S6 described above is stored in the projection data storage unit 41 of the image data generation unit 4 (step S8 in FIG. 5).

  Next, the reconstruction processing unit 42 of the image data generating unit 4 reconstructs the projection data read from the projection data storage unit 41 in the same manner as in the low exposure dose imaging mode, and performs image data S1 in the normal imaging mode. Or SN is generated and displayed on the monitor 52 of the display unit 5. In this case, the projection data of the region [zn1-zn2] (n = 1 to N) is extracted from the projection data of the projection data collection region [z01-z02] continuously collected during the irradiation period [t01-t02]. Then, image data S1 to SN are generated by reconstructing these projection data (steps S9 to S10 in FIG. 5).

  When the projection data collection area width Δh calculated in step S2 is larger than the image data interval Δd, the above-described steps S7 to S10 are executed to generate and display the image data S1 to SN in the normal photographing mode. (Steps S7 to S10 in FIG. 5).

  According to the embodiment of the present invention described above, the projection data collection area width required for generating image data in each of slice slices preset at predetermined intervals in CT imaging to which the helical scan method is applied is the image data. When the interval is smaller than the interval, it is possible to reduce the X-ray exposure dose to the subject by intermittently performing X-ray irradiation on the subject and selectively collecting only the projection data necessary for generating the image data. Become. Therefore, safe helical scan X-ray CT imaging can be performed.

  In particular, when collecting a predetermined number of image data at a relatively coarse image data interval over a wide area of a subject, such as a mass examination, the intermittent X-ray irradiation shown in this embodiment is applied. By doing so, the exposure dose can be greatly reduced.

  In addition, the selection of the low-dose imaging mode and the normal imaging mode is performed by an operator who has been notified of the comparison result between the image data interval and the projection data collection area width, so that an imaging mode optimal for the CT imaging environment is used as an opportunity. You can choose as you like.

  Furthermore, according to the above-described embodiment, a wide range of projection data can be collected in a short time in the same manner as the CT imaging in the normal imaging mode to which the helical scan method is applied, and therefore, it is affected by respiratory movement and the like. High quality image data can be collected, and thus diagnostic accuracy and diagnostic efficiency can be improved.

  As mentioned above, although the Example of this invention has been described, this invention is not limited to the above-mentioned Example, It can change and implement. For example, in the above-described embodiment, the case where the moving speed of the top board 8 in the normal imaging mode and the moving speed of the top board 8 in the low exposure dose imaging mode are set equal to each other has been described. . In particular, in the low exposure dose imaging mode, the time required for collecting projection data can be shortened by making the moving speed in the non-irradiation period of X-rays faster than the moving speed in the irradiation period.

  Moreover, although the case where the tube voltage and tube current in the normal imaging mode and the tube voltage and tube current in the low exposure dose imaging mode are set to be equal has been described, different tube voltages and tube currents may be set.

  On the other hand, in the above-described embodiment, a case where projection data in a plurality of projection data collection areas set in the body axis direction is collected using an X-ray detector in which a plurality of X-ray detection elements are arranged one-dimensionally. As described above, the above-described projection data may be collected using a two-dimensionally arranged X-ray detector.

  Further, although the case where the system control unit 12 compares the collection area width Δh and the image data interval Δd in the low exposure dose imaging mode has been described, a comparison unit that performs these comparisons may be provided independently.

  Furthermore, in the above-described embodiment, when the collection area width Δh in the low exposure dose imaging mode is smaller than the image data interval Δd, the irradiation condition setting unit 1 performs the low exposure based on the imaging mode selection information supplied from the input unit 10. Although the case of setting the X-ray irradiation conditions in the dose imaging mode has been described, the X-ray irradiation conditions in the low dose imaging mode are automatically set based on the comparison result directly supplied from the system control unit 12 or the above-described comparison unit. It doesn't matter.

DESCRIPTION OF SYMBOLS 1 ... Irradiation condition setting part 2 ... X-ray generation part 21 ... X-ray tube 22 ... High voltage generator 23 ... X-ray restrictor 24 ... Slip ring 3 ... Projection data collection part 31 ... X-ray detector 32 ... DAS unit 33 ... Data transmission circuit 4 ... Image data generation part 41 ... Projection data storage part 42 ... Reconstruction processing part 5 ... Display part 51 ... Display data generation part 52 ... Monitor 6 ... Base rotation part 7 ... Base fixing part 8 ... Top plate 9 ... Movement mechanism 91 ... Top / table movement mechanism 92 ... Mechanism control unit 10 ... Input unit 101 ... Imaging condition setting function 102 ... Imaging mode selection function 11 ... Collection area calculation unit 12 ... System control unit 100 ... X-ray CT apparatus

Claims (6)

Based on projection data obtained by irradiating the subject with X-rays while rotating the X-ray tube and the X-ray detector at a high speed around the subject moving in the body axis direction, a plurality of items in the body axis direction are provided. In a helical scan X-ray CT apparatus that generates image data,
Photographing condition setting means for setting photographing conditions including an interval of the image data in the body axis direction;
A collection area calculation means for calculating a collection area of projection data necessary for generating the image data based on the photographing conditions;
An irradiation condition setting means for setting an X-ray irradiation condition based on the imaging condition and the collection area of the projection data;
X-ray generation means having the X-ray tube for irradiating the subject with X-rays based on the X-ray irradiation conditions;
A projection data collecting means having the X-ray detector for detecting X-rays transmitted through the subject and collecting projection data;
Image data generating means for processing the projection data to generate image data,
When the collection area width in the body axis direction of the projection data necessary for generating each of the image data calculated by the collection area calculation means is smaller than the interval of the image data, the irradiation condition setting means, The X-ray CT is characterized in that the X-ray irradiation conditions for enabling selective collection of projection data in the projection data collection region are set by intermittently performing X-ray irradiation by the X-ray generation means. apparatus.   Comparing means for comparing the collection area width of the projection data in the body axis direction and the interval between the image data is provided, and the irradiation condition setting means is intermittent with respect to the subject based on the comparison result of the comparing means. 2. The X-ray CT apparatus according to claim 1, wherein an X-ray irradiation condition in a low-dose imaging mode in which continuous X-ray irradiation is performed or an X-ray irradiation condition in a normal imaging mode in which continuous X-ray irradiation is performed is set. .   Comparison means for comparing the collection area width of the projection data in the body axis direction and the interval of the image data, and an imaging mode selection for selecting a low exposure dose imaging mode or a normal imaging mode based on the comparison result of the comparison means And the irradiation condition setting unit is configured to perform an X-ray irradiation condition in a low-dose imaging mode in which intermittent X-ray irradiation is performed on the subject based on a selection result of the imaging mode selection unit or continuous. 2. The X-ray CT apparatus according to claim 1, wherein X-ray irradiation conditions in a normal imaging mode for performing X-ray irradiation are set.   And a mechanism control means for controlling a top plate on which the subject is placed and a moving mechanism unit for moving the top plate in the body axis direction of the subject at a predetermined speed. The mechanism control means includes the X-ray generation means. When intermittent X-ray irradiation is performed on the subject, the moving mechanism unit is controlled so that the moving speed of the top plate in the non-irradiation period is faster than the moving speed in the irradiation period. The X-ray CT apparatus according to claim 1.   A top plate on which the subject is placed; and the irradiation condition setting means includes at least a moving speed of the top plate under the imaging conditions, a collection area of the projection data, a comparison result of the comparison means, or the imaging mode selection means. The X-ray CT apparatus according to claim 2 or 3, wherein the X-ray irradiation condition in the low exposure dose imaging mode or the X-ray irradiation condition in the normal imaging mode is set based on the selection result. Based on projection data obtained by irradiating the subject with X-rays while rotating the X-ray tube and the X-ray detector at a high speed around the subject moving in the body axis direction, a plurality of items in the body axis direction are provided. For the helical scan X-ray CT system that generates image data,
A shooting condition setting function for setting shooting conditions including an interval of the image data in the body axis direction;
A collection area calculation function for calculating a collection area of projection data necessary for generating the image data based on the imaging conditions;
A comparison function for comparing the collection area width in the body axis direction of the projection data necessary for generating each of the image data calculated by the collection area calculation function and the interval of the image data;
Based on the comparison result of the comparison function, the imaging conditions, and the projection data collection area, X-ray irradiation is intermittently performed on the subject, thereby enabling selective collection of projection data in the projection data collection area. An irradiation condition setting function for setting an X-ray irradiation condition in a low exposure dose imaging mode;
An X-ray generation function for irradiating the subject with X-rays based on the X-ray irradiation conditions;
A projection data collection function for detecting X-rays transmitted through the subject and collecting projection data;
An image data generation control program for executing an image data generation function for processing the projection data to generate image data.

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