JP2010125172A - X-ray ct apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray CT apparatus, imaging the heart of a subject with high image quality and low exposure to radiation and at high speed even when the subject has a comparatively high heart rate. <P>SOLUTION: A helical scan to an imaging region ZR1 including the heart of a subject is divided into a first helical scan performed for about half region SR11 from one end P11 of an imaging region ZR1 in the +z direction and a second helical scan performed for about half region SR12 from the other end P12 of the imaging region ZR1 in the -z direction, and each helical scan is performed within one heartbeat in synchronization with the heartbeat. Thus, the continuity of scan can be maintained to the utmost to more reduce a change in cardiac phase during scanning. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an X-ray CT (Computed Tomography) apparatus.

  As a method of imaging a subject with an X-ray CT apparatus, a method of performing one high-speed high pitch helical scan synchronized with a signal representing the heartbeat of the subject is known. For example, the subject is imaged by a helical scan with a scan width of 40 mm, a gantry rotation period of 0.35 seconds, and a helical pitch of 1 or more. Further, at this time, a helical scan is performed at a predetermined timing (timing) so that the center of the imaging range is scanned at a phase of 75 ± 5% of the heartbeat cycle considered to be the most gentle movement of the heart (for example, (See Patent Document 1, FIG. 25, etc.).

According to this method, the problem of increased exposure dose as seen in prospective imaging methods, the problem of long imaging time as seen in multi-segment imaging methods, banding artifacts ( The problem that many banding artifacts occur can be solved, and a portion (including the heart itself) that fluctuates in synchronization with the heart beat of the subject can be imaged at high speed with low exposure at high speed.
JP 2007-275314 A

  However, according to the above-described method of imaging by one high-speed high-pitch helical scan, when imaging a subject with a relatively high heart rate, the amount of heart fluctuation during the scan increases, resulting in subject blurring. The degradation of image quality may not be negligible.

  In view of the above circumstances, the present invention can image a portion that fluctuates in synchronization with the heart beat of a subject at high speed and high image quality with low exposure even for a subject with a relatively large heart rate. An object is to provide an X-ray CT apparatus.

  In a first aspect, the present invention includes an X-ray tube and an X-ray detector, and X-ray projection data (data) is obtained by scanning a subject using the X-ray tube and the X-ray detector. X-ray CT apparatus comprising: X-ray data collection means for collecting image data; and reconstruction means for reconstructing image data based on the collected X-ray projection data, wherein the X-ray data collection means comprises the subject Each of the plurality of divided ranges obtained by dividing the imaging range set in the body axis direction is helically scanned within one heartbeat in synchronization with a signal representing the heartbeat of the subject. X-ray projection data used to reconstruct image data of a slice corresponding to a position is collected, and a helical scan direction for each of two adjacent divided ranges in the plurality of divided ranges is determined. To provide an X-ray CT apparatus are opposite each other in the body axis direction.

  Here, “in synchronization with the signal” includes executing some matter after a predetermined time has elapsed since the characteristic waveform of the signal was detected.

  Further, “within 1 heartbeat” means within a time corresponding to one heartbeat cycle.

  In a second aspect, the present invention relates to the two divided ranges at a timing when the X-ray data acquisition means scans the division position between the two adjacent divided ranges at the same phase of the signal. An X-ray CT apparatus according to the first aspect for helical scanning is provided.

  In a third aspect, the present invention provides the X-ray data collection means, wherein the predetermined position of the imaging range is between 35% and 50% of the heartbeat period when the R wave in the electrocardiogram waveform is used as a reference, or An X-ray CT apparatus according to the second aspect of the present invention that helically scans a divided range including the predetermined position at a timing scanned at a phase corresponding to a predetermined phase between 65% and 80%.

  In a fourth aspect, the present invention provides the X-ray CT apparatus according to the third aspect, wherein the predetermined position is a center position of the imaging range.

  In a fifth aspect, the present invention provides the X-ray CT apparatus according to any one of the first to fourth aspects, wherein the plurality of division ranges have substantially equal sizes. .

  In a sixth aspect, the present invention provides the X-ray CT apparatus according to any one of the first to fifth aspects, wherein the imaging range includes the heart of the subject.

  In a seventh aspect, the present invention relates to the sixth aspect from the first aspect, wherein the direction of the helical scan with respect to the divided range including one end of the imaging range is the direction from one end to the other end of the imaging range. An X-ray CT apparatus according to any one aspect is provided.

  In an eighth aspect, the present invention provides the second range in which the X-ray data collection means includes a first range including one of the two divided ranges adjacent to each other and the other of the two divided ranges. Are overlapped, and the first range is helically scanned to collect the first X-ray projection data, and the second range is helically scanned to obtain the second X-ray projection data. The first reconstruction unit is configured to reconstruct the image data of the slice corresponding to the position of the overlapping range based on the collected first and second X-ray projection data. An X-ray CT apparatus according to any one of the seventh aspects from the viewpoint is provided.

  In a ninth aspect, the present invention provides the second range in which the X-ray data collection means includes a first range including one of the two divided ranges adjacent to each other and the other of the two divided ranges. Are overlapped, and the first range is helically scanned to collect the first X-ray projection data, and the second range is helically scanned to obtain the second X-ray projection data. And the reconstruction means reconstructs the first image data of the slice corresponding to the position of the overlapping range based on the first X-ray projection data, and the second X-ray From the first aspect, the second image data of the slice is reconstructed based on the projection data, and the third image data of the slice is generated using the first and second image data. X-ray CT of any one of the viewpoints To provide a location.

  In a tenth aspect, in the present invention, the X-ray data collection means is a first range that is a part of one of the two divided ranges adjacent to each other and a part of the other of the two divided ranges. X-ray projection data including one when the second range and the predetermined range are set, the first range is helically scanned and the predetermined X-ray projection data is bisected, and The second range is helically scanned to collect X-ray projection data including the other when the predetermined X-ray projection data is bisected, and the reconstructing means collects one of the collected halves The predetermined X-ray projection data is generated using the other X-ray projection data, and image data of a slice corresponding to each position in the predetermined range is reconstructed based on the generated predetermined X-ray projection data. From the first viewpoint to the seventh To provide an X-ray CT apparatus according to any one aspect of the point.

  Here, the “predetermined X-ray projection data” is, for example, a view angle necessary for reconstructing image data of a slice corresponding to each position in the predetermined range, for example, a fan angle of 180 ° + X-ray beam. Or 360 ° X-ray projection data. In the helical scan, generally, the first part and the last part of the collected X-ray projection data include X-ray projection data that is less than the view angle necessary for reconstruction of image data. Therefore, the reconstruction means, for example, the last part of the X-ray projection data collected by helical scanning the first range and the X-ray projection data collected by helical scanning the second range. Using the first portion, X-ray projection data corresponding to a view angle necessary for reconstructing image data of a slice corresponding to the position in the predetermined range is generated.

  In an eleventh aspect, according to the present invention, each helical scan for the plurality of divided ranges has a scan width of 20 millimeters or more, a rotation period around the body axis direction of 0.5 seconds or less, and the body axis direction. Provided is an X-ray CT apparatus according to any one of the first to tenth aspects, which is performed under the condition that the moving speed is 80 millimeters or more per second.

  Here, the “scan width” is the width in the body axis direction of the X-ray beam on the rotation axis of the helical scan.

  In addition, “the rotation cycle is 0.5 seconds or less” means that the rotation cycle is 0.5 seconds or faster or faster.

  In a twelfth aspect, the present invention provides any one of the first to eleventh aspects, wherein the plurality of division ranges are first and second division ranges obtained by dividing the imaging range into two. An X-ray CT apparatus according to one aspect is provided.

  In a thirteenth aspect, the present invention is directed to the X-ray data collecting means, wherein the X-ray data collecting means sets the first divided range in a reciprocal movement in the body axis direction of the subject or the X-ray tube and the X-ray detector. An X-ray CT apparatus according to the twelfth aspect of the present invention that performs helical scanning and helical scanning of the second divided range on the return path of the reciprocating movement is provided.

  In a fourteenth aspect, the present invention provides the X-ray CT apparatus according to the thirteenth aspect, wherein the X-ray data collection means repeatedly performs a helical scan on the first and second divided ranges by the reciprocating movement a plurality of times. provide.

  According to the present invention, the imaging range of the subject is divided into a plurality of ranges, and each divided range is helically scanned within one heartbeat in synchronization with the heartbeat. At this time, helical scans for two adjacent divided ranges are performed. Since the directions are opposite to each other, the entire imaging range can be scanned with fewer cardiac phase changes while maintaining the continuity of scanning in the imaging range as much as possible, and even for subjects with a relatively large heart rate The region that fluctuates in synchronization with the heart beat can be imaged at high speed with low exposure at high speed.

(First embodiment)
Embodiments according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing an X-ray CT apparatus 100 according to an embodiment of the present invention. The X-ray CT apparatus 100 includes an operation console 1, an imaging table 10, and a scanning gantry 20.

  The operation console 1 includes an input device 2, a central processing unit 3, a data collection buffer (buffer) 5, a monitor 6, and a storage device 7.

  The input device 2 includes a keyboard (not shown), a mouse, and the like, and receives input of various information from an operator. The input device 2 receives input of information for setting scan conditions such as an imaging range of the subject H, an X-ray tube voltage, an X-ray tube current, and the like.

  The data collection buffer 5 collects X-ray projection data for each view sent from the data collection device 25 of the scanning gantry 20. Here, the view is defined as a combination of the view direction (the rotation position of the rotation unit 15) and the position of the cradle 12 when the data collection device 25 collects X-ray projection data.

  The monitor 6 includes a CRT (cathode ray tube), a liquid crystal panel (panel), and the like, and displays an operation screen, a tomographic image, and the like.

  The storage device 7 includes a hard disk, a memory, and the like, and stores various data, programs, and the like.

  The central processing unit 3 executes a scan control process for performing a scout scan or a helical scan of the subject H. Further, the central processing unit 3 stores data input by the input device 2 and X-ray projection data collected by the data collection buffer 5 in the storage device 7 and displays an operation screen, a tomographic image, and the like on the monitor 6. I will let you.

  The imaging table 10 includes a cradle 12 on which the subject H is placed and taken in and out of the opening B of the scanning gantry 20. The cradle 12 is moved up and down and horizontally moved by a motor built in the imaging table 10. Here, the horizontal linear movement direction of the cradle 12, that is, the body axis direction of the subject H is the z direction, the vertical direction is the y direction, and the horizontal direction perpendicular to the z direction and the y direction is the x direction.

  The scanning gantry 20 has an opening B including an imaging space, and includes a rotating unit 15 that rotates around the opening B, and a scanning gantry main body 20a that rotatably supports the rotating unit 15. The rotating unit 15 and the scanning gantry body 20 a are electrically connected via a slip ring 30.

  The rotating unit 15 includes an X-ray tube 21, an X-ray controller 22, an X-ray collimator 23, an X-ray detector 24, a data acquisition device (DAS) 25, and a rotating unit controller 26.

  The X-ray tube 21 and the X-ray detector 24 are arranged to face each other with the opening B interposed therebetween. The X-ray tube 21 is a rotary anode type, and emits X-rays from an X-ray focal point on the rotary anode. The X-ray detector 24 is a multi-row detector having a plurality of detector rows in the slice direction in which a plurality of detection elements for detecting X-rays are arranged in the channel direction. Hereinafter, the X-ray tube 21 and the X-ray detector 24 are also referred to as a data collection system.

  The X-ray controller 22 receives information such as set values of the X-ray tube voltage and X-ray tube current determined by the set scan conditions from the rotating unit controller 26, and the X-ray tube voltage and X-ray tube current are set to these set values. The X-ray tube 21 is controlled so that The X-ray controller 22 controls the generation timing (timing) of X-rays by a control signal from the rotating unit controller 26.

  The collimator 23 controls the position and width of the opening by a control signal from the rotating unit controller 26.

  The data collection device 25 collects data obtained by analog-digital conversion of the output signal of each detection element of the X-ray detector 24 for each view as X-ray projection data, and the data collection buffer 5 Send to.

  The rotation unit controller 26 controls a motor (not shown) of the rotation unit 15, an X-ray controller 22, a collimator 23, a data collection device 25, and the like.

  The scanning gantry body 20 a includes a rotation controller 26 and a controller 29 that controls the imaging table 10. The controller 29 is controlled by a control signal from the central processing unit 3.

  The electrocardiograph 31 generates an electrocardiogram signal representing the heartbeat of the subject H based on an output from a sensor (not shown) connected to the subject H. The electrocardiograph 31 is connected to the controller 29. Thereby, the control controller 29 enables a scanning operation synchronized with the heartbeat of the subject H.

  The central processing unit 3 and the scanning gantry 20 are examples of X-ray data collection means in the present invention.

  Here, the positional relationship between the subject H and the data collection system will be described.

  FIG. 2 is a diagram when the data collection system is viewed in the x direction. The subject H is placed on the cradle 12 and put in and out of the opening B. The X-ray emitted from the X-ray focal point of the X-ray tube 21 is shaped into a cone beam X-ray Xb by a collimator 23 and is irradiated toward the detection surface of the X-ray detector 24. The X-ray detector 24 detects X-rays that have passed through the subject H. When the rotating unit 15 rotates, the X-ray tube 21, the collimator 23, and the X-ray detector 24 rotate around the opening B in the xy plane.

  Here, the scout scan is executed by irradiating the subject H with a low dose of X-rays from the X-ray tube 21 while stopping the rotation of the rotating unit 15 and moving the cradle 12 in the z direction. . Further, a helical scan is executed by irradiating the subject H with X-rays from the X-ray tube 21 while rotating the rotating unit 15 and moving the cradle 12 in the z direction.

  Hereafter, the flow of the cardiac imaging process in this embodiment will be described. In the following description, the scan width (the width in the z direction of the X-ray beam at the iso-center) is 40 mm, the gantry rotation period (the rotation period of the rotating unit 15) is 0.35 seconds / revolution, and the cradle 12 Is 157 mm / sec, the heart rate of the subject H is 75 times / min (heart rate is 0.8 sec), and the helical pitch of the helical scan is 1.375. Here, the helical pitch is a ratio S / D obtained by dividing the subject movement amount S per rotation of the data acquisition system by the width in the z direction of the X-ray beam at the isocenter, that is, the scan width D.

  FIG. 3 is a flowchart of cardiac imaging in the present embodiment.

  In step S1, a scout scan is performed. Specifically, the control controller 29 that has received the control signal from the central processing unit 3 controls the rotating unit 15 and the imaging table 10 via the rotating unit controller 26, and performs the above-described scout scan. Thereby, a scout image of the subject H, for example, a coronal image or a sagittal image of the subject H is obtained. A scout image of the subject H is displayed on the monitor 6.

  In step S2, an imaging range is set.

  FIG. 4 is a diagram illustrating an example of the imaging range set on the scout image.

  In step S2, on the scout image SG of the subject H displayed on the monitor 6, the range in the z direction including the heart HH of the subject H is automatically set by the operator using the input device 2 or by image recognition. specify. For example, as shown in FIG. 4, on the scout image SG of the subject H, a position P11 and a position P12 in the z direction are designated. The central processing unit 3 sets the range from the designated position P11 to the position P12 as the imaging range ZR1.

  In step S3, the imaging range is divided and set. That is, the imaging range ZR1 is divided into a plurality of divided ranges, and a scan range based on each divided range is set.

  For example, as shown in FIG. 4, the central processing unit 3 sets only one division position B1 at the central position C1 of the imaging range ZR1, and divides the imaging range ZR1 into two. That is, the imaging range ZR1 is a range from the position P11 at one end of the imaging range ZR1 to the division position B1, and a range from the position P12 at the other end of the imaging range ZR1 to the division position B1. This is divided into the second divided range BR12.

  Then, the first scan range including the first divided range BR11 and the second scan range including the second divided range BR12 are set so as to partially overlap. Here, as shown in FIG. 4, the range from the position P11 to the position P13 slightly exceeding the division position B1 on the position P12 side is set as the first scan range SR11, and the division position B1 from the position P12 to the position P11 side is set. A range up to a position P14 slightly exceeding is set as the second scan range SR12. That is, the first scan range SR11 and the second scan range SR12 overlap in a minute range TR1 including the division position B1. The width of the overlapping range TR1 is preferably about the thickness of several slices from the viewpoint of reducing exposure, and here, as an example, it is about the thickness of one slice.

  As a result, X-ray projection data sufficient to reconstruct the image data of the slice corresponding to each position in the imaging range ZR1 by performing helical scanning on the first scan range SR11 and the second scan range SR12, respectively. Collected as a whole.

  In step S4, a reference position (predetermined position) in the imaging range ZR1 and a target heart phase (predetermined phase) when scanning the reference position are set. For example, first, the central processing unit 3 obtains an electrocardiogram signal from the electrocardiograph 31 via the controller 29, observes an electrocardiogram waveform of the subject H, and calculates a heartbeat period P. Next, the central processing unit 3 sets a reference position K1 in the imaging range ZR1 and a target cardiac phase TP1 with respect to the reference position K1 based on information input from the operator via the input device 2.

  The reference position K1 and the target cardiac phase TP1 are not particularly limited, but a cardiac phase corresponding to the systole or diastole of the heart is preferable as the target cardiac phase TP1. For example, when the R wave in the electrocardiogram waveform is used as a reference, a cardiac phase between 35% and 50% of the cardiac cycle P or between 65% and 80% of the cardiac cycle P is good. The target cardiac phase TP1 may be set as a cardiac time phase.

  Here, the reference position K1 is set to the center position C1, and the target cardiac phase TP1 is set to 75% ± 5% of the heartbeat period P when the R wave is used as a reference.

  In steps S5 and S6, the first scan range SR11 is helically scanned in the direction from the position P11 at one end of the imaging range ZR1 to the position P12 at the other end, and the second scan range SR12 is set. A second helical scan that performs a helical scan in a direction from the position P12 at the other end of the imaging range ZR1 to the position P11 at one end is executed. When the first helical scan is executed, the X-ray tube 21 is moved relative to, for example, the first movement range XR11 shown in the drawing. Further, when executing the second helical scan, the X-ray tube 21 is moved relative to, for example, the second movement range XR12 in the drawing.

  In step S <b> 5, for example, the central processing unit 3 controls the rotation unit controller 26 via the controller 29 to control the rotation speed of the rotation unit 15. Next, the central processing unit 3 obtains an electrocardiographic signal of the electrocardiograph 31 via the controller 29. When the central processing unit 3 executes the first helical scan, the cradle 12 is used as a condition necessary for scanning the reference position K1 (= division position B1 = center position C1) at the target cardiac phase TP1. The first movement start position M11 and the first movement start core phase J11 at which the movement of the cradle 12 is started are calculated backward in consideration of the time and distance required for the cradle 12 to run (accelerate). Further, when executing the second helical scan, as a condition necessary for scanning the reference position K1 at the target cardiac phase TP1, the second movement start position M12 and the second movement start position M12 for starting the movement of the cradle 12 are used. The movement start heart phase J12 is calculated backward in consideration of the time and distance required for the cradle 12 to run.

  The central processing unit 3 controls the imaging table 10 via the controller 29 and moves the cradle 12 to the first movement start position M11. Then, while observing the electrocardiogram waveform, in response to the scan start command from the operator, the movement of the cradle 12 in the −z direction is performed at the first movement start heart phase J11 after a predetermined waiting time has elapsed. Start. The controller 29 receives control from the central processing unit 3 and controls the X-ray tube 21 via the rotating unit controller 29 and the X-ray controller 22 to control the X-ray irradiation timing. 1 helical scan is executed. Thereby, the first X-ray projection data PD11 sufficient to reconstruct the image data of the slice corresponding to each position of the first scan range SR11 including the overlapping range TR1 is collected.

  Note that when executing the first helical scan, considering the second helical scan to be executed later, the cradle 12 does not stop moving immediately after the first helical scan is completed, and performs the backward calculation first. The second movement start position M12 is moved.

  In step S6, for example, the central processing unit 3 starts the movement of the cradle 12 in the + z direction at the second movement start heart phase J12 after a predetermined waiting time has elapsed while obtaining an electrocardiogram signal. The controller 29 receives control from the central processing unit 3 and controls the X-ray tube 21 via the rotating unit controller 29 and the X-ray controller 22 to control the X-ray irradiation timing. 2 Helical scan is executed. Thereby, the second X-ray projection data PD12 sufficient to reconstruct the image data of the slice corresponding to each position of the second scan range SR12 including the overlapping range TR1 is collected.

  Note that when executing the second helical scan, considering the next first helical scan that may be executed, the cradle 12 moves immediately even after the second helical scan is completed. Without stopping, it is moved to the first movement start position M11.

  FIG. 5 is a diagram illustrating an example of a relationship between an electrocardiogram signal and first and second helical scans in cardiac imaging according to the present embodiment.

  The first and second helical scans in steps S5 and S6 are executed, for example, with a relationship as shown in FIG. In FIG. 5, the horizontal axis is time t, the electrocardiogram waveform HW obtained by the electrocardiograph 31, the heartbeat synchronization signal HB synchronized with the R wave of the electrocardiogram waveform HW, and the on / off state of the helical scan. The time change with SC and the moving speed TV of the cradle 12 is shown.

  The cradle 12 has already stopped at the first movement start position M11 in the first helical scan. In this state, upon receiving a scan start command, the cradle 12 waits for a waiting time Ttw1 calculated from a predetermined heartbeat synchronization signal tr1 based on the latest average heartbeat cycle Th1 (for example, the average of the latest four heartbeat cycles). After the elapse of time, at time Tks1, movement starts in the −z direction. The cradle 12 accelerates at a predetermined acceleration, and reaches a constant speed −V1 at time Tss1 after the elapse of the standby time Tsw1 from the heartbeat synchronization signal tr1. At the same time, at time Tss1, the on / off state SC of the helical scan is turned on, and the first helical scan is started. Then, at time Tse1 after the elapse of time Ts1 from the start of the first helical scan, the on / off state SC of the helical scan is turned off, and the first helical scan is ended. Thereby, the first X-ray projection data PD11 sufficient to reconstruct the image data of the slice corresponding to each position of the first scan range SR11 including the overlapping range TR1 is collected.

  Thereafter, the cradle 12 continues to move at a speed of −V1, starts to decelerate at time Tgs1, and stops completely at time Tge1. Thereby, the cradle 12 becomes the second movement start position M12.

  The cradle 12 performs the first helical scan at time Tks2 after the elapse of the waiting time Ttw2 calculated from the latest average heartbeat period Th1 from the heartbeat synchronization signal tr3 immediately after the end of the first helical scan. The movement starts in the + z direction, which is the opposite direction. The cradle 12 accelerates at a predetermined acceleration, and reaches a constant speed + V1 at time Tss2 after the elapse of the standby time Tsw2 from the heartbeat synchronization signal tr3. At the same time, at time Tss2, the helical scan on / off state SC is turned on, and the second helical scan is started. Then, at time Tse2 after the lapse of time Ts2 from the start of the second helical scan, the on / off state SC of the helical scan is turned off, and the second helical scan is ended. Thereby, the second X-ray projection data PD12 that is sufficient to reconstruct the image data of the slice corresponding to each position of the second scan range SR12 including the overlapping range TR1 is collected.

  Thereafter, the cradle 12 continues to move at a speed of + V1, starts to decelerate at time Tgs2, and stops completely at time Tge2. Thereby, the cradle 12 returns to the first movement start position M11.

  In step 7, an image of the entire imaging range is generated.

  FIG. 6 is a diagram illustrating an example of a correspondence relationship between the first and second X-ray projection data and an image of the entire imaging range.

  The first and second X-ray projection data PD11 and PD12 can be represented as a schematic diagram as shown in the upper part of FIG. 6, for example. Here, the horizontal axis is a coordinate z in the z direction when the position P11 at one end of the imaging range ZR1 is set as a zero reference (one coordinate corresponds to 1 mm of the real space), and the vertical axis is the view angle direction θ ( The view angle direction when the coordinate in the y direction of the X-ray tube 21 is maximized is the 0 ° direction).

  In this example, the imaging range ZR1 is a range in which the z coordinate is 0 to 120, the position P11 at one end of the imaging range ZR1 corresponds to the position at which the z coordinate is 0, and the position P12 at the other end of the imaging range ZR1 is This corresponds to the position where the z coordinate is 120. The division position B1 is the same position as the center position C1 of the imaging range ZR1, and corresponds to a position where the z coordinate is 60.

  The first movement range XR11 is a range where the z coordinate is from −20 to 80, and the second movement range XR12 is a range where the z coordinate is from 140 to 40.

  In the upper part of FIG. 6, the first X-ray projection data PD11 by the first helical scan is obtained by linearly moving the line segment of the width 40 of the z coordinate to the right oblique direction when the scan width D is 40 mm. It can be expressed as a locus portion. Similarly, the second X-ray projection data PD11 obtained by the second helical scan has a locus portion when the line segment of the width 40 of the z coordinate is linearly moved in the diagonally left direction when the scan width D is 40 mm. Can be expressed as

  In order to reconstruct image data, X-ray projection data corresponding to a view angle of at least 180 ° + α (X-ray beam fan angle) is required. Accordingly, the first X-ray projection data PD11 includes, for example, X-ray projection data u whose vertical width corresponds to 180 ° + α in the view angle direction θ as shown in the upper part of FIG. It is expressed as X-ray projection data that is secured in the range SR11, that is, the range from the position P11 to the position P13. Similarly, the second X-ray projection data PD12 is secured in the second scan range SR12, that is, the range from the position P12 to the position P14, for example, as shown in the upper part of FIG. X-ray projection data. Here, the first and second helical scans are executed with the view angle direction θ at the start of scanning set to 0 °.

  The central processing unit 3 reconstructs image data of slices corresponding to the respective positions in the imaging range ZR1 based on the first and second X-ray projection data PD11 and PD12.

  For example, based on the first X-ray projection data PD11, the image data of the slice corresponding to each position in the range from the position P11 to the position P13 is reconstructed, and based on the second X-ray projection data PD12, Image data of a slice corresponding to each position in the range from the position P12 to the position P14 is reconstructed. For the image data of the slice corresponding to the position of the overlapping range TR1 of these two ranges, the image data of the slice reconstructed based on the first X-ray projection data PD11, and the second X-ray projection By averaging the image data of the slice reconstructed based on the data PD12, final image data of the slice is generated. The averaging process here is, for example, a process in which an average value of pixel values of corresponding pixels is used as a new pixel value of the pixel.

  In addition, for example, the first X-ray projection data PD11 and the second X-ray projection data PD12 are combined to generate new X-ray projection data, and the imaging range is based on the new X-ray projection data. Image data of a slice corresponding to each position of ZR1 is reconstructed. The synthesis process here is, for example, a weighted addition process using a weighted addition coefficient corresponding to the position of the z coordinate. Thereby, in the X-ray projection data of overlapping views, it is possible to improve the SN ratio and improve the image quality.

  The central processing unit 3 generates the image G1 of the entire imaging range ZR1 as shown in the lower part of FIG. 6, for example, by the processing as described above. This image G1 is an image obtained by projecting an image of a slice corresponding to each position in the imaging range ZR1 in the y direction.

  The cardiac phase Ph11 in the first helical scan is, for example, a cardiac cycle P that is within one heartbeat as shown in the lower part of FIG. 6 while the X-ray tube 21 moves relative to the first movement range XR11. Of 11% to 91%. Further, the cardiac phase Ph12 in the second helical scan is, for example, a cardiac cycle P that is within one heartbeat as shown in the lower part of FIG. 6 while the X-ray tube 21 moves relative to the second movement range XR12. Of 11% to 91%.

  Accordingly, the image G1 is an image in which the cardiac phase corresponding to each position from the both ends of the imaging range SR1 toward the center changes in, for example, 27% to 75% of the heartbeat period P. Further, in the image G1, the image obtained from the first X-ray projection data PD11 and the image obtained from the second X-ray projection data PD12 are smoothly connected in the vicinity of the center position C1, and banding artifacts are suppressed.

  As described above, according to this embodiment, the imaging range of the subject is divided into two ranges, and the first scan range including the first division range and the second division range including the second division range. The scan range is set to partially overlap, and the first and second scan ranges are each helically scanned within one heartbeat in synchronization with the heartbeat. At this time, the directions of the helical scans with respect to the two scan ranges are mutually set. Since the scanning direction is reversed, it is possible to scan the entire imaging range with less cardiac phase change while maintaining the continuity of scanning in the imaging range as much as possible, and even for a subject with a relatively large heart rate, A site that fluctuates in synchronization with the pulsation can be imaged with high image quality at high speed with low exposure.

  In the present embodiment, the first and second helical scans are executed at the timing when the center position C1 that is the reference position K1 is scanned in the same phase. Thereby, the shift | offset | difference of the joint of the image obtained from a 1st helical scan and the image obtained from a 2nd helical scan can be suppressed.

  In the present embodiment, the same phase corresponds to a predetermined phase between 35% and 50% or 65% and 80% of the heartbeat period when the R wave in the electrocardiogram waveform is used as a reference. I am going to do it. Thereby, the shift | offset | difference of the joint of the image obtained from a 1st helical scan and the image obtained from a 2nd helical scan can further be suppressed.

  In the present embodiment, the division position B1 is the position of the center position C1 of the imaging range ZR1. Thereby, the entire imaging range ZR1 can be scanned with the least cardiac phase change.

  In the present embodiment, the direction of the first helical scan is the direction from the position P11 at one end of the imaging range ZR1 to the position P12 at the other end, and the direction of the second helical scan is other than the imaging range ZR1. The direction is from the end position P12 to the one end position P11. Thereby, the subject H can be efficiently moved when the first and second helical scans are executed.

  In the above-described embodiment, the first helical scan is executed on the forward path of the reciprocating movement in the z direction of the cradle 12 on which the subject H is placed, and the second helical scan is performed on the return path of the reciprocating movement. Running. Thereby, there is no useless switching of the moving direction of the cradle 12 on which the subject H is placed, and continuous imaging of the subject can be performed at high speed.

(Second Embodiment)
In the present embodiment, as shown in FIG. 7, only one division position B2 is set at the center position C2 of the imaging range ZR2, and the imaging range ZR2 is divided into two. That is, the imaging range ZR2 is a range from the position P21 at one end of the imaging range ZR2 to the division position B2, and a range from the position P22 at the other end of the imaging range ZR2 to the division position B2. This is divided into the second divided range BR22.

  Next, a first scan range that is a part of the first divided range BR21 and a second scan range that is a part of the second divided range BR22 are set with a predetermined range TR2 interposed therebetween. Here, as shown in FIG. 7, the range from the position P21 to the position P23 before reaching the division position B2 is set as the first scan range SR21, and from the position P22 to the position P24 before reaching the division position B1. The range is set to the second scan range SR22. That is, the first scan range SR21 and the second scan range SR22 are arranged with the predetermined range TR2 that is a range from the position P23 to the position P24 interposed therebetween. The settable size of the predetermined range TR2 varies depending on the scanning conditions, but here, for example, the thickness is set to about 20 to 30 slices.

  Note that the first scan range SR21 has X-ray projection data (predetermined X-rays) corresponding to view angles necessary to reconstruct image data of slices corresponding to the respective positions of the predetermined range TR2 when the helical scan is performed. (X projection data) is set as a range in which X-ray projection data including one of them is collected. The second scan range SR22 is set as a range in which X-ray projection data including the other when the predetermined X-ray projection data is divided into two when the helical scan is performed is collected. The view angle necessary for reconstructing image data is, for example, 180 ° + X-ray beam fan angle, or 360 ° X-ray projection data.

  Next, the first scan range SR21 is helically scanned to collect the first X-ray projection data PD21, and the second scan range SR22 is helically scanned to collect the second X-ray projection data PD22. As a result, X-ray projection data sufficient to reconstruct the image data of the slice corresponding to each position of the imaging range ZR2 including the predetermined range TR2 is collected as a whole. Note that when the first helical scan is executed, the X-ray tube 21 is moved relative to, for example, the first movement range XR21 of FIG. Further, when executing the second helical scan, the X-ray tube 21 is moved relative to, for example, the second movement range XR22 of FIG.

  Then, the image data of the slice corresponding to each position in the first scan range SR21 is reconstructed based on the first X-ray projection data PD21, and the second scan is performed based on the second X-ray projection data PD22. The image data of the slice corresponding to each position in the range SR22 is reconstructed. Further, one of the two X-ray projection data included in the first X-ray projection data PD21 and the other X-ray projection data included in the second X-ray projection data PD22 are divided into the two. And generating X-ray projection data corresponding to a view angle necessary for reconstructing image data of a slice corresponding to each position of the predetermined range TR2, and based on the generated X-ray projection data, the predetermined range The image data of the slice corresponding to each position of TR2 is reconstructed.

  FIG. 8 is a diagram illustrating an example of a correspondence relationship between the first and second X-ray projection data and the image of the entire imaging range in the present embodiment.

  The first and second X-ray projection data PD21 and PD22 can be represented as a schematic diagram as shown in the upper part of FIG. 8, for example. Here, the horizontal axis is a coordinate z in the z direction when the position P21 at one end of the imaging range ZR2 is set as a zero reference (coordinate 1 corresponds to 1 mm in real space), and the vertical axis is the view angle direction θ (X-ray). The view angle direction when the coordinate in the y direction of the tube 21 is the maximum is the 0 ° direction). The imaging range ZR2 has a z-coordinate range of 0 to 120, the position P21 at one end of the imaging range ZR2 corresponds to the position at which the z-coordinate is 0, and the position P22 at the other end of the imaging range ZR2 has a z-coordinate of 120. The center position C2 of the imaging range ZR2 corresponds to the position where the z coordinate is 60, respectively.

  The first movement range XR21 is a range where the z coordinate is from −20 to 73, and the range in which the image data can be reconstructed only by the first X-ray projection data PD21 is that the z coordinate is from 0 to 53. It is a range. The second movement range XR22 is a range where the z coordinate is 140 to 47, and the range in which image data can be reconstructed only by the second X-ray projection data PD22 is a range where the z coordinate is 120 to 66. It is. A range TR2 in which image data cannot be reconstructed only with the first X-ray projection data PD21 or only with the second X-ray projection data PD22 is a range with z coordinates from 53 to 66.

  In order to reconstruct image data, X-ray projection data corresponding to a view angle of at least 180 ° + α (fan angle of the X-ray beam) is necessary. Accordingly, the first X-ray projection data PD21 is, for example, as shown in the upper part of FIG. 8, the X-ray projection data u whose vertical width corresponds to 180 ° + α of the view angle direction θ has a z coordinate of 0. To X-ray projection data assured in a range from 53 to 53. Similarly, the second X-ray projection data PD22 is, for example, X-ray projection data in which the X-ray projection data u is ensured in the range of z coordinates 120 to 66 as shown in the upper part of FIG. Represented as: Here, the first helical scan is executed with the view angle direction θ at the start of the scan being 120 °, and the second helical scan is executed with the view angle direction θ at the start of the scan being 0 °. ing.

  The central processing unit 3 reconstructs image data of slices corresponding to the respective positions in the imaging range ZR2 based on the first and second X-ray projection data PD21 and PD22.

  Of the first X-ray projection data PD21, the triangular portion TD211 on the −z direction side from the position P21 and the triangular portion TD212 on the + z direction side from the position Q21 are insufficient view angles to reconstruct the image data. Minute X-ray projection data. Further, in the second X-ray projection data PD22, the triangular portion TD221 on the + z direction side from the position P22 and the triangular portion TD222 on the −z direction side from the position Q22 are insufficient to reconstruct the image data. X-ray projection data corresponding to a view angle. Each of the triangular X-ray projection data alone does not contribute to the reconstruction of the image data.

  However, the triangular portion TD212 and the triangular portion TD222 partially overlap in the z direction, and by combining them, a view angle amount sufficient to reconstruct the image data of the slice corresponding to each position in the range TR2. X-ray projection data can be newly generated.

  Therefore, in the present embodiment, X-ray projections corresponding to view angles sufficient to reconstruct the image data of the slice corresponding to each position in the range R23 by combining a part of both the triangular portions TD212 and TD222. Data u ′ is newly generated. Then, based on the newly generated X-ray projection data u ′, the image data of the slice corresponding to each position in the range R23 is reconstructed. Note that the image data of the slice corresponding to each position in the range of the z coordinate from 0 to 53 is reconstructed based on the portion of the first X-ray projection data PD21 excluding the triangular portions TD211 and TD212. Similarly, the image data of the slice corresponding to each position in the range where the z coordinate is 120 to 66 is reconstructed based on the portion excluding the triangular portions TD221 and TD222 in the second X-ray projection data PD22.

  The central processing unit 3 generates, for example, an image G2 of the entire imaging range ZR2 as shown in the lower part of FIG. This image G2 is an image obtained by projecting an image of a slice corresponding to each position in the imaging range ZR2 in the y direction.

  The cardiac phase Ph21 in the first helical scan is a cardiac cycle P that is within one heartbeat, for example, as shown in the lower part of FIG. 8 while the X-ray tube 21 moves relative to the first movement range XR21. Of 11% to 83%. Further, the cardiac phase Ph22 in the second helical scan is, for example, a heartbeat period P that is within one heartbeat as shown in the lower part of FIG. 8 while the X-ray tube 21 moves relative to the second movement range XR22. Of 11% to 83%. Thus, compared with the first embodiment, the change range of the cardiac phase is reduced by the amount that the first and second movement ranges are reduced.

  Therefore, the image G2 is an image in which the cardiac phase corresponding to each position from the both ends of the imaging range ZR2 toward the center changes at, for example, 27% to 75% of the heartbeat period P. Further, in the image G2, the image obtained from the first X-ray projection data PD21 and the image obtained from the second X-ray projection data PD22 are smoothly connected in the vicinity of the center position C2, and banding artifacts are suppressed.

  Incidentally, the change range of the cardiac phase corresponding to each position from the both ends of the imaging range ZR2 toward the center seems to be unchanged at first glance as compared with the first embodiment. However, since the image data near the center position C2 is actually reconstructed based on the X-ray projection data u ′ generated by combining a part of the triangular portions TD212 and TD222, the X-ray projection used for reconstruction is used. The change width of the cardiac phase corresponding to the data is smaller than that in the first embodiment.

  According to such an embodiment, the X-ray projection data that does not contribute to image reconstruction alone is effectively used to reduce unnecessary X-ray projection data, and the first and second scan ranges SR21 and SR22 are reduced. The imaging range ZR2 of the subject H can be imaged with a smaller exposure dose.

  In addition, this invention is not limited to said embodiment, A various deformation | transformation is possible.

  In the above embodiment, the case where the imaging range is divided into two has been described as an example, but the imaging range may be divided into three or more, such as three or four. Also in this case, the directions of the helical scan with respect to each of the two divided ranges adjacent to each other are made opposite to each other in the z direction. More preferably, each division range has a substantially equal size. This makes it difficult for a shift in cardiac phase to occur at each division position, and efficiently performs relative movement in the z direction of the subject or the X-ray tube and the X-ray detector when sequentially scanning each division range. be able to.

  In the above embodiment, cardiac imaging has been described as an example, but the present invention is not limited to this. That is, the imaging range is not limited to the range including the heart, and may be any range as long as it includes a portion that varies in synchronization with the heartbeat. Such a portion that fluctuates in synchronization with the pulsation of the heart also moves with the movement of the heart, so that artifacts associated with the movement are likely to occur in the tomographic image, and the same effect is exhibited. For example, two coronary arteries for feeding the myocardium run on the surface of the heart, and these coronary arteries move greatly with the movement of the heart on the surface of the heart. Therefore, the present invention is particularly effective for imaging coronary arteries.

  In the above embodiment, the subject H that has not been injected with the contrast agent is imaged. Of course, the present invention can be applied to contrast imaging that images the subject H that has been injected with the contrast agent.

  In the above embodiment, the case of the helical scan in which the imaging table 10 moves has been described. Conversely, the present invention can also be applied to an X-ray CT apparatus in which the scanning gantry 20 moves in the body axis direction of the subject. .

  In the above embodiment, the electrocardiogram signal generated by the electrocardiograph 31 is used to execute the helical scan synchronized with the heartbeat. However, it is generated by another signal synchronized with the heartbeat, for example, a pulse meter. A signal or the like may be used.

  In the above embodiment, the subject H is imaged only once, but the subject H is imaged by continuously performing the first and second helical scans a plurality of times as the cradle 12 is reciprocated. May be performed continuously to acquire a time-series image of the subject H. In this case, since the reciprocating movement of the cradle 12, that is, the reciprocating movement of the subject H can be performed without waste, it is efficient.

  In the above embodiment, a general helical scan has been described. However, a variable pitch helical scan in which the helical pitch changes during the scan, and the subject is continuously switched while repeatedly switching the direction of the body axis direction of the helical scan. The same effect can be obtained in the case of helical shuttle scanning.

  In the above-described embodiment, the case where the scanning gantry 20 is not tilted is written, but the same effect can be obtained even in the case of so-called tilt scanning where the scanning gantry 20 is tilted.

  In the above-described embodiment, the division position of the imaging range is set near the center position of the imaging range, but may be set near other positions in the imaging range. The division position of the imaging range may be set automatically based on the set imaging range, or may be set by designation from the operator.

  In the above embodiment, the direction of the first helical scan is the direction from one end of the imaging range to the other end, and the direction of the second helical scan is the direction from the other end to the one end. It may be. That is, the direction of the first helical scan may be the direction from the other end to the one end of the imaging range, and the direction of the second helical scan may be the direction from the one end to the other end.

  In the above embodiment, in the first and second helical scans, the scan width is 40 mm, the gantry rotation period is 0.35 sec / rotation, and the moving speed of the cradle 12 is 157 mm / sec. However, in the first and second helical scans, if the scan width is 20 mm or more, the gantry rotation period is 0.5 seconds or less, and the moving speed of the cradle 12 is 80 mm / second or more, the effect of the present invention can be sufficiently exerted. .

  In the above embodiment, the same scanning method is used regardless of the heart rate of the subject, but the scanning method may be changed according to the heart rate of the subject. For example, when the heart rate is equal to or lower than a predetermined threshold value, a conventional high-pitch helical scan method (method proposed in Patent Document 1) is used, and the heart rate exceeds the predetermined threshold value. Sometimes, the method according to the above-described embodiment in which the helical scan is executed in two steps is used. In the above embodiment, the medical X-ray CT apparatus is written based on the X-ray CT-PET apparatus, the X-ray CT-SPECT apparatus apparatus combined with the industrial X-ray CT apparatus or other apparatuses, etc. But you can use it.

It is a block diagram which shows the X-ray CT apparatus which is one Embodiment of this invention. It is a figure when a data collection system is seen toward the x direction. It is a flowchart of cardiac imaging. It is a figure which shows an example of the imaging range in 1st Embodiment, a division range, and a scanning range. It is a figure which shows an example of the relationship between the electrocardiogram signal in a cardiac imaging, and the 1st and 2nd helical scan. It is a figure which shows an example of the correspondence of the 1st and 2nd X-ray projection data in 1st Embodiment, and the image of the whole imaging range. It is a figure which shows an example of the imaging range, division | segmentation range, and scanning range in 2nd Embodiment. It is a figure which shows an example of the correspondence of the 1st and 2nd X-ray projection data in 2nd Embodiment, and the image of the whole imaging range.

Explanation of symbols

100 X-ray CT apparatus 1 Operation console 2 Input device 3 Central processing unit 5 Data collection buffer 6 Monitor 7 Storage device 10 Imaging table 12 Cradle 20 Scanning gantry main body 21 X-ray tube 22 X-ray controller 23 X-ray collimator 24 X Line detector 25 Data collection device 26 Rotating part controller 29 Control controller 30 Slip ring

Claims (14)

An X-ray tube and an X-ray detector, and X-ray data collection means for collecting X-ray projection data by scanning a subject using the X-ray tube and the X-ray detector; In an X-ray CT apparatus comprising reconstruction means for reconstructing image data based on the X-ray projection data,
The X-ray data collection means includes a plurality of divided ranges obtained by dividing an imaging range set in the body axis direction of the subject within one heartbeat in synchronization with a signal representing the heartbeat of the subject. X-ray projection data used for reconstructing image data of slices corresponding to the respective positions in the imaging range is collected by helical scanning;
The X-ray CT apparatus in which directions of the helical scan with respect to each of two adjacent divided ranges in the plurality of divided ranges are opposite to each other in the body axis direction.   2. The X-ray data collection unit according to claim 1, wherein the two division ranges are helically scanned at a timing at which a division position between the two division ranges adjacent to each other is scanned at the same phase of the signal. X-ray CT system.   The X-ray data collection means has a predetermined position in the imaging range between 35% and 50% or 65% and 80% of the heartbeat cycle when the R wave in the electrocardiogram waveform is used as a reference. The X-ray CT apparatus according to claim 2, wherein the divided range including the predetermined position is helically scanned at a timing scanned at a phase corresponding to the phase.   The X-ray CT apparatus according to claim 3, wherein the predetermined position is a center position of the imaging range.   The X-ray CT apparatus according to claim 1, wherein the plurality of division ranges have substantially equal sizes.   The X-ray CT apparatus according to claim 1, wherein the imaging range includes a heart of the subject.   The X-ray CT apparatus according to claim 1, wherein the direction of the helical scan with respect to the divided range including one end of the imaging range is from one end to the other end of the imaging range. The X-ray data collection means sets a first range including one of the two divided ranges adjacent to each other and a second range including the other of the two divided ranges, partially overlapping, The first range is helically scanned to collect first X-ray projection data, and the second range is helically scanned to collect second X-ray projection data,
8. The image reconstruction apparatus according to claim 1, wherein the reconstructing unit reconstructs image data of a slice corresponding to the position of the overlapping range, based on the collected first and second X-ray projection data. The X-ray CT apparatus according to claim 1. The X-ray data collection means sets a first range including one of the two divided ranges adjacent to each other and a second range including the other of the two divided ranges, partially overlapping, The first range is helically scanned to collect first X-ray projection data, and the second range is helically scanned to collect second X-ray projection data,
The reconstruction means reconstructs the first image data of the slice corresponding to the position of the overlapping range based on the first X-ray projection data, and based on the second X-ray projection data. The second image data of the slice is reconstructed, and the third image data of the slice is generated by using the first and second image data. X-ray CT system. The X-ray data collection means interposes a predetermined range between a first range that is a part of one of the two divided ranges adjacent to each other and a second range that is a part of the other of the two divided ranges. And X-ray projection data including one when the first range is helically scanned to bisect the predetermined X-ray projection data, and the second range is helically scanned to collect the X-ray projection data. Collecting X-ray projection data including the other when the predetermined X-ray projection data is bisected,
The reconstructing unit generates the predetermined X-ray projection data using the collected X-ray projection data of one and the other when the bisection is performed, and based on the generated predetermined X-ray projection data, The X-ray CT apparatus according to any one of claims 1 to 7, wherein image data of a slice corresponding to each position in a predetermined range is reconstructed.   Each helical scan with respect to the plurality of divided ranges is performed under the condition that the scan width is 20 millimeters or more, the rotation period around the body axis direction is 0.5 seconds or less, and the moving speed in the body axis direction is 80 millimeters or more per second. The X-ray CT apparatus according to any one of claims 1 to 10.   The X-ray CT apparatus according to claim 1, wherein the plurality of divided ranges are first and second divided ranges obtained by dividing the imaging range into two.   The X-ray data collection means helically scans the first divided range in the reciprocating movement of the subject or the X-ray tube and the X-ray detector in the body axis direction, and returns to the return path of the reciprocating movement. The X-ray CT apparatus according to claim 12, wherein the second division range is helically scanned. The X-ray CT apparatus according to claim 13, wherein the X-ray data collection unit repeatedly performs a helical scan on the first and second divided ranges by the reciprocating movement a plurality of times.

Images