JP2011172819A - X-ray computed tomography device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray computed tomography device which allows shifting from monitoring scanning to real scanning at a timing with a contrast effect being good. <P>SOLUTION: A scanning mechanism 10 carries out CT-scanning to a subject injected with a contrast medium and collects sequential projection data on the subject. An image-generating part 34 generates data of a sequential CT image on the subject based on the collected sequential projection data. An ROI setting part 36 sets an area of interest on the generated sequential CT image. A time-concentration curve-generating part 38 generates a time-concentration curve regarding the set area of interest based on the data of the sequential CT image. A determination part 42 determines whether to continue the monitoring scanning by the scanning mechanism 10 or to carry out the real scanning by the scanning mechanism 10. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an X-ray computed tomography apparatus that scans a subject into which a contrast medium has been injected with X-rays.

  A contrast agent is injected into the subject in order to diagnose the blood vessel of the subject on the CT image. The X-ray computed tomography apparatus scans a subject into which a contrast medium has been injected with X-rays.

  As one application of scanning by an X-ray computed tomography apparatus using a contrast agent, a function of starting a scan according to the contrast agent concentration has been developed. Specifically, the X-ray computed tomography apparatus performs a scan for monitoring the contrast agent concentration before the main scan. The X-ray computed tomography apparatus repeatedly monitors and scans a subject into which a contrast medium has been injected, and monitors the CT value of the region of interest set on the CT image. Then, when the CT value reaches a preset threshold value, the X-ray computed tomography apparatus has shifted from the monitoring scan to the main scan.

Japanese Patent Laid-Open No. 10-127621

  It is desirable that the threshold value for the transition from the monitoring scan to the main scan is set to a good contrast effect, for example, at the peak of the CT value or around the peak. However, blood flow dynamics vary depending on the subject. Therefore, it is very difficult to set an appropriate threshold in advance according to the subject. One of the adverse effects of the threshold value not being set to an appropriate CT value is, for example, that the CT value does not reach the threshold value depending on the subject. In this case, the main scan may not be executed. Also, depending on the subject, the CT value may greatly exceed the threshold value. In this case, there is a possibility that the main scan is executed before the contrast agent has sufficiently spread to the diagnosis site. Thus, it is very difficult to set a threshold value for a CT value that provides an appropriate contrast effect.

  An object of the present invention is to provide an X-ray computed tomography apparatus capable of shifting from a monitoring scan to a main scan at a timing when the contrast effect is good.

  An X-ray computed tomography apparatus according to a first aspect of the present invention includes a scan mechanism that performs a first CT scan on a subject into which a contrast agent has been injected and collects time-series projection data related to the subject; A generating unit that generates time-series CT image data relating to the subject based on the collected time-series projection data; a setting unit that sets a region of interest on the generated time-series CT image; A generation unit configured to generate a time-series CT value change related to the set region of interest based on data of the time-series CT image; and the first CT scan based on the shape of the generated CT value change To determine whether to continue the scan mechanism or to cause the scan mechanism to execute a second CT scan having a scan condition different from that of the first CT scan. Comprising a part, a.

  According to the present invention, it is possible to provide an X-ray computed tomography apparatus capable of shifting from a monitoring scan to a main scan at a timing when the contrast effect is good.

The figure which shows the structure of the X-ray computed tomography apparatus which concerns on embodiment of this invention. The figure which showed the general scan sequence of CT scan which concerns on this embodiment by time [s] on the horizontal axis, and tube current [mA] on the vertical axis. The figure which shows typically the X-ray which has the 1st irradiation field size (irradiation field size for monitoring scan) set by the X-ray diaphragm of FIG. The figure which shows typically the X-ray which has the 2nd irradiation field size (irradiation field size for this scan) set by the X-ray diaphragm of FIG. The figure which shows typically the time change of CT image regarding the chest produced | generated by the image generation part of FIG. The figure which shows the time density curve regarding the 1st ROI of FIG. 3, and the time density curve regarding the 2nd ROI of FIG. 3 which are generated by the time density curve generation part of FIG. The figure which shows the typical flow of the 1st transfer process performed under control of the system control part of FIG. The figure which shows the determination process in step SA6 of FIG. The figure which shows the typical flow of the 2nd transfer process performed under control of the system control part of FIG. The figure which shows the determination process in step SB6 of FIG. The figure which shows the setting screen (user interface) of the transition conditions displayed on the display part of FIG.

  An X-ray computed tomography apparatus according to an embodiment of the present invention will be described below with reference to the drawings.

  In the X-ray computed tomography apparatus, an X-ray tube and an X-ray detector are combined into one body, and a ROTATE / ROTATE type in which the periphery of the subject is rotated, and a large number of detection elements are arranged in a ring shape. Although there are various types such as a STATIONARY / ROTATE type in which only the X-ray tube rotates around the subject, this embodiment is applicable to any type. Here, the ROTATE / ROTATE type will be described.

  Image reconstruction methods used by the X-ray computed tomography apparatus include a full scan method and a half scan method. In the full scan method, in order to reconstruct CT image data of one slice, projection data for one round around the subject, that is, about 2π [rad] is required. In the half scan method, projection data for π + α [rad] (α: fan angle) is necessary to reconstruct image data of one slice. In this embodiment, any of the full scan method and the half scan method can be applied. However, in the following description, it is assumed that the present embodiment employs the full scan method for specific description.

  In the present embodiment, pre-scanning, main scanning, and monitoring scanning are performed. The prescan is performed before the contrast medium is injected. The main scan is performed for image diagnosis. This scan is performed after the contrast agent is injected and when the contrast agent is sufficiently filled. The monitoring scan is performed for monitoring the contrast agent concentration. The monitoring scan is performed a plurality of times after the contrast agent is injected and before the contrast agent is sufficiently filled. The monitoring scan is performed between the pre-scan and the main scan. The CT scan according to this embodiment is centered on a monitoring scan. Therefore, in the following description of the present embodiment, the CT scan is a monitoring scan unless otherwise specified.

  In addition, the scan region in the present embodiment can be applied to any part of the subject P as long as the contrast agent flows into the region. However, to specifically describe the following, it is assumed that the scan region is the chest of the subject P. In addition, it is assumed that the image diagnosis target in the main scan is the heart.

  FIG. 1 is a diagram showing a configuration of an X-ray computed tomography apparatus 1 according to the present embodiment. As shown in FIG. 1, a scanning mechanism (gantry) 10 and a computer 30 are mounted.

  The scan mechanism 10 has various mechanisms for performing a CT scan of the subject P with X-rays. The scan mechanism 10 repeatedly executes CT scans according to control by the scan control unit 44 in the computer 30.

  The scanning mechanism 10 supports an annular or disk-shaped rotating frame 12 in a rotatable manner. On the inner peripheral side of the rotating frame 12, a scan region into which the subject P placed on the top 14 is inserted is formed. In the present embodiment, a contrast agent for visually confirming a blood vessel on a CT image is injected into the subject P. The top plate 14 is supported by a bed (not shown) so as to be slidable along the longitudinal direction and the vertical direction.

  Here, an XYZ orthogonal coordinate system is defined. The Z axis is defined as the rotation axis of the rotating frame 12. The top plate 14 is disposed so that the longitudinal direction is parallel to the Z-axis direction. The X axis is defined as a horizontal axis, and the Y axis is defined as a vertical axis.

  The rotating frame 12 includes an X-ray tube 16 and an X-ray detector 18 so as to face each other with the subject P placed on the top plate 14 interposed therebetween. The rotating frame 12 receives the supply of the driving signal from the rotation driving unit 20 and continuously rotates the X-ray tube 16 and the X-ray detector 18.

  The X-ray tube 16 generates X-rays in response to application of a high voltage and supply of a filament current from the high voltage generator 22. The interval of X-ray irradiation time on the subject is, for example, 10 times per second. The high voltage generator 22 applies a high voltage to the X-ray tube 16 according to control by the scan controller 44 in the computer 30 and supplies a filament current. An X-ray aperture (X-ray collimator) 24 is attached to the X-ray tube 16 on the X-ray irradiation port side. The X-ray diaphragm 24 limits an irradiation field of X-rays generated from the X-ray tube 16. Specifically, the X-ray diaphragm 24 movably supports a plurality of diaphragm blades made of a substance that shields X-rays. The aperture blade is made of lead, for example. The size and shape of the X-ray irradiation field are changed by adjusting the positions of the plurality of diaphragm blades. The X-ray diaphragm 24 moves the diaphragm blades in response to the drive signal supplied from the scan control unit 44.

  The X-ray detector 18 detects X-rays generated from the X-ray tube 16 and transmitted through the subject P, and generates a current signal corresponding to the detected X-ray intensity. A data acquisition circuit (DAS) 26 is connected to the X-ray detector 18.

  The data collection circuit 26 collects current signals from the X-ray detector 18 according to control by the scan control unit 44. The data acquisition circuit 26 amplifies the collected current signal and digitally converts the amplified current signal to generate projection data that is a digital signal. Projection data is supplied to the computer 30 via the non-contact data transmission unit 26 every time it is generated. By repeating the CT scan by the scanning mechanism 10, time-series projection data is generated and supplied to the computer 30.

  The computer 30 includes a preprocessing unit 32, an image generation unit 34, an ROI setting unit 36, a density index calculation unit 38, a smoothing unit 40, a determination unit 42, a scan control unit 44, a display unit 46, an operation unit 48, and a storage unit 50. And a system control unit 52.

  The preprocessing unit 32 performs preprocessing such as logarithmic conversion and sensitivity correction on the projection data supplied from the data collection circuit 26 in real time. Projection data used for image reconstruction is generated by preprocessing.

  The image generation unit 34 generates CT image data related to the subject P in real time based on the projection data that has been preprocessed. In other words, the image generation unit 34 reconstructs time-series CT image data based on the time-series projection data.

  The ROI setting unit 36 sets an ROI (region of interest) for monitoring the contrast agent concentration in the reconstructed CT image data. The ROI is set in a region where a contrast medium flows, such as a blood vessel region. The ROI may be set automatically by image processing, or may be set manually via the operation unit 48. The ROI is set at the same position on the time-series CT image.

  The time density curve generation unit 38 generates a time density curve related to the set ROI based on time-series CT image data. The time concentration curve is a curve showing the time change of the CT value. The time density curve generation unit 38 generates a time density curve every time a CT image is generated. CT images are generated at a rate of 10 sheets per second, for example. Accordingly, the time density curve is updated at a rate of 10 times per second. In other words, data (points) are plotted on the time density curve at a rate of 10 times per second. In this way, in actuality, the data on the time density curve is not arranged continuously but discretely, and strictly speaking, it is not a curve (line). However, in this embodiment, a discrete data array is also called a curve. The time density curve generation unit 38 may generate a strict curve by linearly interpolating between discrete data.

  The smoothing unit 40 smoothes the time density curve in order to reduce noise components included in the generated time density curve. The smoothing unit 40 performs smoothing every time a time density curve is generated.

  Based on the shape of the smoothed time density curve, the determination unit 42 determines whether the scan mechanism 10 continues the monitoring scan or causes the scan mechanism 10 to execute the main scan. Specifically, the determination unit 42 determines whether or not the time density curve satisfies a transition condition based on a specific shape. The specific shape is a shape drawn by the time density curve when the scan region is filled with the contrast medium. When it is determined to continue the monitoring scan (that is, when it is determined that the time density curve does not have a specific shape), a continuation signal to that effect is supplied to the scan control unit 44. On the other hand, when it is determined that the main scan is to be executed (that is, when it is determined that the time density curve has a specific shape), a shift signal to that effect is supplied to the scan control unit 44.

  The scan control unit 44 controls the scan mechanism 10 to perform a CT scan of the subject P with X-rays. As described above, the scan control unit 44 performs the pre-scan, the monitoring scan, and the main scan. When a continuation signal is supplied during the monitoring scan, the scan control unit 44 scans the scanning mechanism 10 (specifically, the rotation drive unit 20, the high voltage generation unit 22, the X-ray diaphragm 24, And controls the data collection circuit 26). On the other hand, when a transition signal is supplied during the monitoring scan, the scan controller 44 scans the scanning mechanism 10 (specifically, the rotation drive unit 20, the high voltage generation unit 22, The X-ray diaphragm 24 and the data acquisition circuit 26) are controlled.

  The display unit 46 displays the CT image and the time density curve on the display device. As the display device, for example, a CRT display, a liquid crystal display, an organic EL display, a plasma display, or the like can be used.

  The operation unit 48 receives various commands and information input from the operator. For example, the operation unit 48 inputs the ROI setting position via the input device by the user. As an input device, a keyboard, a mouse, a switch, or the like can be used.

  The storage unit 50 stores projection data, CT image data, and time density curve data. The storage unit 50 stores a control program for the X-ray computed tomography apparatus. This control program has a function of shifting from the monitoring scan to the main scan in accordance with the shape of the time density curve.

  The system control unit 52 functions as the center of the X-ray computed tomography apparatus 1. Specifically, the system control unit 52 reads out a control program stored in the storage unit 50 and expands it on the memory, and controls each unit according to the expanded control program. Thereby, the system control unit 52 can shift from the monitoring scan to the main scan according to the shape of the time density curve.

  Hereinafter, an operation example of the X-ray computed tomography apparatus 1 will be described. First, a schematic scan sequence of CT scan according to the present embodiment will be described.

  FIG. 2 is a diagram showing a schematic scan sequence of the CT scan according to the present embodiment, in which the horizontal axis indicates time [s] and the vertical axis indicates tube current [mA]. As shown in FIG. 2, in the present embodiment, the pre-scan, the monitoring scan, and the main scan are performed under the control of the scan control unit 44. Here, it is assumed that pre-scanning is performed at time t1. The pre-scan is performed only once before the contrast medium is injected into the subject P. The position and size of the ROI for monitoring are determined on the CT image obtained by the pre-scan. Next, it is assumed that the injection of the contrast agent into the subject P is started at time t2. Assume that the monitoring scan is started at time t3 after the injection of the contrast agent. The monitoring scan is continued after time t3. As time elapses at time t3 and time t4, the contrast agent concentration in the ROI increases. At time t5, it is assumed that the determination unit 42 determines to shift from the monitoring scan to the main scan. That is, the monitoring scan ends at time t5. It is assumed that the main scan is executed at time t6 after time t5. The time interval between time t5 and time t6 is a transition period from the monitoring scan to the main scan. The transition period is, for example, about 1 second to 2 seconds.

  As shown in FIG. 2, for example, the main scan for image diagnosis is executed at a tube current of 500 mA according to the control of the scan control unit 44. The pre-scan for ROI positioning or the like is performed at a tube current of 100 mA, for example, lower than the main scan in accordance with the control of the scan control unit 44. The monitoring scan for monitoring the contrast agent concentration is performed at a lower current than the pre-scan, for example, at a tube current of 50 mA, under the control of the scan control unit 44.

  When the scan area in the main scan is a volume (three-dimensional area), the X-ray irradiation field size (first irradiation field size) in the pre-scan and the monitoring scan is the X-ray in the main scan in order to reduce the amount of exposure. Is set to be narrower than the irradiation field size (second irradiation field size).

  FIG. 3 is a diagram schematically illustrating X-rays having the first irradiation field size (irradiation field size for monitoring scan) set by the X-ray diaphragm 24. FIG. 4 is a diagram schematically showing X-rays having the second irradiation field size (irradiation field size for the main scan) set by the X-ray diaphragm 24. 3 and 4 are views of the X-ray viewed from the X-axis direction. As shown in FIG. 3, in the case of the first irradiation field size, X-rays are formed into a fan beam by an X-ray diaphragm 24, for example. In the transition period from the monitoring scan to the main scan, the X-ray diaphragm 24 moves the diaphragm blades in order to increase the cone angle (expansion angle along the Z axis) of the X-ray. The X-rays are formed into a cone beam by the movement of the diaphragm blades as shown in FIG.

  Next, a temporal change and a time density curve of the CT image by the contrast agent will be described. FIG. 5 is a diagram schematically showing a temporal change of the CT image related to the chest generated by the image generation unit 34. 5A is a schematic diagram of a CT image related to time t1 and time t2 in FIG. 2, FIG. 5B is a schematic diagram of a CT image related to time t4 in FIG. 2, and FIG. FIG. 3 is a schematic diagram of a CT image related to time t5 and time t6 in FIG. 2. Each CT image in FIG. 5 relates to an axial section (XY section) viewed from the foot side of the subject P. In addition, it is assumed that the higher the CT value, the whiter the pixel region, and the lower the CT value, the blacker the pixel region. The first ROI 61 is set in a pixel region (descending aorta region) 71 corresponding to the descending aorta with relatively little displacement due to heart pulsation or the like, and the second ROI 63 is a pixel region (right ventricle) corresponding to the right ventricle. Region) 73 is set. FIG. 6 is a diagram showing a time density curve related to the first ROI 61 in FIG. 3 and a time density curve related to the second ROI 63 in FIG.

  As shown in FIG. 5, at time t1 and time t2, no contrast agent is present in the right atrium, right ventricle, left atrium, left ventricle, and descending aorta. Therefore, on the CT image related to time t1 and time t2, the right ventricle region 73, the pixel region corresponding to the right atrium (right atrial region) 75, the pixel region corresponding to the left atrium (left atrial region) 77, and the left ventricle are displayed. The corresponding pixel region (left ventricle region) 79 and descending aorta region 71 are not drawn. In addition, the CT image depicts a pixel region (lung region) 81 corresponding to the lung, a pixel region (spine region) 83 corresponding to the spine, and the like.

  As shown in FIG. 5B, at the time t4, the right ventricle and the right atrium are first filled with the contrast agent. Therefore, the CT values of the right ventricular region 73 and the right atrial region 75 reach a peak and are drawn white. Further, at time t4, the contrast medium that has flowed out of the right ventricle and the right atrium circulates through the lungs, and then starts to flow into the left atrium, the left ventricle, and the descending aorta. However, at time t4, the left atrium, left ventricle, and descending aorta are not filled with contrast medium. Therefore, at time t4, the left atrial region 77, the left ventricular region 79, and the descending aorta region 71 are drawn blacker than the right ventricular region 73 and the right atrial region 75. Depending on the start timing of the monitoring scan, the contrast state shown in FIG. 5B may occur at the start of the monitoring scan.

  As shown in FIG. 5C, at time t5 and time t6, since the contrast medium starts to flow out from the right ventricle and the right atrium, the right atrium and the right ventricle are filled with the contrast medium at this time. Not done. Therefore, at the time t5 and the time t6, the right ventricular region 73 and the right atrial region 75 are drawn blacker than the time t4. At time t5 and time t6, the left atrium, left ventricle, and descending aorta are filled with contrast medium. Accordingly, the CT values of the left atrial region 77, the left ventricular region 79, and the descending aorta region 71 reach a peak and are drawn whiter than time t4.

  Since this scan is intended for diagnostic imaging, it is preferable to execute this scan when the CT value is at or near the peak (plateau). On the other hand, typically, the time concentration curve of the contrast agent has a similar shape. That is, on the time density curve, the CT value starts to rise from the start of contrast agent injection, eventually reaches a peak, and falls. The determination unit 42 determines in real time whether or not the latest CT value is near the peak depending on whether or not the time concentration curve generated in real time satisfies the transition condition. When it is determined that the latest CT value is near the peak, the determination unit 42 determines that it is a transition timing from the monitoring scan to the main scan.

  Hereinafter, a transition process from the monitoring scan to the main scan performed under the control of the system control unit 52 will be described. The migration process is divided into two types according to the difference in the migration timing to the main scan. The first transfer process is intended to shift to the main scan when the latest CT value is immediately before the peak. The second transfer process is intended to shift to the main scan when the latest CT value is immediately after the peak. The transition condition regarding the first transition process is different from the transition condition regarding the second transition process. First, the first transition process will be described.

  FIG. 7 is a diagram showing a typical flow of the first transition process performed under the control of the system control unit 52. The system control unit 52 causes the scan control unit 44 to execute a monitoring scan (step SA1). In step S1, the scan control unit 44 controls the scan mechanism 10 according to the scan conditions for the monitoring scan. It is assumed that the scan region in the monitoring scan is a slice cross section related to the chest of the subject. In addition, the monitoring scan is repeatedly performed at intervals of about 10 times per second, for example. For each monitoring scan, projection data related to the slice cross section is generated. The generated projection data is supplied to the computer 30 in real time for each slice section.

  When step SA1 is performed, the system control unit 52 causes the image generation unit 34 to perform generation processing (step SA2). In step SA2, the image generation unit 34 reconstructs the projection data to generate CT image data related to the slice cross section.

  When step SA2 is performed, the system control unit 52 causes the ROI setting unit 36 to perform setting processing (step SA3). In step SA3, the ROI setting unit 36 sets the ROI on the CT image generated in step SA2. The position and size of the ROI are set in advance by the operator via the operation unit 48. For example, the position and size of the ROI are set on the CT image generated by the pre-scan. The ROI setting unit 36 automatically sets the ROI to the same position and size as the preset position and size. In order to specifically describe the following, it is assumed that the ROI is set in the descending aorta region.

  When step SA3 is performed, the system control unit 52 causes the time density curve generation unit 38 to perform generation processing (step SA4). In step SA4, the time concentration curve generation unit 38 generates a time concentration curve related to the ROI set in step SA3. More specifically, the time concentration curve generation unit 38 calculates an index representing the characteristic of the CT value in the ROI set in step SA3. As the index, for example, the average CT value, median value, and centroid value of a plurality of pixels constituting the ROI are applied. In order to carry out the following description specifically, it is assumed that the index is an average CT value. The time concentration curve generation unit 38 plots the calculated average CT value on a plane in which the horizontal axis is defined as time and the vertical axis is defined as CT value. In this way, the time density curve generation unit 38 updates the time density curve based on the average CT value of the ROI each time a CT image is generated. Note that by increasing the size of the ROI, it is possible to reduce the fluctuation range of the average CT value due to the pulsation of the heart and the respiratory motion. The time density curve generated in step SA4 typically includes noise derived from heart pulsation, respiratory motion, image noise, contrast agent inflow, and the like.

  When step SA4 is performed, the system control unit 52 causes the smoothing unit 40 to perform a smoothing process (step SA5). In step S5, the smoothing unit 40 performs a smoothing process on the time density curve generated in step SA4 in order to remove noise. As the smoothing process, for example, a moving average method or a curve approximation method (fitting) is applied. The moving average method is performed based on the average of a plurality of average CT values plotted in the time interval of the average target set on the time density curve. The average target time interval is defined based on the latest scan time. For example, the latest scan time and the time interval from the latest scan time to a predetermined time (for example, 1 second) are defined as the average target time interval. The curve approximation is performed based on a polynomial or a gamma function. Note that the smoothing process according to the present embodiment is not limited to the moving average method and the curve approximation method. Any method that can reduce the noise component without greatly changing the shape of the time density curve can be applied to the smoothing processing according to the present embodiment.

  When step SA5 is performed, the system control unit 52 causes the determination unit 42 to perform determination processing (step SA6). In step S6, the determination unit 42 determines whether or not the smoothed time density curve generated in step SA5 satisfies the transition condition (whether or not it is convex upward). Hereinafter, the determination process in step SA6 will be described in detail with reference to FIG.

  FIG. 8 is a diagram showing the determination process in step SA6. 8A shows a time density curve before smoothing, FIG. 8B shows a time density curve after smoothing, and FIG. 8C shows a time density curve after smoothing. FIG. 8D is a diagram showing a first-order derivative curve of the time concentration curve, and FIG. 8D is a diagram showing a second-order derivative curve of the time concentration curve after smoothing. It is assumed that the contrast agent concentration in the ROI becomes the highest at the start time T6 of the main scan.

  As shown in FIG. 8B, the CT value rises from the prescan start time t3 in the time density curve after smoothing. As the peak P1 (the CT value at the time when the contrast agent concentration is the highest) is approached, the degree of increase (slope) of the CT value decreases. The time when the slope of the CT value is 0 is mathematically defined as the time when the CT value reaches the peak. That is, the smoothed time density curve is convex downward in a time interval from time t3 (from time t3 to time t4 ′). The time density curve after smoothing at time t4 ′ has an inflection point P2. Then, after time t4 ′, the smoothed time density curve becomes convex upward.

  In the first transition process, the determination unit 42 uses, as the transition condition, a characteristic of a time density curve that is generally established that “the CT value slope decreases as the CT value approaches a peak”. Specifically, the determination unit 42 determines whether or not the time density curve smoothed in step A5 is convex upward. The method for determining whether or not the projection is upward may include a case where the first derivative of the time density curve is used and a case where the second derivative is used. First, a case where the first-order differentiation is used will be described with reference to FIG.

  First, the determination unit 42 time-differentiates the smoothed time density curve to generate a first-order differential curve of the time density curve as shown in FIG. In the downwardly convex section (time t4 to time t4 ′), the first-order differential value on the first-order differential curve continues to rise within a positive (+) range. In the upward convex section (time t4 ′ to time t5), the first-order differential value on the first-order differential curve continues to fall within a positive (+) range. The first-order differential curve reaches the peak P3 at time t4 ′.

  When generating the latest first derivative curve, the determination unit 42 determines whether or not the latest first derivative curve has a peak P3 (in other words, the determination unit 42 determines the peak of the latest first derivative curve). Whether to detect P3). When it is determined that the latest first-order derivative curve does not have the peak P3 (when the peak P3 of the latest first-order derivative curve is not detected), the determination unit 42 projects the latest time concentration curve upward. It is determined that it is not. On the other hand, when it is determined that the latest first-order differential curve has a peak P3 (when the latest first-order differential curve peak P3 is detected), the determination unit 42 determines that the latest first-order differential curve has a peak P3. It is determined whether or not it is lowered by a predetermined value V1. When the latest first-order differential value does not fall from the peak P3 by the predetermined value V1, the determination unit 42 determines that the time density curve is not convex upward. On the other hand, when the latest first-order differential value is lowered from the peak P3 by the predetermined value V1, the determination unit 42 determines that the time density curve is convex upward. Alternatively, the determination unit 42 determines that the time density curve is not convex when the latest first-order differential value starts to fall from the peak P3 and the predetermined time T1 has not elapsed, and the latest first-order differential value is the peak P3. When the predetermined time T1 has elapsed since starting to fall, the time density curve may be determined to be convex upward.

  Next, a case where the second-order differentiation is used will be described with reference to FIG. First, the determination unit 42 further time-differentiates the latest first-order differential curve to generate a second-order differential curve of the time density curve as shown in FIG. In the downwardly convex section (time t4 to time t4 ′), the second-order differential value on the second-order differential curve is in the positive (+) range. In the upward convex section (time t4 ′ to time t5), the second-order differential value on the second-order differential curve is in the negative (−) range. The second-order differential value becomes 0 value P4 at time t4 ′.

  When generating the latest second-order differential curve, the determination unit 42 determines whether or not the latest second-order differential curve has a 0 value P4. When it is determined that the latest second-order differential curve does not have the 0 value P4 (when the determination unit 42 does not detect that the latest second-order differential curve is 0 value), the determination unit 42 It is determined that the time density curve is not convex upward. On the other hand, when it is determined that the latest second-order differential curve has a zero value P4 (when the determination unit 42 detects that the latest second-order differential curve has a zero value), the determination unit 42 It is determined whether or not the latest second-order differential value is lowered from the 0 value P4 by a predetermined value V2. When it is determined that the latest second-order differential value has not decreased from the 0 value P4 by the predetermined value V2, the determination unit 42 determines that the time density curve is not convex upward. On the other hand, when it is determined that the latest second-order differential value is lowered from the 0 value P4 by the predetermined value V2, the determination unit 42 determines that the time density curve is convex upward. Alternatively, the determination unit 42 determines that the time density curve is not convex upward when the latest second-order differential value starts to become negative (−) and the predetermined time T2 has not elapsed, and the latest second-order differential value is negative. When the predetermined time T2 has elapsed since the start of (−), the time density curve may be determined to be convex upward.

  Reference values such as the predetermined value V1, the predetermined time T1, the predetermined value V2, and the predetermined time T2 are set in consideration of the characteristics of the time density curve. For example, the reference value may be set according to the slope of the time density curve. For example, when the slope of the time concentration curve is large, it is estimated that it takes time until the contrast agent concentration is stabilized. Therefore, the reference value should be set larger as the slope of the time density curve becomes larger. Conversely, the reference value should be set smaller as the slope of the time density curve becomes smaller. Reference values such as the predetermined value V1, the predetermined time T1, the predetermined value V2, and the predetermined time T2 can be arbitrarily set via the operation unit 48.

  When it is determined in step SA6 that the time density curve is not convex upward (step S6: NO), the system control unit 52 returns to step SA1. Then, Step SA1 to Step SA6 are repeated again. In this way, the processing from step SA1 to step SA6 is repeated until it is determined that the latest time density curve is convex upward. In other words, the processing from step SA1 to step SA6 is repeated until the determination unit 42 detects that the latest time density curve is convex upward.

  If it is determined in step SA6 that the time density curve is convex upward (step SA6: YES), the system control unit 52 causes the scan control unit 44 to perform stop processing (step SA7). In step SA7, the scan control unit 44 controls the scan mechanism 10 to stop the prescan.

  Further, the system control unit 52 may instruct breath holding during the monitoring scan when it is determined that the time density curve is convex upward. The breath holding instruction is given before the main scan in order to reduce the adverse effect of respiratory motion on the CT image. Specifically, as a breath-hold instruction, a voice for a breath-hold instruction recorded in advance is output via a speaker or the like. The voice is often content relating to an instruction to stop breathing, such as “please breathe in and hold” or “please breathe out”. Note that the voice may be an instruction other than holding the breath.

  When step SA7 is performed, the system control unit 52 causes the scan control unit 44 to execute the main scan (step SA8). In step SA8, the scan control unit 44 controls the scan mechanism 10 according to the scan conditions for the main scan, and executes the main scan. The main scan may be a normal scan performed with the top 14 stationary, or a helical scan performed while the top 14 is moved. Further, the scan area of the main scan may be a slice instead of a volume. In the case of volume, a Feldkamp reconstruction method considering the cone angle may be used. If the cone angle is small even for a volume (for example, for four detection elements), a CT image is reconstructed for each detection element array, and volume data is generated by regarding each CT image as a parallel beam. Good.

  When step SA8 is performed, the system control unit 44 ends the first transition process.

  As described above, the transition from the monitoring scan to the main scan is triggered by the fact that the time density curve is convex upward. The transition period from the monitoring scan to the main scan is about 1 second to 2 seconds. Considering these facts, it is presumed that the latest CT value has reached the vicinity of the peak during execution of the main scan. Thus, according to the first transition process, it is possible to shift to the main scan when the latest CT value having a good contrast effect is immediately before the peak.

  Next, the second transition process performed under the control of the system control unit 52 will be described. FIG. 9 is a diagram illustrating a typical flow of the second migration process. Note that steps SB1, SB2, SB3, SB4, SB5, SB7, and SB8 of the second migration process and steps SA1, SA2, SA3, SA4, SA5, SA7, and SA8 of the first migration process are the same. Therefore, only step SB6 will be described.

  When step SB5 is performed, system control unit 52 causes determination unit 42 to perform determination processing (step SB6). In step SB6, the determination unit 42 determines whether or not the smoothed time density curve generated in step SB5 satisfies the transition condition (whether or not the time density curve has a peak). Hereinafter, the determination process in step SB6 will be described in detail with reference to FIG.

  FIG. 10 is a diagram illustrating the determination process in step SB6. 10A shows a time density curve before smoothing, FIG. 10B shows a time density curve after smoothing, and FIG. 10C shows a smoothed time density curve. It is a figure which shows the 1st derivative curve of a time concentration curve. In FIG. 10, it is assumed that the CT value reaches the peak P5 at time t4 ′.

  In the second transition process, the determination unit 42 uses a characteristic of a time density curve that is generally established as “the CT value decreases when the peak is passed” as the transition condition. Specifically, the determination unit 42 determines whether or not the smoothed time density curve has a peak P5. The method for determining whether or not the peak P5 is present includes a case where the smoothed time density curve is used as it is, and a case where the first derivative of the smoothed time density curve is used. First, a case where the smoothed time density curve is used as it is will be described.

  First, the determination unit 42 specifies the maximum CT value in the latest smoothed time density curve. Whether or not the identified maximum CT value is the peak P5 cannot be determined at the present time. Next, the determination unit 42 determines whether or not the latest CT value has decreased by a predetermined value V3 from the maximum CT value. When it is determined that the latest CT value is lower than the maximum CT value by the predetermined value V3, the determination unit 42 determines that the smoothed time density curve does not have the peak P5 (in other words, The determination unit 42 did not detect the peak of the latest time concentration curve). On the other hand, when it is determined that the latest CT value is smaller than the predetermined value V3 from the maximum CT value, the determination unit 42 determines that the smoothed time density curve has a peak P5 (in other words, The determination unit 42 detected the peak of the latest time concentration curve). Alternatively, the determination unit 42 determines that the time density curve after smoothing does not have the peak P5 when the latest CT value starts to decrease from the maximum CT value and the predetermined period T3 has not elapsed, and the latest CT value When the value starts to decrease from the maximum CT value and the predetermined period T3 has elapsed, it may be determined that the time density curve after smoothing has the peak P5.

  Next, a case where the first-order differentiation is used will be described with reference to FIG. First, the determination unit 42 time-differentiates the time density curve after smoothing, and generates a first-order differential curve of the time density curve as shown in FIG. In the section (time t3 to t4 ′) in which the CT value increases toward the peak, the first-order differential value is positive (+). In the section (time t4 ′ to t5) in which the CT value is decreasing from the peak, the first-order differential value is negative (−). At time t4 ′, the first-order differential value is 0 value P6.

  When generating the latest first-order differential curve, the determination unit 42 determines whether or not the latest first-order differential curve has a 0 value P6. When it is determined that it does not have the 0 value P6 (in other words, when the determination unit 42 has not detected that the latest first-order differential curve is 0 value), the determination unit 42 Is determined not to have the peak P5. On the other hand, when it is determined that the latest first-order differential curve has a zero value P6 (in other words, when the determination unit 42 detects that the latest first-order differential curve has a zero value), the determination The unit 42 determines whether or not the latest first-order differential value is lowered from the 0 value P6 by a predetermined value V4. When it is determined that the latest first-order differential value has not decreased from the 0 value P6 by the predetermined value V4, the determination unit 42 determines that the smoothed time density curve does not have a peak. On the other hand, when it is determined that the latest first-order differential value is lowered from 0 by the predetermined value V4, the determination unit determines that the time density curve has a peak. Alternatively, the determination unit 42 determines that the time density curve does not have a peak when the first-order differential value starts to become negative (−) and the predetermined time T4 has not elapsed, and the first-order differential value is negative (− ), When the predetermined time T4 has elapsed, it may be determined that the time density curve has a peak.

  As in the first transition process, reference values such as the predetermined value V3, the predetermined time T3, the predetermined value V4, and the predetermined time T4 are set in consideration of the characteristics of the time density curve. Reference values such as the predetermined value V3, the predetermined time T3, the predetermined value V4, and the predetermined time T4 can be arbitrarily set via the operation unit 48.

  When it is determined in step SB6 that the time density curve does not have a peak (step S6: NO), the system control unit 52 returns to step SB1. Then, Step SB1 to Step SB6 are repeated again. In this way, the processing from step SB1 to step SB6 is repeated until it is determined that the latest time density curve has a peak. In other words, the processing from step SB1 to step SB6 is repeated until the determination unit 42 detects the latest peak of the time density curve.

  If it is determined in step SB6 that the time density curve has a peak (step SB6: YES), in other words, if a peak is detected, the system control unit 52 stops the monitoring scan in the scan control unit 44. (Step SB7), and causes the scan control unit 44 to perform a main scan (Step SB8).

  When step SB8 is performed, the system control unit 52 ends the second transition process.

  As described above, the transition from the monitoring scan to the main scan is triggered by the fact that the time density curve has a peak. The transition period from the monitoring scan to the main scan is about 1 second to 2 seconds. Considering these facts, it is estimated that the CT value at the time of execution of the main scan remains at a level slightly lower than the peak. Therefore, it is estimated that the contrast effect is good when the main scan is executed. Thus, according to the second transition process, it is possible to shift to the main scan when the latest CT value having a good contrast effect is immediately after the peak.

  Note that the condition for shifting from the monitoring scan to the main scan is not limited to only the condition relating to the shape of the time density curve. For example, the condition relating to the shape of the time density curve and the condition relating to the CT value of the time density curve may be combined. That is, when the latest time density curve satisfies both the shape-related condition and the CT value-related condition, the determining unit 42 determines to shift from the monitoring scan to the main scan. On the other hand, the determination unit 42 determines that the monitoring scan is continued when the latest time density curve does not satisfy at least one of the condition related to the shape and the condition related to the CT value. As the condition regarding the shape, for example, the latest CT value is greater than or less than a preset threshold value, and the like are employed. Examples of the transition condition for the combination in this case include that the time density curve is convex upward and the latest CT value is 250 HU or more. In addition, as a condition regarding other shapes, for example, the latest CT value may be a predetermined value higher than the CT value at the reference time. As the reference time, for example, non-contrast or immediately after the start of the monitoring scan is adopted. Thus, by combining the conditions related to the shape of the time density curve and the conditions related to the CT value, erroneous determination of the transition condition when the time density curve exhibits an abnormal behavior can be reduced.

  In the description of the first transition process and the second transition process, the ROI is set at one place. However, the present embodiment need not be limited to this, and the ROI may be set at a plurality of locations. In this case, a time concentration curve is generated for each of the plurality of ROIs. When all the time density curves satisfy the transition condition, the determination unit 42 determines to shift from the monitoring scan to the main scan. If there is even one time density curve that does not satisfy the transition condition, the determination unit 42 determines to continue the monitoring scan. All the above-mentioned conditions are selectively applied as the transition conditions.

  Next, the transition condition setting screen (user interface) displayed by the display unit 46 will be described. FIG. 11 is a diagram showing an example of the transition condition setting screen 91. As shown in FIG. 11, the setting screen 91 includes a CT image display area 93 and a transition condition setting area 95. In the display area 93, a CT image generated by the pre-scan is displayed. The operator sets the ROI via the operation unit 48 while observing the CT image. Here, it is assumed that the first ROI and the second ROI are set. The setting area 95 includes setting areas 951 and 953 for each ROI. In the setting areas 951 and 953, for example, a check box 97 for selecting the type of transition condition is displayed in a selectable manner. In FIG. 11, “peak” and “convex upward” are displayed so as to be selectable as conditions regarding the shape of the time density curve. “Peak” corresponds to the first transition process described above. “Upward convex” corresponds to the second transition process described above. Further, as a condition regarding the CT value of the time density curve, a threshold value input field 98 and a comparison expression selection field 99 are displayed. An arbitrary threshold value is input to the input field 98 via the operation unit 48. In the selection column 99, a comparison expression between the latest CT value and the threshold value for satisfying the transition condition is displayed so as to be selectable. For example, in the selection field 99, “above” and “below” are displayed so as to be selectable in a pull-down menu format.

  Further, the setting area 95 includes an optional function selection area 955 for shifting from the monitoring scan to the main scan. In the selection area 955, an optional function is displayed by a check box 97 so as to be selectable. In FIG. 11, the presence or absence of a breath holding instruction during the monitoring scan is displayed so as to be selectable. When the detail setting button BU is selected via the operation unit 48, a detail setting screen for a breath holding instruction is displayed. On the detailed setting screen, for example, the output timing of the breath holding instruction can be set.

As described above, the X-ray computed tomography apparatus 1 determines the transition timing from the monitoring scan to the main scan based on the shape of the time density curve. Therefore, even when the CT value at the peak is abnormally low or high, the X-ray computed tomography apparatus 1 can shift from the monitoring scan to the main scan near the peak. Also,
Thus, according to the present embodiment, it is possible to provide an X-ray computed tomography apparatus capable of shifting from the monitoring scan to the main scan at a timing when the contrast effect is good.

  In this embodiment, the ROI is set in the descending aorta and the right ventricle. However, the ROI setting location is not limited to this. If the object of image diagnosis is the heart, the ROI may be set, for example, in another aorta such as the ascending aorta, the left ventricle, the left atrium, the right atrium, or the like. Further, if the image diagnosis target is the liver, the ROI is preferably installed in the carotid artery regardless of the aorta and the image diagnosis target is the head.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  As described above, according to the present invention, it is possible to provide an X-ray computed tomography apparatus capable of shifting from the monitoring scan to the main scan at a timing when the contrast effect is good.

  DESCRIPTION OF SYMBOLS 1 ... X-ray computed tomography apparatus, 10 ... Imaging mechanism, 12 ... Rotating frame, 14 ... Top plate, 16 ... X-ray tube, 18 ... X-ray detector, 20 ... Rotation drive part, 22 ... High voltage generation part, 24 ... X-ray diaphragm, 26 ... Data acquisition circuit (DAS), 28 ... Non-contact data transmission unit, 30 ... Computer, 32 ... Preprocessing unit, 34 ... Image generation unit, 36 ... ROI setting unit, 38 ... Time density curve Generating unit, 40 ... smoothing unit, 42 ... determining unit, 44 ... scan control unit, 46 ... display unit, 48 ... operation unit, 50 ... storage unit, 52 ... system control unit

Claims (5)

A scan mechanism that performs a first CT scan on a subject injected with a contrast agent and collects time-series projection data relating to the subject;
A generating unit for generating time-series CT image data related to the subject based on the collected time-series projection data;
A setting unit for setting a region of interest on the generated time-series CT image;
A generation unit configured to generate a time-series CT value change related to the set region of interest based on data of the time-series CT image;
Based on the shape of the generated CT value change, the first CT scan is continued by the scan mechanism, or a second CT scan having a scan condition different from the first CT scan is scanned. A determination unit for determining whether the mechanism is to be executed;
An X-ray computed tomography apparatus comprising:   The determination unit causes the scanning mechanism to execute the second CT scan when it is detected that the peak of the generated CT value change or the generated CT value change is convex upward The X-ray computed tomography apparatus according to claim 1, wherein   The determination unit, when not detecting that the generated CT value change peak or the generated CT value change is convex upward, causes the scanning mechanism to continue the first CT scan. The X-ray computed tomography apparatus according to 1. A smoothing unit for smoothing the generated CT value change;
The determination unit determines whether to continue the first CT scan or to execute the second CT scan based on the smoothed CT value change shape,
The X-ray computed tomography apparatus according to claim 1.   The determination unit determines whether the first CT scan is to be continued by the scan mechanism or the second CT scan is to be executed by the scan mechanism based on a combination of the shape and a preset threshold value. The X-ray computed tomography apparatus according to claim 1, wherein the determination is performed.

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