JP2013153826A - X-ray ct apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray CT apparatus capable of reducing burdens on a patient when performing diagnostic imaging of a blood vessel region, and improving positioning accuracy of a non-contrast image and a contrast image.SOLUTION: In an X-ray CT apparatus of an embodiment, a main detector detects X-rays transmitted through the region of interest. A detector for a trigger detects X-rays transmitted through a peripheral region. A control means receives a detection result of the detector for a trigger during a monitoring scan mode, and when it is determined that a contrast agent has reached the peripheral region, switches to a scan mode to perform non-contrast scan to the region of interest to which the image contrast has not reached, and when predetermined time elapses after the end of the non-contrast scan, switches to the scan mode to perform contrast scan to the region of interest filled with the contrast agent.

Description

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

  An X-ray CT (Computer Tomography) apparatus performs image diagnosis on a tomographic image obtained by scanning a region of interest of a subject with X-rays.

  Examples of the region of interest include a blood vessel region including the heart. The image diagnosis of the region of interest will be described with reference to FIG. FIG. 8 is a diagram showing a scan sequence with a schematic angiography of a CT scan. In FIG. 8, the horizontal axis represents time [s], and the vertical axis represents tube current [mA].

  In the CT scan shown in FIG. 8, the non-contrast scan (t1-t2), the injection of the contrast agent into the subject (t3), and the monitoring scan (t4-t6) for monitoring whether the region of interest is sufficiently filled with the contrast agent , And a contrast scan (t7-t8).

  The non-contrast can shown by t1-t2 in FIG. 8 is executed before the contrast agent is injected into the subject. A non-contrast image is acquired by scanning the region of interest with X-rays. The tube current at that time is indicated by i1. In the monitoring scan indicated by t4-t6 in FIG. 8, the blood vessel region is scanned with a low-dose X-ray to detect whether or not the contrast agent is sufficiently filled in the blood vessel region. The tube current at that time is indicated by i2. In the contrast scan indicated by t7 to t8 in FIG. 8, a contrast image is acquired by scanning a region of interest sufficiently filled with a contrast agent with X-rays. The tube current at that time is indicated by i1.

  By subtracting the non-contrast image from the acquired contrast image, a subtra image is obtained, and it is possible to perform image diagnosis of a blood vessel region on the subtra image (for example, Patent Document 1).

  During contrast-enhanced and non-contrast-enhanced scans, each subject needs to hold their breath for about 10 seconds.

JP 2011-172819 A

  Therefore, in the conventional X-ray CT apparatus, when performing an image diagnosis of a blood vessel region, the patient is forced to hold the breath twice. These two breath holdings put a heavy burden on the patient.

  In addition, since the non-contrast image and the contrast image are taken with different breaths and stops, the position reproducibility of body movement is poor, and when creating a subtra image, a shift occurs in the position and shape of the part, and the presence or absence of contrast A false image greater than the difference may occur.

  An object of the present embodiment is to provide an X-ray CT apparatus capable of reducing a burden on a patient and obtaining a subtra image with a small position and shape deviation when performing an image diagnosis of a blood vessel region.

  The X-ray CT apparatus according to the present embodiment includes an X-ray tube, a main detector, a trigger detector, and control means. The X-ray tube is based on a scan mode that irradiates a region of interest of a subject placed on a bed with X-rays and a monitoring scan mode that irradiates a peripheral region including at least a part of the periphery of the region of interest Perform a scan. The main detector detects X-rays that have passed through the region of interest. The trigger detector detects X-rays transmitted through the peripheral area. When the control means receives the detection result of the trigger detector in the monitoring scan mode and determines that the contrast medium has reached the surrounding area, the control means sets the scan mode to the region of interest where the contrast medium has not reached. A non-contrast scan is performed, and when a predetermined time elapses from the end of the non-contrast scan, a contrast scan is performed on a region of interest filled with a contrast agent by setting the scan mode.

1 is a block diagram showing a configuration of an X-ray CT apparatus according to the present embodiment. The figure which shows the structure of an X-ray tube typically. The figure which shows typically an X-ray CT apparatus when a contrast agent reaches | attains a peripheral region. The figure which shows the general scan sequence of CT scan. The figure which shows typically the X-ray CT apparatus at the time of a non-contrast scan. The figure which shows typically the X-ray CT apparatus at the time of a contrast scan. The figure which shows the detector for a trigger which concerns on a modification. The figure which shows the general scan sequence of the conventional CT scan.

  Hereinafter, an embodiment of an X-ray CT apparatus will be described with reference to the drawings.

  The configuration of the X-ray CT apparatus will be described with reference to FIG. FIG. 1 is a block diagram showing the configuration of the X-ray CT apparatus.

  As shown in FIG. 1, the X-ray CT apparatus 1 includes a gantry 10 and a console 30.

  The gantry 10 includes a rotating frame 12, an X-ray tube 16, a main detector 18, a trigger detector 19, a rotation driving unit 20, a high voltage generating unit 22, a collimator 24, a gate means 25, and a data acquisition circuit (DAS). 26.

  The main body of the gantry 10 rotatably supports an annular or disk-shaped rotating frame 12. 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 recognizing 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. Therefore, the body axis of the subject P is parallel to the Z axis. The X axis is defined as a horizontal axis, and the Y axis is defined as a vertical axis.

  Note that the X-ray CT apparatus 1 has a ROTATE / ROTATE type in which the X-ray tube 16 and the main detector 18 and the like rotate as one body, and a large number of detection elements arranged in a ring shape. There are various types, such as a STATIONARY / ROTATE type in which only the X-ray tube 16 rotates around the subject, and the present embodiment can be applied to any type. Here, the X-ray CT apparatus 1 will be described as a ROTATE / ROTATE type.

  The rotating frame 12 is provided with an X-ray tube 16, a main detector 18, and a trigger detector 19.

  The rotating frame 12 receives the drive signal from the rotation driving unit 20 and continuously rotates the X-ray tube 16, the main detector 18, and the trigger detector 19.

  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.

  FIG. 2 is a diagram schematically showing the structure of the X-ray tube 16 and is a partially enlarged cross-sectional view of the X-ray tube 16 taken along the Z-axis direction. As shown in FIG. 2, the X-ray tube 16 has a first emission part 161 and a second emission part 162. The first emission part 161 or the second emission part 162 is an X-ray emission surface at the anode of the X-ray tube 16.

  The first emission unit 161 has an inclined surface that irradiates X-rays in the scan mode in the direction of the main detector 18 (indicated by D1 in FIG. 2). Here, the scan mode refers to a mode in which the region of interest of the subject P is irradiated with X-rays. The scan mode includes a contrast scan and a non-contrast scan depending on the presence or absence of contrast medium injection. In FIG. 2, the inclination angle of the first emitting portion 161 with respect to the Z-axis direction (the body axis direction shown in FIG. 3) is indicated by θ1.

  The region of interest in the present embodiment can be applied to any part of the subject P as long as it is a region into which a contrast agent is introduced. A non-contrast scan is performed before the contrast agent is flowed into the region of interest. A contrast scan is performed after the region of interest is sufficiently filled with contrast agent.

  FIG. 3 is a diagram schematically showing the X-ray CT apparatus when the contrast medium reaches the peripheral region. In FIG. 3, the annular artery a1 is indicated by a broken line, and the pulmonary vein 2 is indicated by a one-dot chain line. Hereinafter, the region of interest will be described as the region of the annular artery a1 including the heart. Further, a peripheral region including a part of the periphery of the region of interest will be described as a region including the pulmonary vein a2. The contrast medium injected into the subject P circulates through the lungs from the right atrium and right ventricle, and then flows from the pulmonary vein a2 into the left atrium and left ventricle. Moreover, it flows into the annular artery a1 from the left ventricle and the aorta.

  The second emission unit 162 has an inclined surface that irradiates X-rays in the direction of the trigger detector 19 (indicated by D2 or D2 'in FIG. 2) in the monitoring scan mode. Here, the monitoring scan mode refers to a mode in which the peripheral region is irradiated with X-rays. Details of the peripheral area will be described later. In FIG. 2, the inclination angles of the second emission part 162 with respect to the Z-axis direction are indicated by θ 2 and θ 2 ′. As shown in FIG. 2, the magnitude relationship between the inclination angles θ1, θ2, and θ2 ′ is expressed by θ2 ′ <θ1 <θ2.

  The X-ray tube 16, the main detector 18, and the trigger detector 19 are arranged so as to face each other with the subject P placed on the top 14.

  As shown in FIGS. 1 and 3, the main detector 18 moves an X-ray detection element group in which a plurality of X-ray detection elements are arranged in a direction orthogonal to the body axis (Z axis) of the subject P in the Z-axis direction. Are arranged in multiple rows.

The trigger detector 19 is disposed at least at a part of the periphery of the main detector 18. In the present embodiment, the trigger detector 19 is disposed at both side positions in the body axis direction (Z-axis direction) of the subject P with the main detector 18 therebetween. The trigger detector 19 is configured by arranging an X-ray detection element group at a position away from the main detector 18 in the body axis direction. The trigger detector 19 is arranged to be movable in the body axis direction with respect to the main detector 18.
The reason why the trigger detector 19 is disposed at a position away from the main detector 18 in the body axis direction is that the peripheral region is the pulmonary vein a2. The main detectors 18 are arranged on both sides of the body axis in order to correspond to various regions of interest and surrounding regions, and even if the patient is in the opposite direction (either head or foot first) This is also possible.

  The X-ray irradiation time interval on the subject is, for example, once every 5 seconds (one scan). The high voltage generator 22 applies a high voltage to the X-ray tube 16 according to control by the scan controller 41 in the console 30 and supplies a filament current. A collimator (X-ray diaphragm) 24 and a gate means 25 are provided on the X-ray irradiation port side of the X-ray tube 16.

  The collimator 24 includes a first path 241 that limits a region (irradiation field) irradiated with X-rays emitted from the first emission unit 161 to a region of interest (a region including the annular artery a1 illustrated in FIG. 1), and a second emission. And a pair of second paths 242 that limit a region irradiated with X-rays emitted from the unit 162 to a peripheral region (a region including the pulmonary vein a2 shown in FIG. 1). X-rays passing through the first path 241 and passing through the region of interest are detected by the main detector 18. The trigger detector 19 detects X-rays that have passed through the second path 242 and have passed through the peripheral region.

  The pair of second paths 242 are arranged at both side positions in the body axis direction (Z-axis direction) of the subject P with the first path 241 therebetween. Specifically, the collimator 24 has a shielding member made of a substance that shields X-rays (for example, lead), and supports the shielding member so as to be movable. The size and shape of the X-ray irradiation field are changed by adjusting the position of the shielding member. The collimator 24 receives the drive signal from the scan control unit 41 and moves the shielding member.

  By providing the first emission part 161, the second emission part 162, the first path 241 and the second path 242, the irradiation field can be limited. However, some X-rays emitted from the first emission part 161 may pass through the second path 242. In addition, part of the X-rays emitted from the second emission unit 162 may pass through the first path 241. Thereby, the irradiation field cannot be sufficiently limited. In order to sufficiently limit the irradiation field, a gate means 25 is provided.

  The gate means 25 has a pair of gate portions 251 and is configured to open / close the first path 241 and the second path 242. Specifically, the pair of gate portions 251 are disposed so as to be movable along the Z-axis direction so as to face the outlet of the first path 241 and the outlet of the pair of second paths 242. When the pair of gate portions 251 are separated from each other, the outlet of the first path 241 is opened and the pair of second paths 242 is closed (see FIGS. 5 and 6). Further, when the pair of gate portions 251 move close to each other and move to one side, the outlet of the first path 241 is closed and either one of the pair of second paths 242 is opened (see FIG. 3). .

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

  The trigger detector 19 detects X-rays generated from the X-ray tube 16 and transmitted through the peripheral area, and generates a current signal corresponding to the detected X-ray intensity. A data acquisition circuit (DAS) 26 is connected to the trigger detector 19.

  The data collection circuit 26 collects current signals from the main detector 18 in accordance with control by the scan control unit 41. 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. Each time projection data is generated, it is supplied to the console 30 via a non-contact data transmission unit (not shown). By repeating the CT scan, time-series projection data is generated and supplied to the console 30.

  The console 30 includes a preprocessing unit 31, a reconstruction unit 32, a system control unit 40, a scan control unit 41, a determination unit 42, a timer 43, an operation unit 44, a display unit 45, and a storage unit 46.

  The preprocessing unit 31 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 reconstruction unit 32 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 reconstruction unit 32 reconstructs time-series CT image data (CT values) based on the time-series projection data.

  Image reconstruction methods used by the X-ray CT 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.

  The system control unit 40 functions as the center of the X-ray CT apparatus 1. Specifically, the system control unit 40 reads out the control program stored in the storage unit 46 and expands it on the memory, and controls each unit according to the expanded control program. Accordingly, the system control unit 40 can execute a CT scan.

  The scan control unit 41 controls the gantry 10 (the rotation drive unit 20, the high voltage generation unit 22, the collimator 24, the gate unit 25, and the data collection circuit 26) in order to execute the CT scan.

  The determination unit 42 determines whether or not the contrast agent has reached the peripheral region based on the CT value. Specifically, the determination unit 42 outputs a determination result to the scan control unit 41 when it is determined that the CT value of the peripheral region has become “h1”. “H1” is a value slightly larger than the CT value “h0” of the peripheral region at the time of non-contrast scanning. The system control unit 40, the scan control unit 41, and the determination unit 42 may be referred to as control means.

  As the timer 43, a countdown timer is used. The countdown timer receives a non-contrast scan end instruction signal, starts counting down, and outputs a time-up signal when a predetermined time “T” elapses. The scan control unit 41 receives the time-up signal and outputs an instruction to start a contrast scan to the gantry 10. Note that the timer 43 may be a count-up timer. The time “T” is a time during which the contrast medium is recognized to reach the entire region of interest from the peripheral region, and is obtained empirically (see FIG. 4).

  The operation unit 44 receives various commands and information input from the operator. For example, the operation unit 44 inputs a CT value “h1” and a predetermined time “T” through the input device by the user. As an input device, a keyboard, a mouse, a switch, or the like can be used.

  The display unit 45 displays the CT image 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 storage unit 46 stores projection data and CT image data. In addition, the storage unit 46 stores in advance a control program, a CT value “h1”, and a time “T”.

  The outline of the CT scan according to this embodiment will be described below with reference to FIG. FIG. 4 is a diagram showing a schematic scan sequence of CT scan. In FIG. 4, the horizontal axis represents time [s] and CT value [HU], and the vertical axis represents tube current [mA]. The CT value may be referred to as a pixel value.

  The CT scan is executed by the gantry 10 in response to an instruction from the scan control unit 41.

  As described above, in the conventional CT scan shown in FIG. 8, the non-contrast scan (t1-t2), the injection of the contrast agent (t3), and the monitoring scan (t4) for monitoring whether the region of interest is sufficiently filled with the contrast agent. -T6) and contrast scan (t7-t8).

  On the other hand, in this embodiment, as shown in FIG. 4, as shown in FIG. 4, a contrast scan (t 1 ′), a monitoring scan (t 2 ′ −t 4 ′) for monitoring whether the contrast medium has reached the surrounding area The non-contrast scan, (t5′-t6 ′) and contrast scan (t7′-t8 ′) are executed in this order.

  The detection that the contrast medium has reached the peripheral region is based on the result of detecting the X-rays that have passed through the peripheral region. Examples of detection results include projection data and CT image data (CT value). In the present embodiment, CT scanning will be described on the assumption that CT values are used as examples of detection results.

  As shown in FIG. 4, when the contrast medium is injected into the subject P, the variation of the CT value in the region of interest is indicated by a solid line in FIG. 4, and the variation of the CT value in the peripheral region is indicated by a broken line in FIG.

  As can be seen from FIG. 4, the CT value in the region of interest rises slightly at t5 'to indicate "h2" and reaches "h3" at t7'. The CT value “h3” is a value close to the peak value. The CT value “h2” indicates that the contrast medium hardly reaches the region of interest, and there is no problem even if the subtra image is created using the non-contrast image acquired by the scan. The CT value “h3” represents that the region of interest is sufficiently filled with the contrast agent and the contrast scan may be started.

  The CT value in the peripheral region shows a low value “h0” between (t1′−t3 ′) and slightly increases to “h1” at t4 ′. The CT value “h0” represents that the contrast agent has not reached the peripheral region. The CT value “h1” indicates that the contrast agent has reached the peripheral region.

  In the above CT scan, the non-contrast scan (t5′-t6 ′) is followed by the contrast scan (t7′-t8 ′), so that the patient can hold his breath only for (t5′-t8 ′). What is necessary is just to hold a patient's breath in one time, and it becomes possible to reduce a burden of a patient. Furthermore, since there is almost no difference in body movement, the risk of generating a false image due to the displacement of the subtra image obtained by both (non-contrast image and contrast image) is reduced.

  The general scan sequence of the CT scan has been described above. That is, a non-contrast scan and a contrast scan are executed after the monitoring scan.

  Next, details of the CT scan executed by the X-ray CT apparatus 1 will be described with reference to FIGS. FIG. 5 is a diagram schematically illustrating an X-ray CT apparatus at the time of non-contrast scanning, and FIG. 6 is a diagram schematically illustrating the X-ray CT apparatus at the time of contrast scanning.

(Monitoring scan)
FIG. 4 shows the time t1 ′ when the contrast medium is introduced into the subject P. The scan control unit 41 issues an instruction to start the monitoring scan to the gantry 10 in response to the contrast agent being put into the subject P. Examples of the case where the contrast medium has been injected into the subject P include that the signal has been output as the contrast medium has been input, and that an instruction has been output by operating the operation unit 44 before and after the injection of the contrast medium. Including that.

  In response to the instruction to start the monitoring scan, the gate unit 251 moves. As a result, the first path 241 is closed and one of the second paths 242 is opened. The other second path 242 remains closed (t2'-t3 'shown in FIG. 4).

  In response to an instruction to start a monitoring scan, the high voltage generator 22 supplies predetermined power to the X-ray tube 16. Further, the rotation drive unit 20 rotates the rotating frame 12. As a result, the X-ray tube 16, the main detector 18, and the trigger detector 19 rotate around the subject P.

  As shown in FIG. 3, when one second path 242 is opened, the X-rays emitted from the second emission part 162 pass through the one second path 242 and pass through the peripheral region. The trigger detector 19 detects X-rays transmitted through the peripheral area. The trigger detector 19 outputs a current signal corresponding to the detected X-ray intensity to the data acquisition circuit 26. The data collection circuit 26 collects current signals, converts them into digital signals, and outputs projection data (digital signals). The preprocessing unit 31 performs preprocessing such as logarithmic conversion and sensitivity correction on the projection data. The reconstruction unit 32 reconstructs CT image data (CT value) based on the projection data that has been preprocessed. The determination unit 42 determines whether or not the reconstructed CT value has reached “h1” (state t3′−t4 ′ shown in FIG. 4). When the determination unit 42 determines that the CT value has reached “h1”, the determination unit 42 outputs a signal to that effect to the scan control unit 41.

  In response to the determination result by the determination unit 42 that the CT value has reached “h1”, the scan control unit 41 outputs an instruction to end the monitoring scan to the gantry 10. In response to the instruction to end the monitoring scan, the high voltage generator 22 stops supplying power to the X-ray tube 16. Further, the rotation drive unit 20 stops the rotation of the rotating frame 12 (state t4 ′ shown in FIG. 4). During the monitoring scan (between t2 'and t4' shown in FIG. 4), the patient does not need to hold his / her breath.

(Non-contrast scan)
Next, the scan control unit 41 outputs a non-contrast scan start instruction to the gantry 10. In response to the instruction to start the non-contrast scan, the gate unit 251 moves. As a result, the first path 241 is opened and the second path 242 is closed. (T5′-t6 ′ state shown in FIG. 4).

  In response to an instruction to start a monitoring scan, the high voltage generator 22 supplies predetermined power to the X-ray tube 16. Further, the rotation drive unit 20 rotates the rotating frame 12. As a result, the X-ray tube 16, the main detector 18, and the trigger detector 19 rotate around the subject P.

  FIG. 5 shows a state where the contrast agent reaches the peripheral region (region including the pulmonary vein a2) but does not reach the region of interest (region including the annular artery a1). As shown in FIG. 5, when the first path 241 is opened, the X-rays emitted from the first emission unit 161 pass through the region of interest through the first path 241. The main detector 18 detects X-rays that have passed through the region of interest. The main detector 18 outputs a current signal corresponding to the detected X-ray intensity to the data acquisition circuit 26. The data collection circuit 26 collects current signals, converts them into digital signals, and outputs projection data (digital signals). The preprocessing unit 31 performs preprocessing such as logarithmic conversion and sensitivity correction on the projection data. The reconstruction unit 32 reconstructs CT image data (CT value) based on the projection data that has been preprocessed. Thereby, it is possible to obtain a CT image of the region of interest during non-contrast imaging.

  The scan control unit 41 outputs an instruction to end the non-contrast scan to the gantry 10 after a predetermined time. In response to the instruction to end the non-contrast scan, the high voltage generator 22 stops supplying power to the X-ray tube 16. Further, the rotation drive unit 20 stops the rotation of the rotating frame 12 (state t6 ′ shown in FIG. 4). During the non-contrast scan (between t5 'and t6' shown in FIG. 4), the patient holds his / her breath.

  In other words, the non-contrast scan is performed after the contrast agent reaches the peripheral region and before the contrast agent reaches the region of interest. The CT value at the start of the non-contrast scan is “h2” (see FIG. 4). The start time of the non-contrast scan may be t4 '(simultaneously with the monitoring scan end instruction).

  Further, the scan control unit 41 outputs an instruction to end the non-contrast scan to the timer 43. The timer 43 receives a non-contrast scan end instruction signal, starts counting down, and outputs a time-up signal when a predetermined time T elapses.

(Contrast scan)
Next, the scan control unit 41 receives the time-up signal and outputs an instruction to start a contrast scan to the gantry 10. In response to the instruction to start the non-contrast scan, the high voltage generator 22 supplies predetermined power to the X-ray tube 16. Further, the rotation drive unit 20 rotates the rotating frame 12. As a result, the X-ray tube 16, the main detector 18, and the trigger detector 19 rotate around the subject P. At this time, the pair of gate portions 251 do not move together, the first path 241 remains open, and both the second paths 242 remain closed (t7′-t8 shown in FIG. 4). 'State).

  FIG. 6 shows a state in which the contrast agent reaches the peripheral region (region including the pulmonary vein a2) and further fills the region of interest (region including the annular artery a1). As shown in FIG. 6, since the first path 241 remains open and both the second paths 242 remain closed, the X-rays emitted from the first emission unit 161 pass through the first path 241. Through and through the region of interest. The main detector 18 detects X-rays that have passed through the region of interest.

  The acquisition of CT images from the detection of X-rays is the same as in the non-contrast scan described above. That is, the main detector 18 outputs a current signal corresponding to the detected X-ray intensity to the data acquisition circuit 26. The data collection circuit 26 collects current signals, converts them into digital signals, and outputs projection data (digital signals). The preprocessing unit 31 performs preprocessing such as logarithmic conversion and sensitivity correction on the projection data. The reconstruction unit 32 reconstructs CT image data (CT value) based on the projection data that has been preprocessed. Thereby, a CT image of the region of interest at the time of contrast can be acquired.

During the contrast scan (between t7 ′ and t8 ′ shown in FIG. 4), the patient holds his / her breath.
Therefore, the patient holds his / her breath between the non-contrast scan and the contrast scan (between t5′-t8 ′ shown in FIG. 4), but the non-contrast scan and the contrast scan are continuously executed. Stopping becomes a short time (for example, 10 seconds), and the burden on the patient can be reduced.

  In addition, since non-contrast and contrast images are obtained within the same breath-holding period, it is possible to obtain a good quality subtra image with a small positional shift due to body movement.

  That is, the contrast scan is executed after the non-contrast scan, and is executed after a predetermined time T has elapsed after the non-contrast scan is completed. The CT value at the start of the contrast scan is “h3” (see FIG. 4).

(Modification)
Next, a modification will be described with reference to FIG. FIG. 7 is a diagram showing a trigger detector according to a modification.

  As shown in FIG. 7, the trigger detector 19 is arranged to be movable in the body axis direction with respect to the main detector 18. By moving in the body axis direction with respect to the trigger detector 19, it is possible to adjust the position of the peripheral region for detecting whether or not the contrast agent has arrived, and when determining that the contrast agent has arrived, t 4 ′. It is possible to adjust the timing.

  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.

1 X-ray CT system 10 Mount (gantry)
12 Rotating frame 14 Top plate 16 X-ray tube 161 First emitting part 162 Second emitting part 18 X-ray detector 19 Triggering detector 20 Rotation driving part 22 High voltage generating part 24 X-ray diaphragm 241 First pass 242 Second Pass 25 Gate unit 251 Gate unit 26 Data collection circuit (DAS)
30 Console 31 Pre-processing unit 32 Reconfiguration unit 40 System control unit 41 Scan control unit 42 Determination unit 43 Timer 44 Operation unit 45 Display unit 46 Storage unit

Claims (6)

X in which scanning is performed in a scan mode in which X-rays are irradiated to a region of interest of a subject placed on a bed, and a monitoring scan mode in which X-rays are irradiated to a peripheral region including at least a part of the periphery of the region of interest A wire tube,
A main detector for detecting X-rays transmitted through the region of interest;
A trigger detector for detecting X-rays transmitted through the peripheral area;
In the monitoring scan mode, when the detection result of the trigger detector is received and it is determined that the contrast medium has reached the surrounding area, the scan mode is set to the region of interest where the contrast medium has not reached. A control means for performing a non-contrast scan and performing a contrast scan for a region of interest filled with a contrast agent by entering the scan mode when a predetermined time has elapsed from the end of the non-contrast scan;
An X-ray CT apparatus characterized by comprising: The X-ray tube has a first emission unit that irradiates the X-ray in the direction of the main detector in the scan mode, and a second that irradiates the X-ray in the direction of the trigger detector in the monitoring scan mode. The X-ray CT apparatus according to claim 1, further comprising: an emission unit. A collimator comprising: a first path that passes only X-rays that are irradiated in the direction of the region of interest; and a second path that passes only X-rays that are irradiated in the direction of the peripheral area;
Gate means for opening the first path when in the scan mode and closing the second path, closing the first path when in the monitoring scan mode, and opening the second path;
The X-ray CT apparatus according to claim 1, further comprising: The X-ray CT apparatus according to claim 3, wherein the trigger detector is disposed at both side positions in the body axis direction of the subject with the main detector interposed therebetween. The main detector is configured by arranging a plurality of X-ray detection element groups in which a plurality of X-ray detection elements are arranged in a direction orthogonal to the body axis in multiple rows in the body axis direction of the subject,
The X-ray CT apparatus according to claim 4, wherein the trigger detector is configured by arranging the X-ray detection element group at a position away from the main detector in the body axis direction. .   The X-ray CT apparatus according to claim 5, wherein the trigger detector is arranged to be movable in the body axis direction with respect to the main detector.

Images