JP5689925B2 - X-ray CT system - Google Patents

Description

  The present invention relates to an X-ray CT apparatus that exposes a subject to X-rays, collects projection data, and reconstructs an image from the collected projection data, and more particularly to a heart that performs imaging in synchronization with the cardiac cycle of the heart. It relates to electronic synchronous shooting.

  Conventionally, an X-ray CT (Computed Tomography) apparatus collects projection data by exposing X-rays to a subject, and detecting X-rays transmitted through the subject, and reconstructs an image from the collected projection data. . In an examination using such an X-ray CT apparatus, a contrast agent is often used to take a clear image of an organ or blood vessel to be imaged. Since the contrast agent flows out of the organs and blood vessels over time due to blood flow, when using the contrast agent, the timing of exposing the X-ray to the imaging target is important.

  Therefore, for example, in Patent Document 1, CT values in a region of interest set in continuously obtained images are sequentially measured, and based on the change over time, imaging conditions (tube current, imaging start timing, end) A technique for controlling timing and the like is disclosed.

  In recent years, a heart examination using an X-ray CT apparatus is generally performed. When the heart is imaged with an X-ray CT apparatus, the above-described contrast agent is used, and electrocardiographic synchronization imaging is performed in which imaging is performed in synchronization with the heartbeat cycle of the heart. In electrocardiographic synchronization imaging, the heartbeat cycle of the heart is detected using an electrocardiograph, and projection data is collected in a specific phase range for each detected heartbeat cycle. At this time, X-ray exposure is intermittently performed every heartbeat cycle in order to suppress the exposure dose to the subject.

  And in the examination of the heart using the X-ray CT apparatus, there are various types depending on the purpose of the examination and the target part. For example, myocardial perfusion is a test that examines the blood flow of the myocardium, CTA (CT Angiography) is a test that examines stenosis of the coronary artery, etc., and CFA (Cardiac Function Analysis) is a function of the entire heart. This is a test to check (cardiac function).

  As described above, there are a plurality of types of heart examinations using the X-ray CT apparatus, and the purpose of the examination and the parts to be examined are different from each other. The phase range of the projection data required for reconstruction and the time resolution of the image required for the inspection are also different for each type of inspection.

  Here, time resolution is a temporal element included in an image, and an image with less influence of motion is obtained by improving (shortening) the time resolution when reconstructing an image from projection data. Can do. As reconstruction methods for improving the time resolution, there are half reconstruction, segment reconstruction, and the like.

  Half reconstruction is a method of reconstructing an image using projection data collected while the X-ray tube rotates in a range of 180 degrees + α (α is a fan angle). The time resolution can be reduced to about 1/2 when compared with the case of reconstructing (full reconstruction).

  On the other hand, segment reconstruction is performed by extracting projection data having the same cross section and the same phase from projection data for a predetermined number of heartbeats, and combining the plurality of extracted projection data into projection data in a range of 180 degrees + α. In addition, this is a method of performing half reconstruction. In this segment reconstruction, when the heart rate to be used is n, the time resolution can be reduced to about (180 + α) / n as compared with the case of reconstructing an image from projection data in a 360-degree range. It is possible to further improve the time resolution. A set of projection data used for one segment reconstruction is hereinafter referred to as a projection data set.

  For each examination, considering the optimal X-ray exposure timing, phase range of projection data, and time resolution, for example, myocardial perfusion only needs to be able to confirm myocardial blood flow for examination purposes. Myocardium. Therefore, in myocardial perfusion, the X-ray exposure timing is not particularly limited, and the projection data only needs to be in a specific phase range. Further, since the myocardium at the target site is an organ having a larger structure than a blood vessel or the like, the time resolution is not so required.

  In addition, CTA is for checking the stenosis of the coronary artery for the purpose of examination, and the target site is a blood vessel. Therefore, in CTA, the X-ray exposure timing should be as high as possible in the concentration of the contrast agent, and the projection data only needs to be in a specific phase range. In addition, since blood vessels are very fine organs, high time resolution is required.

  Moreover, CFA is to examine cardiac function for the purpose of examination, and the target site is the entire heart. Therefore, in CFA, the X-ray exposure timing should be as high as possible in the concentration of the contrast agent, and the projection data requires the entire phase range in the cardiac cycle. Moreover, since it is a large organ called the whole heart, time resolution is not so required.

  As described above, the X-ray exposure timing necessary for capturing an image required for inspection, the phase range of projection data required for reconstructing the image, and the time resolution are different for each type of inspection. Is different. For this reason, usually, imaging is performed according to the type of inspection.

JP 2004-1173779 A

  However, in practice, in consideration of the burden on the patient as the subject, the above-described plurality of examinations are often performed together in a series of electrocardiogram synchronous imaging. In such a case, the operator performs X-rays on the heart in the necessary phase range while measuring the optimal timing while checking the concentration of the contrast medium according to the type of examination in a series of electrocardiographic imaging. In addition, it is necessary to operate the X-ray CT apparatus so as to reconstruct an image from projection data by a reconstruction method that meets the requirements. Conventionally, this operation has been performed manually, but has become very complicated.

  Therefore, when multiple examinations are performed together in a series of ECG-synchronized imaging, how to efficiently collect the projection data required for each examination while suppressing the exposure to the subject, the necessary images The major issue is how to reconstruct

  The present invention has been made to solve the above-described problems caused by the prior art, and in the case where a plurality of examinations are performed collectively by a series of electrocardiogram synchronous imaging, each examination is performed while suppressing the exposure dose to the subject. An object of the present invention is to provide an X-ray CT apparatus capable of efficiently collecting necessary projection data and reconstructing a necessary image.

In order to solve the above-described problems and achieve the object, the present invention according to claim 1 collects electrocardiogram information, and also collects projection data by exposing X-rays. The collected electrocardiogram information and projection An X-ray CT apparatus that reconstructs an image based on data, and a concentration calculation unit that obtains the concentration of a contrast agent in a region of interest over time, and when a plurality of examinations are performed in a series of electrocardiogram synchronous imaging, Reconstructing condition changing means for changing a reconstructing condition relating to image reconstruction corresponding to each of the plurality of examinations during the series of electrocardiogram synchronous imaging based on the density obtained by the density calculating means; , Provided.

According to the present invention of claim 1 Symbol placement, case, efficiently collect the necessary projection data for each inspection while suppressing the radiation exposure to the subject a plurality of inspection is performed together with a series of electrocardiographic synchronized imaging As a result, it is possible to reconstruct a necessary image.

It is explanatory drawing for demonstrating the concept of the electrocardiogram synchronous imaging by the X-ray CT apparatus which concerns on the present Example 1. FIG. 1 is a functional block diagram illustrating a configuration of an X-ray CT apparatus according to a first embodiment. 3 is a flowchart illustrating a processing procedure of the X-ray CT apparatus according to the first embodiment. It is explanatory drawing for demonstrating the concept of the electrocardiogram synchronous imaging by the X-ray CT apparatus which concerns on the present Example 2. FIG. It is explanatory drawing for demonstrating the concept of the electrocardiogram synchronous imaging by the X-ray CT apparatus which concerns on the present Example 3. FIG. It is explanatory drawing for demonstrating the concept of the electrocardiogram synchronous imaging by the X-ray CT apparatus which concerns on the present Example 4. FIG. It is explanatory drawing (1) for demonstrating the concept of the electrocardiogram synchronous imaging by the X-ray CT apparatus which concerns on the present Example 5. FIG. It is explanatory drawing (2) for demonstrating the concept of the electrocardiogram synchronous imaging by the X-ray CT apparatus which concerns on the present Example 5. FIG. It is explanatory drawing (3) for demonstrating the concept of the electrocardiogram synchronous imaging by the X-ray CT apparatus which concerns on the present Example 5. FIG. It is explanatory drawing (4) for demonstrating the concept of the electrocardiogram synchronous imaging by the X-ray CT apparatus which concerns on the present Example 5. FIG.

  Exemplary embodiments of an X-ray CT apparatus according to the present invention will be described below in detail with reference to the accompanying drawings. Note that the X-ray CT apparatus described here can take images of various parts of the subject as in the case of a general X-ray CT apparatus. The explanation will be focused on the case of shooting. Here, a description will be given assuming that two or more examinations of myocardial perfusion, CTA, and CFA are performed collectively in a series of electrocardiographic imaging.

  First, the concept of electrocardiogram synchronous imaging by the X-ray CT apparatus according to the first embodiment will be described. FIG. 1 is an explanatory diagram for explaining the concept of electrocardiographic synchronization imaging by the X-ray CT apparatus according to the first embodiment. This figure shows the temporal change in CT value and the X-ray exposure timing in an image reconstructed after contrast medium injection. In the figure, TDC represents a change in CT value over time, P11 to P18 indicate the X-ray exposure timing, the horizontal width indicates the X-ray exposure period, and the height indicates the X-ray exposure. Represents the exposure dose.

  As shown in the figure, the X-ray CT apparatus according to the first embodiment calculates the cardiac cycle of the subject's heart based on the electrocardiogram signal ("R wave" shown in the figure) output from the electrocardiograph. Detection is performed, X-rays are exposed to the heart in a specific phase range for each detected cardiac cycle, projection data is collected, and an image is reconstructed from the collected projection data.

  This X-ray CT apparatus calculates the CT value of the image in the region of interest over time as an index value indicating the concentration of the contrast medium injected into the heart, and based on the calculated CT value, the image is obtained from the projection data. The main feature is that the reconstruction method is changed at the time of reconstruction.

  Specifically, as shown in the figure, the X-ray CT apparatus calculates a CT value of an image in a predetermined region of interest, and projection is performed while the calculated CT value does not exceed a predetermined threshold value. When the image is reconstructed from data, the reconstruction method is half reconstruction (“HALF-EGR” shown in the figure). On the other hand, while the calculated CT value exceeds a predetermined threshold, the reconstruction method is used. Is a segment reconstruction ("SEGMENT-EGR" shown in the figure).

  That is, in the X-ray CT apparatus according to the first embodiment, projection data is collected in a specific phase range at a timing when the concentration of the contrast agent in the region of interest is low, and an image is obtained by half reconstruction from the collected projection data. Reconfigured. This image is suitable for myocardial perfusion in which the X-ray exposure timing is not particularly limited, projection data in a specific phase range is required, and time resolution is not required so much.

  On the other hand, at the timing when the concentration of the contrast agent in the region of interest is high, projection data is collected in a specific phase range, and an image is reconstructed by segment reconstruction from the collected projection data. This image is required to be exposed to X-rays at the highest possible concentration of the contrast agent, only needs projection data in a specific phase range, and is suitable for CTA requiring high time resolution. .

  Due to such a feature, in the X-ray CT apparatus according to the first embodiment, when a plurality of examinations (myocardial perfusion and CTA) are performed collectively by a series of electrocardiogram synchronous imaging, the exposure dose to the subject is reduced. Projection data necessary for each inspection is efficiently collected while suppressing, and a necessary image can be reconstructed.

  Next, the configuration of the X-ray CT apparatus according to the first embodiment will be described. FIG. 2 is a functional block diagram illustrating the configuration of the X-ray CT apparatus according to the first embodiment. As shown in FIG. 1, the X-ray CT apparatus includes a gantry device 10, a couch device 20, and a console device 30.

  The gantry 10 is an apparatus that collects projection data by exposing the subject P to X-rays, and includes a high voltage generator 11, an X-ray tube 12, an X-ray detector 13, and a data collector 14. , A rotating frame 15, a gantry driving unit 16, and an electrocardiograph 17.

  The high voltage generator 11 is a device that supplies a high voltage to the X-ray tube 12, and the X-ray tube 12 is a vacuum tube that generates X-rays by the high voltage supplied by the high voltage generator 11. The X-ray detector 13 is a detector that detects X-rays that have passed through the subject P, and the data collection unit 14 is an apparatus that generates projection data using the X-rays detected by the X-ray detector 13. is there.

  The rotating frame 15 is an annular frame that rotates continuously at high speed, and supports the X-ray tube 12 and the X-ray detector 13 so as to face each other with the subject P interposed therebetween. The gantry drive unit 16 is a drive device that rotates the rotary frame 15 to rotate the X-ray tube 12 and the X-ray detector 13 on a circular orbit around the subject P. The electrocardiograph 17 is a device that detects a weak current generated from the heart of the subject P via an electrode attached to the subject P, and outputs an electrocardiogram signal based on the detected current.

  The couch device 20 is a device on which the subject P is placed, and includes a couchtop 22 and a couch driving device 21. The top plate 22 is a plate on which the subject P is placed during imaging, and the bed driving device 21 is a device that moves the top plate 22 in the slice direction.

  The console device 30 is a device that accepts an operation of the X-ray CT apparatus by an operator and reconstructs an image from projection data collected by the gantry device 10 image, and includes an input device 31, a display device 32, and scan control. A unit 33, a preprocessing unit 34, a projection data storage unit 35, an image reconstruction processing unit 36, an image storage unit 37, a CT value calculation unit 38, and a system control unit 39.

  The input device 31 is a device used by an operator to input an instruction to the X-ray CT apparatus, such as a mouse or a keyboard, and the display device 32 is a device that displays an image stored in an image storage unit 37 described later. . The scan control unit 33 is controlled by the system control unit 39 to be described later, based on the imaging conditions instructed from the system control unit 39, the high voltage generation unit 11, the data collection unit 14, the gantry driving unit 16, and the bed driving device. 21 is a processing unit that exposes X-rays to the heart of the subject P by driving 21 and collects projection data.

  The preprocessing unit 34 is a processing unit that performs preprocessing such as sensitivity correction on the projection data generated by the data collection unit 14. The projection data storage unit 35 is a projection data that has been preprocessed by the preprocessing unit 34. Is a storage unit.

  The image reconstruction processing unit 36 reconstructs an image from the projection data stored in the projection data storage unit 35 based on the reconstruction conditions instructed by the system control unit 39 under the control of the system control unit 39 described later. It is the process part which comprises. The image reconstruction processing unit 36 has a function of reconstructing an image by at least half reconstruction and segment reconstruction. Based on the reconstruction conditions instructed by the system control unit 39, half reconstruction and segment reconstruction are performed. Change the reconfiguration method to and from the configuration. Here, it is assumed that the heart rate used when an image is reconstructed by segment reconstruction is set in advance by the operator.

  The image storage unit 37 is a storage unit that stores the image reconstructed by the image reconstruction processing unit 36. The CT value calculation unit 38 is a processing unit that calculates the CT value in the region of interest based on the image stored in the image storage unit 37. Specifically, the CT value calculation unit 38 reads the reconstructed image from the image storage unit 37 each time an image is reconstructed by the image reconstruction processing unit 36, and for each read image, The CT value in the region of interest set in advance is calculated and notified to the system control unit 39 sequentially. Note that the region of interest for calculating the CT value may be set manually by the operator in advance, or the heart region may be automatically detected from the reconstructed image and set.

  The system control unit 39 is a processing unit that performs overall control of the X-ray CT apparatus by controlling operations of the gantry device 10, the couch device 20, and the console device 30. For example, when electrocardiogram synchronous imaging is performed, the system control unit 39 is based on an instruction from an operator input using the input device 31 and an electrocardiogram signal output from the electrocardiograph 17. Thus, the scan control unit 33 is controlled to collect projection data, and the image reconstruction processing unit 36 is controlled based on the notification sent from the CT value calculation unit 38 to reconstruct an image from the projection data.

  Specifically, when the contrast medium is injected into the subject P and the imaging start instruction is received from the operator, the system control unit 39 first controls the scan control unit 33 to scan the heart of the subject P. The top plate 22 is moved until the position is reached. When the top 22 moves to the scan position, the system control unit 39 detects the heartbeat cycle based on the cycle of the R wave of the electrocardiogram signal output from the electrocardiograph 17 and controls the scan control unit 33, X-rays are exposed to the heart of the subject P in a specific phase range for each detected heartbeat period, and projection data is collected.

  At this time, the system control unit 39 instructs the scanning control unit 33 on imaging conditions. The imaging conditions include a tube voltage / tube current supplied from the high voltage generator 11 to the X-ray tube 12, an X-ray exposure timing, an X-ray exposure period, and the like. Here, the tube voltage / tube current and the X-ray exposure period are set in advance by the operator. The X-ray exposure timing is automatically set based on the heartbeat period and the phase range set in advance by the operator.

  In addition to collecting projection data, the system control unit 39 inputs CT values sequentially notified from the CT value calculation unit 38, and controls the image reconstruction processing unit 36 based on the temporal change of the input CT values. Then, an image is reconstructed from the projection data.

  At this time, the system control unit 39 instructs the image reconstruction processing unit 36 on reconstruction conditions. This reconstruction condition includes a reconstruction method used when an image is reconstructed from projection data. When the reconstruction condition is instructed, the system control unit 39 determines whether or not the CT value input from the CT value calculation unit 38 exceeds a predetermined threshold value. The reconstruction method of the reconstruction condition instructed to the reconstruction processing unit 36 is assumed to be segment reconstruction. On the other hand, if the input CT value does not exceed the predetermined threshold value, the system control unit 39 sets the reconstruction method instructed to the image reconstruction processing unit 36 as half reconstruction.

  Thereby, as long as the CT value calculated by the CT value calculation unit 38 does not exceed a predetermined threshold value, the reconstruction method when an image is reconstructed from projection data is half reconstruction, while the CT value is While the predetermined threshold is exceeded, the reconstruction method is segment reconstruction. Note that the predetermined threshold used here is set in advance by the operator based on the absolute CT value, the relative CT value, or the change rate of the CT value.

  When the system control unit 39 receives an imaging end instruction from the operator, the system control unit 39 controls the system control unit 39 to stop the X-ray exposure and the rotation of the rotary frame 15 and is outside the gantry device 10. The top plate 22 is moved to a predetermined position.

  Next, a processing procedure of the X-ray CT apparatus according to the first embodiment will be described. FIG. 3 is a flowchart illustrating the processing procedure of the X-ray CT apparatus according to the first embodiment. As shown in the figure, in this X-ray CT apparatus, when the console apparatus 30 receives an imaging start instruction from the operator (Yes in step S101), the bed apparatus 20 reaches the scan position of the heart of the subject P. The top plate 22 is moved to (step S102).

  Subsequently, the gantry device 10 exposes X-rays to the heart of the subject P in a specific phase range for each heartbeat cycle (step S103), and the console device 30 reconstructs an image from the projection data (step S104). Based on the reconstructed image, a CT value in the region of interest is calculated (step S105).

  If the CT value exceeds the predetermined threshold (Yes at Step S106), the console device 30 changes the reconstruction method used when reconstructing the image to segment reconstruction (Step S107). If the input CT value does not exceed the predetermined threshold (No at Step S106), the reconstruction method is changed to half reconstruction (Step S108).

  Thereafter, the console device 30 repeats the processing from step S103 to S108 until a photographing end instruction is received from the operator (step S109, No). When an imaging end instruction is received from the operator (step S109, Yes), the X-ray exposure is suspended (step S110), and then the bed apparatus 20 is a predetermined outside the gantry apparatus 10. The top plate 22 is moved to the position (step S111).

  Note that, here, the operator has instructed the start and end of imaging, but for example, imaging may be automatically started and ended based on the CT value.

  As described above, in the first embodiment, the CT value calculation unit 38 calculates the CT value in the region of interest over time, and the system control unit 39 calculates the CT value calculated by the CT value calculation unit 38. Since the reconstruction method is changed between half reconstruction and segment reconstruction so that the temporal resolution changes based on whether a predetermined threshold is exceeded, multiple examinations are a series of ECG-synchronous imaging In the case of performing all together, the projection data necessary for each examination can be efficiently collected and the necessary image can be reconstructed while suppressing the exposure amount to the subject.

  Specifically, in the first embodiment, when the concentration of the contrast agent is low, projection data is collected in a specific phase range, and an image is reconstructed by half reconstruction, while the concentration of the contrast agent is high. At timing, projection data is collected in a specific phase range, and an image is reconstructed by segment reconstruction. Therefore, an image suitable for myocardial perfusion and CTA can be obtained.

  By the way, in the first embodiment, the reconstruction method is the segment reconstruction while the CT value in the region of interest exceeds the predetermined threshold, and the reconstruction method is used while the CT value does not exceed the predetermined threshold. However, when the image is reconstructed from a projection data set for a predetermined heart rate used for segment reconstruction after the reconstruction method is changed to segment reconstruction. Thus, the reconstruction method may be returned to the half reconstruction. Therefore, hereinafter, such a case will be described as a third embodiment.

  FIG. 4 is an explanatory diagram for explaining the concept of electrocardiographic synchronization imaging by the X-ray CT apparatus according to the second embodiment. As shown in the figure, in the X-ray CT apparatus according to the second embodiment, the system control unit 39 of the console device 30 determines whether or not the CT value input from the CT value calculation unit 38 exceeds a predetermined threshold value. If the CT value exceeds the threshold value when the determination is made, the image reconstruction processing unit 36 is instructed for a reconstruction condition in which the reconstruction method is segment reconstruction, and is used in segment reconstruction. When the image is reconstructed from a set of projection data for a predetermined heart rate (a set of projection data collected at P23 and P24 shown in the figure), an instruction is given to return the reconstruction method to half reconstruction. Here, it is assumed that the heart rate (in the example of the figure, the heart rate is 2) used when an image is reconstructed by segment reconstruction is set in advance by the operator.

  As described above, in the second embodiment, the system control unit 39 reconstructs only the projection data set corresponding to the heart rate used in the segment reconstruction after the CT value in the region of interest exceeds the predetermined threshold. Since the segment reconstruction is performed, the time during which the segment reconstruction is used can be minimized. Since segment reconstruction requires projection data for a plurality of heartbeats, it takes time to obtain an image when compared with half reconstruction. Therefore, if the time during which segment reconstruction is used is minimized, the time required for the entire imaging is shortened, and as a result, the exposure amount of the subject P can be suppressed.

  In the first embodiment, the case where the operator sets the X-ray exposure period included in the imaging conditions in advance has been described. For example, when the CT value exceeds a predetermined threshold, the X-ray exposure period is set. The exposure period may be extended to a predetermined size. Therefore, hereinafter, such a case will be described as a third embodiment.

  FIG. 5 is an explanatory diagram for explaining the concept of electrocardiogram synchronous imaging by the X-ray CT apparatus according to the third embodiment. As shown in the figure, in the X-ray CT apparatus according to the third embodiment, the system control unit 39 of the console apparatus 30 determines whether or not the CT value input from the CT value calculation unit 38 exceeds a predetermined threshold value. If the CT value exceeds the threshold value at the time of determination, the imaging conditions are instructed to extend the X-ray exposure period to a predetermined size to the scan control unit 33 (P34 shown in the figure). See).

  Here, the predetermined size for extending the X-ray exposure period is set in advance by the operator. For example, when the range from a certain R wave to the next R wave is defined as 0% to 100% as a unit representing the size of the phase range, the system control unit 39 is normally 65% to 85%. On the other hand, the photographing conditions are changed so that the phase range is 0% to 99% or 50% to 100%.

  Thus, for example, as shown in the figure, if the exposure period of X-rays irradiated at the timing of P34 is expanded to a size that includes the entire phase of the heartbeat cycle, projections collected by exposure during that period Since all the phases of the heartbeat cycle are included in the data, any phase image can be reconstructed. In the figure, a case is shown in which an image is reconstructed by half reconstruction from projection data collected at the timing of P34.

  As described above, in the third embodiment, when the CT value in the region of interest exceeds the predetermined threshold, the system control unit 39 sets the imaging condition so as to extend the X-ray exposure period to a predetermined size. Therefore, in addition to myocardial perfusion, an image suitable for CFA that needs to collect projection data in the entire phase range of the cardiac cycle can be obtained by a series of electrocardiographic imaging.

  In the third embodiment, the case has been described in which the X-ray exposure period is expanded to a predetermined size while the CT value in the region of interest exceeds the predetermined threshold. If the exposure time is exceeded, the exposure period may be extended to a predetermined size, and X-rays may be continuously exposed for a predetermined heart rate. Therefore, hereinafter, such a case will be described as a fourth embodiment.

  FIG. 6 is an explanatory diagram for explaining the concept of electrocardiogram synchronous imaging by the X-ray CT apparatus according to the fourth embodiment. As shown in the figure, in the X-ray CT apparatus according to the fourth embodiment, the system control unit 39 of the console apparatus 30 determines whether or not the CT value input from the CT calculation measurement unit 38 exceeds a predetermined threshold value. If the CT value exceeds the threshold when the determination is made, the X-ray exposure period is predetermined for the scan controller 33 by a predetermined heart rate (the heart rate is 2 in the example in the figure). The shooting conditions are instructed so as to be expanded to the size (see P43 shown in the figure).

  As a result, for example, as shown in the figure, the X-ray exposure period irradiated at the timing of P43 is expanded to a size that includes the entire phase of the heartbeat cycle, and then used for segment reconstruction. If X-rays are continuously exposed for the heart rate, the projection data collected by exposure during that period will include the entire phase of the heart cycle, so that any phase image can be reconstructed. In addition, segment reconstruction can be performed using projection data collected by exposure during that period.

  As described above, in the fourth embodiment, when the CT value in the region of interest exceeds the predetermined threshold, the system control unit 39 expands the exposure period to a predetermined size and then sets the predetermined heart rate. Because the imaging conditions are instructed so that only X-rays are continuously exposed, in addition to myocardial perfusion and CTA, an image suitable for CFA that needs to collect projection data in the entire phase range of the cardiac cycle is also included. It can be obtained by electronic synchronous shooting.

  Further, in the first to fourth embodiments described so far, the case where the tube current supplied from the high voltage generator 11 to the X-ray tube 12 is set in advance by the operator has been described. While the CT value of exceeds the predetermined threshold, the tube current may be increased to a predetermined value. By increasing the tube current supplied from the high voltage generator 11, the dose of X-rays generated from the X-ray tube 12 increases, and as a result, an image in which the imaging target is more clearly projected can be obtained. It becomes like this.

  Therefore, hereinafter, such a case will be described as a fifth embodiment. FIGS. 7 to 10 are explanatory views (1) to (4) for explaining the concept of electrocardiogram synchronous imaging by the X-ray CT apparatus according to the fifth embodiment, which are described in the first to fourth embodiments, respectively. In ECG synchronous imaging, the tube current is increased to a predetermined value while the CT value exceeds a predetermined threshold.

  As shown in FIG. 7, in this case, in the X-ray CT apparatus according to the first embodiment, the system control unit 39 of the console apparatus 30 performs image reconstruction while the CT value in the region of interest exceeds a predetermined threshold. The reconstruction processing unit 36 is instructed with a reconstruction condition in which the reconstruction method is segment reconstruction, and the scan control unit 33 is instructed with imaging conditions so as to increase the tube current to a predetermined value (same as above). (See P14 and P15 in the figure).

  Thereby, at the timing when the concentration of the contrast agent is high, strong X-rays are emitted and projection data is collected, and an image is reconstructed from the collected projection data by half reconstruction. Since this image shows a region to be imaged (for example, a coronary artery) more clearly than an image captured without enhancing X-rays, an image more suitable for CTA can be obtained. become able to.

  Also, as shown in FIG. 8, in this case, in the X-ray CT apparatus according to the second embodiment, the system control unit 39 of the console device 30 displays an image when the CT value in the region of interest exceeds the threshold value. A reconstruction processing unit 36 is instructed for reconstruction conditions with the reconstruction method being segment reconstruction, and a set of projection data for a predetermined heart rate used in segment reconstruction (P23 and P When the image is reconstructed from the projection data set collected in P24), the reconstruction method is instructed to return to half reconstruction, and the tube current is increased to a predetermined value to the scan control unit 33. In this way, the imaging conditions are instructed, and at the time when X-rays corresponding to a predetermined heart rate are irradiated, the tube current is instructed to return to the original intensity (see P23 and P24 shown in the figure).

  This minimizes the time during which segment reconstruction is used, and provides an image in which the region to be imaged (for example, a coronary artery) is more clearly reflected, thereby reducing the exposure amount of the subject P, An image more suitable for CTA can be obtained.

  Further, as shown in FIG. 9, in this case, in the X-ray CT apparatus according to the third embodiment, the system control unit 39 of the console device 30 scans when the CT value in the region of interest exceeds the threshold value. An imaging condition is instructed to the control unit 33 so as to extend the X-ray exposure period to a predetermined size and to increase the tube current to a predetermined value (see P34 shown in the figure).

  As a result, the image reconstructed from the projection data collected in a wide phase range is more clearly reflected in the region to be imaged than the image captured without intensifying X-rays. An image more suitable for CFA can be obtained.

  In the figure, for easy understanding, the dose of X-rays exposed at the timing of P35 is shown as the same size as the dose of X-rays exposed at the timings of P31 to P33. However, since the temperature of the filament of the X-ray tube 12 does not decrease immediately, the X-ray dose exposed at the timing of P35 following the timing of P34 is actually exposed at the timing of P31 to P33. Larger than the X-ray dose.

  As shown in FIG. 10, in this case, in the X-ray CT apparatus according to the fourth embodiment, the system control unit 39 of the console device 30 scans when the CT value in the region of interest exceeds the threshold value. To the control unit 33, the X-ray exposure period is increased to a predetermined value by a predetermined heart rate (in the example of FIG. 2, the heart rate is 2), and the tube current is increased to a predetermined value. Is instructed on the shooting conditions (see P43 shown in the figure).

  As a result, an image reconstructed from projection data collected in a plurality of heartbeat cycles and in a wide phase range is more clearly imaged than an image taken without intensifying X-rays. Since the image is projected, an image more suitable for CTA and CFA can be obtained.

  As described above, in Example 5, when the concentration of the contrast agent is high, the dose of X-rays to be exposed increases, and an image is reconstructed by segment reconstruction, or X-ray exposure is performed. Since the period is extended, the projection data necessary for each examination can be collected more efficiently, and a necessary image can be reconstructed.

  In each of the embodiments described above, it is determined whether or not the CT value in the region of interest exceeds a predetermined threshold, and based on the determination result, the reconstruction method, the X-ray exposure period, Although the case of automatically switching the X-ray exposure dose has been described, the GUI (Graphical User Interface) for changing the reconstruction method, the X-ray exposure period, and the X-ray exposure dose at the operator's discretion ) May be included in the X-ray CT apparatus.

  In that case, for example, the system control unit 39 displays a graphic representing the temporal change of the CT value in the region of interest and the X-ray exposure timing, such as the TDC and P11 to P18 shown in FIG. Further, an operation for the displayed graphic is received via the input device 31 such as a mouse or a keyboard. Based on the received operation, an imaging condition is instructed to the scan control unit 33 or an image reconstruction process is performed. The reconstruction condition, the X-ray exposure period, and the X-ray exposure dose are changed by instructing a reconstruction condition to the unit 36.

  In each of the embodiments described above, the case where two or more examinations of myocardial perfusion, CTA, and CFA are performed together in a series of electrocardiographic imaging has been described. The present invention is not limited to this, and the present invention can be similarly applied even when other types of inspections are performed.

  As described above, the X-ray CT apparatus according to the present invention is useful in electrocardiogram synchronous imaging, and is particularly suitable when a plurality of examinations are performed collectively in a series of imaging.

DESCRIPTION OF SYMBOLS 10 Mount apparatus 11 High voltage generation part 12 X-ray tube 13 X-ray detector 14 Data collection part 15 Rotating frame 16 Mount drive part 17 Electrocardiograph 20 Bed apparatus 21 Bed drive apparatus 22 Top plate 30 Console apparatus 31 Input apparatus 32 Display Device 33 Scan control unit 34 Preprocessing unit 35 Projection data storage unit 36 Image reconstruction processing unit 37 Image storage unit 38 CT value calculation unit 39 System control unit

Claims (8)

An X-ray CT apparatus that collects electrocardiogram information, collects projection data by exposing X-rays, and reconstructs an image based on the collected electrocardiogram information and projection data,
A concentration calculating means for determining the concentration of the contrast agent in the region of interest over time;
When a plurality of examinations are performed in a series of electrocardiogram synchronous imaging, an image corresponding to each of the plurality of examinations is reproduced during the series of electrocardiogram synchronous imaging based on the density obtained by the density calculation means. Reconfiguration condition changing means for changing the configuration reconfiguration conditions;
An X-ray CT apparatus comprising:   The X-ray CT apparatus according to claim 1, further comprising: an imaging condition changing unit that changes an imaging condition related to the X-ray exposure based on the density obtained by the density calculating unit.   The reconstruction condition changing means changes the reconstruction method included in the reconstruction condition so that the temporal resolution of the reconstructed image changes based on the density obtained by the density calculating means. The X-ray CT apparatus according to claim 1, wherein the X-ray CT apparatus is characterized. 3. The X-ray imaging apparatus according to claim 2 , wherein the imaging condition changing unit changes the imaging condition so that an X-ray exposure period changes based on the density obtained by the density calculating unit. Line CT device. The imaging condition changing means, based on the concentration obtained by the concentration calculating means, according to claim 2 or 4, characterized in that to change the photographing conditions such exposure dose of the X-ray is changed X-ray CT system.   The X-ray CT apparatus according to claim 1, wherein the density calculation unit calculates a CT value of an image in the region of interest as an index value of the density. The reconstruction condition changing means changes the reconstruction condition based on whether the concentration exceeds a predetermined threshold value,
6. The X-ray CT apparatus according to claim 2, 4 or 5, wherein the imaging condition changing unit changes the imaging condition based on whether the density exceeds the predetermined threshold.   The X-ray CT apparatus according to claim 7, wherein the predetermined threshold is an absolute CT value, a relative CT value, or a threshold defined based on a change rate of the CT value.

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