JP4744662B2 - X-ray CT system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a single-slice X-ray CT apparatus that captures an X-ray image by an X-ray detector array for one column, and a multi-slice that acquires an X-ray image by an X-ray detector array for a plurality of columns. In particular, the present invention relates to an X-ray CT apparatus that enables a transition from a monitoring scan to a main scan in a contrast examination at an accurate timing.
[0002]
[Prior art]
A conventional X-ray CT apparatus is provided with a function of shifting to imaging in a contrast examination in accordance with the circulatory dynamics corresponding to the patient and the site. When this imaging is designated, the X-ray CT apparatus continuously exposes a X-ray with a smaller dose than the normal imaging to the subject, and obtains a tomographic image of a desired part of the subject in real time. The monitoring scan which is reconfigured and displayed on the monitor display unit is performed. The operator sets a region of interest (ROI) at a desired site on the tomographic image displayed by the monitoring scan, and sets the average CT value in the ROI at which the main scan is started as a threshold value. Then, the injector is operated to inject a contrast medium into the subject.
[0003]
The X-ray CT apparatus calculates an average CT value in the ROI when each setting is performed. The average CT value in this ROI shows a higher value as the amount of contrast agent that reaches the region where the ROI is set increases. The X-ray CT apparatus sequentially compares the average CT value and the threshold value, and starts the main scan at a timing when a predetermined time has elapsed since the average CT value exceeded the threshold value.
[0004]
As a result, a monitoring scan is started as shown in FIG. 3, and the contrast medium injected at time t1 is distributed to the region where the ROI is set, and the average CT value in the ROI is the same as the threshold value. The monitoring scan is terminated at time t2, and the main scan can be automatically started from time t3 when a predetermined time has elapsed.
[0005]
When the main scan is started, the X-ray CT apparatus performs imaging by exposing a normal dose of X-rays to the subject. As a result, imaging can be performed at a timing when the contrast agent has sufficiently spread to the desired site of the subject, and a clear captured image of the desired site can be obtained.
[0006]
[Problems to be solved by the invention]
Here, FIG. 4 is a graph in which the horizontal axis represents the time axis and the vertical axis represents the CT value. As can be seen from FIG. 4, the average CT value in the ROI indicated by the solid line in FIG. It fluctuates according to the breathing of the subject indicated by the dotted line in the figure. For this reason, in conventional X-ray CT apparatuses, the average CT value exceeds the threshold before the contrast agent reaches the desired part of the subject sufficiently due to fluctuations in the average CT value due to respiration in contrast examination. There is a problem that causes a disadvantage that the main scan is started.
[0007]
The present invention has been made in view of the above-described problems, and can detect an accurate CT value without being affected by body movement such as breathing, and can start a main scan at an accurate timing. An object is to provide an X-ray CT apparatus.
[0008]
[Means for Solving the Problems]
The present invention according to claim 1 is an X-ray CT apparatus having image reconstruction means for collecting data of a subject into which a contrast medium has been injected by an X-ray imaging means and reconstructing an image based on the data. CT value calculating means for calculating a CT value of a desired part based on an image obtained by monitoring scan, body motion detecting means for detecting substantially periodic body motion of the subject, and from the body motion detecting means stable incorporation selected CT values of the state, monitoring the scan are compared with the loaded CT value with a predetermined threshold value among based on the body motion detection output CT value calculated by the CT value calculating means And a control means for determining the start of the main scan and the start of the main scan.
[0009]
The CT value calculated by the CT value calculating means varies depending on the body movement of the subject. For this reason, in the X-ray CT apparatus, periodic body movements of the subject such as respiratory fluctuations and heartbeats are detected by the body movement detection means. Based on the body motion detection output, the control means selects and captures a CT value with a stable value among the CT values calculated by the CT value calculation means, and acquires the acquired CT value and the threshold value. In comparison, the end of the monitoring scan and the start of the main scan are determined. Thereby, since the shift from the monitoring scan to the main scan can be achieved based on the CT value having a stable value, the shift from the monitoring scan to the main scan can be achieved at an accurate timing.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
[First Embodiment]
(overall structure)
The X-ray CT apparatus according to the present invention can be applied to an X-ray CT system as shown in FIG. The X-ray CT system according to the first embodiment of the present invention includes an X-ray CT apparatus 1 that takes a tomographic image of a subject, an injector 2 that injects a contrast medium into the subject, and an X-ray CT apparatus 1. And a monitor display unit 3 for displaying a tomographic image or the like photographed in FIG.
[0015]
(Configuration of X-ray CT apparatus 1)
The X-ray CT apparatus 1 includes a gantry rotating unit 6 that captures an X-ray image such as a tomographic image of a subject 5 placed on a bed 4, and data collection that collects an X-ray image captured by the gantry rotating unit 6. A pre-processing unit 8 (DAS), a pre-processing unit 8 that performs a predetermined filtering process on the collected data from the data collecting unit 4 by, for example, a convolution filter as a pre-processing of image reconstruction, An image reconstruction unit 9 that performs image reconstruction processing based on the collected data and forms a tomographic image of the subject 5 and an operation unit 10 for performing imaging conditions and various settings are provided.
[0016]
The gantry rotating unit 6 includes an X-ray tube 11 and an X-ray detector 12 that are provided so as to rotate along the inner periphery of the gantry while maintaining a mutually opposing positional relationship. So-called helical scanning is possible, in which imaging is performed spirally while moving by a predetermined pitch. As the X-ray detector 12, a detector array in which a plurality of (for example, 1000 channels) X-ray detection elements are arranged in parallel along a direction (slice direction) orthogonal to the rotation axis direction is used. A multi-slice X-ray detector is provided that is arranged in parallel for a plurality of rows. As the X-ray detector 12, an X-ray detector for single slice in which only one detector row is provided may be provided.
[0017]
The operation unit 10 is provided with an ROI setting unit 13 and a threshold value setting unit 14, and the operator operates the ROI setting unit 13 to form a tomogram formed by the image reconstruction unit 9. By setting the region of interest (ROI) on the image and operating the threshold value setting unit 14, the average CT value in the ROI when performing the main scan from the monitoring scan (pilot scan) in the contrast examination Is set as a threshold value.
[0018]
The X-ray CT apparatus 1 includes an adder 15 that superimposes the ROI set by the ROI setting unit 13 on the tomographic image formed by the image reconstruction unit 9 and displays the image on the monitor display unit 3, and an image reconstruction unit. Based on the tomographic image formed by the configuration unit 9, an average CT value calculating unit 16 that calculates an average CT value in the ROI set on the tomographic image, and a respiratory sensor 17 that detects respiratory fluctuations of the subject 5. Based on the respiratory detection output from the respiratory sensor 17, the average CT value calculated by the average CT value calculation unit 16, and the threshold value set by the threshold value setting unit 10, It has a control unit 18 for controlling the scanning timing and controlling the entire X-ray CT apparatus.
[0019]
(Operation of the first embodiment)
Next, the operation in the contrast examination of the X-ray CT system of the first embodiment having such a configuration will be described. When performing a contrast examination, the operator operates the operation unit 10 to designate the contrast examination.
[0020]
(Supervised scan mode)
When this designation is detected, the control unit 18 of the X-ray CT apparatus 1 enters the “monitoring scan mode” and continuously applies X-rays with a smaller dose to the subject 5 placed on the bed 4 than during normal imaging. The X-ray tube 11 and the X-ray detector 12 of the gantry rotating unit 6 are controlled so as to perform exposure and imaging. As a result, an X-ray image formed by exposing the small dose of X-rays to the subject 5 is captured by the X-ray detector 12.
[0021]
The DAS 7 collects collected data corresponding to the X-ray image captured by the X-ray detector 12 and supplies it to the preprocessing unit 8. The pre-processing unit 8 performs a filtering process on the collected data using a convolution filter such as a ramachandran, and supplies this to the image reconstruction unit 9. The image reconstruction unit 9 performs a real-time image reconstruction process on the tomographic image of the subject 5 by using, for example, a filtered back projection method based on the collected data subjected to the filtering process, and this is displayed on the monitor display unit via the adder 15. 3 is supplied. As a result, a tomographic image of the subject 5 captured in the monitoring scan mode is displayed on the monitor display unit 3.
[0022]
(ROI and threshold settings)
Next, when the tomographic image is designated in this way, the operator operates the ROI setting unit 13 of the operation unit 10 based on the tomographic image displayed on the monitor display unit 3 to perform a desired operation on the tomographic image. ROI is set for the part. In addition to this setting, the operator sets the value of the average CT value in the ROI as the threshold value when switching from the monitoring scan mode to the main scan mode.
[0023]
When the ROI is set, the adder 15 superimposes the set ROI on the tomographic image that is reconstructed and supplied in real time from the image reconstruction unit 9, and supplies this to the monitor display unit 3. To display. Further, the average CT value calculation unit 16 calculates the average value of the CT values in the set ROI based on the reconstructed image from the image reconstruction unit 9, and supplies this to the control unit 18.
[0024]
An operator, in real time, observes a tomographic image of a desired site in the ROI displayed on the monitor display unit 3, operates the injector 2 at the desired timing, and injects a contrast agent into the subject 5. . As a result, the contrast agent gradually spreads to a desired part of the subject 5, and the average CT value calculated by the average CT value calculation unit 16 gradually increases with the amount of the contrast agent that spreads. Will be.
[0025]
(Transition to main scan mode)
Here, as described above, the subject 5 is provided with the respiration sensor 17 for detecting respiration variation, and the respiration sensor output that varies substantially periodically as shown in FIG. Is supplied to the control unit 18. In the respiration sensor output waveform shown in FIG. 2A, the upper peak is the peak of inhalation (inspiration) of the subject, and the down peak is the exhalation (exhalation) of the subject's air. Each peak is shown.
[0026]
The control unit 18 monitors the respiration sensor output supplied from the respiration sensor 17 and supplies it from the average CT value calculation unit 16 at the timing of the upper peak of the respiration sensor output, for example, as indicated by an arrow in FIG. The average CT value obtained is taken in. As shown in FIG. 2 (b), the average CT value changes due to body movement caused by breathing of the subject. However, at the timing of the upper peak of the respiratory sensor output, the average CT value is calculated from the average CT value calculation unit 16. By taking in the average CT value, it is possible to take out only the average CT value in a stable state by removing the average CT value that has fluctuated due to respiration.
[0027]
It should be noted that the timing at which this average CT value is captured is other than the timing of the upper peak of the respiratory sensor output, such as the timing of the down peak of the respiratory sensor output or the timing between the upper peak and the down peak of the respiratory sensor output. Any timing may be used as long as the average CT value in a stable state can be taken in.
[0028]
Next, when the control unit 18 takes in the average CT value in a stable state in this way, the control unit 18 compares the average CT value with the threshold value set via the threshold value setting unit 14. . Then, as shown in FIG. 3, the monitoring scan mode is terminated at the timing (time t2) when the average CT value exceeds the threshold value, and the “main scan mode” is passed after a predetermined time (between time t2 and time t3). ”. Thus, since it is possible to shift to the main scan mode based on the average CT value in a stable state, the main scan mode can be shifted at an accurate timing without being affected by body movement such as breathing of the subject. Can do.
[0029]
Note that the average CT value may temporarily exceed the threshold value due to a detection error of the respiration sensor 17 and a calculation error of the average CT value calculation unit 16. Therefore, in the X-ray CT system, the control unit 18 counts the number of times that the average CT value exceeds the threshold value. Then, when the number of times of excess exceeds a predetermined number, the mode shifts from the monitoring scan mode to the main scan mode. The predetermined time (between time t2 and time t3) is a counting period of the excess times. Thereby, it is possible to shift to the main scan mode at an accurate timing without being affected by the detection error of the respiration sensor 17 or the calculation error of the average CT value calculation unit 16.
[0030]
When shifting to the main scan mode, the control unit 18 controls the gantry rotating unit 6 so as to perform imaging by exposing a normal dose of X-rays to the subject 5. As described above, in the X-ray CT system, only the average CT value in a stable state is detected, and the transition to the main scan mode is made accordingly. The main scan can be started in a sufficiently spread state, and a clear captured image of a desired part can be obtained via the image reconstruction unit 9 and the monitor display unit 3.
[0031]
(Effects of the first embodiment)
As is clear from the above description, the X-ray CT system according to the first embodiment of the present invention is based on the respiratory sensor output in the monitoring scan in the contrast examination. Since the CT value is taken in and the transition to the main scan is attempted based on the average CT value, it is possible to shift to the main scan mode at an accurate timing without being affected by body movement due to breathing. For this reason, the main scan can be started in a state where the contrast agent has sufficiently spread over the desired part of the subject, and a clear captured image of the desired part can be obtained.
[0032]
[Second Embodiment]
Next, an X-ray CT system according to a second embodiment of the present invention will be described. The X-ray CT system of the first embodiment described above selects and captures the average CT value from the average CT value calculation unit 16 based on the respiratory sensor output, and shifts to the main scan based on the average CT value. However, the X-ray CT system according to the second embodiment controls the reconstruction timing of the image reconstruction unit 9 based on the respiration sensor output, and from the reconstructed image whose timing is controlled. Based on the calculated average CT value, the shift to the main scan is intended. Note that the second embodiment is different from the first embodiment described above only in this point. For this reason, in the following description, only the difference between the two will be described, and redundant description will be omitted.
[0033]
(Configuration and operation of the second embodiment)
In other words, the X-ray CT system according to the second embodiment has a configuration in which the control unit 18 controls the reconstruction timing of the image reconstruction unit 9 as shown by a one-dot chain line in FIG.
[0034]
Specifically, when the respiration sensor output is supplied from the respiration sensor 17 in the monitoring scan mode, the control unit 18 performs the reconfiguration processing at the timing of the upper peak of the respiration sensor output as shown in FIG. The image reconstruction unit 9 is controlled. As a result, the image reconstruction unit 9 intermittently performs image reconstruction processing at the timing of the upper peak of the respiration sensor output, and supplies this reconstructed image to the average CT value calculation unit 16.
[0035]
The average CT value calculation unit 16 calculates the average CT value in the ROI based on this reconstructed image. As described above, the timing of the upper peak of the respiration sensor output is affected by the body movement due to respiration. This is the timing at which no average CT value is obtained. Therefore, by controlling the reconstruction timing of the image reconstruction unit 9 in this manner, the control unit 18 is supplied with an average CT value that is not affected by body movement due to respiration. As described above, the control unit 18 shifts from the monitoring scan mode to the main scan mode based on the average CT value.
[0036]
(Effect of the second embodiment)
Thereby, it is possible to shift to the main scan at a stable timing without being affected by body movement due to respiration, and the same effect as the X-ray CT system of the first embodiment described above can be obtained. .
[0037]
The timing for controlling the image reconstruction unit 9 is not the timing of the upper peak of the respiration sensor output, but the timing of the down peak of the respiration sensor output, or between the upper peak and the down peak of the respiration sensor output. It is the same as in the first embodiment that the average CT value only needs to be stable, such as timing.
[0038]
[Third Embodiment]
Next, an X-ray CT system according to a third embodiment of the present invention will be described. The X-ray CT system of the first embodiment described above selects and captures the average CT value from the average CT value calculation unit 16 based on the respiratory sensor output, and shifts to the main scan based on the average CT value. However, the X-ray CT system of the third embodiment controls the scan timing of the gantry rotating unit 6 in the monitoring scan mode based on the respiratory sensor output, and is imaged at this scan timing. Based on the average CT value calculated from the reconstructed image, the shift to the main scan is intended. The third embodiment is different from the first embodiment only in this point. For this reason, in the following description, only the difference between the two will be described, and redundant description will be omitted.
[0039]
(Configuration and operation of the third embodiment)
That is, in the X-ray CT system according to the third embodiment, when the respiration sensor output is supplied from the respiration sensor 17 shown in FIG. 1 in the monitor scan mode, the control unit 18 shown in FIG. As described above, the gantry rotating unit 6 is controlled so that the monitoring scan is intermittently performed at the timing of the upper peak of the respiration sensor output. As a result, the image reconstruction unit 9 intermittently performs image reconstruction processing at the timing of the upper peak of the respiration sensor output.
[0040]
The average CT value calculation unit 16 calculates the average CT value in the ROI based on the reconstructed image formed intermittently. As described above, the timing of the upper peak of the respiration sensor output is a timing at which an average CT value that is not affected by body movement due to respiration is obtained. For this reason, by controlling the scan timing of the gantry rotating unit 6 in this way, the average CT value that is not affected by body movement due to breathing is supplied to the control unit 18. As described above, the control unit 18 shifts from the monitoring scan mode to the main scan mode based on the average CT value.
[0041]
(Effect of the third embodiment)
Thereby, it is possible to shift to the main scan at a stable timing without being affected by body movement due to respiration, and the same effect as the X-ray CT system of the first embodiment described above can be obtained. In addition, since the monitoring scan is intermittently performed, the exposure of the subject in the monitoring scan mode can be greatly reduced.
[0042]
It should be noted that the scan timing of the gantry rotating unit 6 is other than the timing of the upper peak of the respiratory sensor output, the timing of the down peak of the respiratory sensor output, the timing between the upper peak and the down peak of the respiratory sensor output, etc. The timing at which the average CT value is stabilized is the same as in the first embodiment.
[0043]
[Fourth Embodiment]
Next, an X-ray CT system according to a fourth embodiment of the present invention will be described. In the X-ray CT system of each of the above-described embodiments, the respiratory sensor output of the respiratory sensor 17 is used as the body motion detection output of the subject. Instead of the sensor 17, an electrocardiographic sensor that outputs electrocardiographic information corresponding to the movement of the subject's heart is provided. Based on the electrocardiographic information, the average CT value is read from the average CT value calculating unit 16. By doing so, it is possible to shift from the monitoring scan to the main scan at a more accurate timing. The fourth embodiment is different from the above-described embodiments only in this point. For this reason, in the following description, only the difference will be described and redundant description will be omitted.
[0044]
(Configuration and operation of the fourth embodiment)
That is, as described in the above embodiments, the method of taking the average CT value based on the respiration sensor output of the respiration sensor 17 is, for example, when setting and monitoring the ROI in the aorta above the diaphragm Although effective, when the ROI is set to the heart or the aorta near the heart, the portion where the ROI is set moves depending on the heartbeat, so there is a possibility that the average CT value in the ROI cannot be monitored accurately.
[0045]
For this reason, in the X-ray CT system of the fourth embodiment, an electrocardiographic sensor for detecting the motion of the subject's heart is provided instead of the respiratory sensor 17. Then, the control unit 18 calculates an average CT value by selecting an average CT value corresponding to, for example, a diastole (or systole) of the heart which is a predetermined phase timing based on the electrocardiogram information from the electrocardiogram sensor. Capture from the unit 16, control the transition timing from the monitoring scan to the main scan, control the reconstruction timing of the image reconstruction unit 9, or control the scan timing of the gantry rotation unit 6.
[0046]
As a result, even when the ROI is set to the heart or the aorta near the heart, it is possible to accurately detect a change in the CT value within the ROI without being affected by the movement of the heart. It can be made possible to migrate accurately.
[0047]
Finally, each of the above-described embodiments is only an example of the present invention, and the present invention is not limited to this. For this reason, as long as it is the range which does not deviate from the technical idea which concerns on this invention, even if it is except the above-mentioned embodiment, of course, various changes according to a design etc. are possible.
[0048]
【The invention's effect】
The X-ray CT apparatus according to the present invention can shift from the monitoring scan to the main scan at an accurate timing without being affected by body movements such as breathing and the heart in the contrast examination. In addition, by intermittently controlling the X-ray exposure during the monitoring scan according to body movement such as breathing, the exposure dose of the subject during the monitoring scan can be greatly reduced, and the X-ray CT can be reduced. The safety of the apparatus can be improved.
[Brief description of the drawings]
FIG. 1 is a block diagram of an X-ray CT system according to a first embodiment to which an X-ray CT apparatus according to the present invention is applied.
FIG. 2 is an X-ray CT system according to a second embodiment in which an X-ray CT system according to the present invention is applied; FIG. 10 is a diagram for explaining image reconstruction timing at the time of monitoring scan and scan timing at the time of monitoring scan of the X-ray CT system of the third embodiment to which the X-ray CT apparatus according to the present invention is applied.
FIG. 3 is a diagram for explaining imaging timing in a contrast examination of a conventional X-ray CT apparatus.
FIG. 4 is a diagram for explaining an average CT value whose value varies with respiration.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... X-ray CT apparatus, 2 ... Injector, 3 ... Monitor display part, 4 ... Bed, 5 ... Subject, 6 ... Mount rotation part, 7 ... Data collection part (DAS), 8 ... Pre-processing part, 9 ... Image Reconstruction unit, 10 ... operation unit, 11 ... X-ray tube, 12 ... X-ray detector, 13 ... region of interest (ROI) setting unit, 14 ... threshold setting unit, 15 ... adder, 16 ... average CT value Calculation part, 17 ... respiration sensor, 18 ... control part

Claims (3)

In an X-ray CT apparatus having image reconstruction means for collecting data of a subject into which a contrast agent has been injected by an X-ray imaging means and reconstructing an image based on the data,
CT value calculating means for calculating a CT value of a desired part based on an image obtained by monitoring scan;
Body motion detecting means for detecting substantially periodic body motion of the subject;
Based on the body motion detection output from the body motion detection means, a stable CT value is selected from the CT values calculated by the CT value calculation means, and the captured CT value and a predetermined threshold value are selected. And a control means for determining the end of the monitoring scan and the start of the main scan,
An X-ray CT apparatus comprising:   The X-ray CT apparatus according to claim 1, wherein the body motion detection unit is a respiration sensor that detects a respiratory state of the subject or an electrocardiographic sensor that detects a heart motion of the subject. The threshold value is, the X-ray CT apparatus of any one of claims 1 or 2, characterized in that an average value of the CT values of the set in the ROI to a desired site.

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