JP4025677B2 - X-ray CT system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an X-ray CT apparatus including an electrocardiogram information acquisition unit that acquires electrocardiogram information.
[0002]
[Prior art]
Conventionally, heart region imaging using an X-ray CT apparatus has a slower scanning speed than the pulsation of the heart of the human body, so that a pseudo image called a motion artifact caused by the motion of the heart in the reconstructed tomographic image The image was not suitable for clinical diagnosis. In order to solve this problem, it is conceivable to increase the scanning speed as much as possible, and an ultra-first CT apparatus is known as an implementation of this. This is also called an electron beam CT apparatus, has a scan speed of about 100 ms, and enables clear tomography as if the heart is stopped. However, this ultra first CT apparatus is expensive and large. On the other hand, an ECG gate imaging method has been devised in addition to a method that enables imaging of the heart region by increasing the scan speed (see, for example, Patent Document 1 and Patent Document 2). This is because the projection data is continuously collected over several heartbeats on the same slice plane, and the time and the heartbeat phase width are set with reference to the R wave of the electrocardiogram information recorded at the same time. Only projection data of the same cardiac time phase is collected from the data, and a tomographic image is reconstructed by the ECG reconstruction means.
[0003]
Next, this ECG gate imaging method will be described.
An X-ray source and a detector are placed opposite to each other with the subject sandwiched between the scanner, and the heart region of the subject is irradiated with X-rays while limiting the X-ray irradiation region from the X-ray source with a collimator. X-rays that have passed through are detected by a detector, and an electrocardiograph is attached to the subject, and projection data of the heart region in the vicinity of the R wave is obtained while capturing electrocardiographic information from the electrocardiograph. FIG. 5 shows an electrocardiographic waveform 1 in which the positions of the Q wave, the R wave, and the S wave are shown. The heart is most expanded in the vicinity of the R wave, and the movement of the heart is the slowest. Therefore, while capturing this electrocardiogram information with an electrocardiograph, the heart region near the R wave is photographed to collect projection data. FIG. 6 is a schematic diagram schematically showing the projection data collected in this way. In the figure, the horizontal axis represents the detector channel direction, and the vertical axis represents the projection angle. Although the electrocardiogram information 3 is recorded together with the projection data 2 of the heart region, the actual projection data is not a waveform as shown in FIG. These are shown in correspondence with each other.
[0004]
After imaging of the heart region, the ECG reconstruction means processes the projection data as follows to obtain a reconstructed image.
Here, it is described as spiral imaging using a four-row multi-slice X-ray CT apparatus, and as shown in FIG. 7, four detector trajectories 15 to 18 are shown, and the scan cycle is 1.0 second interval. Further, as can be seen from the electrocardiogram information 3 shown together, the heartbeat period is 0.8 seconds. As shown in the figure, the heartbeat started from the 0.0 second position and the scan are synchronized at the 4.0 second position. As projection data necessary for reconstruction, it is necessary to collect data having different projection angles and the same cardiac phase. In the figure, in the projection data starting from the 0.0 second position to the 4.0 second position (excluding 4.0 seconds), the R wave has occurred 5 times, so it is 5 times in 4.0 seconds. There will be projection data with different phases. This is shown in the collection areas 4-8. Since the projection data for 360 degrees is collected in five times, one collection area becomes projection data for 72 degrees. In terms of time, the scan cycle is 1.0 second, so the temporal width of one collection area is 200 ms (1 s / 5 times). These projection data are data having the same cardiac phase and different projection angles, and the slice positions are also different because of the helical scan. The projection data groups in the collection areas 4 to 8 are shown in the range of one scan cycle as shown in FIG.
[0005]
The collection areas 6a to 10a in FIG. 8 are obtained by translating the collection areas 5 to 8 in FIG. 7 and the collection areas 9 and 10 with the heartbeat and the scan period 200 ms after the R wave after the synchronization described above. . The collection area 9 is projection data having the same projection angle and cardiac time phase as the collection area 4 and a slice position of 4 cycles, that is, 4 s ahead. The relationship between the collection region 5 and the collection region 10 is the same as the relationship between the collection region 4 and the collection region 9. FIG. 9A shows only the left main part of FIG. A discontinuous region 11 is generated in the body axis direction between the collection region 4 and the collection region 9a by a helical scan. In the discontinuous area 11, data is calculated using simple linear interpolation or the like, and is set as the interpolation area 12 as shown in FIG. The discontinuous region 13 between the collection region 5 and the collection region 10a is also set as the interpolation region 14. Thereafter, as shown in FIG. 9B, desired slice positions SLA and SLB are designated, and a reconstructed image at the designated position is obtained.
[0006]
[Patent Document 1]
JP-A-9-75336 [Patent Document 2]
JP 2002-330961 A
[Problems to be solved by the invention]
However, in the conventional X-ray CT apparatus adopting the ECG gate imaging method, a tomographic image in the ventricular diastole or the like can be captured, so that an abnormal movement of the ventricular wall and an abnormal coronary artery can be observed. Since the image reconstruction processing is performed by combining the projection data by the ECG reconstruction means after the image is taken, it is impossible to observe the heart image while photographing the heart region.
[0008]
An object of the present invention is to provide an X-ray CT apparatus capable of observing a heart image while photographing a heart region .
[0009]
[Means for Solving the Problems]
To achieve the above object, the present invention provides slice position setting means for setting a plurality of consecutive slice positions of a subject, electrocardiogram information obtaining means for obtaining electrocardiogram information of the subject, and electrocardiogram information. Collection means for collecting projection data obtained by the detector with the same heartbeat phase from electrocardiogram information obtained by the obtaining means, and X-rays irradiated to each slice position set by the slice position setting means A detector for detecting projection X-rays to obtain projection data, reconstruction means for reconstructing a tomographic image at the slice position of the subject using the projection data obtained by the detector, and in X-ray CT apparatus having means for displaying a tomographic image reconstructed, and, with reference to the phase of the cardiac phase and the scan period of the electrocardiogram information acquired by the electrocardiographic information acquiring means A delay time setting means for setting the delay time of the projection data; and after the delay time set by the delay time setting means has elapsed, the collecting means for the discontinuous region in the opposite axial direction of the same projection angle corresponding to the slice position. Interpolating means for interpolating collected projection data to obtain projection data of the discontinuous area, and the reconstruction means use the discontinuous area projection data obtained by the interpolating means to slice position of the subject The tomographic images are sequentially reconstructed, and the display means displays the sequentially reconstructed tomographic projection images .
[0011]
According to a second aspect of the present invention, in the same-centric phase projection data used for the reconstruction means, there is a function of sequentially switching from the projection data that has been reconstructed to the projection data to be reconstructed next. A buffering means is further provided .
[0012]
In such an X-ray CT apparatus according to the present invention, the buffering means sequentially replaces the projection data of the acquisition region, thereby holding projection data for obtaining tomographic increase at various slice positions with a simple configuration. Can do.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a flowchart showing the operation of an X-ray CT apparatus according to an embodiment of the present invention.
First, in step S1, a patient as a subject is placed and fixed on a bed of an X-ray CT apparatus, and then an electrocardiogram information obtaining unit such as an electrocardiograph obtains the subject's electrocardiogram information to obtain an average heart rate. obtain. In step S2 before and after this, the slice position of the heart region to be reconstructed before the acquisition of projection data is determined, and the scan speed of the X-ray CT apparatus is set. In subsequent step S3, various procedures relating to the cardiac imaging function are performed. That is, the ECG delay time is calculated from the average heart rate obtained in step S1, the scan speed set in step S2, and the like. For example, an ECG delay time in which both phases overlap is calculated from the heart rate phase of the average heart rate and the phase of the scan cycle of the X-ray CT apparatus, and a predetermined delay whose details will be described later by the setting means based on the ECG delay time. Set the time.
[0014]
In the next step S4, CT imaging of the heart region is performed. Although detailed illustration is omitted at this time, projection data of the same heartbeat phase (cardiac time phase) is sequentially collected by the collecting means from the electrocardiographic information by the electrocardiographic information acquiring means, and the above-described predetermined delay time elapses. After interpolating the discontinuous area in the opposite axis direction of the same projection angle corresponding to the first slice position that has already been set by interpolation means, from the projection data collected as corresponding to the first slice position specified after the delay time has elapsed The tomographic image is reconstructed by the delay time linked reconstruction means. In the next step S5, the reconstructed tomographic image is displayed on the display means. Depending on the number of slice positions, step S4 and step S5 are repeated to display tomographic images at the respective slice positions on the display means.
[0015]
As can be seen from this flowchart, the X-ray CT apparatus includes an electrocardiogram information acquisition unit that acquires electrocardiogram information of a subject, a detector that obtains projection data by detecting X-rays irradiated on the subject from an X-ray source, A delay time setting means for setting a delay time determined from an ECG delay time in which the heartbeat phase of the electrocardiogram information and the phase of the scan cycle overlap, a determination means for determining a slice position to be reconstructed before collecting projection data, Collecting means for sequentially collecting projection data of the same cardiac phase from electrocardiographic information by the information acquisition means, and interpolating discontinuous regions in the body axis direction of the same projection angle corresponding to the slice position after the delay time has passed, to obtain projection data Interpolating means that obtains projection data at a designated slice position after the delay time has elapsed from the collecting means, and reconstructs a tomographic image. And a reconstruction unit.
[0016]
An electrocardiograph is attached to the subject, and the heart region near the R wave is photographed while capturing electrocardiogram information from the electrocardiogram information collecting means composed of the electrocardiograph and the like, and the projection data is as shown in FIG. To collect. At this time, the heart is most expanded in the vicinity of the R wave, and the movement of the heart is the slowest. Therefore, when reconstruction is performed using the projection data of the same part, it is clear that the heart is stationary. Can be obtained. At this time, the projection data is obtained by irradiating the heart region of the subject with the X-ray source and the detector facing each other with the scanner interposed therebetween, and limiting the X-ray irradiation region from the X-ray source with the collimator. The X-ray that has passed through the heart region of the subject is detected by a detector.
[0017]
Next, various calculations and settings related to the cardiac imaging function described in step S3 of FIG. 1 will be described.
First, the determination means for determining the slice position to be reconstructed before projection data collection as shown in step S2 will be described. For example, as shown in FIG. 2, the first slice position 20a and the last slice position 20n are set in the body axis direction, the number of sheets and the interval between them are designated, and the other slice positions 20b to 20m are wavy. Determine as shown in.
[0018]
Next, the determination of the ECG delay time and delay time setting means for setting a predetermined delay time determined from the ECG delay time will be described.
As already described with reference to FIG. 7, the scan cycle is 1.0 second, and as can be seen from the electrocardiogram information 3, the heartbeat cycle is 0.8 second. As shown in the figure, the heartbeat and the scan started from the 0.0 second position are synchronized with the heartbeat period and the scan period overlapping at the 4.0 second position. The ECG delay is 4.2 seconds obtained by adding the time width of one acquisition area (to be described later), that is, the segment width of 200 ms, to the time required for the heartbeat phase of the electrocardiogram information 3 and the phase of the scan cycle to overlap each other. It's time. Based on the ECG delay time of 4.2 seconds, a predetermined delay time, here, 4.2 seconds is determined as a desired predetermined time, and this delay time is set as shown in FIG. 2 by a delay time setting means (not shown). When calculating the predetermined delay time as described above, a heartbeat period is obtained from the electrocardiogram information 3. The heartbeat period can be calculated based on an R wave or the like stored in the projection data, or the heart of the subject. It can also be obtained by an electrocardiogram information acquisition means before taking a region image.
[0019]
After setting the predetermined delay time, the heart region CT imaging in step S4 is performed, and the collecting means for sequentially collecting projection data of the same cardiac phase at that time will be described.
As projection data necessary for reconstruction, it is necessary to collect data having different projection angles and the same cardiac phase. As shown in FIG. 2 and FIG. 7, in the projection data starting from the 0.0 second position and extending to the 4.0 second position (excluding 4.0 seconds), the R wave has occurred five times, and thus 4.0. There are projection data having different time phases for five times per second. This is shown in FIG. 2 for collection areas 4-9. Since the projection data for 360 degrees is collected in five times, one collection area becomes projection data for 72 degrees. In terms of time, the scan cycle is 1.0 second, so the temporal width of one collection area is 200 ms (1 s / 5 times). These projection data are data having the same cardiac phase and different projection angles, and the slice positions are also different because of the helical scan. The acquisition areas 9 and 10 show projection data 200 ms after the R wave after the heartbeat and the scan period are synchronized, the projection angle and the cardiac time phase are the same, and the slice position is 4 cycles, that is, 4 s ahead of the projection data. It has become.
[0020]
FIG. 3 is an explanatory diagram showing the data collection operation by the collection means described above over time.
As shown in FIG. 3A, data in the collection areas 4 to 6 are collected 1.8 seconds after the start of scanning, but at this time, projection data required for reconstruction is insufficient. Further, as shown in FIG. 3B, after 2.6 seconds, data in the collection areas 4 to 7 is collected, but even at this time, the projection data necessary for reconstruction is insufficient. Further, as shown in FIG. 3C, data in the collection areas 4 to 7 are collected after 3.4 seconds, but no projection data exists in the projection data area for the first 72 degrees.
[0021]
However, the situation changes after 4.2 seconds. Actually, even if the collection area 9 data after 4.2 seconds is collected, the first 72 degrees data does not overlap with the slice position because of the spiral scan, and the gap area 11 is generated. However, since this can calculate data from the collection area 4 and the collection area 9 using simple linear interpolation or the like and obtain projection data as an interpolation area by interpolation, at this time, a predetermined delay time elapses by the interpolation means. Later, projection data is obtained by interpolating a discontinuous region in the opposite axial direction of the same projection angle corresponding to the slice position 20a. In this way, a reconstructed image at a desired slice position 20a can be obtained after 4.2 seconds have elapsed.
[0022]
After a predetermined delay time has elapsed, the delay time interlocking reconstruction means acquires projection data at the designated slice position 20 from the collection means, reconstructs a tomographic image, and displays it on the display means.
[0023]
According to such an X-ray CT apparatus, the predetermined delay time calculated from the ECG delay time is set by the delay time setting means, and the projection data at the designated slice position is acquired from the acquisition means after the predetermined delay time has elapsed. Since the tomographic image is reconstructed by the delay time interlocking reconstruction means, after the entire heart region is imaged once as in the prior art, the image reconstruction processing is not performed by combining the projection data. The tomographic image at the slice position 20a can be reconstructed after a predetermined delay time has elapsed, and the heart image can be observed while photographing the heart region. Moreover, based on the R wave of the electrocardiogram obtained by the electrocardiogram information collecting means, projection data having the same cardiac time phase and different projection angles are collected by the collecting means, and this is obtained by using the delay time interlocking reconstruction means to obtain a slice at the slice position 20a Since the captured image is reconstructed, it is possible to provide a clear cardiac tomographic image as if the heart is stationary after the delay time elapses while capturing the heart region.
[0024]
Subsequent to the reconstruction of the slice position 20a described above, the reconstruction of the next slice position 20b is similarly performed. When obtaining a tomographic image of the slice position 20c, after the collection means collects the projection data of each of the collection areas 4 to 9 in FIG. 3, when the projection data of the next collection area 10 is collected, that is, this time the collection area When a predetermined delay time elapses from 5, a gap region 13 is generated between the collection region 5 and the collection region 10 as in the case of the collection region 5 and the collection region 9. However, since the interpolating unit is configured to interpolate the discontinuous region in the opposite axial direction having the same projection angle corresponding to the slice position after the delay time has elapsed, a predetermined delay time is obtained from the collection region 5. After a lapse of time, data is calculated from the collection area 5 and the collection area 10 using linear interpolation or the like to obtain projection data of the gap area 13. The delay time interlocking reconstruction means is configured to reconstruct a tomographic image by acquiring projection data at a designated slice position from the collection means after the delay time has elapsed, so that a predetermined delay from the collection area 5 is obtained. When the time elapses, the slice position 20c is reconstructed.
[0025]
In this way, by repeating the same processing as in the case of the first slice position 20a described above, the heart is stopped at each slice position 20b to 20n after the delay time elapses while each of the next slice positions 20b to 20n is imaged. A clear heart tomographic image can be obtained. This process is repeated until a tomographic image at the last slice position 20n is obtained and sequentially displayed on the display means in real time, so that this clear image can be observed while photographing.
[0026]
At this time, the X-ray CT apparatus described above has a collecting means for sequentially collecting projection data of the same cardiac phase using the electrocardiogram information by the electrocardiogram information obtaining means in order to obtain a reconstructed image at the next slice position. Although provided, it is preferable to add buffering means for buffering projection data having the same cardiac phase and erasing projection data whose reconstruction has been completed after a predetermined delay time. That is, as shown in FIGS. 3A to 3D, each acquisition corresponding to at least a predetermined delay time until the tomographic image at the first slice position 20a is reconstructed by the delay time interlocking reconstruction means. Buffering means for holding projection data of the areas 4 to 8 is provided. When the buffering means completes the reconstruction of the tomographic image at the slice position 20a as shown in FIG. 4 (A), the buffering means reconstructs the tomographic image at the next slice position 20b as shown in FIG. 4 (B). Projection data that is not necessary for this, that is, projection data in the collection area 4 is erased. This is sequentially performed as the slice position is changed.
[0027]
In this way, the buffering means sequentially replaces the projection data of the collection area, so that the projection data for obtaining the tomographic increase at various slice positions can be held with a simple configuration. Needless to say, this buffering means is provided on the memory of the arithmetic unit.
[0028]
In the above-described embodiment, the spiral imaging using the 4-row multi-slice X-ray CT apparatus has been described. However, the present invention is not limited to this, and imaging in a state where the bed is stopped or a single-slice X-ray CT apparatus. It can also be applied to. In the embodiment described above, the ECG delay time of 4.2 seconds is set as the predetermined delay time by the delay time setting means, but the predetermined delay is set as close as possible to the ECG delay time based on the ECG delay time. The time can be set by the delay time setting means. In any case, it has a determination means for determining a slice position to be reconstructed before collecting projection data, and after the delay time has elapsed, the projection data is obtained by interpolating the discontinuous region in the opposite axial direction of the same projection angle corresponding to the slice position. An interpolating unit that obtains projection data at a designated slice position after the delay time elapses, and a delay time interlocking reconstructing unit that reconstructs a tomographic image after the delay time elapses. A tomographic image can be reconstructed from an early stage.
[0029]
As described above, the X-ray CT apparatus according to the present invention can perform reconstruction after a certain predetermined delay time while imaging the heart region, and it is clear that the heart is stationary. A tomographic image of the heart region can be observed while photographing the heart region.
[Brief description of the drawings]
FIG. 1 is a flowchart showing an operation of an X-ray CT apparatus according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram of projection data obtained by the X-ray CT apparatus shown in FIG.
FIG. 3 is an explanatory diagram of reconstruction means in the X-ray CT apparatus shown in FIG.
4 is an explanatory diagram of buffering means in the X-ray CT apparatus shown in FIG. 1. FIG.
FIG. 5 is an electrocardiogram waveform diagram.
FIG. 6 is a schematic diagram of projection data.
FIG. 7 is an explanatory diagram showing projection data together with electrocardiogram information.
FIG. 8 is an explanatory diagram showing an initial state of a reconstruction method in a conventional X-ray CT apparatus.
FIG. 9 is an explanatory diagram showing another state of the reconstruction method in the conventional X-ray CT apparatus.
[Explanation of symbols]
4 to 10 Collection region 11, 13 Gap region 12, 14 Interpolation region 20a to 20n Slice position

Claims (2)

Electrocardiogram information acquisition means for acquiring electrocardiogram information of the subject, and detection for obtaining projection data by detecting X-rays irradiated to the subject from an X-ray source under a set scan cycle different from the heartbeat cycle And an ECG reconstruction unit that reconstructs a tomographic image of a subject using projection data from the detector, the heartbeat phase of the electrocardiographic information and the phase of the scan period overlap. A delay time setting means for setting a delay time determined from the ECG delay time, a determination means for determining a slice position to be reconstructed, and the same cardiac time phase from the electrocardiogram information by the electrocardiogram information acquisition means after the start of scanning. Including a collection unit that sequentially collects projection data and an ECG reconstruction unit that dynamically performs reconstruction. The ECG reconstruction unit includes:
Before the delay time elapses, the first reconstructed image is obtained by performing reconstruction using the projection data of the same cardiac time phase of the electrocardiogram information collected multiple times before the delay time,
After the delay time has elapsed, every time the projection data of the same cardiac time phase of the electrocardiogram information is collected, the projection data of the same time phase collected several times before the collection and the collected projection data are used. And reconstructed one after another to obtain the reconstructed image dynamically,
An X-ray CT apparatus characterized by that.   2. The apparatus according to claim 1, wherein the collecting means has buffering means for buffering projection data of the same cardiac time phase and erasing projection data that has been reconstructed after the delay time. X-ray CT system.

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