JP4503727B2 - X-ray CT system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an X-ray CT apparatus for reconstructing an image relating to a cross section inside a subject, that is, a tomographic image, based on multidirectional projection data relating to the subject.
[0002]
[Prior art]
Many X-ray CT apparatuses in recent years have an electrocardiographic synchronization function. As shown in FIG. 13, characteristic waves such as P wave, Q wave, R wave, S wave, and T wave are captured in the electrocardiogram. One heartbeat is divided into a systole A, a relaxation period B, and an equivalent relaxation period CDE. The variation in the size of the heart is large in the systole A and the relaxation period B, and is small in the equivalent relaxation period CDE.
[0003]
In the electrocardiogram synchronization function, for example, projection data is collected after a certain time from the R wave. This data collection operation is repeated in order to align projection data of, for example, 360 ° in which the size of the heart is substantially the same and the projection directions are different. Based on this aligned projection data, a tomographic image free from artifacts due to heart size fluctuations can be reconstructed.
[0004]
[Problems to be solved by the invention]
However, this ECG synchronization function requires a very long scan time. Consider obtaining a tomographic image of systole A with an apparatus of 750 mse / rotation. Since the systolic period A is generally 200 msec, it takes four times the heartbeat period to align the projection data of the systolic period A by 360 °. Since the cardiac cycle is typically 1 second, the scan time is as long as 4 seconds.
[0005]
For this reason, the subject must continue to be exposed to X-rays for a long time of 4 seconds. In addition, when the X-ray intensity is reduced in order to reduce the X-ray exposure amount of the subject, the image quality is deteriorated.
[0006]
An object of the present invention is to provide an X-ray CT apparatus capable of achieving both reduction of an X-ray exposure amount and suppression of image quality deterioration in an electrocardiogram synchronous scan.
[0007]
[Means for Solving the Problems]
The present invention employs the following means in order to solve the above problems. The invention of claim 1 is directed to an X-ray tube, a high-voltage generator for applying a high voltage to the X-ray tube to generate X-rays from the X-ray tube, and a subject from the X-ray tube A detector for detecting an incoming X-ray, a reconstruction processor for reconstructing a tomographic image based on projection data detected by the detector, an electrocardiograph for measuring an electrocardiogram relating to the subject, and the electrocardiogram The X-ray irradiation to the subject is stopped during a specific period within the heartbeat cycle of the subject, and the X-ray is irradiated to the subject during a period other than the specific period; and A controller that controls the X-ray tube and the detector to rotate more than a total angle of 180 ° and the fan angle indicating the X-ray spread angle from the end of the specific period to the beginning of the next specific period When The reconfiguration processor comprises: Reconstruct projection data continuously acquired from the end of the specified period to the beginning of the next specified period Do It is characterized by that.
[0008]
According to a second aspect of the present invention, there is provided an X-ray tube, a high voltage generator for applying a high voltage to the X-ray tube to generate X-rays from the X-ray tube, and a subject from the X-ray tube. A detector for detecting X-rays coming through, a reconstruction processor for reconstructing a tomographic image based on projection data detected by the detector, an electrocardiograph for measuring an electrocardiogram relating to the subject, Controlling the high-voltage generator based on the electrocardiogram to stop the generation of the X-rays in a specific period within the heartbeat cycle of the subject and generate the X-rays in a period other than the specific period; The X-ray tube and the detector are controlled to rotate more than a total angle of 180 ° and the fan angle indicating the X-ray spread angle from the end of the specific period to the beginning of the next specific period. With the controller The reconfiguration processor comprises: Reconstruct projection data continuously acquired from the end of the specified period to the beginning of the next specified period Do It is characterized by that.
[0009]
According to a tenth aspect of the present invention, there is provided an X-ray tube, a high voltage generator for applying a high voltage to the X-ray tube to generate X-rays from the X-ray tube, and a subject from the X-ray tube. A detector for detecting X-rays coming through, a reconstruction processor for reconstructing a tomographic image based on projection data detected by the detector, an electrocardiograph for measuring an electrocardiogram relating to the subject, In order to increase the intensity of the X-ray in a period other than the specific period than the specific period in the heartbeat cycle of the subject, the high-voltage generator is controlled based on the electrocardiogram, and the X-ray tube and the A controller for controlling the detector to rotate more than a total angle of 180 ° and the fan angle indicating the X-ray spread angle from the end of the specific period to the beginning of the next specific period; The reconfiguration processor comprises: Reconstruct projection data continuously acquired from the end of the specified period to the beginning of the next specified period Do It is characterized by that.
[0011]
The invention of claim 11 is directed to an X-ray tube, a high-voltage generator for applying a high voltage to the X-ray tube to generate X-rays from the X-ray tube, and a subject from the X-ray tube A tomographic image is reconstructed based on a detector that detects incoming X-rays, an open / close shutter disposed between the X-ray tube and the subject, and projection data detected by the detector. A reconstruction processor, an electrocardiograph for measuring an electrocardiogram associated with the subject, and shielding the X-rays during a specific period within the heartbeat cycle of the subject and passing the X-rays during a period other than the specific period In addition, the opening and closing of the shutter is controlled based on the electrocardiogram, and the X-ray tube and the detector have an X-ray spread angle of 180 ° from the end of the specific period to the beginning of the next specific period. It is controlled to rotate more than the total angle with the indicated fan angle. And a controller for The reconfiguration processor comprises: Reconstruct projection data continuously acquired from the end of the specified period to the beginning of the next specified period Do It is characterized by that.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the X-ray CT apparatus of the present invention will be described in detail by a preferred embodiment with reference to the drawings.
[0014]
(First embodiment)
FIG. 1 is a diagram showing a configuration of an X-ray CT apparatus according to the present invention. An X-ray tube 21 and a multi-channel X-ray detector 23 are mounted on the rotary base 25 in an arrangement that faces each other with the subject on the bed table 15a of the bed. The rotating gantry 25 rotates under the control of the gantry / bed controller 13. As the rotary mount 25 rotates, the X-ray tube 21 and the X-ray detector 23 rotate around the subject. When a high voltage is applied from the high voltage generator 19 to the X-ray tube 21, X-rays are generated from the X-ray tube 21. X-rays generated from the X-ray tube 21 and transmitted through the subject are detected by the detector 23 and collected as projection data by the data collection unit 27.
[0015]
The bed table 15 a of the bed is moved by the bed table driver 15. The gantry / bed controller 13 comprehensively controls the rotation of the rotary gantry 25 and the movement of the bed table. This overall control can synchronize the continuous movement of the bed table during the continuous rotation of the rotary mount 25. As a result, a so-called helical scan in which the X-ray tube 21 moves in a spiral (see FIG. 3) relative to the subject and collects projection data at a plurality of positions on the spiral trajectory can be realized.
[0016]
The electrocardiograph 16 detects a weak current generated by the excitement of the subject's heart, and outputs a time change of the detected current as an electrocardiogram. Based on the waveform of the electrocardiogram, the system controller 11 controls a scan operation including generation of X-rays (electrocardiogram synchronization function).
[0017]
FIG. 2 shows an example of an electrocardiogram. As is well known, characteristic waveforms such as P wave, Q wave, R wave, S wave, and T wave appear in the heartbeat cycle in the electrocardiogram. A systole in which the heart contracts comes after a certain period of time from the most characteristic R wave. This systole is followed by a relaxation period in which the heart expands. These contraction period and relaxation period are periods in which the size of the heart fluctuates drastically. The period from immediately after the relaxation period to just before the contraction period of the next heartbeat cycle is a period in which the variation in the size of the heart, which is called an equivalent relaxation period, is relatively gentle.
[0018]
The system controller 11 picks up, for example, an R wave from the electrocardiogram. Further, the system controller 11 obtains an R wave interval, that is, a heartbeat cycle. Further, the system controller 11 obtains the delay time of the systole relative to the R wave and the length of the total period (specific period) of the systole and the relaxation period based on the cycle of the heartbeat. The internal memory (ROM) of the system controller 11 associates the delay time of the systole with respect to the R wave and the total length of the systole and the relaxation period for each of various heartbeat periods. Yes.
[0019]
The system controller 11 supplies an X-ray control signal for controlling the generation of X-rays to the X-ray control device 17. For example, when the X-ray control signal is zero or at a LOW level, no high voltage is applied from the high voltage generator 19 to the X-ray tube 21, so no X-rays are generated from the X-ray tube 21. On the other hand, when the X-ray control signal is at a HIGH level, a high voltage is applied from the high voltage generator 19 to the X-ray tube 21, so that X-rays are generated from the X-ray tube 21. The system controller 11 sets the X-ray control signal to zero or LOW level during the total period (specific period) of the specified systole and relaxation period, while it is at a period other than the specific period (equal relaxation period). Sets the X-ray control signal to HIGH level. As a result, X-rays stop during a specific period and occur during a period other than the specific period, so that projection data is not detected during the specific period, but projection data is detected during a period other than the specific period. . FIG. 3 shows a spiral trajectory of the X-ray tube 21. The period AB and the period CD are specific periods during which no X-rays are generated.
[0020]
The system controller 11 controls the rotational speed of the rotating gantry 25 based on the length of a specific period during which no X-rays are generated. In this apparatus, so-called half reconstruction processing for reconstructing a tomographic image from projection data for 180 ° + fan angle is employed for image reconstruction. That is, a tomographic image can be reconstructed only by collecting projection data for 180 ° + fan angle.
[0021]
Therefore, the system controller 11 is most preferable from the viewpoint of reducing exposure so that the rotation frame 25 rotates at an angle of (180 ° + fan angle) or more during a period in which X-rays are generated (period other than the specific period). In such a way that the rotary mount 25 rotates at an angle of (180 ° + fan angle), in other words, during a specific period when no X-rays are generated, the rotary mount 25 is 360 ° − (180 ° + fan angle) or less. The rotation speed of the rotary gantry 25 is set so that the angle is rotated.
[0022]
The system controller 11 also supplies the X-ray control signal to the data collection unit 27 and the data compensation processor 31. The data collection unit 27 amplifies and converts the output current of the X-ray detector 23 into digital data. The digital data is information called projection data reflected on the X-ray transmittance of the subject. The data collection unit 27 collects only the data detected by the X-ray detector 23 during a specific period in which X-rays are generated according to the X-ray control signal, and the X-ray detector in a period in which no X-rays are generated. Data detected in 23 is not collected. The projection data collected by the data collection unit 27 is subjected to preprocessing such as offset correction and reference correction by the preprocessing unit 29 and then supplied to the data compensation processor 31.
[0023]
The data compensation processor 31 compensates for 360 ° − (180 ° + fan angle) projection data not collected from the actually collected projection data for (180 ° + fan angle) to obtain 360 ° worth of projection data. Align projection data. This compensation process is common in half reconstruction processing, and assigns projection data (opposite data) collected when the X-ray tube 21 is on the opposite side to projection data to be compensated.
[0024]
The projection data created by the data compensation processor 31 is temporarily stored in the data storage unit 33 together with the projection data actually collected. The tomographic image reconstruction processor 35 reconstructs a tomographic image of the subject based on the 360 ° projection data temporarily stored in the data storage unit 33. The display unit 37 displays the tomographic image of the subject reconstructed by the tomographic image reconstruction processor 35 on the monitor.
[0025]
Next, the operation of the X-ray CT apparatus configured as described above will be described with reference to the drawings. First, before actually collecting projection data, the system controller 11 inputs an electrocardiogram of the subject as shown in FIG. 2 from the electrocardiograph 16, picks up an R wave from this electrocardiogram, and picks up the picked up R wave. Based on this period, the delay time of the systole from the R wave and the length of the total period (specific period) of the systole and the relaxation period are obtained.
[0026]
Next, projection data is actually collected by helical scanning. At this time, the rotation speed of the rotating gantry 25 is adjusted so that the rotating gantry 25 rotates an angle of (180 ° + fan angle) during a period in which X-rays are generated (a period other than the specific period). The system controller 11 picks up an R wave from the electrocardiogram from the electrocardiograph 16 and generates an X-ray control signal when the delay time obtained in advance has elapsed from the R wave. The HIGH level is lowered to zero or LOW level where no X-rays are generated. Thereby, the generation of X-rays is stopped from the start point of the systole. For example, X-rays are not generated from the X-ray tube 21 during the period AB and the period CD in FIG.
[0027]
The zero or LOW level of the X-ray control signal is maintained for the length of a specific period obtained in advance. This stops the generation of X-rays from the start point of the systole to at least the end point of the diastole. Then, the level of the X-ray control signal is restored to HIGH, and the generation of X-rays is restarted. X-rays are generated during the period BB'-A in FIG. 5, and the generation of X-rays is stopped during the period A-A'-B. That is, projection data is collected during the period BB′-A, and no projection data is collected during the period A-A′-B.
[0028]
FIG. 4 shows the trajectory of the X-ray tube 21 viewed from directly above the gantry. In FIG. 4, the horizontal axis corresponds to the moving distance of the bed table 15 a, and the vertical axis corresponds to the rotation angle of the X-ray tube 21. Here, the X-ray tube 21 makes one rotation in 0.5 seconds, and the bed table 15a moves 10 mm in 0.5 seconds in which the X-ray tube 21 makes one rotation.
[0029]
The projection data collected by the data collection unit 27 is sent to the data compensation processor 31 via the preprocessing unit 29. The data compensation processor 31 recognizes the X-ray stop period based on the X-ray exposure stop signal from the system controller 11, and compensates the projection data in this period based on the actually collected projection data.
[0030]
In the period from point A to point B in FIG. 4, the projection data compensated by a dotted line is shown. Also, the three arrows in FIG. 5 indicate that the projection data for the X-ray stop period is created using the projection data for the period during which X-rays are generated. FIG. 6 shows projection data for one scan period (360 °).
[0031]
One tomographic image is reconstructed for each rotation based on the actually collected projection data for 360 ° and the compensated projection data. Further, as shown in FIG. 7, for example, in a high time resolution operation in which a tomographic image is reconstructed one by one every rotation of 30 °, projection data for continuous 180 ° + fan angle is not available (C1). , C2) can occur. In this case, data is compensated as necessary.
[0032]
Next, the projection data compensation process will be described with reference to FIGS. 8 and 9, the point a is the base point of the X-ray tube 21, and the X-ray is stopped during the period from point A-point a-point b-point B, and is generated during the period B-A. is doing. The view angle when the X-ray tube 21 is at the point b is α, and the fan angle indicating the spread angle of the X-ray beam is 2γ. Let Xb be the position of the X-ray focal point when the X-ray tube 21 is at point b. An angle formed by the X-ray focal point Xb, the rotation center O, and the detection element k is defined as θ. The X-ray path connecting the X-ray focal point Xb and the detection element k is Xbk, and the CT value detected by the detection element k is, for example, 10.
[0033]
Here, creation of data detected by the detection element k when the X-ray tube 21 is at the point b will be described. In FIG. 9, when the X-ray focal point Xk of the X-ray tube 21 is at the position of the detecting element k in FIG. 8, the detecting element corresponding to the X-ray focal point Xb is b. At this time, the X-ray path connecting the X-ray focal point Xk and the detection element b is Xkb, which matches the path Xbk of the projection data to be compensated. In this way, the CT value of the projection data whose X-ray path matches or is closest is assigned to the CT value of the projection data to be compensated. Similarly, by assigning CT values of projection data having the same X-ray path to other data, the projection data in the X-ray stop period can be compensated.
[0034]
There is a limit to the data that can be compensated. The angle corresponding to the data that can be compensated is
360 °-(180 ° + fan angle)
It is. For example, if the fan angle is 45 °, the angle is 135 °.
[0035]
Converting this angle into time, the time is
Scanning speed x 135 ° / 360 °
It becomes.
[0036]
Here, if the scanning speed is 0.5 sec / 360 °, for example, the time corresponding to the angle is 188 msec. Since the heartbeat of a healthy person is about 70 times per minute, the total period of the systolic and relaxing periods of the heart is about 200 msec. For this reason, the time corresponding to the angle substantially corresponds to the total period of the systole and the relaxation period of the heart.
[0037]
Therefore, the data created by this reflection (data that can be compensated) can be applied to the total period of the systole and the relaxation period, and seamless image reconstruction for 360 ° is possible.
[0038]
Then, the projection data compensated by the data compensation processor 31 and the projection data from the preprocessing unit 29 are temporarily stored in the data storage unit 33, and the tomographic image reconstruction processor 35 is based on the projection data from the data storage unit 33. Reconstructs a tomographic image of the subject.
[0039]
When the first scan period SC1 ends, the second scan period SC2 starts. However, there is no X-ray stop period in the second scan period SC2. If the time for one scan period is 0.5 seconds, the time for one scan period is 1 second, so that there is an X-ray stop period for every odd number of scans. For this reason, as shown in FIGS. 3 and 4, X-ray stop periods A to B exist in the first scan period SC1, and X-ray stop periods C to D exist in the third scan period SC3. It will be.
[0040]
In this way, when a helical scan is performed and the tomographic image reconstruction processor 35 reconstructs an image based on the obtained helical scan data, three-dimensional volume data of the heart is obtained.
[0041]
As described above, according to the X-ray CT apparatus of the embodiment, based on the electrocardiogram measured by the electrocardiograph 16, the system controller 11 has a change period in which the heart shape change is large within one heartbeat period, for example, Since the generation of X-rays to the subject is stopped until the total period of the sum of the systole and the relaxation phase of the heart is synchronized with the R wave in the heartbeat data, the generation of X-rays to the subject is minimized. In addition, the ECG synchronization scan can be performed.
[0042]
In particular, in the X-ray CT apparatus of the embodiment, since the helical scan is performed, X-ray exposure to the subject is performed a plurality of times, but since there is an X-ray stop period, the X-ray exposure dose to the subject is reduced. The effect is great. In addition, since the position of the X-ray stop period changes, for example, X-rays can be exposed to the lesion regardless of the position of the lesion, so a clear image of the lesion can be obtained. And thus an appropriate diagnosis can be made.
[0043]
When the data compensation processor 31 creates projection data in the change period in which X-ray generation is stopped based on the projection data in the X-ray generation period excluding the change period in one scan period, the tomographic image reconstruction processor 35 Since the tomographic image of the subject is reconstructed based on the created projection data in the change period and projection data in the X-ray generation period, a 360 ° seamless image can be reconstructed, An image in a change period with a large shape change is also a clear image.
[0044]
Further, the system controller 11 sets the scan time in one scan period based on the time in the change period and the angle range data unnecessary for the half reconstruction process. That is, if an appropriate scan time is selected, a 360 ° seamless image can be reconstructed.
[0045]
Further, the system controller 11 sets the time of the X-ray stop period to be shorter than the time obtained by the following equation (1).
[0046]
Scan time × {360 ° − (180 ° + fan angle)} / 360 °
(1)
That is, the angle range data unnecessary for the half reconstruction process is divided by 360, the obtained value is multiplied by the scan time in one scan period, and the time in the change period is set smaller than the obtained value. Reconstructs seamless images in minutes.
[0047]
As described above, according to the present embodiment, X-ray generation is stopped during a specific period within the heartbeat cycle, and X-rays are generated during a period other than the specific period within the heartbeat cycle. Therefore, the subject is not irradiated with X-rays during a specific period, and the subject is irradiated with X-rays only during a period other than the specific period within the heartbeat cycle. For this reason, the X-ray exposure dose is reduced by an amount corresponding to a specific period, compared to the conventional case in which the subject is continuously irradiated with X-rays during the heartbeat cycle. Moreover, since the X-ray intensity during periods other than the specific period can be made higher than before, image quality deterioration can be suppressed.
[0048]
The present invention is not limited to the embodiments described above. In the embodiment, the present invention is applied to a helical scan. However, for example, the present invention can also be applied to a conventional scan.
[0049]
This conventional scan is a scan that makes one rotation around the target cross section. When it is desired to obtain images of a plurality of cross sections, for example, cross section A and cross section B, data is first collected while rotating around the cross section A, and then a bed on which the subject is placed, or an X-ray focus and detector Is moved so that the section B and the rotation surface are aligned. After that, data is collected while rotating around the subject as in the cross section A.
[0050]
In the embodiment, the data compensation processor 31 is provided outside the tomogram reconstruction processor 35, but the data compensation processor 31 may be provided inside the tomogram reconstruction processor 35, for example. In this case, in the tomogram reconstruction processor 35, the data compensation processor 31 creates projection data when the X-ray is OFF when the image is reconstructed, and then the projection data when the tomogram reconstruction processor 35 is X-ray OFF. The image reconstruction may be performed using.
[0051]
Furthermore, in the embodiments, single slice CT has been described. However, the present invention is not limited to a single row, and the multi-slice CT has a two-dimensional detector array in which a plurality of rows are arranged in the body axis direction of the subject. You may apply to. According to this multi-slice CT, using a two-dimensional detector array, projection data for a plurality of slices can be collected in one scan operation, and a plurality of tomographic images (volume data) can be obtained.
[0052]
In the embodiment, the system controller 11 generates the X-ray control signal. For example, the R-wave trigger from the electrocardiograph 16 is directly input by the X-ray controller 17 without using the system controller 11. The X-ray control device 17 may generate an X-ray generation control signal based on the R wave trigger.
[0053]
In the embodiment, the scan speed is set to 0.5 seconds so that the X-ray stop period is within the same angle range for every odd scan. For example, the scan speed is arbitrarily set. Thus, the angle range of the X-ray stop period may be different for each scan. Thereby, since it can be set as the scan according to the heart rate speed of each patient, a patient's burden can be eased.
[0054]
The X-ray CT apparatus of the type of the embodiment is a third generation (R / R method) CT apparatus. However, the rotary mount 25 is not limited to this type, and the detector extends over 360 °. It may be a so-called fourth generation (R / S method) arranged around the subject and rotating only the X-ray beam generation source 21. Further, in addition to the detector, the X-ray beam generation source 21 may also be a so-called fifth generation (S / S method) arranged around the subject over 360 °.
[0055]
Further, in the above description, the generation of X-rays is stopped during the X-ray stop period. However, as shown in FIG. 10, the generation of X-rays is continuously generated without stopping, and only during a specific period. Even if the X-ray intensity is reduced more than the period, the exposure reduction effect is produced.
[0056]
(Second embodiment)
FIG. 11 shows a configuration diagram of an X-ray CT apparatus according to the second embodiment of the present invention. In FIG. 11, the same parts as those in FIG. In this embodiment, a high-speed shutter 22 is provided between the X-ray tube 21 and the subject. The high-speed shutter 22 is geometrically combined with a plurality of lead plates that shield X-rays so that they can be opened and closed at high speed. When the high-speed shutter 22 is open, X-rays are irradiated to the subject, but when the high-speed shutter 22 is closed, X-rays are shielded, so that the X-rays are not irradiated to the subject. The opening / closing operation of the high-speed shutter 22 is controlled by the shutter controller 24 under the system controller 11.
[0057]
FIG. 12 shows the opening / closing operation of the high-speed shutter under the control of the shutter controller of FIG. As shown in FIG. 12, in this embodiment, X-rays are continuously generated. On the other hand, the high-speed shutter 22 is closed during the total period (specific period) of the systole and the relaxation period, and is opened during the other periods.
[0058]
Therefore, according to the present embodiment, the subject is not irradiated with X-rays during a specific period, and the subject is irradiated with X-rays only during a period other than the specific period within the heartbeat cycle. For this reason, the X-ray exposure dose is reduced by an amount corresponding to the specific period, compared to the conventional case of continuously irradiating X-rays during the heartbeat cycle. In addition, since the X-ray intensity during periods other than the specific period can be made higher than before, image quality deterioration can be suppressed.
[0059]
【The invention's effect】
According to the present invention, X-ray irradiation to a subject is stopped during a specific period within the heartbeat cycle, and X-rays are irradiated to the subject during a period other than the specific period within the heartbeat cycle. Therefore, the amount of X-ray exposure is reduced by an amount corresponding to a specific period, compared to the conventional case in which the subject is continuously irradiated with X-rays during the heartbeat cycle. In addition, since the X-ray intensity during periods other than the specific period can be made higher than before, image quality deterioration can be suppressed.
[0060]
Further, even if the X-ray irradiation to the subject is not stopped during the specific period, the exposure dose can be reduced only by reducing the intensity of the X-ray irradiated to the subject during the specific period.
[0061]
The X-ray irradiation / irradiation stop operation for the subject is realized by opening and closing the shutter, and the exposure dose can be reduced.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an X-ray CT apparatus according to a first embodiment of the present invention.
FIG. 2 is a diagram showing an X-ray generation operation under the control of the system controller of FIG. 1;
3 is a perspective view showing a helical movement locus of the X-ray tube under the control of the gantry / bed controller of FIG. 1; FIG.
4 is a view of a helical movement locus of an X-ray tube as viewed from directly above, which is controlled by the gantry / bed controller of FIG. 1. FIG.
FIG. 5 is an explanatory diagram of a half reconstruction process performed by the tomographic image reconstruction processor of FIG. 1;
6 is a conceptual diagram of data compensation processing by the data compensation processor of FIG. 1;
7 is a diagram showing a sequence of tomogram reconstruction processing by the tomogram reconstruction processor of FIG. 1; FIG.
FIG. 8 is a diagram showing the geometry of an X-ray tube or the like during an X-ray rest period in the first embodiment.
FIG. 9 is a diagram showing the geometry of an X-ray tube or the like during an X-ray generation period in the first embodiment.
10 is a diagram showing another X-ray generation operation under the control of the system controller in FIG. 1. FIG.
FIG. 11 is a configuration diagram of an X-ray CT apparatus according to a second embodiment of the present invention.
12 is a diagram showing an opening / closing operation of a high-speed shutter under the control of the system controller of FIG.
FIG. 13 is a diagram showing a general electrocardiogram waveform.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... X-ray CT apparatus, 11 ... System controller, 13 ... Base / bed controller, 15 ... Bed table driver, 16 ... Electrocardiograph, 17 ... X-ray controller, 19 ... High voltage generator, 21 ... X-ray tube , 23 ... X-ray detector, 25 ... Rotating frame, 27 ... Data collection unit, 29 ... Pre-processing unit, 31 ... Data compensation processor, 33 ... Data storage unit, 35 ... Tomographic image reconstruction processor, 37 ... Display unit.

Claims (18)

An X-ray tube;
A high voltage generator for applying a high voltage to the X-ray tube to generate X-rays from the X-ray tube;
A detector for detecting X-rays coming from the X-ray tube through the subject;
A reconstruction processor for reconstructing a tomographic image based on projection data detected by the detector;
An electrocardiograph for measuring an electrocardiogram associated with the subject;
Means for stopping irradiation of the X-ray to the subject during a specific period in the heartbeat cycle of the subject and irradiating the X-ray to the subject during a period other than the specific period based on the electrocardiogram; ,
The X-ray tube and the detector are controlled to rotate more than a total angle of 180 ° and the fan angle indicating the X-ray spread angle from the end of the specific period to the beginning of the next specific period. With a controller ,
It said reconstruction processor is, X-rays CT apparatus characterized by reconstructing the continuously acquired projection data to the beginning of the next specified period from the end of the specified period. An X-ray tube;
A high voltage generator for applying a high voltage to the X-ray tube to generate X-rays from the X-ray tube;
A detector for detecting X-rays coming from the X-ray tube through the subject;
A reconstruction processor for reconstructing a tomographic image based on projection data detected by the detector;
An electrocardiograph for measuring an electrocardiogram associated with the subject;
Controlling the high-voltage generator based on the electrocardiogram to stop the generation of the X-rays in a specific period within the heartbeat cycle of the subject and generate the X-rays in a period other than the specific period; The X-ray tube and the detector are controlled to rotate more than a total angle of 180 ° and the fan angle indicating the X-ray spread angle from the end of the specific period to the beginning of the next specific period. With a controller ,
It said reconstruction processor is, X-rays CT apparatus characterized by reconstructing the continuously acquired projection data to the beginning of the next specified period from the end of the specified period.   The X-ray CT apparatus according to claim 2, wherein the specific period includes a systole and a relaxation period in which a heart shape change is relatively large.   The X-ray CT apparatus according to claim 2, further comprising a compensation processor that compensates projection data corresponding to the specific period based on projection data detected in a period other than the specific period.   The X-ray CT apparatus according to claim 4, wherein the compensation processor assigns opposite data of the detected projection data to projection data corresponding to the specific period.   The X-ray CT apparatus according to claim 4, wherein the reconstruction processor reconstructs the tomographic image based on the compensated projection data and the detected projection data.   The reconstruction processor reconstructs the tomographic image based on projection data that is detected during a period other than the specific period and is equal to or greater than a total angle of 180 ° and a fan angle indicating the X-ray spread angle. The X-ray CT apparatus according to claim 2.   The controller divides the value obtained by subtracting the total angle from 360 by 360, and multiplies the obtained value by one scan time required for one rotation of the X-ray tube. The X-ray CT apparatus according to claim 7, wherein the specific period is adjusted to less than 8.   The X-ray CT apparatus according to claim 2, wherein the projection data is detected at a plurality of positions on a spiral orbit of the X-ray tube with respect to the subject. An X-ray tube;
A high voltage generator for applying a high voltage to the X-ray tube to generate X-rays from the X-ray tube;
A detector for detecting X-rays coming from the X-ray tube through the subject;
A reconstruction processor for reconstructing a tomographic image based on projection data detected by the detector;
An electrocardiograph for measuring an electrocardiogram associated with the subject;
In order to increase the intensity of the X-ray in a period other than the specific period than the specific period in the heartbeat cycle of the subject, the high-voltage generator is controlled based on the electrocardiogram, and the X-ray tube and the And a controller for controlling the detector to rotate more than a total angle of 180 ° and a fan angle indicating a spread angle of the X-ray from the end of the specific period to the beginning of the next specific period ,
It said reconstruction processor is, X-rays CT apparatus characterized by reconstructing the continuously acquired projection data to the beginning of the next specified period from the end of the specified period. An X-ray tube;
A high voltage generator for applying a high voltage to the X-ray tube to generate X-rays from the X-ray tube;
A detector for detecting X-rays coming from the X-ray tube through the subject;
An openable / closable shutter disposed between the X-ray tube and the subject;
A reconstruction processor for reconstructing a tomographic image based on projection data detected by the detector;
An electrocardiograph for measuring an electrocardiogram associated with the subject;
Controlling the opening and closing of the shutter based on the electrocardiogram so as to shield the X-ray during a specific period in the heartbeat cycle of the subject and pass the X-ray during a period other than the specific period; tube and the detector, from the end of the specified period to the beginning of the next specified period, and a controller for controlling to rotate over the total angle of a fan angle showing a spread angle of 180 ° with said X-ray Prepared,
It said reconstruction processor is, X-rays CT apparatus characterized by reconstructing the continuously acquired projection data to the beginning of the next specified period from the end of the specified period.   The X-ray CT apparatus according to claim 11, wherein the specific period includes a systole and a relaxation period in which a heart shape change is relatively large.   The X-ray CT apparatus according to claim 11, further comprising a compensation processor that compensates projection data corresponding to the specific period based on projection data detected in a period other than the specific period.   The X-ray CT apparatus according to claim 13, wherein the compensation processor assigns opposite data of the detected projection data to projection data corresponding to the specific period. The reconstruction processor includes the compensated projection data;
The X-ray CT apparatus according to claim 13, wherein the tomographic image is reconstructed based on the detected projection data.   The reconstruction processor reconstructs the tomographic image based on projection data that is detected during a period other than the specific period and is equal to or greater than a total angle of 180 ° and a fan angle indicating the X-ray spread angle. The X-ray CT apparatus according to claim 11.   The controller divides the value obtained by subtracting the total angle from 360 by 360, and multiplies the obtained value by one scan time required for one rotation of the X-ray tube. The X-ray CT apparatus according to claim 16, wherein the specific period is adjusted to be less than the X-ray CT apparatus.   The X-ray CT apparatus according to claim 11, wherein the projection data is detected at a plurality of positions on a spiral orbit of the X-ray tube with respect to the subject.

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