JP2000051208A - X-ray ct - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the reduction of an X-ray exposure and the suppression of picture deterioration compatible in an electrocardiographic synchronizing scanning. SOLUTION: This device is provided with a high voltage generator 19 applying a high voltage to an X-ray tube 21 in order to generate X-rays from the tube 21, a detector 23 detecting the X-rays coming from the tube 21 through a subject, a tomographic image reconstituting processor 33 reconstituting a tomographic image based on projection data detected by the detector 23, an electrocardiograph 16 measuring an electrocardiogram concerning the subject and a system controller 11 controlling a high voltage generator 19 to stop the generation of the X-rays in a specific period in the cardiac cycle of the subject and to generate the X-rays for a period except the specific period.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field 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 projection data of the subject in multiple directions.

[0002]

2. Description of the Related Art Many recent X-ray CT apparatuses have an ECG synchronization function. As shown in FIG. 13, in the electrocardiogram,
Characteristic waves such as P wave, Q wave, R wave, S wave, and T wave are captured. One heartbeat is divided into systole A, diastole B, and equal volume diastole CDE. The variation in the size of the heart is large in the systolic period A and the diastolic period B, and is small in the equivalent diastolic period CDE.

In the electrocardiogram synchronization function, for example, projection data is collected after a certain time from the R wave. In this data collection operation, the size of the heart is almost the same,
This is repeated to align projection data having different projection directions by, for example, 360 °. Based on the aligned projection data, a tomographic image free from artifacts due to a change in the size of the heart can be reconstructed.

[0004]

However, this ECG synchronization function requires a very long scan time. 750ms
It is considered that a tomographic image in systole A is obtained by an e / rotation device. Since the systole A is generally 200 msec, it takes four times as long as the heartbeat period to align the projection data of the systole A by 360 °. Since the cardiac cycle is typically one second, the scan time can be as long as four seconds.

[0005] Therefore, the subject must be exposed to X-rays for a long time of 4 seconds. Moreover, when the X-ray intensity is reduced to reduce the X-ray exposure of the subject,
The image quality will be degraded.

According to the present invention, an X-ray
An object of the present invention is to provide an X-ray CT apparatus capable of achieving both a reduction in radiation exposure and suppression of image quality deterioration.

[0007]

The present invention employs the following means in order to solve the above-mentioned problems. The invention of claim 1 is
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 detecting X-rays coming from the X-ray tube via a subject A detector,
Based on the projection data detected by the detector, a reconstruction processor that reconstructs a tomographic image, an electrocardiograph that measures an electrocardiogram regarding the subject, and based on the electrocardiogram,
Means for stopping irradiation of the subject with the X-rays during a specific period in the heartbeat cycle of the subject, and irradiating the subject with the X-rays during a period other than the specific period. I do.

According to the present invention, X-ray irradiation to the subject is stopped during a specific period in the heartbeat cycle, and X-rays are irradiated to the subject during periods other than the specific period in the heartbeat cycle. Therefore, the X-ray exposure dose is reduced by the amount corresponding to the specific period, as compared with the related art 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, deterioration in image quality can be suppressed.

The invention according to claim 10 is 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 the X-ray tube. A detector for detecting X-rays coming from the subject via the subject, a reconstruction processor for reconstructing a tomographic image based on the projection data detected by the detector, and an electrocardiogram for measuring an electrocardiogram related to the subject A high-voltage generator based on the electrocardiogram in order to reduce the intensity of the X-ray during a specific period in the heartbeat cycle of the subject and increase the intensity of the X-ray during a period other than the specific period. And a controller for controlling the device.

According to the present invention, the controller reduces the intensity of the X-ray during a specific period in the heartbeat cycle of the subject,
The high voltage generator is controlled based on the electrocardiogram in order to increase the intensity of X-rays during a period other than the specific period. That is,
Even if the X-ray irradiation on the subject is not stopped during the specific period, the exposure dose can be reduced only by lowering the intensity of the X-ray irradiated on the subject during the specific period.

[0011] The invention of claim 11 is 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 an X-ray tube. A detector for detecting an X-ray arriving via the sample, an open / close shutter disposed between the X-ray tube and the subject, and a tomographic image based on projection data detected by the detector. A reconstruction processor for reconstructing, an electrocardiograph for measuring an electrocardiogram related to the subject, shielding the X-rays for a specific period in a heart cycle of the subject, and applying the X-rays for a period other than the specific period. A controller for controlling the opening and closing of the shutter based on the electrocardiogram for passing.

According to the present invention, the controller shields the X-rays during a specific period in the heartbeat cycle of the subject and opens and closes the shutter based on the electrocardiogram in order to pass the X-rays during a period other than the specific period. Control. That is, X to the subject
The switching operation of the line irradiation / irradiation stop is realized by opening and closing the shutter, and the exposure dose can be reduced.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments of the X-ray CT apparatus according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows an X-ray CT according to the present invention.
FIG. 2 is a diagram illustrating a configuration of an apparatus. An X-ray tube 21 and a multi-channel X-ray detector 23 are mounted on the rotating gantry 25 in an arrangement facing each other across a subject on a bed table 15a serving as a bed. The rotating base 25 is
It rotates under the control of the gantry / bed controller 13. With the rotation of the rotating gantry 25, the X-ray tube 21 and the X-ray detector 23 rotate around the subject. High voltage generator 1
When a high voltage is applied to X-ray tube 21 from X-ray tube 2, X-ray tube 2
1 generates X-rays. X-rays generated from the X-ray tube 21 and transmitted through the subject are detected by the detector 23 and collected by the data collection unit 27 as projection data.

The bed table 15a of the bed is moved by the bed table driver 15. The gantry / bed controller 13 integrally controls the rotation of the rotary gantry 25 and the movement of the bed table. This comprehensive control allows the continuous movement of the bed table to be performed synchronously while the rotary gantry 25 is continuously rotating. This makes it possible to realize 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 orbit.

The electrocardiograph 16 detects a weak current caused by the excitation 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 an X-ray (electrocardiographic synchronization function).

FIG. 2 shows an example of an electrocardiogram. As is well known, a characteristic waveform such as a P wave, a Q wave, an R wave, an S wave, and a T wave appears in a heart cycle in an electrocardiogram. Almost constant time after the most characteristic R-wave, a systole occurs where the heart contracts. This systole is followed by a diastole, in which the heart expands. The contraction period and the relaxation period are periods in which the size of the heart fluctuates drastically. The period from immediately after the diastole to immediately before the contraction period of the next heart cycle,
This is a period in which the fluctuations in the size of the heart, called isotonic periods, are relatively mild.

The system controller 11 picks up, for example, an R wave from the electrocardiogram. Further, the system controller 11 obtains the interval of the R wave, that is, the cycle of the heartbeat. Further, the system controller 11 determines a delay time of the systole with respect to the R wave based on the cycle of the heartbeat,
The length of the total period (specific period) of the systole and the diastole is determined. The internal memory (ROM) of the system controller 11 correlates the delay time of the systole with respect to the R wave and the total length of the systole and the diastole for each of various heartbeat cycles. I have.

The system controller 11 supplies an X-ray control signal for controlling the generation of X-rays to the X-ray controller 17. For example, if the X-ray control signal is zero or LOW
At the time of the level, the X-ray tube 21
X-rays are not generated from the X-ray tube 21 because no high voltage is applied to the X-ray tube. On the other hand, when the X-ray control signal is at the 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 LO during the total period (specified period) of the specified systole and diastole.
The X-ray control signal is set to the W level, while the X-ray control signal is set to the HIGH level during a period other than the specific period (equivalent relaxation period). As a result, the X-ray stops during the specific period and is generated during the period other than the specific period, so that the projection data is not detected during the specific period, but the projection data is detected during the 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.

The system controller 11 controls the rotation speed of the rotating gantry 25 based on the length of a specific period during which no X-rays are generated. In this device, 180 °
A so-called half reconstruction process for reconstructing a tomographic image from the projection data for the + fan angle is employed. That is, 1
As long as you collect projection data for 80 ° + fan angle,
The tomographic image can be reconstructed.

Therefore, the system controller 11
Most preferably, from the viewpoint of reduction of radiation exposure, the rotating gantry 2 is rotated so that the rotating gantry 25 rotates at an angle of (180 ° + fan angle) or more during a period in which a line is generated (a period other than a specific period).
5 rotates the angle of (180 ° + fan angle), in other words, during a specific period during which no X-rays are generated, the rotating gantry 25 sets the angle equal to or less than 360 ° − (180 ° + fan angle). The rotation speed of the rotating gantry 25 is set so as to rotate.

The system controller 11 transmits the X-ray control signal to the data collection unit 27 and the data compensation processor 3.
1 is also supplied. The data collection unit 27 includes the X-ray detector 23
Output current is amplified and converted into digital data. The digital data is information called projection data that is reflected on the X-ray transmittance of the subject. Data collection unit 27
Collects only data detected by the X-ray detector 23 during a specific period during which X-rays are generated, according to the X-ray control signal,
Data detected by the X-ray detector 23 during the period when no X-ray is generated is not collected. The projection data collected by the data collection unit 27 is supplied to the data compensation processor 31 after undergoing preprocessing such as offset correction and reference correction in the preprocessing unit 29.

The data compensation processor 31 compensates for projection data for 360 ° − (180 ° + fan angle) that has not been collected from projection data for (180 ° + fan angle) that has actually been collected. Align projection data for °.
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.

The projection data generated by the data compensation processor 31 is temporarily stored in the data storage unit 33 together with the actually collected projection data. The tomographic image reconstruction processor 35 temporarily stores the data in the data storage unit 33.
A tomographic image of the subject is reconstructed based on the projection data for 60 °. The display unit 37 displays the tomographic image reconstruction processor 3
5 displays the tomographic image of the subject reconstructed on the monitor.

Next, the operation of the X-ray CT apparatus configured as described above will be described with reference to the drawings. First, the system controller 11 inputs an electrocardiogram of the subject as shown in FIG. 2 from the electrocardiograph 16 before actually collecting the projection data, picks up an R wave from the electrocardiogram, and picks up the picked-up R wave. , The delay time of the systole from the R-wave and the length of the total period (specific period) of the systole and the diastole are obtained.

Next, the projection data is actually collected by helical scan. At this time, the rotation speed of the rotating gantry 25 changes during the period in which X-rays are generated (period other than the specific period)
The rotation gantry 25 is adjusted to rotate by an angle of (180 ° + fan angle). Then, the system controller 11 picks up the R-wave from the electrocardiogram from the electrocardiograph 16 and generates an X-ray control signal from the R-wave at the time when a delay time obtained in advance elapses. From HIGH level, it goes down to zero or LOW level where X-rays are not generated. Thus, the generation of X-rays is stopped from the start point of the systole. For example, no X-rays are generated from the X-ray tube 21 during the AB period and the CD period in FIG.

The zero or LOW level of the X-ray control signal is maintained for a predetermined period determined in advance. This means that from the beginning of systole to at least the end of diastole,
X-ray generation is stopped. 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.
X-ray generation is stopped during the period A'-B. That is,
Projection data is collected during the period BB'-A, and AA '
No projection data is collected during period -B.

FIG. 4 shows the trajectory of the X-ray tube 21 as viewed from directly above the gantry. 4, the horizontal axis corresponds to the moving distance of the bed table 15a, 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
Move 10 mm during 0.5 seconds of rotation.

The projection data collected by the data collection unit 27 is transmitted to the data compensation processor 31 via the preprocessing unit 29.
Sent to The data compensation processor 31 recognizes the X-ray stop period based on the X-ray emission stop signal from the system controller 11, and compensates the projection data in this period based on the actually collected projection data.

In the period from point A to point B in FIG.
The dotted line indicates the compensated projection data. The three arrows in FIG. 5 indicate that the projection data during the X-ray stop period is created using the projection data during the period during which X-rays are generated. FIG. 6 shows projection data for one scan period (360 °).

Based on a total of 360 ° of actually acquired projection data and compensated projection data, one rotation per rotation
A tomographic image is reconstructed one by one. Further, as shown in FIG. 7, in a high time resolution operation in which a tomographic image is reconstructed one by one every 30 ° rotation, for example, projection data for continuous 180 ° + fan angle is not prepared (C1). , C2) can occur. In this case, the data is compensated as needed.

Next, a process of compensating the projection data will be described with reference to FIGS. 8 and 9, a point a is a base point of the X-ray tube 21 and an X-ray is a point A-.
During the period from point a to point b to point B,
During the period. 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. The position of the X-ray focal point when the X-ray tube 21 is at the point b is defined as Xb. The angle between the X-ray focal point Xb, the rotation center O, and the detection element k is defined as θ. X-ray focus Xb
It is assumed that the X-ray path connecting the detection element k and the detection element k is Xbk, and the CT value detected by the detection element k is 10, for example.

Here, the creation of data detected by the detection element k when the X-ray tube 21 is at the point b will be described. 9, when the X-ray focal point Xk of the X-ray tube 21 is located at the position of the detection element k in FIG. 8, the detection element corresponding to the X-ray focal point Xb is set to 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. By similarly assigning the CT values of the projection data having the same X-ray path to other data, the projection data in the X-ray stop period can be compensated.

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). For example, if the fan angle is 45 °, the angle is 135 °.

When this angle is converted into time, the time is given by (scan speed × 135 ° / 360 °).

Here, if the scanning speed is, for example, 0.5 sec / 360 °, the time corresponding to the angle is 188 m
sec. Since the heartbeat of a healthy person is about 70 beats per minute, the total period of the systole and diastole of the heart is about 20
It is 0 msec. Therefore, the time corresponding to the angle is
Approximately corresponds to the total systolic and diastolic period of the heart.

Therefore, the data (compensatable data) created by this reflection can be applied to the total period of the above-mentioned systole and diastole, and a seamless image reconstruction of 360 ° is possible.

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 is reconstructed based on the projection data from the data storage unit 33. Configuration processor 3
5 reconstructs a tomographic image of the subject.

When the first scan period SC1 ends, a second scan period SC2 starts, but there is no X-ray suspension period in the second scan period SC2. Assuming that the time of one scan period is 0.5 second, the time of one scan period is one second, so that an X-ray stop period exists for every odd number of scans. For this reason, as shown in FIGS. 3 and 4, X is set within the first scan period SC1.
There is a line stop period AB, and a third scan period SC3
X-ray suspension periods C to D exist within the period.

When the helical scan is performed in this manner, and the tomographic image reconstruction processor 35 reconstructs an image using the obtained helical scan data, three-dimensional volume data of the heart is obtained.

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 determines that the change in the shape of the heart within one heartbeat period is large. For example, in order to stop the generation of X-rays in the subject until the elapse of the total period of the systole and the diastole of the heart in synchronization with the R wave in the heart rate data, the generation of X-rays in the subject is performed. Can be minimized, and an ECG-gated scan can be performed.

In particular, in the X-ray CT apparatus according to the embodiment, since the helical scan is performed, the subject is subjected to the X-ray multiple times.
X-ray exposure is performed, but since there is an X-ray suspension period, the amount of X-ray exposure to the subject is reduced, and the effect is great. Also, X
Since the position of the line stop period changes, for example, no matter where the lesion is located, X-rays can be emitted to the lesion, so that a clear image of the lesion can be obtained. Yes, so that an appropriate diagnosis can be made.

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 is performed. Since the processor 35 reconstructs a tomographic image of the subject based on the created projection data during the change period and the projection data during the X-ray generation period, the processor 35 can reconstruct a seamless image of 360 °. The image in the change period in which the heart shape change is large also becomes a clear image.

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 the scan time is appropriately selected, a seamless image for 360 ° can be reconstructed.

The system controller 11 sets the time of the X-ray suspension period shorter than the time obtained by the following equation (1).

Scan time × {360 ° − (180 ° + fan angle)} / 360 ° (1) That is, the angle range data unnecessary for the half reconstruction process is divided by 360, and the obtained value is obtained. Is multiplied by the scan time in one scan period, and the time in the change period is set smaller than the obtained value, so that a seamless image of 360 ° can be reconstructed.

As described above, according to the present embodiment, the generation of X-rays is stopped during the specific period in the heartbeat cycle, and the X-ray is generated during periods other than the specific period in the heartbeat cycle. Therefore, the subject is not irradiated with the X-ray during the specific period, and the subject is irradiated with the X-ray only during a period other than the specific period in the heartbeat cycle. For this reason, the X-ray exposure dose is reduced by an amount corresponding to the specific period as compared with the related art 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, deterioration in image quality can be suppressed.

The present invention is not limited to the above embodiment. In the embodiment, the present invention is applied to a helical scan. However, for example, the present invention can be applied to a conventional scan.

The conventional scan is a scan in which the periphery of a target section is rotated once. To obtain images of a plurality of sections, for example, section A and section B,
First, data is collected while rotating around the section A once, and then the bed on which the subject is placed or the X-ray focal point and the detector are moved so that the section B and the rotation plane are aligned. Then, the cross section A
Data is collected while making one rotation around the subject in the same manner as in.

Although the data compensation processor 31 is provided outside the tomographic image reconstruction processor 35 in the embodiment, for example, the data compensation processor 31 may be provided inside the tomographic image reconstruction processor 35. In this case, in the tomographic image reconstruction processor 35, the data compensation processor 31 creates projection data at the time of X-ray OFF at the time of image reconstruction, and thereafter, the tomographic image reconstruction processor 35
The image reconstruction may be performed using the projection data when the line is OFF.

Further, in the embodiment, the single slice CT has been described. However, the present invention has a two-dimensional detector array in which detectors are arranged not in one row but in a plurality of rows also in the body axis direction of the subject. It may be applied to multi-slice CT. According to this multi-slice CT, projection data for a plurality of slices can be collected by one scanning operation using a two-dimensional detector array, and a plurality of tomographic images (volume data) can be obtained.

In the embodiment, the system controller 11 generates the X-ray control signal. However, for example, the X-ray controller 17 directly outputs the R-wave trigger from the electrocardiograph 16 without passing through the system controller 11. The X-ray control device 17 may input the X-ray generation control signal based on the R-wave trigger.

Further, in the embodiment, the scan speed is set to 0.5 second so that the X-ray stop period is set to be within the same angle range for each odd-numbered scan. , The angle range of the X-ray suspension period may be different for each scan. As a result, the scan can be performed in accordance with the heart rate speed of each patient, so that the burden on the patient can be reduced.

The X-ray CT apparatus of the type according to the embodiment is a third-generation (R / R type) CT apparatus.
The detector is arranged around the subject over an angle of 4 °, and only the X-ray beam source 21 rotates so-called fourth generation (R /
S method). Further, in addition to the detector, the X-ray beam source 21 may be a so-called fifth generation (S / S type) which is arranged around the subject over 360 °.

Further, in the above description, the generation of X-rays is stopped during the X-ray suspension period. However, as shown in FIG. However, even if the X-ray intensity is reduced more than in the other periods, the effect of reducing the exposure can be obtained.

(Second Embodiment) FIG. 11 shows a configuration diagram of an X-ray CT apparatus according to a second embodiment of the present invention. FIG.
In FIG. 7, 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 for shielding X-rays so that the shutter can be opened and closed at a high speed. When the high-speed shutter 22 is open, the subject is irradiated with X-rays.
Since the rays are shielded, no X-rays are emitted to the subject. The opening and closing operation of the high-speed shutter 22 is controlled by a shutter controller 24 under the control of the system controller 11.

FIG. 12 shows the opening and 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 contraction period and the relaxation period, and is opened during the other period.

Therefore, according to the present embodiment, the subject is not irradiated with X-rays during the specific period, but is irradiated with the X-ray only during periods other than the specific period in the heartbeat cycle. For this reason,
During the heartbeat cycle, the X-ray exposure is reduced by an amount corresponding to a specific period, as compared with the conventional method of continuously irradiating X-rays.
Moreover, since the X-ray intensity during periods other than the specific period can be made higher than before, deterioration in image quality can be suppressed.

[0059]

According to the present invention, X-ray irradiation to the subject is stopped during a specific period in the heartbeat cycle, and X-rays are irradiated to the subject during periods other than the specific period in the heartbeat cycle. . Therefore, the X-ray exposure dose is reduced by the amount corresponding to the specific period, as compared with the related art 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, deterioration in image quality can be suppressed.

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.

Further, the switching operation of X-ray irradiation / irradiation stop to 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;

FIG. 3 is a view showing X controlled by a gantry / bed controller shown in FIG. 1;
It is a perspective view which shows the helical movement locus of a wire tube.

FIG. 4 is a view showing X under the control of the gantry / bed controller of FIG. 1;
It is the figure which looked at the helical movement locus of a wire tube from right above.

FIG. 5 is an explanatory diagram of a half reconstruction process by the tomographic image reconstruction processor of FIG. 1;

FIG. 6 is a conceptual diagram of a data compensation process by the data compensation processor of FIG. 1;

FIG. 7 is a diagram showing a sequence of a tomographic image reconstruction process by the tomographic image reconstruction processor of FIG. 1;

FIG. 8 is a diagram showing a 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 a geometry of an X-ray tube or the like during an X-ray generation period in the first embodiment.

FIG. 10 is a diagram showing another X-ray generation operation under the control of the system controller of FIG. 1;

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. 11;

FIG. 13 is a diagram showing a general electrocardiographic waveform.

[Explanation of symbols]

10 X-ray CT apparatus, 11 System controller, 1
3 ... gantry / 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 stand, 27 ... Data collection unit, 29 ... Pre-processing unit, 3
1 Data Compensation Processor 33 Data Storage 35
... Tomographic image reconstruction processor, 37 ... Display unit.

Claims (18)

[Claims] 1. 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 an X-ray tube coming from the X-ray tube via a subject A detector that detects X-rays, a reconstruction processor that reconstructs a tomographic image based on the projection data detected by the detector, an electrocardiograph that measures an electrocardiogram related to the subject, and based on the electrocardiogram. Means for stopping irradiation of the subject with the X-rays during a specific period in the heartbeat cycle of the subject, and irradiating the subject with the X-rays during a period other than the specific period. An X-ray CT apparatus characterized by the above-mentioned. 2. 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 an X-ray tube coming from the X-ray tube via a subject. A detector that detects an X-ray, a reconstruction processor that reconstructs a tomographic image based on the projection data detected by the detector, an electrocardiograph that measures an electrocardiogram related to the subject, A controller for controlling the high-voltage generator based on the electrocardiogram to stop generating the X-rays during a specific period in a heartbeat cycle and generate the X-rays during a period other than the specific period. An X-ray CT apparatus characterized by the above-mentioned. 3. The X-ray CT apparatus according to claim 2, wherein the specific period includes a systole and a diastole in which a change in the shape of the heart is relatively large. 4. The projection data corresponding to the specific period,
The X-ray CT apparatus according to claim 2, further comprising a compensation processor that compensates based on projection data detected during a period other than the specific period. 5. The compensation processor according to claim 4, wherein the compensation processor assigns opposite data of the detected projection data to projection data corresponding to the specific period.
An X-ray CT apparatus according to claim 1. 6. The X-ray CT according to claim 4, wherein the reconstruction processor reconstructs the tomographic image based on the compensated projection data and the detected projection data. apparatus. 7. The tomographic image based on projection data detected in a period other than the specific period and equal to or greater than a total angle of 180 ° and a fan angle indicating a spread angle of the X-rays. 3. The X-ray CT apparatus according to claim 2, wherein: 8. The controller divides a 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 be less than the obtained time. 9. The X-ray CT apparatus according to claim 2, wherein the projection data is detected at a plurality of positions on a spiral trajectory of the X-ray tube with respect to the subject. 10. 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 an X-ray tube coming from the X-ray tube via a subject. A detector that detects an X-ray, a reconstruction processor that reconstructs a tomographic image based on the projection data detected by the detector, an electrocardiograph that measures an electrocardiogram related to the subject, A controller that controls the high-voltage generator based on the electrocardiogram to reduce the intensity of the X-ray during a specific period in a heartbeat cycle and increase the intensity of the X-ray during a period other than the specific period. An X-ray CT apparatus comprising: 11. 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 an X-ray tube coming from the X-ray tube via a subject. A detector for detecting X-rays, an openable / closable shutter disposed between the X-ray tube and the subject, and a reconstruction for reconstructing a tomographic image based on the projection data detected by the detector. A processor, an electrocardiograph for measuring an electrocardiogram relating to the subject, and for shielding the X-rays during a specific period in a cardiac cycle of the subject, and passing the X-rays during a period other than the specific period, A controller for controlling opening and closing of the shutter based on the electrocardiogram.
T device. 12. The X-ray CT apparatus according to claim 11, wherein the specific period includes a systole and a diastole in which a change in the shape of the heart is relatively large. 13. 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 during a period other than the specific period. . 14. The X-ray CT apparatus according to claim 13, wherein the compensation processor assigns facing data of the detected projection data to projection data corresponding to the specific period. 15. The X-ray CT according to claim 13, wherein the reconstruction processor reconstructs the tomographic image based on the compensated projection data and the detected projection data. apparatus. 16. The tomographic image based on projection data that is equal to or greater than a total angle of 180 ° and a fan angle indicating the spread angle of the X-rays detected during a period other than the specific period. 13. The X-ray CT apparatus according to claim 11, wherein is reconstructed. 17. The controller divides a 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. 17. The X-ray CT apparatus according to claim 16, wherein the specific period is adjusted to be less than the obtained time. 18. The X-ray CT apparatus according to claim 11, wherein the projection data is detected at a plurality of positions on a spiral trajectory of the X-ray tube with respect to the subject.