JPH10155785A - X--ray ct device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent troubles from generating even when a trigger signal misses by a method wherein data collection missing angle information due to a missing of a trigger signal is obtained by monitoring the trigger signal, and an image re-constituting operation is performed by correcting the data for the missing angle. SOLUTION: When a rotary frame 12 rotates, an angle detecting signal which is generated in order from an angle detector 17, is transmitted to a trigger signal generating circuit 18, and a trigger signal generates, and this signal is transmitted to a data collecting device 15 and is used as a trigger signal for the data collection. When a missing is detected by a monitoring circuit 21 (when no inputting of a next trigger signal after a specified interval is detected), a missing detection signal is input to a correcting circuit 19 from the monitoring circuit 21, and the correcting circuit 19, e.g. outputs the data before that again, and inputs the data in an image re-constitution operating device 20. By doing so, all the data after the missing of the trigger signal are avoided from being operated while being shifted.

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 used for medical diagnosis or industrial inspection.

[0002]

2. Description of the Related Art An X-ray CT apparatus measures an X-ray attenuation distribution in a substance from a plurality of angles in a rotation direction, and processes the collected data to generate an X-ray absorption coefficient distribution image at a specific cross section in the substance. It is to be reconfigured. Usually, an X-ray tube and an X-ray detector are mounted on a rotating frame, and the X-ray is rotated by rotating the rotating frame.
The line irradiation direction is rotated, and by detecting the rotation of the rotating frame, an angle detection signal is output at each fixed angle of the rotation. Since angle detection signals are sequentially generated with the rotation of the rotating frame, a trigger signal is generated from this signal, and data for each angle is collected from the output of the X-ray detector in accordance with the trigger signal.

[0003]

However, in the conventional X-ray CT apparatus, when a trigger signal is lost for some reason, data is not collected at the irradiation angle, and data is collected at that angle. There is a problem that required data is missing.

That is, it is often the case that a malfunction or the like occurs at the time of detecting an angle or at the time of a trigger signal, in which case the trigger signal is lost.
If the trigger signal is lost, no data is collected in response to the trigger signal, so that data at the irradiation angle is lost.

Conventionally, even if there is such a missing data collection, the process proceeds as it is. Therefore, the data of the next angle is used as the missing irradiation angle data, and the subsequent data is used. Are all shifted by one. Then, inconveniences such as generation of artifacts in the reconstructed image are brought about. Further, in an X-ray CT apparatus of a spiral scan which continuously obtains images of a large number of slices by continuously rotating in a spiral shape, the angle of subsequent data shifts each time data is lost, so that the image rotates in the slice plane. I will.

In view of the above, it is an object of the present invention to provide an X-ray CT apparatus improved so that no inconvenience occurs even when a trigger signal based on an X-ray irradiation angle detection signal is lost.

[0007]

In order to achieve the above object, an X-ray CT apparatus according to the present invention comprises an X-ray generating means, an X-ray detecting means, a means for rotating an X-ray irradiation direction, and Angle detecting means for detecting an irradiation angle, means for generating a trigger signal based on the angle detecting signal, and data collecting means for collecting an output of the X-ray detecting means in accordance with the trigger signal and collecting data at each angle Means for monitoring the trigger signal and obtaining information on data collection missing angle due to the missing trigger signal; data correcting means for correcting data of the missing angle based on the detected data collection missing angle information; and Image reconstruction means for performing an image reconstruction operation using the subsequent data.

When the X-ray irradiation direction is rotated,
The irradiation angles are sequentially detected, and a trigger signal is generated according to the sequentially generated angle detection signal. By taking in the output of the X-ray detection means in response to this trigger signal,
Data at each illumination angle is collected. If a trigger signal is lost for some reason, such as a malfunction of the angle detection means or the trigger signal generation means, data collection at the irradiation angle is not performed, and data to be collected at that angle is lost. Therefore, by monitoring the trigger signal, information on the data collection missing angle is obtained. At the angle indicated by the data collection missing angle information, no data has been collected. For example, data at the missing angle is obtained by interpolation from normal data at an angle near the missing angle, or 180 ° Missing data is corrected by, for example, using the data of the direction angle as the missing angle data. Since the image reconstruction calculation is performed using the data corrected in this way, inconveniences such as artifacts due to missing data can be solved.

[0009]

Next, embodiments of the present invention will be described in detail with reference to the drawings. In FIG. 1, a gantry 11 holds a rotatable frame 12 rotatably.
A line detector 14 and a data collection device 15 are mounted. The X-ray detector 14 is a multi-channel detector in which many detector elements are arranged in an arc shape, and is arranged to face the X-ray tube 13. Each channel of the X-ray detector 14 is connected to a data acquisition device 15.

The rotary frame 12 is driven to rotate as indicated by an arrow by a rotary drive mechanism 16 including a motor and a belt pulley mechanism. Then, the rotation angle of the rotating frame 12 is detected by the angle detector 17. The angle detector 17 can be configured to detect a marker provided on the rotating frame 12, for example. Irregularities and slits may be provided on the outer peripheral portion of the rotating frame 12 as angle markers (for example, provided at every 1 °), and these may be detected by an optical detector. Alternatively, it may be configured to detect the rotation of the motor of the rotation drive mechanism 16.

Therefore, when the rotating frame 12 is rotated, an angle detection signal is sequentially generated from the angle detector 17 at every 1 °, for example. The angle detection signal is sent to the trigger signal generation circuit 18 and shaped into a waveform, so that a trigger signal corresponding to the timing of the angle detection signal for each 1 ° is generated as shown in FIG. This trigger signal is sent to the data collection device 15 and used as a trigger signal for the data collection.

That is, when the rotary frame 12 is rotated while irradiating X-rays from the X-ray tube 13 and the trigger signal is sequentially generated at every 1 ° of the rotation as described above, if the trigger signal is generated at every 1 ° of the rotation, Data collection by the X-ray detector 14 in multiple channels is performed by the data collection device 15. Therefore, for example, data collection for each angle, such as 1 °, 2 °, 3 °,... From the reference angle, is sequentially performed.

By the way, the trigger signal which should be generated every 1 ° may be lost for some reason. This occurs, for example, when the detection operation of the optical detector causes an error due to dust or dust.
At this time, for example, as shown in FIG. 2, no trigger signal to be generated at 5 ° is generated, and data collection at 5 ° is not performed. The next trigger signal is generated when the rotating frame 12 is at the 6 ° position, and the data collected at this time is output after the data collected when the rotating frame 12 is at the 4 ° position.

In the image reconstruction arithmetic unit 20, arithmetic processing is performed assuming that data is sequentially input at every 1 °. When 360 data are input, all data are collected and one image is obtained. Are reconstructed. That is, the data input after the 4 ° data is treated as 5 ° data even though it is actually 6 ° data. Therefore, if the trigger signal at 5 ° is lost as described above, the angles of all the data after 6 ° are treated as data at an angle shifted by 1 °, and the image reconstruction calculation is performed. As a result, artifacts occur in the reconstructed image. Alternatively, when performing a spiral scan by continuously moving the bed table on which the subject is placed at right angles to the paper while rotating the rotating frame 12 continuously, if the data collection of 5 ° is always missing, one rotation is required. , The tomographic image of each slice obtained for each rotation is rotated by 1 ° for each slice.

For this purpose, here, a trigger signal monitoring circuit 21 and a data correction circuit 19 are provided.
The monitoring circuit 21 monitors the interval between trigger signals. Since the rotation speed of the rotating frame 12 is almost constant, FIG.
As shown by, the interval of the trigger signal generated at every 1 ° should be a constant time T under normal circumstances. If the trigger signal is lost due to an error, this interval does not become T (almost 2T if one is lost, and approximately 3T if two are missing). By detecting that this interval is not near T, information on the lack of the trigger signal and the angle at which the trigger signal is missing can be obtained.

If a loss detection signal is generated immediately when a loss is detected in the monitoring circuit 21 (when it is detected that the next trigger signal is not input at the interval T), the timing at which the loss detection signal is generated It can be seen that the data acquisition was not performed because there was no trigger signal of the angle in the above. Therefore, when the missing detection signal is input from the monitoring circuit 21 to the correction circuit 19, the correction circuit 19 immediately outputs, for example, the previous data (4 ° data) again. Then, the data of 4 ° is input to the image reconstruction calculation device 20 twice consecutively, so that the inconvenience of calculating all the data after 6 ° as being shifted by 1 ° can be avoided.

Thus, even if the trigger signal is lost,
You can immediately correct the missing data,
The image reconstruction calculation device 20 can perform the image calculation processing in real time without any hindrance, can obtain an image without artifacts in real time, or in the spiral scan, an image sequentially obtained for each image is one of the images. The disadvantage of rotating each time can be avoided.

In the above description, when the data is lost, the correction circuit 19 outputs the immediately preceding data again to correct the missing data. However, the multi-channel data output from the data collection device 15 is output several times ( If the data is stored in a buffer or the like (for several degrees), it is also possible to perform the interpolation calculation using the data of the angles before and after the missing data to make correction. For example, if the data of 5 ° is missing as described above, the average value of the data of 4 ° and 6 ° is output as the data of 5 °. Alternatively, it is also possible to correct the data so that the data of the irradiation angle (185 °) in the opposite direction to 180 ° is used as the data of 5 °.

In the above description, the raw data is corrected in real time. However, when the raw data is stored and stored and later used to perform an image reconstruction operation, the angle information for which data collection is missing is used. The correction may be performed by using the correction.
In this case, the correction circuit 19 (or another circuit) encodes and stores the timing of the missing detection signal generated from the monitoring circuit 21.

In addition, it goes without saying that the specific configuration and the like can be variously changed without departing from the spirit of the present invention.

[0021]

As described above, the X-ray C of the present invention
According to the T device, even when the trigger signal based on the X-ray irradiation angle detection signal is lost, it is possible to prevent inconvenience by correcting the missing angle data.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a time chart for explaining the operation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Gantry 12 Rotating frame 13 X-ray tube 14 X-ray detector 15 Data acquisition device 16 Rotation drive mechanism 17 Angle detector 18 Trigger signal generator 19 Correction circuit 20 Image reconstruction arithmetic unit 21 Monitoring circuit

Claims (1)

[Claims] 1. An X-ray generating means, an X-ray detecting means, a means for rotating an X-ray irradiation direction, an angle detecting means for detecting an irradiation angle thereof, and a means for generating a trigger signal from the angle detection signal. Data acquisition means for capturing the output of the X-ray detection means in response to the trigger signal and collecting data at each angle; and means for monitoring the trigger signal and obtaining data collection missing angle information due to lack of the trigger signal. Data correction means for correcting the data of the missing angle based on the detected data collection missing angle information, and image reconstruction means for performing an image reconstruction operation using the corrected data. X-ray CT apparatus.