JPH10277024A - X-ray ct system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately correct the time-based fluctuation of X-ray intensity. SOLUTION: From data obtained from the respective channels of a multi-channel X-ray detector 14, by a data-for-correction extraction device 18, the data by X-rays passed through the absent area of an object 10 are extracted as the data for correction based on information for a range takable by the data by the X-rays passed through the absent area of the object 10 stored in a storage device 22. By using the data for the correction, in a correction device 19, the correction for the X-ray intensity fluctuation of the other data is performed.

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 In an X-ray CT apparatus, X-rays are generated due to temporal fluctuations in the output of a high voltage generator for generating X-rays.
Fluctuations in line intensity are inevitable, which has a negative effect on the reconstructed image. Therefore, in the related art, X-ray intensity fluctuations are captured by using the output of a calibration channel provided at a position that is least affected by the subject, and the data of other channels is corrected accordingly. This calibration channel normally uses several channels at both ends of the multi-channel detector.

[0003]

However, in the conventional configuration in which the X-ray intensity fluctuation is corrected by using data of a specific calibration channel, there is a problem that the temporal fluctuation of the X-ray intensity cannot be accurately corrected. .

That is, in general, when an X-ray CT apparatus measures an X-ray intensity distribution from a certain direction with a multi-channel X-ray detector, not all channels are detected at the same time in time. Data is sequentially obtained for each channel in a specific order (sequence) such as to the end. Therefore, when using the outputs of several channels at both ends of the multi-channel detector as calibration data, the data obtained at the earliest time and the data obtained at the latest time are used (normally). , By their average value), the data obtained during that time will be calibrated. Therefore, a temporal change in the X-ray intensity between the two points in time when the calibration data is obtained is a calibration that is not considered at all and becomes inaccurate.

In view of the above, it is an object of the present invention to provide an X-ray CT apparatus improved so that X-ray intensity fluctuations can be accurately corrected and an excellent image can be reconstructed.

[0006]

In order to achieve the above object, an X-ray CT apparatus according to the present invention comprises an X-ray generator, a multi-channel X-ray detector, an X-ray generator, and an X-ray generator. Means for rotating the detecting means, means for obtaining data from each channel of the X-ray detecting means at each rotation angle thereof, and information on the range of possible data for each channel in the non-existent region of the subject which has been inputted in advance. Calibration data extraction means for extracting appropriate data as calibration data based on the calibration data; calibration means for calibrating other data based on the extracted calibration data; and image reconstruction operation using the calibrated data. And an image reconstructing means.

[0007] Which channel of the multi-channel X-ray detecting means is used for acquiring the calibration data is not predetermined, and when an actual subject is imaged, the X-rays passing through the non-existent area of the subject are not determined. Is used as the calibration data. That is, information on the range that can be taken by the data of each channel in the non-existent region of the subject is obtained by collecting data from each channel in a state where the subject is not placed in advance, and this is input in advance. Based on this information, when the subject is actually placed, it can be determined whether the data of each channel is based on X-rays passing through the subject-existing area or X-rays passing through the non-subject-existing area. . Therefore, if the subject is small, such as an arm or a leg,
Since X-rays passing through the non-subject area enter many channels near both ends, data obtained from many channels near these two ends are used as calibration data. Also, when data obtained by X-rays passing through the gap between the body and the arm is obtained from a channel near the center,
This is also used as calibration data. Therefore, not only data at both ends of a fixed time to obtain data from each channel of the multi-channel detector but also data at many points can be used as calibration data, so mathematically advanced data such as spline interpolation can be used. By performing the interpolation processing, it is possible to accurately calibrate the influence of the temporal variation of the X-ray intensity on the data of the other channels.

[0008]

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 a large number (for example, 800) of 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 shown 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. Thus, when the rotating frame 12 is rotated, an angle detection signal is sequentially generated from the angle detector 17 at every 1 °, for example, and sent to the data collection device 15 to be used as a trigger signal for the data collection.

That is, when the rotating frame 12 is rotated while irradiating X-rays from the X-ray tube 13, the X
Figure 2 shows the distribution of data for multiple channels for each beam irradiation direction.
It is obtained as follows. Assuming that there are 800 channels of the multi-channel X-ray detector 14, for example (from the left end in FIG. 1 to the right), data are sequentially obtained in time from channel numbers 0 to 799. Generally, X-rays that have passed through the region where the subject 10 exists are absorbed by the subject 10, so that the data are small. Becomes big. Therefore, in FIG. 2, the data of the channel near the center is small.

On the other hand, in the storage device 22, when the subject 10 does not exist, information on a range in which data of each channel can be taken is stored in advance. For this purpose, it is necessary to perform measurement in advance in which the X-ray irradiation conditions are variously changed and data from each channel is collected while the subject 10 is not placed. It is desirable that these data be stored in the storage device 22 after being made into a database according to the X-ray irradiation conditions and the channel number.

Therefore, the calibration data extracting device 18 converts the data of each channel into the X through the area where the subject 10 exists based on the information stored in the storage device 22.
X due to line or through area where subject 10 does not exist
It can be determined whether or not it is a line. The data determined to be the latter is extracted as calibration data.

The calibration data is used by the calibration device 19 to calibrate X-ray intensity fluctuations for data of other channels. At that time, in most cases, data of a large number of channels can be used as calibration data, so that accurate calibration can be performed by a mathematically advanced interpolation method such as spline interpolation. That is, it is considered that the calibration data is based on X-rays passing through an area where the subject 10 does not exist, and represents the intensity of the X-rays emitted from the X-ray tube 13 itself. X-ray data that has passed through the region where the subject 10 is present also includes the influence of this X-ray intensity variation, but cannot be directly observed from the data. However, since the number of samplings of the calibration data is large, it is possible to obtain a value close to the actual X-ray intensity fluctuation at the time when the calibration data cannot be obtained by spline interpolation or the like. Therefore, based on such interpolation processing, following the actual X-ray intensity fluctuation included in the X-ray data passing through the area where the subject 10 is present, and removing the influence more accurately. Can be.

By the way, in the past, several channels at both ends were determined as channels for acquiring the calibration data, and only the future data was used as the calibration data. However, it is impossible to perform mathematically advanced interpolation as described above, and usually only an average value is obtained and calibration is performed based on the average value, which is inaccurate.

The data corrected for the influence of the X-ray intensity fluctuation by the calibration device 19 is sent to the image reconstruction device 20 and subjected to image reconstruction calculation processing, and the obtained image is sent to the image display device 21 for display. Is done. Therefore, artifacts on the reconstructed image due to the fluctuation of the X-ray intensity can be significantly improved, and a stable high-quality reconstructed image can be obtained.

The above description relates to the embodiment of the present invention, and it goes without saying that the specific configuration and the like can be variously changed without departing from the spirit of the present invention.

[0017]

As described above, the X-ray C of the present invention
According to the T apparatus, it is possible to calibrate the X-ray intensity while accurately detecting the fluctuation, and to obtain a stable high-quality reconstructed image.

[Brief description of the drawings]

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

FIG. 2 is a graph showing data distribution.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Subject 11 Gantry 12 Rotating frame 13 X-ray tube 14 Multi-channel X-ray detector 15 Data collection device 16 Rotation drive mechanism 17 Angle detector 18 Calibration data extraction device 19 Calibration device 20 Image reconstruction device 21 Image display device 22 Storage apparatus

Claims (1)

[Claims] 1. An X-ray generating means, a multi-channel X-ray detecting means, a means for rotating the X-ray generating means and the X-ray detecting means, and each channel of the X-ray detecting means at a respective rotation angle. A calibration data extraction unit that extracts appropriate data as calibration data based on information about a range in which data of each channel in a non-existent region of a subject is input in advance. An X-ray CT apparatus comprising: a calibration unit that calibrates other data based on the calibration data; and an image reconstruction unit that performs an image reconstruction operation using the data after calibration.