JPS60126143A - X-ray tomographic apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an X-ray tomography device (hereinafter abbreviated as X-ray CT), and more specifically, to an improvement in optical axis adjustment of an X-ray detector that detects X-rays. Regarding the X-ray CT performed.

(Prior technology) An X-ray fan beam is projected onto the subject from multiple angles, the X-rays that have passed through the subject are detected, a large amount of projection data is obtained, and this projection data is used to determine the X-ray absorption of the subject. ljICT, which reconstructs tomographic images based on the distribution of

In this case, the X-ray detector that detects transmitted X-rays is
As shown in FIG. 1, it is placed facing an X-ray source 2 with a subject 1 at its center. This X-ray detector 3 is composed of a large number of detection channels, and is arranged on the circumference around the X-ray source 2 as shown in the figure.

When reconstructing a tomographic image of the subject 1 using projection data detected by the X-ray detector 3 having such a configuration, the image is reconstructed with the center position 4 of the detector 3 as a reference. This center position is the center of the X-ray source 2 and the X-ray source 2 and X-ray detector 3.
The rotation center O when rotated integrally with respect to the subject 1
(The subject is placed so that its center is located approximately at this center of rotation.) X
If the center position 4 of the line detector 3 deviates from this straight line, artifacts will occur in the reconstructed image.

Aligning the center position 4 of the X-ray detector 3 on the straight line connecting the X-ray source 2 and the rotation center 0 is called optical axis alignment, and it must be adjusted with an accuracy of usually 1/10011+1. There is.

However, this front axis adjustment is not very easy and is not normally performed during use after the product is shipped. For this reason, mechanical deviations occur due to changes over time, causing the center position of the X-ray detector to deviate from the straight line, resulting in deterioration of resolution, artifacts, and the like.

(Object of the Invention) The present invention has been made in view of these drawbacks, and its purpose is to perform rough adjustment of the optical axis and then calibrate the center position of the detector with high accuracy. The object of the present invention is to provide X-ray CT that does not cause artifacts and performs reconstruction based on the values.

(Structure of the Invention) The present inventions that achieve such objects have different angles. Projecting X-rays onto the subject from multiple directions, calculating the distribution of X-ray absorption of the subject using the obtained projection data, and reconstructing a tomographic image of the subject. In an X-ray tomographic imaging device displayed on a display device, projection data of a perfect circular phantom placed at the rotation center of the X-ray source and X-ray detector is obtained, and X-ray detection is performed from this projection data in each view. The X-ray detector is characterized by comprising a center position calculation means for calculating the optical axis center position of the X-ray detector, and configured to calibrate the optical axis center position of the X-ray detector using the value obtained by the center position calculation means. be.

(Example) Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a configuration diagram showing an embodiment of the present invention.

In the figure, projection signals detected by multiple channels of the X-ray detector 3 are guided to a data acquisition device 21. A data acquisition device scans and reads the projection signals (current signals) of a large number of channels, and then converts and outputs the digital signals.

The projection data of each channel of the detector, which has been converted into a digital signal in this way, is stored in the memory 22 for each projection angle (for each view). After acquiring projection data for all views, the data is taken out from the memory 22 in an appropriate order, guided to the reconstruction calculation circuit 23, and subjected to predetermined data processing and calculation processing. Thereby, a tomographic image of the subject can be reconstructed, and the reconstructed image data is output to the display device 24 and displayed.

Note that a data acquisition device 21 and a memory 2 for storing its output are provided.
2. Operations related to the display device M24 for displaying reconstructed image data are similar to those in conventional devices.

The apparatus of the present invention is characterized in that it is provided with center position calculation means 25 that calculates the optical axis center position of the X-ray detector from the projection data of the phantom. That is, the apparatus of the present invention is capable of automatically configuring the center position of the optical axis of the X-ray detector.

In the apparatus of the present invention, first, a phantom with a perfect circular cross section made of a material with a large X-ray absorption coefficient is placed so that its center approximately coincides with the rotation center O, and the object projection data is collected. Similarly, projection data from multiple angles is obtained.

Next, the center position calculating means 25 determines the projection width of the phantom from the projection data for each view, and converts the center of the phantom image into the position of the X-ray detector 3 from this. FIG. 3 shows an example of how the center of the phantom image changes with respect to the X-ray detector 3 for each view.The center position calculation means 25 calculates the deviation of each view as described above, and further The center of the deviation width is determined and the center point is output as the optical axis center position of the detector.

Based on the optical axis center position determined in this way, the projection data of each view will be used for image reconstruction calculations.

It is not necessary to calibrate the optical axis position as described above all the time.
Depending on the aging of the line detector, it is sufficient to carry out countermeasures as appropriate. Note that the optical axis position (channel number) is stored until the next calibration is performed.

Furthermore, for a reconstruction method in which image reconstruction is performed with the optical axis center position of the X-ray detector set at a virtual position slightly shifted from the actual physical center position, the optical axis Of course, adjustments can be applied.

(Effects of the Invention) As explained above, according to the present invention, the optical axis center position of the X-ray detector can be calibrated based on the projection data of the phantom. This eliminates the need for axis adjustment, makes it possible to compensate for deviations in the optical axis center position due to changes over time, and contributes to reducing artifacts.

Furthermore, since the optical axis calibration according to the present invention is easy to operate and takes a short time, it has the effect of shortening the time required for maintenance and inspection of the apparatus, and has a great practical effect.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing the positional relationship between an X-ray source and an X of the center point of the phantom
FIG. 3 is an explanatory diagram showing a shift with respect to a line detector. 1... Subject 2... XwA source 3... X-ray detector 21... Data recording device 22.
...Memory 23...Reconfiguration calculation circuit 24...Display device 25...Center position calculation means

Claims (1)

[Claims] X-rays are projected onto the subject from multiple directions at different angles, and the obtained projection data is used to calculate the X-rays of the subject.
In an X-ray tomographic imaging apparatus that reconstructs a tomographic image of the subject by determining the distribution of radiation absorption and displays the reconstructed image on a display device, a A center position calculation means is provided which obtains projection data of a perfectly circular phantom and calculates the optical axis center position of the X-ray detector from this projection data in each view. An X-ray tomographic imaging apparatus characterized by being configured to calibrate the optical axis center position of an X-ray detector.