JPH0225612B2 - - Google Patents

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
This invention relates to an X-ray CT with improved optical axis adjustment of a ray detector.

(Prior art) X-ray fan beams are projected onto the subject from multiple angles, the X-rays that have passed through the subject are detected to obtain a large amount of projection data, and this projection data is used to determine the X-ray absorption of the subject. X-ray CT, which reconstructs tomographic images by determining the distribution of , is well known.

In this case, the X-ray detector that detects the transmitted X-rays is
It is arranged facing the radiation source 2. This X-ray detector 3 is composed of a large number of detection channels, and is arranged on a circumference centered on 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 4 of the detector 3 as a reference. This center 4 is the center of the X-ray source 2 and
Connect the rotation center O when the radiation source 2 and the X-ray detector 3 are rotated integrally with respect to the subject 1 (the subject is placed so that its center is approximately located at this rotation center) It needs to be placed in a straight line. The image reconstruction calculation circuit reconstructs the tomographic image assuming that the center 4 of the X-ray detector 3 is on this straight line, so if the center 4 deviates from this straight line, artifacts will appear in the reconstructed image. occurs.

The center 4 of the X-ray detector 3 is the center of rotation O between the X-ray source 2 and the center 4 of the X-ray detector 3.
Optical axis alignment is the process of aligning the optical axis on the straight line connecting the two (hereinafter referred to as the optical axis), and usually needs to be adjusted with an accuracy of approximately 1/100 mm.

However, this optical axis adjustment is troublesome and is usually not performed during use after the product is shipped. For this reason, mechanical deviations occur due to changes over time, and
There is a drawback that the center of the line detector deviates from the straight line, resulting in degraded resolution and artifacts. Furthermore, if a mechanical deviation occurs and this defect cannot be ignored, the troublesome optical axis adjustment (mechanical adjustment) must be performed again to remove the mechanical deviation.

(Objective of the Invention) The present invention has been made in view of the above-mentioned drawbacks, and its purpose is that once the optical axis is adjusted, the optical axis can be adjusted without the need for mechanical optical axis adjustment thereafter.
An object of the present invention is to provide an X-ray CT capable of obtaining tomographic images without deterioration in resolution and without artifacts.

(Structure of the Invention) The present invention achieves the above object by projecting X-rays onto a subject from a number of directions with different angles, and using the obtained projection data, a reconstruction calculation circuit performs calculations. In an X-ray tomography device that calculates the distribution of X-ray absorption of a subject, reconstructs a tomographic image of the subject, and displays the reconstructed image on a display device, the center of rotation of the X-ray source and the X-ray detector The center of the projection width of the phantom onto the X-ray detector is determined for each view from the projection data for each view of a perfectly circular phantom placed so that its center is approximately at the center of the phantom. The reconstruction calculation circuit includes a center position calculation means for determining the center position of the fluctuation width and providing data indicating the center position to a reconstruction calculation circuit, and the reconstruction calculation circuit detects the center position obtained by the center position calculation means by X-ray detection. This is characterized in that it is used as the center position of the optical axis of the instrument to reconstruct a tomographic image.

(Embodiments) Hereinafter, embodiments of the present invention will be described in detail 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. The data acquisition device 21 scans and reads projection signals (current signals) of a large number of channels, converts the read signals into digital signals, and outputs the converted signals. In this way, X converted into a digital signal
The projection data of each channel of the line detector 3 is stored in the memory 22 for each projection angle (for each view). After collecting projection data for all views,
The data are 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 this reconstructed image data is output to the display device 24 and displayed.

The operations of the data acquisition device 21, the memory 22 for storing its output, and the display device 24 for displaying reconstructed image data are the same as in conventional devices.

The apparatus of the present invention includes center position calculation means 25 for determining the position of the optical axis on the X-ray detector (herein referred to as the optical axis center position of the X-ray detector) from the projection data of the phantom. It is distinctive in that it has been established. In other words, conventionally, the center 4 of the X-ray detector 3 is treated as the optical axis center position, and even if a mechanical error occurs and the X-ray detector 3 moves and the center 4 deviates from the optical axis, image reconstruction will not be possible. Sometimes, the shifted center 4 is treated as the optical axis center position, but in the apparatus of the present invention, the optical axis center position of the X-ray detector 3 can be shifted.

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 calculation means 25 calculates the center of the projection width of the phantom onto the X-ray detector 3 by converting it into a position on the X-ray detector 3 from the projection data for each view. Figure 3 shows an example of how the center of the projection width of the phantom changes (shifts) with respect to the X-ray detector 3 for each view, and the range of variation (amplitude) is the difference between the center of rotation O and the center of the phantom. Approximately proportional to the interval. After determining the center of the projection width of each view as described above, the center position calculation means 25 determines the center position of the fluctuation width (center position of the amplitude), and sends data indicating the center position to the X-ray detector. Output to 3.

The center position obtained in this manner will be used as the optical axis center position during image reconstruction calculations.

It is not necessary to constantly calibrate (shift) the optical axis position as described above, and it is only necessary to perform it as appropriate in consideration of changes in the X-ray detector over time. Note that the previously determined optical axis center position (channel number) is stored until the next calibration is performed.

Of course, the present invention can also be applied to a reconstruction method in which image reconstruction is performed by setting the optical axis center position of the X-ray detector at a virtual position slightly shifted from the actual physical center position. It is.

(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, thereby eliminating the need for troublesome mechanical optical axis adjustment. , it is possible to prevent deterioration of resolution due to changes over time and reduce 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 FIG. 3 is an explanatory diagram showing how the center of the projection width of the image changes with respect to the X-ray detector. 1... Subject, 2... X-ray source, 3... X-ray detector, 21... Data recording device, 22... Memory,
23...Reconfiguration arithmetic circuit, 24...Display device, 2
5... Center position calculation means.

Claims (1)

[Claims] 1 X-rays are projected onto the subject from a number of directions with different angles from each other, and using the obtained projection data, a reconstruction calculation circuit calculates the distribution of X-ray absorption of the subject and calculates the distribution of X-ray absorption of the subject. In an X-ray tomographic imaging device that reconstructs a tomographic image and displays the reconstructed image on a display device, a perfect circular shape is placed so that its center is approximately at the center of rotation of the X-ray source and X-ray detector. From the projection data for each view of the Phantom,
A center position calculation means for determining the center of the projection width of the phantom onto the X-ray detector for each view, then determining the center position of the fluctuation width of the center, and providing data indicating the center position to the reconstruction calculation circuit. X-ray tomography, characterized in that the reconstruction calculation circuit reconstructs a tomographic image using the center position obtained by the center position calculation means as the optical axis center position of the X-ray detector. Device.