JPH0441018B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to an X
Regarding X-ray CT equipment, especially equipment with small X-ray capacity,
The present invention relates to a calibration measurement technique that is effective for devices with a large effective field of view, devices with a fast X-ray measurement cycle, and the like.

[Background technology]

FIG. 1 is a diagram showing a measurement time chart of a general X-ray CT apparatus, and _t1 is an offset measurement time. During this offset measurement time _t1 , offset data of the measurement system before X-ray irradiation is measured.
t ₂ is the X-ray exposure time, t ₃ is the data measurement time after the X-ray transmission of each subject, and one measurement cycle is from time t ₁ to t ₃ .

Figure 2 is a schematic diagram for explaining calibration measurement of a general X-ray CT device.
is an X-ray tube, and 2 to 4 are calibration phantoms. The calibration phantoms 2 to 4 are set at the center of the measurement area. Generally, several calibration phantoms are available depending on the effective field of view. 5 is a detector. The X-ray tube 1 and the detector 5 are always provided at opposing positions, and perform X-ray measurements while rotating around a calibration phantom. The data measured using the calibration phantoms 2 to 4 is taken as calibration data. The shape of the X-ray attenuation data is shown in FIG. In Fig. 3, the horizontal axis is the channel position ch of the detector 5, and the vertical axis is the X-ray attenuation measurement data D, A2.
is the X-ray attenuation measurement data D of the calibration phantom 2, A3 is the X-ray attenuation measurement data of the calibration phantom 3, and A4 is the X-ray attenuation measurement data of the calibration phantom 4. The calibration phantoms 2 to 4 are generally made of water, acrylic resin, polyethylene, etc. whose X-ray absorption coefficient changes are similar to those of the human body.

Figure 4 is a diagram showing the shape of the X-ray attenuation data of the calibration phantoms 2 to 4 and the X-ray attenuation shape of the subject in a certain effective field of view, where Os is the X-ray attenuation data of the subject and Fs is the calibration. This is the X-ray attenuation data of the Brachyon phantom.

Generally, the object is smaller than the effective field of view, so if the X-ray conditions are the same during calibration and during object measurement, the X-ray attenuation data for calibration will be 2 times the X-ray attenuation data for the object, as shown in Figure 4. The size becomes three times as large, and effective correction cannot be performed due to S/N problems in the measurement system, linearity errors, etc.

Therefore, either double or triple the X-ray dose only during calibration measurement, or double or triple the X-ray exposure time shown in Figure 1 [Since the detection circuit is an integral type, the output is equivalent to UP]
The correction effect is enhanced by approximating the X-ray attenuation data of the calibration and the X-ray attenuation data of the subject as an output waveform as shown in FIG.

However, with this method, as the speed of CT equipment increases, the X-ray exposure time is inevitably limited, so a large-capacity X-ray tube with a high dose and high load factor is required, and the cost of the equipment is high. There was a problem. Another drawback is that the problem of insufficient dose becomes even more serious as the speed increases and the effective field of view expands.

[Purpose of the invention]

An object of the present invention is to provide an X-ray CT system with
Despite increasing the speed of CT equipment and expanding the effective field of view,
The object of the present invention is to provide a technical means that can perform good calibration measurements without increasing the capacity of an X-ray tube.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Summary of the invention]

In order to achieve the above-mentioned object, the present invention basically includes an X-ray tube and an X-ray detector that are arranged opposite to each other centering on an object and rotate around the object, and The ray detector is composed of a plurality of X-ray detection elements arranged in parallel in the rotation direction, and corrects the object measurement data output from each of these X-ray detection elements with the phantom measurement data to detect the object. In an X-ray CT apparatus that creates tomographic image data, data from each X-ray detection element within an effective field of view obtained by passing through the phantom out of the fantome measurement data is transmitted through the object out of the object measurement data. Phantom movement that allows the phantom to be positioned at a predetermined position along the X-ray emission direction so that the amount of attenuation of data from each X-ray detection element and the measurement area within the effective field of view obtained by It was designed to provide the means.

Generally, in an X-ray CT device, an X-ray detector detects X-rays that have passed through a subject, and before creating tomographic image data of the subject from subject measurement data that is the detection data of this X-ray detector. ,
The object measurement data is corrected using the phantom measurement data.

Phantom measurement data is obtained by transmitting X-rays through a so-called phantom made of a uniform material with approximately the same X-ray absorption coefficient as the subject.
Data obtained by correcting the subject measurement data using the phantom measurement data is obtained by removing variations in sensitivity of each X-ray detection element constituting the X-ray detector.

Therefore, in order to accurately and reliably eliminate variations in the sensitivity of each X-ray detection element, it is necessary to combine the data from each X-ray detection element within the effective field of view obtained by transmitting through the subject among the subject measurement data, and the data from the phantom. It is desirable that the amount of attenuation of the data from each X-ray detection element within the effective field of view obtained by transmitting through the phantom among the measurement data is the same as the measurement area.

However, from the perspective of each X-ray detection element, the subject and the phantom are positioned under the same conditions.

The present invention provides for the X-ray CT apparatus itself to be equipped with a phantom moving means that can move the phantom to position it at a predetermined position along the X-ray radiation direction even if the phantom is not of an appropriate size compared to the subject. Therefore, the above requirements are satisfied.

That is, in consideration of the fact that as the phantom moves along the X-ray emission direction, the number of X-ray detection elements within the effective field of view obtained through transmission without changing the amount of attenuation at the center of the phantom changes. The phantom is positioned at a predetermined position by the phantom moving means so that the number of the X-ray detection elements is approximately the same as the number of X-ray detection elements within the effective field of view obtained by transmitting through the subject; The purpose is to obtain phantom measurement data.

Therefore, similar phantom measurement data can be obtained with a simple configuration without increasing the capacity of the X-ray tube.

[Structure of the invention]

Hereinafter, the configuration of the present invention will be explained along with examples.

FIG. 6 is a reproduction diagram for explaining the principle of calibration measurement of the present invention. Components that are the same as those shown in FIG. .

In FIG. 6, 6 and 7 are calibration phantoms.

The calibration method of the present invention performs measurements by fixing the X-ray tube 1 and detector 5 without rotating them.

In the conventional system, a phantom 6 is required for the calibration phantom that covers the dotted fan-shaped area shown in FIG. At this time, if the X-ray exposure time or X-ray dose is not sufficient, the amount of X-ray attenuation of the subject and the amount of X-ray attenuation of the phantom differ greatly, as shown in FIG. For example, normally the abdomen of the human body is 1/200 to 1/400, 350mmφ
It is about 1/440 for polyethylene of 420mmφ, and 1/1500 for polyethylene of 420mmφ. Moreover, the difference becomes larger as the effective field of view becomes larger. Therefore, if we use a calibration phantom 7 whose amount of X-ray attenuation is close to that of the subject and shift it to the X-ray tube 1 side instead of placing it at the center of the effective field of view, we can perform calibration measurements as shown in Figure 7. As shown, the required effective field of view can be secured without increasing the capacity of the X-ray tube 1, and calibration measurement close to subject attenuation can be performed. That is, in view of the fact that as the phantom moves along the X-ray emission direction, the number of X-ray detection elements within the effective field of view obtained by passing through this phantom changes,
The number of X-ray detection elements is made to be approximately the same as the number of X-ray detection elements within the effective field of view obtained by passing through the object. Since the effective field of view can be adjusted simply by changing the shift amount of the calibration phantom 7, there is no need to prepare a number of calibration phantoms to match the effective field of view as in the past.

FIG. 8 is a diagram for explaining an X-ray CT apparatus according to an embodiment of the present invention based on the above-mentioned principle, and is a sectional view of essential parts showing a schematic configuration thereof.

In FIG. 8, 10 is an X-ray CT scanner device;
11 is an X-ray tube; 12 is a detector;
It is located opposite. Reference numeral 13 denotes a calibration phantom of a predetermined size, which, as described above, is made of an object whose amount of X-ray attenuation approximates that of the subject. This calibration phantom 13 is removably attached to the bed 15 by a fixture 14 so as to be placed on the center line of the X-ray beam. The bed 15 is one that can be moved up and down. Even if the effective field of view increases by moving the bed 15 up and down, the calibration phantom 13
can be set at an appropriate position, making it possible to perform appropriate calibration measurements.

〔effect〕

As explained above, according to the novel technical means disclosed in this application, the following effects can be obtained.

(1) X that composes the tomographic plane of the object by correcting the object measurement data using the phantom measurement data
In a X-ray CT device, a plurality of different calibration data can be provided by moving a phantom up and down corresponding to the effective field of view, which is close to the amount of X-ray attenuation of the subject.

(2) According to (1) above, even if the speed of the X-ray CT device is increased and the effective field of view is expanded, good calibration measurement can be performed without increasing the capacity of the X-ray tube.

(3) According to (1) above, the variable width of the X-ray beam can be made small, so even an X-ray tube with a small capacity can be used, and the cost of the apparatus can be reduced.

(4) According to (1) above, since it is not necessary to take a long time for X-ray exposure, it becomes possible to shorten the X-ray measurement period, and the control of the measurement system becomes easy.

(5) Due to (1) and (4) above, speeding up is possible.

[Brief explanation of drawings]

Figure 1 is a diagram showing the measurement time chart of a general X-ray CT device, and Figure 2 is a diagram showing the measurement time chart of a general X-ray CT device.
Fig. 3 is a diagram showing the X-ray attenuation data of the calibration phantom in Fig. 2, and Fig. 4 is a schematic diagram for explaining the calibration measurement of the device. A diagram showing the X-ray attenuation data of the phantom and the X-ray attenuation data of the subject, Figure 5 is a diagram showing a comparison of the X-ray attenuation data of the calibration phantom using the variable X-ray dose method, and Figure 6 is the diagram showing the X-ray attenuation data of the subject. Fig. 7 is a reproduction diagram for explaining the principle of calibration of the invention.
Figure 6 shows a comparison of X-ray attenuation data of the calibration phantom, and Figure 8 shows an X-ray CT of an embodiment of the present invention based on the above principle.
FIG. 2 is a diagram for explaining the device, and is a cross-sectional view of a main part showing a schematic configuration thereof. In the figure, 10...X-ray CT scanner device, 11...
... X-ray tube, 12 ... Detector, 13 ... Calibration phantom, 14 ... Fixture, 15 ...
...It's Betsudo.

Claims (1)

[Claims] 1.Equipped with an X-ray tube and an X-ray detector that are arranged opposite to each other with the object as the center and rotate around the object, and the X-ray detector has a plurality of X-ray detectors arranged in parallel in the direction of rotation thereof. In an X-ray CT apparatus, the X-ray CT apparatus is composed of X-ray detection elements, and corrects object measurement data output from each of these X-ray detection elements using phantom measurement data to create tomographic image data of the object. Of these, the data from each X-ray detection element within the effective field of view obtained by transmitting through the phantom is the same as the data from each X-ray detection element within the effective field of view obtained by transmitting through the subject among the object measurement data. An X-ray device characterized by comprising a phantom moving means capable of moving the phantom to position the phantom at a predetermined position along the X-ray radiation direction so that the amount of attenuation and the measurement area are substantially the same.
CT device.