JPH10201752A - X-ray computed tomograph(ct) - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a good image without any virtual image even if a scintillation element and the like is used to detect an X-ray radiation. SOLUTION: When an instruction for operating a device is provided, the whole X-ray CT is set up to be in movable state, by an arithmetic control part 4 thereafter, prior to photographing, the arithmetic control part 4 gives instructions to an X-ray generating part 1 to e the X-ray which has an exposure rate (M) to stabilize a sensitivity of each of the scintillation elements in an X-ray detecting element 2. When the X-ray irradiation of the exposure (M) is completed, calibration correcting a function showing a relationship between output of an X-ray sensing element and X-ray absorbed dose is conducted, after that, radiography of the subject 3 is conducted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray detector provided with an X-ray detector comprising a large number of fluorescent elements that receive X-rays and emit light and photoelectric conversion elements that convert the amount of light emitted from the fluorescent elements into electric signals. It relates to a CT apparatus.

[0002]

2. Description of the Related Art In recent years, a solid X-ray detector using a scintillator element or the like has been used as an X-ray detector used in an X-ray CT apparatus in order to improve the detection accuracy in place of the conventional ionization chamber system using xenon gas. Vessels are widely used.

Such a solid-state X-ray detector uses an X-ray detection element comprising a scintillator element for converting incident X-rays into light and a photodiode for detecting the light converted by the scintillator element and outputting it as an electric signal. It has a configuration in which about 500 to 1000 channels are arranged in an arc shape around the wire tube.

[0004]

However, in an X-ray solid-state detector using a scintillator element or the like, as shown in FIG. 6, the sensitivity of the detection element, particularly the emission intensity of the fluorescent element, is obtained by irradiating X-rays. Is reduced.

In such a case, the time of non-irradiation of the X-ray to the X-ray detector is long, and the rate of decrease in sensitivity increases immediately after the start of X-ray irradiation, and the variation in sensitivity among the X-ray detection elements also increases. .

For this reason, in an X-ray CT apparatus using a scintillator element or the like as an X-ray detector, even if calibration or the like is performed prior to imaging, variations due to deterioration in sensitivity of each detection element cannot be completely corrected, and artifacts in an image taken However, there is a problem that a virtual image such as that described above occurs.

In order to solve these problems, the present invention provides an X-ray CT which can obtain a good image without a virtual image even when a scintillator element or the like is used for an X-ray detector.
The purpose is to provide the device.

[0008]

In order to achieve the above object, the present invention provides an X-ray generator, a fluorescent element which emits light upon receiving X-rays, and a photoelectric element which converts the amount of light emitted from the fluorescent element into an electric signal. An X-ray CT apparatus having an X-ray detector in which a plurality of conversion elements are combined, wherein the X-ray detector receives radiation damage to the X-ray detector prior to imaging of an object, and the output sensitivity is substantially constant. Control means for irradiating X-rays from the X-ray generation unit is provided.

[0009] The X-ray irradiation amount is not less than 5000 mAs.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG.
This will be described with reference to FIG.

FIG. 1 is a schematic view of an X-ray CT apparatus according to an embodiment of the present invention, in which an X-ray generation unit 1 and an X-ray detection unit 2 are arranged opposite to each other with a subject 3 interposed therebetween. X-ray generator 1
The X-ray tube and the X-ray detection unit 2 are rotated integrally while irradiating the subject 3 with X-rays from the X-ray tube, and the X-ray detection unit 2 rotates the X-ray tube and the X-ray detection unit 2 from the X-ray detection unit 2 approximately 360 ° or approximately 180 °. Is obtained.

The X-ray generator 1 mainly comprises an X-ray tube and a high voltage source, and the high voltage source is usually installed at a position distant from the main body of the X-ray CT apparatus.

The X-ray detecting section 2 is an X-ray detecting element comprising a scintillator element for converting incident X-rays into light and a photodiode for detecting the light converted by the scintillator element and outputting it as an electric signal. The apparatus has a configuration in which about 500 to 1000 channels are arranged in an arc around the generating unit, and after performing processing that is normally required such as amplification on data obtained from each channel, performs A / D conversion, and performs operation control. 4 The arithmetic control unit 4 controls the operation of the entire X-ray CT apparatus, and calculates a tomographic image of the subject 3 based on the data for each channel transmitted from the X-ray detection unit 2. In addition, when the X-ray CT apparatus is started up or when there is no X-ray irradiation for a long time, the arithmetic and control unit 4 controls the X-rays so that the sensitivity of each of the scintillator elements becomes stable.
The X-ray generation unit 1 is provided to perform X-ray irradiation.

Next, the operation of the present invention will be described with reference to the flowcharts shown in FIGS.

First, when an instruction to operate the apparatus is issued (usually once a day for use when the apparatus is used),
After setting up the entire X-ray CT apparatus in an operable state (S1), the arithmetic control unit 4 sets an irradiation dose M sufficient to stabilize the sensitivity of each X-ray detection element of the X-ray detection unit 2 before imaging. The X-ray generation unit 1 is instructed to irradiate X-rays.
Here, the dose M of X-rays sufficient to stabilize the sensitivity is obtained in advance and stored in the arithmetic and control unit 4, and the process of obtaining the dose M will be described with reference to the flowchart shown in FIG.

The arithmetic control unit 4 controls the X-ray generation unit 1
An instruction to irradiate X-rays is issued (S11), and data obtained from the X-ray detector 2 is monitored for each X-ray detection element, and all X-rays are detected.
X-rays are emitted until the rate of change of the line detection element output reaches a predetermined value α (a value close to 1) (S12). In FIG. 4, the outputs of the two X-ray detection elements are represented by the sensitivity indicating the ratio at the beginning of the irradiation. The portion where the rate of change is equal to or less than the predetermined value α is where the sensitivity of the X-ray detection element becomes constant.

When the rates of change of the outputs of all the X-ray detection elements become equal to or less than a predetermined value α, the integrated irradiation dose M at that time is calculated and stored (S13).

Thus, the amount of X-rays to be irradiated until the sensitivity of each X-ray detecting element becomes constant is calculated.

In FIG. 2, when the irradiation of the X-ray of the irradiation dose M is completed, calibration of the output of each X-ray detecting element is performed (S3).

In the calibration, as shown in FIG. 5, X-rays absorbed by a known absorption amount Z are irradiated, and predetermined data processing (usually, Y = -logX, X: output of X-ray detection element) The following correction is performed on a function obtained in advance, which indicates the relationship between the output Y and the amount of absorption Z, to which the above (3) has been applied.

Z = (Y 1 / Y 0) × Y This calibration is performed to correct the variation of each X-ray detecting element in the relation between the output Y of each X-ray detecting element and the X-ray absorption amount Z. , But each X
Since the general variation in sensitivity for each line detection element has been corrected by the X-ray irradiation shown in step 2 (S2), highly accurate calibration can be performed.

When the calibration is completed, the imaging mode of the subject 3 is entered, and normal tomographic imaging is performed (S
4).

Accordingly, prior to imaging of the subject 3, X-rays that always have a constant detector sensitivity are applied to each X-ray detecting element, so that imaging of the subject 3 is always performed by the X-ray detecting element sensitivity. Is constant. Therefore, in an X-ray CT apparatus having a scintillator element or the like as an X-ray detection element, a good image with few artifacts can be obtained.

Further, when the X-ray CT apparatus is operated, it can also serve as so-called aging for stabilizing the X-ray tube. In comparison, it does not take much time until imaging.

In the above-described embodiment, the X-ray irradiation amount at which the sensitivity of each X-ray detecting element is constant is obtained in advance. However, a normal X-ray detecting element, for example, an apparatus using a scintillator element or the like may be used. For example, the sensitivity is stabilized by irradiating X-rays of about 5000 mAs. Therefore, the amount of X-ray irradiation performed before imaging may be fixed to a predetermined value of about 5000 mAs or more.

Further, in the above-described embodiment, an example in which X-ray irradiation is performed during operation of the apparatus has been described. Even when the irradiation is not performed for a predetermined time, the irradiation may be performed at the time of imaging the subject. In the embodiment described above, the X-ray detector is mounted on the X-ray CT apparatus,
X-rays were applied to stabilize the sensitivity of each detection element. However, if sufficient X-rays were applied to the X-ray detector before mounting on the X-ray CT system, the sensitivity of each X-ray detection element could be improved. Of X-rays performed before the operation of the X-ray CT apparatus is reduced.

[0027]

According to the present invention, prior to subject imaging,
Since X-rays that always keep the detector sensitivity constant are applied to each detection element, the subject is always imaged with the detection element sensitivity kept constant, and the X-ray is used as a fluorescent element such as a scintillator element. In an X-ray CT apparatus having a detection element, a good image with few artifacts can be obtained.

In the present invention, when the X-ray CT apparatus is operated, so-called aging for stabilizing the X-ray tube can also be performed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an X-ray CT apparatus according to the present invention.

FIG. 2 is a diagram illustrating an operation of an arithmetic control unit according to the present invention.

FIG. 3 is a diagram showing an operation of an arithmetic control unit for obtaining an X-ray irradiation amount that makes the output sensitivity of the detector constant.

FIG. 4 is a diagram showing a change in sensitivity of a detector with respect to an X irradiation dose.

FIG. 5 is a diagram showing a calibration operation.

FIG. 6 is a diagram showing a change in sensitivity of a detector with respect to an X irradiation dose.

[Explanation of symbols]

 1 X-ray generation unit 2 X-ray detection unit 3 Subject 4 Calculation control unit

Claims (2)

[Claims] 1. An X-ray having an X-ray generation unit, an X-ray detector in which a large number of fluorescent elements that receive X-rays and emit light, and a large number of photoelectric conversion elements that convert the amount of light emitted from the fluorescent elements into electric signals are provided. In the CT apparatus, it is preferable that the X-ray detector further includes control means for irradiating the X-ray detector with X-rays from the X-ray generation unit, the X-ray detector being subjected to radiation damage and the output sensitivity being substantially constant prior to subject imaging. Characteristic X-ray CT apparatus. 2. The X-ray CT apparatus according to claim 1, wherein the irradiation amount of the X-ray is 5000 mAs or more.