JPH05150050A - Measured data correcting method - Google Patents

Abstract

PURPOSE:To correct the ununiformity of a measured image by measuring a correcting phantom once before measuring a measured object so as to obtain a correction factor for correcting sensitivity dispersion among detecting elements and the time change of the detecting elements, and using this correction factor. CONSTITUTION:Prior to the measurement of a photographed body 26, a correcting phantom 1 (acrylic) close to the soft tissue of a human body is measured. The CdTe semiconductor detector 22 of an image receiving device is provided with 128 detecting elements disposed linearly, and scanned synchronously with an X-ray generator 21 to photograph the X-ray image of the photographed body 26. During the scanning period, the data of 150 lines is sampled, and the images of 128X150 picture elements can be obtained. In this case, the average value LAVm of all the detecting elements of the phantom 1 is obtained by an arithmetic unit 23, and also the average value AV of the whole data resulted from corrective measurement is obtained by the arithmetic unit 23. The correction factor LM of each line is then obtained by Lm=AV/ LAVm. The measured data of each detecting element having measured the photographed body 26 is multiplied by this factor Lm to correct a change with the elapse of time.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a medical X-ray diagnostic apparatus,
The present invention relates to a correction method of measurement data used in a bone mineral quantification device, a nondestructive inspection device, an X-ray analysis device, and the like.

[0002]

2. Description of the Related Art In recent years, a radiation detector composed of a plurality of detecting elements has come to be used in a radiation measuring device, particularly in a two-dimensional image receiving device for γ rays or X rays.

In a radiation measuring instrument using a plurality of radiation detecting elements, particularly in an apparatus for scanning a plurality of radiation detecting elements to receive a two-dimensional image of X-rays or γ-rays, variations in the sensitivity of the detectors between the elements. And non-uniformity of the image due to the change with time become a problem. Further, in a device that quantifies a substance based on the measurement result, the accuracy in the measurement plane varies.

For this reason, in general, before the measurement is started, in order to know the sensitivity variation between the elements, the calibration phantom, which is close to the actual measurement target, is measured once, and the radiation intensity of each detection element is measured from the measured value. , The correction coefficient between the elements is obtained by the arithmetic unit. As a result, variations in the sensitivity of the detection elements among the elements are corrected, and image non-uniformity due to variations in the elements is eliminated.

[0005]

However, in the above-mentioned conventional method, when a two-dimensional image of radiation is measured in a short time, due to a transient change of the voltage driving the detection element,
The sensitivity of the detection element changes. In the case of a semiconductor detector such as Si or CdTe, a voltage is applied to an electrode provided on the semiconductor surface to generate an electric field, and electric charges generated inside the semiconductor are extracted from the radiation to detect the radiation. Immediately after the voltage is applied, the electric field is not stable, so that the magnitude of the induced current detected changes. As a result, even if radiation of the same intensity is measured, the measured value changes with time. Therefore, there is a problem that image unevenness occurs in the scanning direction of each element of the detector.

Further, there is a problem in that the precision in the measurement plane varies even when the substance is quantified by performing a calculation process using the measurement data.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a measurement method in which there is no sensitivity variation in radiation measurement, that is, there is no unevenness in the image.

[0008]

In order to achieve this object, in the data calibration method of the present invention, the time change of the detector is simultaneously corrected when performing the correction measurement for correcting the sensitivity variation between the detection elements. The correction coefficient is obtained by dividing the average value of all data obtained by the correction measurement by the average value of the measurement results of all the detection elements at a certain time. This correction factor is multiplied by the measured radiation intensity.

[0009]

Thus, by measuring the calibration phantom once before measuring the object to be measured, it is possible to obtain the correction coefficient for correcting the sensitivity variation between the detection elements and the time change of the detection elements. By using this correction coefficient, it is possible to calibrate the non-uniformity of the measurement image between elements and due to changes over time of each element, and it is possible to perform highly accurate image measurement. In addition, the accuracy in the measurement plane is improved even when the substance is quantified by performing the calculation process using the measurement data.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of an X-ray image receiving device using a CdTe semiconductor detector. This X-ray image receiving device includes an X-ray generator 21, a CdTe semiconductor detector 22, a calculation device 23 for calculating measurement data, and a storage device 2 for storing data.
4 and a display device 25 that displays an image. C
As shown in FIG. 2, the dTe semiconductor detector 22 is composed of 128 detection elements arranged in a straight line. Cd
The Te semiconductor detector 22 is scanned in synchronization with the X-ray generator 21 and can capture a two-dimensional X-ray transmission image of the subject 26. Data of 150 lines is sampled during the scanning period to obtain a two-dimensional transmission image of 128 × 150 pixels.

The X-ray transmission intensity is measured by the photon counting method. In each detection element, the current pulse generated by the interaction with the X-ray is amplified by the amplifier 27,
It is counted by the counter 28. A two-dimensional X-ray transmission image can be obtained by displaying the count value as a shade on the display device 25.

Before measuring the object, first, a correction phantom as shown in FIG. 3 is measured. It is desirable that the constituent phantom is made of a material that can obtain an X-ray transmission intensity almost the same as that of the measurement target. In the present embodiment, assuming that the subject is a human body, it is made of acryl having a thickness of 15 cm, which has an attenuation coefficient close to that of human soft tissue.

The measurement result of the 20th detecting element is shown in FIG. From FIG. 4, the count number is increasing despite measuring the acrylic phantom with a certain thickness.
It can be seen that the sensitivity of this detection element has changed.

An average value AV of all measurement data of this correction phantom was obtained by a computing device. The average value AV is 106
It was 30 counts.

Next, a correction coefficient for correcting the sensitivity variation between elements, which has been conventionally performed, is obtained. The correction coefficient C _n (n = 1 to 128) of each detection element is obtained by (Equation 1).

[0016]

[Equation 1]

However, CAV _n is 1 to 1 of each detecting element.
It is the average value of 150 data of 50 samplings.

Further, a coefficient L _m (m = 1 to 150) for correcting a change with time of the sensitivity peculiar to each detecting element is obtained. L _m is a value obtained by dividing all data AV by the average LAV _m of 128 detection elements in each line, and is represented by (Equation 2).

[0019]

[Equation 2]

FIG. 5 shows the average LAV _m of 128 detection elements in each line, and FIG. 6 shows the correction coefficient L _m obtained based on (Equation 2).

The correction coefficients C _n and L _m are calculated by the arithmetic unit and stored in the storage unit. After this, the subject was measured. M of the n-th detection element of the measurement result
Let the X-ray intensity of the line be I _mn . This measurement result is multiplied by n correction coefficients C _n and L _m to obtain data I ′ _mn in which the temporal change and the variation between the detection elements are corrected. The data of each pixel is as shown in (Equation 3).

[0022]

[Equation 3]

As a result of this calculation, if the variation in sensitivity among the detection elements and the change with time of each detection element are substantially constant, there is no difference in sensitivity in the measurement of each pixel.

FIG. 7 shows the correction result of the 20th detector element. Compared to FIG. 4, the change in the count number in the line direction is smaller, and the correction effect can be seen.

As described above, the non-uniformity between pixels is eliminated, and when a uniform subject is photographed, a uniform image is obtained.

When a plurality of discriminators for discriminating pulse wave heights are provided and counting is performed for each energy band of incident radiation based on the pulse wave heights, a correction count _Lm is provided for each energy band. It is possible to correct the change with time in the count number for each energy band. When the substance is quantified by using the count numbers of these two energy bands, the accuracy in the measurement plane is improved.

Further, even when the scanning speed of the radiation detector is different, that is, when the measurement time per line is different, correction can be easily performed by performing correction measurement.

In this embodiment, the radiation detector is a CdTe semiconductor radiation detector, but Si, Ge, HgI ₂ , G
Needless to say, the same effect can be realized as a correction method for a semiconductor detector using aAs or the like, a detector using a scintillator, or a radiation detector such as an ionization chamber.

[0029]

As described above, according to the present invention, the correction coefficient for correcting the change with time of each detection element is obtained from the data in the correction measurement, and the measurement data is corrected by this coefficient, whereby the sensitivity variation between the detection elements is increased. It is possible to realize an image without variation between pixels by correcting the change with time of the detection element very easily at the same time as correcting

[Brief description of drawings]

FIG. 1 is a diagram showing an X-ray image receiving apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a CdTe semiconductor detector according to an embodiment of the present invention.

FIG. 3 is a diagram showing a correction phantom according to an embodiment of the present invention.

FIG. 4 is a diagram showing a correction measurement result in an example of the present invention.

FIG. 5 is a diagram showing an average value of changes in the line direction of the correction measurement results in the example of the present invention.

FIG. 6 is a diagram showing a correction coefficient obtained in the embodiment of the present invention.

FIG. 7 is a diagram showing a correction result in the example of the present invention.

[Explanation of symbols]

 1 Correction Phantom 21 X-ray Generator 22 CdTe Semiconductor Detector 23 Computing Device 24 Storage Device 25 Display Device 26 Subject 27 Fan Beam X-ray 28 Amplifier 29 Counter 30 CdTe

Claims (2)

[Claims] 1. An apparatus for measuring radiation by scanning a radiation detector including a single or a plurality of detection elements, measuring a correction phantom, and calculating an average value of all data of the measurement data in each measurement line. A measurement data correction method, wherein a value obtained by dividing an average value of measurement data of a detection element is used as a correction coefficient, and the measurement result is multiplied by the correction coefficient to correct the measurement data due to a change with time of the detector. 2. The measurement data correction method according to claim 1, wherein the radiation detector is a CdTe semiconductor detector.