JP3030950B2 - Calibration phantom and data calibration method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a medical X-ray diagnostic apparatus,
The present invention relates to a calibration phantom and a data calibration method used for a bone mineral quantifying device, a nondestructive testing device, an X-ray analyzer, and the like.

[0002]

2. Description of the Related Art In a radiation measuring device using a plurality of radiation detecting elements, a calibration phantom is generally measured once before starting the measurement in order to know the sensitivity variation between the elements. From the value indicating the radiation intensity of each detection element, a correction coefficient between the elements is obtained by the arithmetic unit. Thereafter, actual measurement is performed, and a value indicating the radiation intensity of each element obtained therefrom is multiplied by a correction coefficient to obtain a measurement result.

A calibration phantom for correcting the sensitivity of the radiation detecting element is made of a material having a uniform absorption of radiation in a range to be measured. For example, the calibration phantom 5 shown in FIG. 4 uses an acrylic plate having a constant thickness.

[0004] In addition, in a substance quantifying device composed of radiation and a radiation detector, in order to obtain the accuracy of the measured quantitative value with good reproducibility, a phantom having a known content is measured before starting the measurement. Is calculated.

[0005]

In a quantitative apparatus using a large number of radiation detecting elements, a measurement for correcting the sensitivity between the radiation detecting elements and a measurement for obtaining a calibration coefficient of the measured value must be performed. First, at least two measurement operations must be performed before measuring the measurement target.

[0006]

The radiation source comprises a radiation source and a plurality of radiation detecting elements arranged one-dimensionally.
And said plurality of radiation detection elements a calibration phantom for use in quantifying apparatus of a synchronous scanning a substance with the
The substance to be quantified is provided on the calibration phantom.
And the radiation transmitted through the substance
The substance is provided so as to be detected by a radiation detecting element.
Calibration
Radiation transmitted only through the phantom area
A calibration phantom detected by a plurality of radiation detection elements is used. The phantom is measured, and the sensitivity correction coefficient between the radiation detection elements and the calibration coefficient of the measured density are calculated at the same time.

[0007]

By this means, the sensitivity correction coefficient between the radiation detecting elements and the calibration coefficient of the measurement density can be obtained simultaneously by one measurement.

Further, the linearity of the content can be accurately calibrated by only one measurement.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.

(Embodiment 1) FIG. 1 is an external view of an embodiment of a calibration phantom of the present invention. The calibration phantom of the present embodiment is used when quantifying the amount of minerals mainly including Ca and P in human bones. In this embodiment, for simplicity,
The description will be limited to the determination of Ca. Acrylic board 1 with 12cm thickness
A bone-equivalent phantom 2 having a thickness of 1 cm is fitted in the central part of the figure. The mass attenuation coefficient of the acrylic plate with respect to 60 keV γ-rays is 0.190 cm ² / cm, and the bone equivalent phantom 2 has a composition almost equal to that of a human bone, and the mass attenuation coefficient is 0.274 cm ² / g. During the bone equivalent phantom,
It contains Ca, and its Ca content D _CaF is 1.0 g / cm ³
It is. On the other hand, Ca is not contained in the acrylic,
It has an attenuation coefficient approximately equal to that of human soft tissue.

Using the calibration phantom 5, the measurement data was calibrated as follows. Fig. 2
As shown in the figure, 51 using the X-ray generator 3 and CdTe
It comprises a multi-channel semiconductor X-ray detector 4 composed of two channels 7.

An object to be measured is placed between the X-ray generator 3 and the multi-channel semiconductor X-ray detector 4, and the X-ray generator 3 and the multi-channel semiconductor X-ray detector 4 are scanned synchronously. And a two-dimensional area is measured. In the multi-channel semiconductor X-ray detector 4, the high-energy X-ray intensity and the low-energy X-ray intensity are simultaneously and separately measured.

The calibration phantom 5 shown in FIG. 1 was set such that X-rays 6 transmitted through the bone equivalent phantom 2 were measured in all the channels 7 of the multi-channel semiconductor X-ray detector 4. From the data obtained by measuring the calibration phantom 5, the sensitivity correction coefficient between channels of the semiconductor X-ray detector and the calibration coefficient of the quantitative value were obtained as follows.

First, the sensitivity correction coefficient will be described. First, the measurement intensity of the high energy X-ray is performed. For each channel, 512 data are obtained by scanning. The average value AV of all the 512 × 512 data thus obtained is obtained. X of m line of nth channel
_{Let the} line intensity be C _n (m). C _n (1) to C _n (51
The average value C _n av of the 512 pieces of data up to 2) was calculated, and the correction coefficient C _n H was obtained as (Equation 1) for each channel.

[0015]

(Equation 1)

This was also performed for the measured intensity of low energy X-rays. The scanning direction of the measured area includes the bone equivalent phantom, which is different from the case of measuring the same material as before, but this method is possible because each channel always measures the same material. It is.

Next, the density of Ca per unit area of the bone equivalent phantom in the calibration phantom was calculated. The average value was calculated for each of the high energy X-ray intensity and the low energy X-ray intensity transmitted through the bone equivalent phantom.
The average value was similarly calculated for the data of the acrylic part. The Ca density D _CaH per unit area in the bone equivalent phantom was calculated from these results using four measured values and based on the energy difference method. From this, the calibration coefficient D of the measured density was obtained by (Equation 2).

[0018]

(Equation 2)

An object to be measured was set in place of the calibration phantom, and the measurement was performed in the same manner. In order to correct the sensitivity variation between channels, the measured X-ray intensity of each line of n channels is multiplied by an inter-channel sensitivity correction coefficient C _n H.

Using the data after the sensitivity correction, the Ca density in the measurement object is calculated. The calculation method is the same as that for obtaining the calibration coefficient, and the energy difference method is used. A value D × D _Cam obtained by multiplying the obtained Ca density D _Cam by the calibration coefficient D was defined as the Ca density to be measured.

According to the above method, sensitivity correction and measurement density calibration could be performed by one preliminary measurement.

(Embodiment 2) FIG. 3 is an external view of another embodiment of the calibration phantom of the present invention. Phantom materials 11 and 12 having the same amount of Ca per unit volume but having different thicknesses are provided at two locations on a calibration phantom 5 of an acrylic plate. Since the thickness of the phantom material 12 was １ ／ of that of the phantom material 11, the amount of Ca per unit area was also 1
/ 2. Ca of these phantom materials 11 and 12
The amounts are known, both D _ca11 and D _ca12 .

Like the first embodiment, the multi-channel X-ray detector is designed to cover all the channels.

This calibration phantom was measured in the same manner as in Example 1 to determine the sensitivity correction coefficient between channels C _n H.

Next, the Ca density per unit area of the phantom materials 11 and 12 was similarly obtained based on the energy difference method. The calculated Ca densities of the phantom materials 11 and 12 are D _CaH11 and D _CaH12 , respectively. These two Ca
From the density, a calibration equation (Equation 3) is obtained that also takes into account the linearity with respect to the density of the density quantifier on that day.

[0026]

(Equation 3)

Here, in (Equation 3), y is the calibrated Ca density, D _cam is the measured density, k is the proportionality constant, D
₀ is a constant. k and D ₀ are (Equation 4) and (Equation 5), respectively.

[0028]

(Equation 4)

[0029]

(Equation 5)

As described above, the measured value D _cam can be calibrated with higher accuracy according to (Equation 3). In the present embodiment, two types of phantom materials having different thicknesses are used in the calibration phantom. However, the phantom materials having three or more thicknesses may be used. Also in this case, the least square method is used.
By obtaining a calibration formula such as (Equation 3), it is possible to perform calibration with good linearity with respect to density.

The Ca-containing phantom material in the calibration phantom may have a constant thickness and a different Ca content.

The method of this embodiment can be similarly applied to elements other than Ca by using phantoms made of materials having different densities or thicknesses. Further, the present invention can be applied to the sum of the densities of a plurality of elements and the compound density.

As the multi-channel X-ray detector, it is also possible to use a semiconductor X-ray detector and a number of scintillation detectors made of cadmium tungstate arranged in addition to the semiconductor X-ray detector.

If the detector cannot identify and measure the X-ray energy as in the first embodiment,
It is also possible by switching the tube voltage of the X-ray tube to change the energy spectrum.

[0035]

By using the calibration phantom and the data calibration method of this embodiment, the channel sensitivity correction of the multi-channel radiation detector and the calibration of the measurement density can be performed at the same time, so that the prior measurement can be easily performed once. Could do it.

Further, the linearity of the measured density could be calibrated well.

[Brief description of the drawings]

FIG. 1 is an external view of an embodiment of a calibration phantom of the present invention.

FIG. 2 is a configuration diagram of a quantitative device using the calibration phantom of the embodiment of FIG. 1;

FIG. 3 is an external view of another embodiment of the calibration phantom of the present invention.

FIG. 4 is an external view of a conventional calibration phantom.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Acrylic board 2 Bone equivalent phantom 3 X-ray generator 4 Multichannel semiconductor X-ray detector 5 Calibration phantom 6 X-ray 11 Phantom material 12 Phantom material

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Tsutsui 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. 34207 (JP, U) JP-A 1-117315 (JP, U) JP-A 62-142305 (JP, U) JP-A 57-46966 (JP, Y2) (58) Fields investigated (Int. Cl. ⁷ , DB name) A61B 6/00-6/14

Claims (5)

(57) [Claims] 1. A radiation source, comprising: a plurality of radiation detecting elements arranged one-dimensionally;
Used as a quantitative device for substances that scans synchronously with the ray detector
The substance as a calibration phantom, the substance to be quantified is provided on a calibration phantom, radiation that has passed through the pre-Symbol substances are detected in all of the plurality of radiation detecting elements for The calibration is provided and the substance is not provided
Radiation transmitted only through the area of the
The substance as detected by the plurality of radiation detection elements
A phantom for calibration, characterized by being provided with: 2. The calibration phantom according to claim 1, wherein two or more substances to be quantified are provided, and the thickness of each substance is different. 3. In a substance quantifying apparatus comprising a radiation source and a plurality of radiation detecting elements, by measuring a calibration phantom, sensitivity correction between the radiation detecting elements and calibration of a quantitative value of the measured substance are simultaneously performed. Data calibration method characterized by performing. 4. A radiation source and a plurality of one-dimensionally arranged radiation sources.
A radiation detecting element, wherein the radiation source and the plurality of
In a quantitative device for substances that scans synchronously with the radiation detector
The calibration phantom includes two or more portions having different contents of the substance to be measured ,
A data calibration method characterized by performing calibration of linearity of a quantitative value with respect to a content of a substance by measuring respective portions having different contents of the substance. 5. The data calibration method according to claim 3, wherein the radiation source is an X-ray tube, and the radiation detecting element is a multi-channel semiconductor radiation detector.