JPS62211549A - Radiation image processing method - Google Patents

Abstract

PURPOSE:To display the concentration of the property itself of the material in a subject or gradations when a different material is contained by obtaining an absorption coefficient ratio from transmission images obtained by radial rays which differ in energy and visualizing it as an image. CONSTITUTION:The object is photographed by being projected with >=2 kinds of different-energy radiation in the same direction. The natural logarithmic value of the ratio of the incident radiation intensity and transmitted radiation intensity of each picture element of a transmission radiation image for each energy value is compared with that for another different energy value. A value measured by this method is the real ratio of mean absorption coefficients of radiation-transmitted parts to the different radial rays. Namely, an image consisting of those picture elements is an image from which information on the thickness of the subject is removed. This image consists of only the nature of the material constituting the subject to radiation.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to an image processing method used in an X-ray diagnostic device used in medical treatment or a non-destructive inspection device used in industry.

Conventional technology The component of the transmitted image obtained by irradiating radiation from one direction of the object and the transmitted radiation basically consists of the product of absorption coefficient and thickness. Figure 2 shows the basic principle of radiation transmission. Consider the radiation that passes through the shaded area of object 1 shown in FIG. Incident intensity of radiation of specific energy 2, l1n (IC).

The transmission intensity is calculated as (E), and the average absorption coefficient of the shaded area is μ.
(If it is an illusion and the thickness is X, the following formula holds true.

Iout(IC)=Iin(IC))Cp(μ(IC)
・)C) ・-・-(1) As shown in equation (1), the change in the intensity of transmitted radiation is the product μ(K) of μCX) and X
・It is a change in the components of X.

That is, a transmitted radiation image always includes information about the thickness of the subject.

Problems to be Solved by the Invention Since the transmitted image always includes the thickness information of the object,
The image only has a geometrical meaning as a shadow.

Among transmitted radiation images, for example, in medical X-ray images, what is required for X-ray diagnostics is the μ(IC) of the subject.
Normally, a doctor who performs X-ray diagnosis performs morphological pattern recognition in his head and reads changes in μ(E)·X as changes in μ(E).

Means for solving the problem: Photograph the subject by irradiating two or more types of radiation with different energies from the same direction, and calculate the incident radiation intensity and the transmitted radiation of each pixel of the transmitted radiation image for one energy. The ratio is taken of the natural logarithm of the ratio of the intensities and the natural logarithm of the ratio of the incident radiation intensity to the transmitted radiation intensity of each pixel of the images obtained for different energies.

Effect: The value measured by the method described above is only the ratio of the average absorption coefficient for different radiations in the area through which the radiation has passed.In other words, the image composed of those pixels is an image without information about the thickness of the object. becomes. Therefore, this image is an image consisting only of the radiation-resistant properties of the materials that make up the subject.

Example The method of the present invention will be explained according to the basic principle shown in FIG.

Letting the energy of different radiation be El+”2,
The transmitted intensity of radiation is expressed by the following equation.

out (li:+)=l1n(L)6Xp(4(
L)・xl ・−(2) Iout(Ez)=Iin(E
z) eXl) (, u(E+) ”X ) −(3)
If we take the logarithms of both sides and transform them, as can be seen from equations (4) and (5), the thickness X of the object is commonly included on the right side. Therefore, (4), (
5) By taking the ratio of the equation, X can be eliminated as follows.

Here, since the input radiation intensity can be measured in advance, I in (E) can be treated as a constant and can be expressed as in the following equation.

Rewriting equation (7) using equation (8), we can see that by processing the transmission images taken using radiation of different energy as described above, It becomes possible to erase information regarding the thickness X, and it is possible to convert into an image consisting only of the absorption coefficient μ of the subject.

The meaning of the value μ(L)/μ(Ez) expressed by equation (8) will be explained using X-rays.

FIG. 3 shows the linear absorption coefficient (am) of bones and muscles with respect to the X-ray tube voltage (KVp). As shown in the figure, the absorption coefficient value and its slope differ depending on the substance.

For example, tube voltage 140 KVp (effective energy 6
a KeV ) and the absorption coefficient at a tube voltage of 80 KVp (effective energy 48 KeV), the ratio of the absorption coefficient of bone or muscle is as follows.

i) In the case of muscles 11) In the case of bones The ratio of absorption coefficients at a specific energy differs depending on the substance, and by determining this ratio, the shading of the image due to the thickness of the object is removed from the image, and the It becomes possible to fix the constituent substances of For example, if a value of 1.11 is obtained as shown in equation (9), it can be determined that this tissue is composed of muscle tissue.

FIG. 1 is a diagram schematically showing a method for obtaining an image based on the principle of the present invention. It is assumed that a is a cross section of the object 1, and that there is a foreign object 2, that is, a location with a different absorption coefficient inside. b, c indicate the X-ray transmission intensity corresponding to different energies of incident X-rays, b corresponds to low-energy X-rays,
C corresponds to high energy X-rays. From these two data, based on the principle of the present invention, the absorption coefficient ratio μ(El)/
When μ(TL2) is calculated and its intensity distribution is displayed, it becomes as shown in d, and there is no shading difference due to the difference in the thickness of the object, and only the parts with different absorption coefficients have a shading difference. As a result, the presence of the foreign substance 2, which has been hidden in the change in shading of the image due to the change in the thickness of the object, becomes clearly visible by displaying the image made up of the absorption coefficient ratio.

Here, the incident intensity l1n (
To measure K), before photographing the subject 1, measure l1n (IE) without the subject, or if the subject 1 is smaller than the screen size, as shown in Figure 1, c. The X-ray intensity that does not pass through the object may be used as rin (E).

Further, as the radiation image detection means that can be used in the present invention, means for converting the film density obtained by film photography into electrical signals, means for converting the output image plane of a fluorescent screen or image intensifier into electrical signals using an image pickup tube,
Alternatively, there is a means of scanning a radiation sensor such as an ionization chamber or a semiconductor and converting it into an electrical signal.

Furthermore, as a radiation source of different energies, it is also possible to use an X-ray source that emits energy in a wide range beyond the energy band that has sufficient energy resolution on the detector side.

By using the present invention, for example, in medical applications, it is possible to directly view only information on changes in the internal structure of the subject, consisting only of the absorption coefficient, without being confused by the shape of the subject.

Furthermore, if this device is used not only for medical purposes but also for destructive inspections, it will be possible to remove changes in shape due to the thickness of the object from the image, allowing fixed measurement of not only the internal shape of the object but also the materials that make up the object. For example, if a cavity exists inside the camera, the depth of the cavity was previously unknown, but by removing the parameter of the thickness of the subject, it becomes possible to measure the depth of the cavity.

Effects of the Invention According to the present invention, the absorption coefficient ratio μ(L)/μ(Ih) is obtained from transmitted images obtained using radiation of different energies, and by converting the ratio into an image, it is possible to It is possible to remove the unavoidable shading caused by the thickness of the object in a transmitted image of incident radiation, and to truly display the density of the physical properties of the substance within the object, or the shading when different substances are included.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a radiation image processing method according to an embodiment of the present invention, FIG. 2 is a diagram showing the basic principle of radiation transmission, and FIG. 3 is a graph showing absorption coefficients of bones and muscles. 1...Subject, 2...Foreign object. Name of agent: Patent attorney Toshio Nakao and 1 other person
1 Figure (Yunoi i Zu-1 Figure 2 Ii 9 (E) ↓ 1ouj,, (Sh Figure 3 Blue Electric Z Engineering (K Vr)

Claims (1)

[Claims] Obtain transmitted image information obtained by irradiating the same subject with two or more types of radiation of different energy from the same direction, and calculate the incident radiation intensity from each pixel component information of the transmitted image obtained by radiation of one energy. Two values: a value obtained by taking the logarithm of the ratio of transmitted radiation intensity, and a value obtained by taking the logarithm of the ratio of incident radiation intensity and transmitted radiation intensity from each pixel component information of the transmitted image obtained by radiation of other energy. A radiation image processing method characterized in that an image is obtained using a ratio of pixel components.