JPS61172538A - X-ray diagnostic apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to an X-ray diagnostic apparatus having a density correction function when performing imaging with X-rays of different energies.

The X-ray absorption coefficient of conventional technical materials is 1. Since the results differ due to differences in materials and differences in X-ray energy, by subtracting images taken with X-rays of different energies,
New images that cannot be captured with a single energy can be obtained. Such a method is called the energy difference method. The energy difference method in medical X-ray images is used to obtain an image of only bone components or an image of only soft tissue components excluding bone components from a conventional X-ray transmission image.

Problems to be Solved by the Invention However, when performing imaging using X-rays with different energies, the resulting image may not be as it is due to changes in the X-ray irradiation dose due to the change in energy and changes in the absorption coefficient of tissues. Even with subtraction, the desired image cannot be obtained. Therefore, we developed a method to find the optimal difference conditions by subtracting the images by repeatedly trying to make the image densities of specific parts of images with different X-ray energies the same (for example, soft tissue or bone parts). I'm taking it. However, since this method requires so-called trial and error, it is very time-consuming and complicated work.

Means for Solving the Problem When a standard phantom with multiple thicknesses is provided and a difference image of images taken with different X-ray energies is obtained, the specified thickness of the standard phantom image in both images is After making corrections so that the density of is constant, the difference calculation is performed.

For production The effect of this technical means is as follows.

In other words, making the concentrations corresponding to a specific phantom thickness the same in both images taken with different energies means that By making the density the same, and taking the difference between the two images, it is possible to erase the image of a specific region or organ. In this way, by specifying a specific phantom thickness, it is possible to easily obtain a differential image of any site or organ. image extraction is also possible.

EXAMPLES Hereinafter, examples of the present invention will be described based on the drawings. 1st
The figure is a diagram showing the basic configuration of the present invention.

A standard phantom is placed between the oX-ray generator 1 and the X-ray sensor 6, which are detected by the X-ray sensor 6 and displayed on the display 9 through the main computer 7 and the image processing section 8, within the field of view of the obtained image.

A standard phantom image is always included in the image obtained by irradiating X-rays with different energies, and by making the density of the phantom of a specific thickness in both images the same, that thickness can be determined. The density of parts and organs corresponding to the phantom can be made the same, and by subtracting both images, it is possible to subtract only a specific part or organ, or to reconstruct an image of only a specific part or organ. Next, we will discuss images obtained using X-rays of different energies and their processing methods. Figure 2 is a diagram showing the relationship between X-ray energy and the mass absorption coefficient of substances, and shows the relationship between iodine, which is used as a contrast agent.

0 indicates the absorption coefficient of bones and muscles, and the intensity of X-rays transmitted through these substances is expressed by the following formula.

I (E) = I () (E) e so (-ρ・μ(E)
・d(ri) ・・・・・・・・・・・・・・・・・・
(1) Io (E) X-ray intensity I (El: Transmitted X-ray intensity ρ: Density (f/crtl) μ(]li1: Mass absorption coefficient (d/9) ρ・μ(E) Two lines Absorption coefficient (ctn) d(x): Thickness of the object As can be seen from equation (1), the transmitted X-ray intensity at a specific energy E depends on the absorption coefficient.For example, in Fig. 2, the mass of bones and muscles The absorption coefficient depends on the X-ray energy, and although there is no difference between the two in the high X-ray energy range, there is a difference between the two as the X-ray energy decreases.Furthermore, iodine changes greatly depending on the X-ray energy. As described above, in X-ray images taken using X-rays of different energies, the contrast of iodine, bones, muscles, etc. differs.

Figure 3 shows the X-ray intensity distribution at different energies.・The X-ray intensity distribution indicated by Tal in the figure is the X-ray tube applied voltage of 80
kVp, thickness O=5 am (7) This is the intensity distribution when the kl plate is used as a filter, and the X-ray execution energy is 45 KeV. Also, X shown in (b)
The line intensity distribution is the intensity distribution when the X-ray tube applied voltage is 14 okVp and a 0.5 mm thick 0.0 mm copper plate is used as a filter, and the X-ray execution energy is 90 KeV. By using these two types of energy X-rays, f
It is possible to separate hard and soft tissues such as bones and muscles as shown in Figure a2, and to perform contrast imaging using iodine. .

Next, we will discuss how to perform image difference using a standard phantom. FIG. 4 shows an example of a standard phantom. As shown in the figure, the standard sample is (1), beaten ~ (V)
It is shaped like multiple steps. FIG. 6 shows an example of a transmitted image taken using this standard phantom. FIG. 6(a) is a chest X-ray image, in which a standard phantom is placed at the lower right of the image. The transmitted X-ray intensity distribution on the line connected by A-A' in this image is shown in (b). (b) A change in intensity appears due to the difference in thickness of the middle phantom. (b
The marks (i) and (v) in 1 correspond to the thickness of the standard phantom shown in FIG. For example, let the thickness of a portion with a thickness of 110 be d (Xl, and the different X-ray energies E1.E2
The transmitted X-ray intensity is expressed by the following formula.

1 (El)=Io(El)@Immediately(-ρ､E,)d(!
)) ・・・・・・・・・・・・(2) If both sides are divided by the incident X-ray intensity and normalized, the set of X-ray energies of E2 (a), (+) will be different energy E1. The transmitted intensity of the E2 X-ray is normalized by the incident X-ray intensity. By correcting these values so that they are equal,
By calculating the difference between different images, it is possible to obtain an image excluding a region or organ that exhibits the same absorption as the standard phantom's specific thickness d (El), or an image of only the reverse button region or organ.

There are two methods for correcting this value. First, the obtained image is image-processed, and all images are corrected so that the values of equations (3) and (4) are equal. This is a method that only requires arithmetic calculations.

The second method is to set the incident X-ray intensity in advance so that the transmitted X-ray intensity transmitted through a specific thickness of the standard phantom and detected by the X-ray detector is equal, and then generate X-rays using X-rays of different energies. A similar result can be obtained by obtaining a transparent image and subtracting the two images.

In addition, as a standard phantom used in the present invention, a resin whose X-ray absorption is equivalent to that of soft tissues, such as acrylic resin or polyethylene bioequivalent resin, is used to perform soft tissue subtraction.
By using a material whose X-ray absorption is equivalent to that of bone tissue, the phantom can be used satisfactorily as a standard phantom.

Effects of the Invention The present invention provides a standard phantom that is placed in an X-ray diagnostic apparatus that performs imaging by irradiating X-rays with different energies and extracts images of necessary parts or organs of a subject using a differential method. By correcting the image using the X-ray intensity that passes through the thickness, it is possible to easily obtain a desired differential image.The present invention makes diagnosis routine. becomes possible,
The efficiency of doctors and technicians in the radiology department can be greatly improved.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the basic configuration of the present invention, Figure 2 is a diagram showing the relationship between X-ray energy and mass absorption coefficient of a substance, and Figure 5 is a diagram showing an example of a transmission image taken using a standard phantom. . 1... X-ray generator, 2... X-ray beam, 3... Group/object to be inspected, 5, 11... Standard phantom, 6... - X-ray sensor, 8... Image processing section. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 32 X-ray energy °'-E (kzoV) Figure 3 Elevation and displacement (kvP)

Claims (3)

[Claims] (1) Equipped with an X-ray generator that generates X-rays of different energies, an X-ray detector that detects the X-rays that have passed through the object to be inspected and converts them into electrical signals, and a standard phantom. An X-ray diagnostic apparatus characterized by having a function of correcting the density of an image taken by X-rays based on the intensity of X-rays transmitted through a standard phantom. (2) The X-ray diagnostic apparatus according to claim 1, wherein the standard phantom is made of a material having an X-ray absorption coefficient close to that of biological soft tissue. (3) The X-ray diagnostic apparatus according to claim 1, wherein the standard phantom is a phantom having a plurality of thicknesses.