JPS6410219B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a simple reference scale used during X-ray imaging of blood vessel diameters in order to quantify the analysis of blood vessel images in X-ray images of blood vessels.

X-rays, invented by Roentgen, can observe the inside of a living body non-invasively and are widely used in the medical field, and have the same effect on photographic film as visible light. An X-ray photographic film is made up of a light-sensitive emulsion layer and a base, and when the film is irradiated with X-rays, the silver bromide microcrystals contained in the light-sensitive emulsion layer undergo a change, forming a latent image. When the film after X-ray irradiation is developed, the silver bromide that has been affected by the X-rays is reduced to become silver particles. Silver bromide, which is not affected by the X-rays, remains as it is and is dissolved during fixing and removed from the film, making it transparent. Further, the reduced silver particles remain on the film and turn black. A grayscale image is formed on the X-ray photographic film depending on the magnitude of the X-ray absorption coefficient of the subject when the X-rays pass through the subject.

Sufficient density images can be obtained in an X-ray photograph when the body remains in its natural state only when the X-ray absorption coefficient of the organ to be measured differs significantly from that of the surrounding tissue. The difference in X-ray absorption coefficient between the target object and the surrounding tissue is extremely small. In order to obtain clear X-ray images, it is necessary to inject into the organ to be measured a substance that absorbs or transmits X-rays better than the surrounding tissue. As contrast agents for the vascular system, organic iodinated contrast agents, which have a large X-ray absorption coefficient, are most often used.

Entrusting various substances necessary for the metabolism of the living body to the blood,
Observation during angiography as a conduit for transporting blood from one part of the body to another is extremely important for diagnosing circulatory system diseases and elucidating the physiological functions of the vascular circulatory system. Reading the blood vessel diameter from X-ray images, which is an important element in dimensional analysis of blood vessels, is
Much depends on the visual judgment of the doctor. With increasing awareness of preventive medicine and public health management, the amount of vascular images to be processed is increasing dramatically. On the other hand, there is a serious shortage of doctors and skilled laboratory technicians, and there is an extremely strong social need to quantitatively automate the conventional visual inspection-based processing.

Conventionally, the following methods have been used to quantify blood vessel diameter from X-ray images.

(1) Enlarge the image of the X-ray photographic film on a screen with a slide projector, or
A method in which blood vessels are enlarged using a photo enlarger and printed onto photographic paper, and an observer uses a ruler to measure the diameter of blood vessels from these enlarged images.

(2) The X-ray photographic film image can be enlarged with a microscope and measured visually by an observer, or the microscope image can be photographed with a television camera, the output video signal can be binarized, and the blood vessel diameter can be determined from the width. How to measure.

In method (1) above, since the X-ray film image is magnified with a lens, blurring occurs and the boundaries between the blood vessel, the background, and the blood vessel wall become blurred, resulting in measurement errors and the possibility of minute differences in the diameter of the blood vessel. Changes are extremely difficult to detect. Also,
Since the measurement is performed solely by human labor, there are variations in measurement accuracy among the individual measurers, and there is a limit to the number of points and images that can be processed, making it extremely difficult to process a large amount of X-ray photographic film.

Method (2) is mainly used to measure the diameter of microvessels, and when the image is enlarged with a microscope, the measurement accuracy improves compared to method (1), but the number of points that can be processed in one measurement is Since it is a single point, it takes a lot of effort and time to measure many points from one image, and this is to meet the social demand for quantification of a large number of images. is extremely difficult.

As mentioned above, in the conventional measurement method of blood vessel diameter,
The reference object is not captured in the line image,
Since measurements are based solely on visual judgment, there has been no fast, accurate, and economical method for processing and quantifying a large number of X-ray photographic images.

In view of the current situation, the present inventors have conducted intensive studies on quantifying blood vessel diameters from X-ray photographic film images, and as a result, have completed the present invention. That is, the present invention relates to a simple reference scale that is characterized in that it is imaged at the same time as the object to be measured or under the same conditions during X-ray imaging of the vascular system in order to quantify the diameter of a blood vessel from an X-ray image of the vascular system. It is something.

For this reason, several kinds of elongated holes with circular cross sections, each with a different diameter and each diameter known, are made in a material whose X-ray absorption coefficient is equivalent to that of the human body or a living body for experimental research. , inject physiological saline and an angiographic contrast agent at the same concentration as that used during angiography into each of these several types of holes (or into the pipe corresponding to the blood vessel inserted into each hole), and seal both ends. It is characterized by

Hereinafter, as an example of the present invention, a reference scale used for X-ray imaging of the vascular system of an experimental research animal will be described in detail.

FIG. 1 shows an outline of the reference scale of the present invention, and FIGS. 2a and 2b are a front view and a side view thereof. The reference scale main body 1 was made of acrylic resin with an X-ray absorption coefficient close to that of a living body, and its thickness was 7 mm. The diameter of the blood vessel to be observed is 0.5 to 2.
Since the diameter is within the range of 0.58 to 1.67 mm, the reference scale main body 1 is equipped with 5 mm diameters, as shown in Figure 1.
A hole 2 corresponding to the type model blood vessel is made using a drill. The finished diameter of the hole is determined accurately using a microscope or a magnification projector. The thickness of the reference scale main body 1 is adjusted so that it becomes equivalent to the X-ray absorption coefficient of the measurement target part of the experimental research animal. If the X-ray absorption coefficient of the measurement part is large and difficult to adjust based on the thickness alone, the absorption coefficient is adjusted using a filter 3 made of aluminum or the like.

Next, a method of injecting physiological saline equivalent to blood and a contrast medium into various long and narrow holes of the reference scale main body 1 corresponding to model blood vessels will be explained. FIG. 3 is a schematic diagram of a device for this purpose. First, the reference scale main body 1 is placed vertically into a container 4, this container 4 is placed in a vacuum vergeur 5, and the inside of the vergeur 5 is evacuated using the vacuum pump 6. A container 7 provided at the top is filled with physiological saline or an angiographic contrast agent, and when the inside of the vergeure 5 is vacuumed, the container 8 is opened and the contrast agent in the container 7 is dripped into the reference scale body 1. Gradually fill with contrast medium. When each pipe of the reference scale main body 1 is filled with the contrast medium, close the pot 8, let air into the vacuum vergeure 5, take out the reference scale main body 1, close the screws and gaskets provided at both ends of the pipes, and contrast. Seal the agent.

In the present invention, first, as a reference scale for a model blood vessel before a contrast medium is injected, a model blood vessel reference scale was manufactured in which only physiological saline was injected into the reference scale main body 1 by the method described above. Next, for blood vessel imaging, three types of reference scales were prepared using urografin, a water-soluble organic iodine agent for urinary tract and angiography, with urografin concentrations of 30%, 60%, and 76%.

The four types of reference scales for vascular system contrast produced as described above were taken with X-ray photographs, and the fact that they can be used as scales will be explained below.

FIG. 4 is a schematic diagram of the X-ray imaging apparatus. With the X-ray imaging device used, with the soft X-ray imaging device, tube 9
The tube voltage is 80kV, the tube current is 30mA, and the tube 9
The distance between the object and the reference scale 1 is
The X-ray exposure time was set to 490mm, the subject and film were in close contact, and the X-ray exposure time was 0.16 seconds. The film used was a high-sensitivity film for soft X-ray photography. After X-ray exposure, the film in the film cassette 10 was developed for 5 minutes using an X-ray developer (Sofdol) at a developer temperature of 20°C. FIG. 5 shows an image of a blood vessel serving as a reference blood vessel taken on a film after development and fixation.

When the X-ray photographic film produced through the development and fixing process is irradiated with a white light beam of intensity _I0 , the intensity of the transmitted light is I, and the photographic density D is defined by the following equation.

D=logI ₀ /I (1) The photographic density of the center of the model blood vessel in the X-ray image shown in FIG. 5 was measured using a photographic densitometer.

FIG. 6 is a curve showing the relationship between the photographic density D of the X-ray photographic film used in the present invention and the relative exposure amount of X-rays. The vertical axis is the photographic density D, and the horizontal axis is the logarithm of the relative exposure amount.

If there is a linear relationship between the photographic density D and the amount of X-ray light exposed on the film, then
The X-ray dose of radiographed images can be evaluated.

As can be seen from Figure 6, photographic density and X-ray exposure do not have a linear relationship, so the X-ray exposure can be read from the characteristic curve in Figure 6 and the X-ray image can be evaluated based on the X-ray exposure. There is a need to do. The characteristic curve in Figure 6 is obtained by applying a known exposure amount to the film, measuring the resulting density of the photographic film, and showing the photographic density against the relative exposure amount scaled logarithmically. It is.

When the X-ray transmission phenomenon when the reference scale in FIG. 1 is X-rayed is modeled, the result is as shown in FIG. 7. The X-ray absorption coefficient of the blood vessel on the reference scale is μ ₁ , its diameter is x, the X-ray absorption coefficient of the acrylic resin facing the living tissue around the blood vessel is μ ₂ , its thickness is d, and the X-ray source is X-ray intensity I ₁
The intensity of the X-rays reaching the photographic film is I ₃
shall be.

When the X-rays of intensity I ₁ generated in the X-ray source pass through the model blood vessel in the first stage, the intensity I ₂ of the output X-rays is given by the following equation according to the power law.

I ₂ = I ₁ e ^- 〓 ^1x ...(2) Since the X-rays with intensity I ₂ that have passed through the model blood vessel further pass through the acrylic resin, the intensity I ₃ of the X-rays that reach the film is It will look like this:

I ₃ = I ₁ (e ^- 〓 ^1x ×e ^- 〓 ^2d ) ...(3) Taking the logarithm of both sides of equation (3), we get logI ₃ = logI ₁ −μ ₁ xloge−μ ₂ dloge loge=K. Then, logI ₃ −logI ₁ =Kμ ₁ x−Kμ ₂ d E=logI ₃ /I ₁ = −Kμ ₁ x−Kμ ₂ d ...(4) The left side of equation (4) is the relative exposure amount of X-rays. is the logarithm of
In equation (4), the second term on the right side is a constant value, and the blood vessel diameter x can be found by measuring the logarithm of the relative exposure amount.

The relationship between the blood vessel diameter x and the logarithm of the relative exposure amount of X-rays is shown in a graph as shown in FIG. The horizontal axis is the blood vessel diameter X, and the vertical axis is the logarithm of the relative exposure amount of X-rays. As can be seen from this figure, a proportional relationship exists between the blood vessel diameter x and the logarithm E of the relative exposure amount of X-rays, indicating that equation (4) holds true. That is, it has become clear that the reference scale of the present invention can be used as a standard blood vessel during X-ray imaging of the vascular system. In the above embodiment, the angiographic agent or physiological saline was injected directly into the hole 2, but in this invention, a pipe corresponding to a blood vessel is inserted into the hole 2, and the angiographic agent or physiological saline is injected into the pipe. Needless to say, this includes those injected with saline.

As explained above, according to the present invention, several types of elongated cross sections with different diameters and known diameters corresponding to the blood vessels to be imaged by X-ray are formed in a circular shape in a material whose X-ray absorption coefficient is equivalent to that of a living body. Holes were drilled and each hole was injected with an angiographic contrast agent at the same concentration as used during angiography or physiological saline equivalent to blood and sealed, so it was easy to quantify the vascular system from X-ray images. , measurement can be made faster and simpler than conventional blood vessel diameter measurement methods, and blood vessel diameters can be quantified with high precision and reliability in a large number of X-ray images. In addition, by using artificial blood vessels, it is possible to quantify the blood vessel wall, and compared to conventional methods, using this simple reference scale greatly improves the analysis of blood vessel images from X-ray images and saves labor. It is valid.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the standard scale, Figure 2 a, b
are front and side views of the reference scale, Fig. 3 is a schematic diagram of the reference scale manufacturing device, Fig. 4 is a schematic diagram of the X-ray photographing device, Fig. 5 is an X-ray photographic film image, and Fig. 6 is the photographic density. 7 is an X-ray transmission model, and FIG. 8 is a diagram showing the relationship between the blood vessel diameter and the logarithm of the X-ray relative exposure. 1: Reference scale body, 2: Hole, 3: Filter, 6: Vacuum pump, 9: X-ray tube, 10: Film cassette.

Claims (1)

[Claims] 1. In a material whose X-ray absorption coefficient is equivalent to that of the human body or a living body for experimental research, several types of elongated holes with circular cross-sections, each with a different diameter and each diameter known, corresponding to the blood vessels to be X-ray contrasted, are drilled. , a standard for vascular system imaging characterized by injecting into each of these holes an angiographic contrast agent at the same concentration as used during angiography or a physiological saline solution equivalent to blood, and sealing both ends of these holes. scale.