JP2853065B2 - X-ray imaging method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray imaging method, and more particularly, to a transmission type X-ray system capable of greatly reducing exposure dose and obtaining high resolution.
The present invention relates to a line imaging method.

[0002] This type of X-ray imaging method is useful in the field of medical diagnosis and can diagnose an affected part in the body at an early stage, and is useful.

[0003]

2. Description of the Related Art In general, a transmission type X-ray imaging method is frequently used in medical diagnosis of a diseased part in a body. That is, X-rays are emitted from an X-ray tube and transmitted through an object, and then directly imaged by an image intensifier (hereinafter, referred to as "II") camera or photographed by an X-ray film The following configuration is adopted.

[0004] In this case, in general, to obtain an appropriate X-ray image, the irradiation dose of the X-ray is increased, and it is necessary to capture a large number of X-ray images from various angles. There is a problem that doctors and the like are forced to receive large doses. According to the announcement of the National Academy of Sciences in December 1989, the relationship between radiation dose and radiation damage was proportional,
In particular, it has been shown that the morbidity of radiation damage (for example, stomach cancer, etc.) can be increased three to four times when a low level radiation is irradiated for a relatively short time and many times. X-ray CT and other methods have a great effect on real-time diagnosis of affected areas,
The X-ray irradiation dose increases according to the imaging time.

[0005]

On the other hand, in the X-ray imaging method, for example, when imaging a bone, there is a problem that a so-called beam hardening phenomenon occurs in which the thickness of the bone is not proportional to the degree of blackening of the bone image on the X-ray film. There is also. In other words, X-rays show a continuous energy spectrum distribution, but there is a problem in performing accurate imaging because this distribution pattern is inclined to one side.
In the above X-ray CT method, this beam hardening phenomenon
Although complicated correction is temporarily performed by a computer to solve the problem, there is a problem that the cost of the equipment is greatly increased. At present, more than 100 years have passed since the discovery of X-rays, although there is a description of elimination (avoidance) of the beam hardening phenomenon in a part of the technical book on X-rays, the beam hardening phenomenon cannot be achieved by any conventional technology. There is nothing to completely eliminate (avoid). Based on such a technical idea, it is extremely difficult for a person skilled in the art to think back to the technical idea of how much the variation of the effective energy of X-rays can be controlled by a filter to completely eliminate the beam hardening phenomenon. Probably. That is, without knowing any technical matter which brings about the fluctuation of the effective energy of X-rays in the ± 0% region in the filter, for example, the conventional method of using Al
It is considered that satisfactory results cannot be obtained even if an attempt is made to avoid the beam hardening phenomenon by adding a thin filter of 2.5 mm or less.

A configuration for overcoming the X-ray beam hardening phenomenon is disclosed in US Pat.
No. 561 and US Patent Application No. 299,538 are proposed. In these cases, X-rays from the same X-ray tube are received by one sensor without passing through the object to be measured, and the other sensor passes through a filter having no change in the linear absorption coefficient due to the thickness of the object to be measured and the object to be measured. After receiving the X-rays obtained, the ratio of the intensities of the two is obtained, thereby effectively avoiding the effect of the beam hardening phenomenon and realizing highly accurate analysis of the measurement object.

The present invention intends to create an effective X-ray imaging method based on the configuration for avoiding the beam hardening phenomenon in the above-mentioned prior invention.

SUMMARY OF THE INVENTION It is an object of the present invention to significantly reduce the radiation dose of X-rays, reduce the radiation dose to patients, doctors or operators, minimize radiation damage, and reduce the beam hardening phenomenon. The present invention is to provide an X-ray imaging method capable of effectively avoiding the problem and enabling high-resolution imaging.

[0009]

SUMMARY OF THE INVENTION According to the present invention, an object of the present invention is to emit X-rays from an X-ray tube and to emit X-rays from the X-ray tube.
In an X-ray imaging method in which X-rays are passed through a filter, X-rays passing through the filter are passed through an imaging target, and then imaged by an imaging device, fluctuations in the effective energy of X-rays emitted from an X-ray tube Is achieved within ± 10% in the filter.

[0010]

According to the present invention constructed as described above, since the variation in the effective energy of X-rays is suppressed to within ± 10% to irradiate the object to be imaged, the beam hardening phenomenon can be effectively avoided to achieve a good result. In addition to obtaining the resolution, the effect of remarkably reducing the irradiation dose is realized. Therefore, in the present invention, since the variation of the effective energy of the X-rays is suppressed to ± 0% in the filter, the beam hardening phenomenon is completely eliminated, and even if the thickness of the same subject changes, particularly, The linear absorption coefficient (μ) shows a substantially constant value and becomes a substantially straight line on the graph. Therefore, it may not be necessary to correct the X-ray quality (linearity).

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, there is shown a system 10 employed in an X-ray imaging method according to the present invention.
0 includes an X-ray source 11 such as an X-ray tube. For example, a hard X-ray beam of 1 ° or less is provided from the X-ray source 11, and a rotating filter disk 12 is provided below the X-ray source.
Is arranged. A number of filter members 13, 13a are spaced apart from each other in the circumferential direction on the rotary filter disk 12.
.. 13n are arranged, and when rotated by an appropriate angle by the rotation driving device 14, a large number of filter members 1 are formed.
One of 3, 13a, 13b,... 13n is disposed immediately below the X-ray source 11. Also, the filter members 13, 13a, 13
b,... 13n are various applied voltages to the X-ray source 11,
In other words, the X-ray source is varied so as to correspond to the various X-ray spectrum distributions from the X-ray source 11, and is set so that the fluctuation of the effective energy of the emitted X-ray is within ± 10%.

X-ray source 11 and rotary filter disk 1
The two rotation driving devices 14 are provided so as to be controllable by the X-ray control device 15 and the filter control device 16, respectively.
The filter control device 16 is linked to the X-ray control device 15 so that a filter member corresponding to the effective energy of the X-ray can be indexed. The X-rays that have passed through the rotary filter disk 12 are irradiated on the imaging target OJ placed on the imaging table 17, and at this time, the imaging target OJ is captured on the X-ray film in the film cassette 18.

On the other hand, if necessary, the film cassette 18 is removed, and the X-rays that have passed through the object to be imaged O.I. I. Camera 1
9 in this case, in which case I.I. I. Camera 19
Is connected to a camera control device 20 to receive suitable control. I. X taken by camera 19
A line image is converted into an image processing device 21 via a camera control device 20.
To the CRT 2 linked to the image processing apparatus 21.
In step 2, the image is output as a perspective image.

Thus, in the system 10 described above, X
The irradiation energy of X-rays is adjusted by the X-ray controller 15 and X-rays are emitted from the X-ray source 11. Then, the irradiated X-rays are passed through one of the indexed filter members 13, 13a, 13b,..., 13n by operating the rotary filter disk 12 so that the fluctuation of the effective energy of the X-rays is kept within ± 10%. . At this time, the operation of the rotary filter disk 12 is performed by driving the rotary drive unit 14 by the filter control unit 16 in accordance with the output from the X-ray control unit 15 to the X-ray source 11. The X-rays that have passed through the filter member are irradiated to the object to be imaged, and an image is obtained by the so-called direct imaging method on the X-ray film in the film cassette 18 or I.
I. Through the camera 19, the camera control device 20 and the image processing device 21, a fluoroscopic image is obtained on the CRT 22.

Experimental Example 1 The X-ray imaging method according to the present invention was adopted,
The thickness of the Al plate is gradually reduced from 0 mm to 10.
The X-ray spectrum distribution was measured using a pure germanium semiconductor detector and a pulse height analyzer while changing the distance to 0 mm in five steps. As a result, as shown in FIG. 2, the effective energy distribution did not have a slope, and the broken line P1 connecting the center values of the energy distribution became substantially vertical. Therefore, it has been found that according to the X-ray imaging method, the influence of the beam hardening phenomenon can be substantially avoided and the resolution can be improved. In this experiment, the tube voltage of the X-ray source 11 was set to 120 kV and the tube current was set to 50 μA.

Comparative Example 1 The same imaging method as in Experimental Example 1 was adopted except that the rotary filter disk was omitted, and an Al plate was used as an imaging target.
The thickness of the Al laminated plate was gradually changed in four steps from 0 mm to 2.0 mm, and the X-ray spectrum distribution was measured by a pure germanium semiconductor detector and a pulse height analyzer. As a result, FIG.
As shown in the figure, the effective energy distribution was inclined. That is, the dashed straight line P2 connecting the center values of the effective energies was inclined under the influence of the beam hardening phenomenon, the fluctuation range of the effective energy reached about ± 22%, and the resolution was reduced.

Comparative Example 2 The same imaging method as in Experimental Example 1 was adopted except that the rotary filter disk was omitted, and an Ag plate was used as an object to be imaged, and the thickness of the Ag plate was gradually reduced from 0 mm to 0.2 m.
m, and the X-ray spectrum distribution was measured with a pure germanium semiconductor detector and a pulse height analyzer.
As a result, as shown in FIG. 3B, the dashed straight line P3 connecting the center values of the effective energy is more greatly affected by the beam hardening phenomenon than in the case of Al shown in FIG. 3A, and the fluctuation range of the effective energy is about ± 31%. And it was found that the resolution was further reduced.

As apparent from Comparative Examples 1 and 2, it is considered that the larger the atomic number of the object to be imaged, the more the beam hardening phenomenon occurs. Therefore, taking into account one of the atomic numbers of the object to be imaged as a parameter, the beam hardening phenomenon is avoided, that is, a rotating filter disk is used so that a straight line connecting the central values of the effective energy in the effective energy distribution of the X-ray does not have an inclination. If the upper filter member is selected and indexed and rotated, a good image can be obtained regardless of the imaging target. Thus, in Comparative Examples 1 and 2, the effective energy fluctuated depending on the imaging target or the atomic number as shown in FIG. 7, but according to Experimental Example 1 of the present invention, as shown in FIG. Regardless, fluctuations in the effective energy were substantially suppressed, and qualitative and quantitative discrimination became possible.

In the imaging method according to the present invention, on the other hand, although the effective energy fluctuates due to changes in conditions such as power supply voltage, current, room temperature, and humidity, the effective energy is 100 keV.
In the following cases, the fluctuation is kept within ± 10 keV, and
When the voltage exceeds 0 keV, the steady state of the effective energy can be achieved by keeping the fluctuation within ± 10% of the fluctuation. In other words, the slope of the straight line connecting the center values of the effective energy as shown by the broken line P1 in FIG. 2 is effectively suppressed, and the variation of the effective energy is within ± 10%, more preferably, close to ± 0%. X-rays immediately after the irradiation are filtered.

Experimental Example 2 The X-ray imaging method according to the present invention was adopted,
These plates are gradually laminated, and the degree of blackening until the image of the peripheral edge of the Al plate of the uppermost layer remains and the image of the central portion becomes invisible becomes I. I. It was monitored on a CRT through a camera.
Thus, the minimum visible thickness of the Al plate as an imaging target was measured. In addition, a copper wire ring having a diameter of 0.6 mm is placed on the upper surface of the Al plate as an imaging target, and the Al plate is gradually laminated, and blackening is performed until the image of the copper wire ring positioned at the top becomes invisible. Degree I. I. It was monitored on a CRT through a camera. Thus, the maximum visible thickness of the Al plate as an imaging target was measured. In this embodiment, the tube voltage of the X-ray source was set to 80 kV and the tube current was set to 1 mA.

Comparative Example 3 The same imaging method as in Experimental Example 2 was adopted except that the use of the rotating filter disk was omitted, and the minimum thickness and the maximum thickness of the Al plate were measured in the same manner as in Experimental Example 2.

FIG. 4 shows the relationship between the thickness of the Al plate and the degree of blackening in Experimental Example 2 and Comparative Example 3. FIG. 5 shows the visible range (depth of focus) of the Al plate and the thickness gradient of the Al plate based on FIG. As a result, the irradiation dose R1 in the experimental example 2 according to the present invention was 54 mR / min, which was 2.7% {(R1 / R2) × 100} compared to the irradiation dose R2 of 2,020 mR / min in the comparative example. It has dropped dramatically.
Further, in Experimental Example 2, the minimum thickness T1 of the Al plate until the center of the uppermost Al plate became invisible was 2.4 cm,
In Comparative Example 3, the minimum thickness T2 of the Al plate until the center of the Al plate of the uppermost layer became invisible was 4.0 cm, and in the case of the present invention, 60% although the irradiation dose was drastically reduced to 1/37. {(T1 / T2) × 100}. On the other hand, in the experimental example, the maximum thickness T3 of the Al plate until the image of the copper wire ring located at the top becomes invisible is 7.4 cm.
In Comparative Example 3, the maximum thickness T4 of the Al plate until the image of the copper wire ring located at the top became invisible was 8.6c.
86% ｛(T3 / T4) x
It stayed at about 100｝. Therefore, in the case of Experimental Example 2, the visible range Z1 of the Al plate during X-ray transmission is 5.0 cm.
(T3-T1), but in the case of the comparative example 3, the visible range Z2 is 4.6 cm (T4-T2), and according to the experimental example 2, it is 109% ｛(Z1 / Z) as compared with the comparative example 3.
2) x100 °, it was found that the visible range was widened.

Experimental Examples 3 to 7 Further, as shown in Table 1, the imaging object and the tube voltage were changed, and the irradiation dose and the visible range of the image of the imaging object were measured in the same manner as in Experimental Example 2. In this case, the filter members were appropriately changed as shown in Table 1 according to the tube voltage of the X-ray source.

[0024]

[Table 1]

Comparative Examples 4 to 8 Further, as shown in Table 1, the irradiation object and the visible range of the image of the object were measured in the same manner as in Comparative Example 3 by changing the imaging object and the tube voltage.

Experimental Examples 3 to 7 and Comparative Examples 4 to 8
As is clear from the results, the irradiation dose can be drastically reduced to 1/8 to 1/25 by the X-ray imaging method according to the present invention,
As a result, the exposure dose to the operator can be minimized, and satisfactory resolution can be maintained. This is extremely useful in the field of medical diagnosis, and the resolution of the imaging target is significantly improved, and the visible range is wide. It has been found that high quality X-ray images can be provided.

Further, when X-ray imaging is performed by the X-ray imaging method according to the present invention, the tube voltage under normal imaging conditions is increased by 10 to 20%.
Even if it is increased, it is possible to greatly reduce the irradiation dose, and it is possible to obtain an extremely high-quality X-ray image using a commercially available X-ray film.

Experimental Examples 8 and 9 As shown in Table 2, X-ray images were obtained with commercially available X-ray films while increasing the tube voltage under normal imaging conditions by 20%. Table 2 shows the irradiation dose of each experimental example in comparison with the irradiation dose under normal imaging conditions.

[0029]

[Table 2]

Experimental Example 10 X-ray images were obtained in the same manner as in Experimental Examples 8 and 9, except that the tube voltage was increased by 10% and 20% with respect to the tube voltage under normal photographing conditions. Table 2 shows the irradiation dose in comparison with the irradiation dose under normal imaging conditions. Actually, the filter member of Experimental Example 8 is Al0.415 mm,
The filter member of Experimental Example 9 was composed of 0.30 mm of Al and 0.70 mm of Cu, and the filter member of Experimental Example 10 was composed of 0.40 mm of Cu and Ag 0.20 mm.
The results described above were obtained by using each of the components constituted by mm. Of course, the filter components used herein are well known.

Comparative Examples 9, 10, and 11 X-ray images were obtained in the same manner as in Experimental Examples 8, 9, and 10, except that the use of a rotating filter disk was omitted. Table 2
Shows the irradiation doses.

In Experimental Examples 8 to 10 and Comparative Examples 9 to 11, the tube current was about 100 mA. Table 2 shows the irradiation dose ratios of Experimental Examples 8 to 10, and Comparative Example 10
It is represented as 0.

These Experimental Examples 8 to 10 and Comparative Examples 9 to
As is clear from the results of FIG. 11, the irradiation dose was reduced to １ ／ to わ ら ず despite the increase in the tube voltage to 10% or 20%.
It dropped sharply to 1/11.

In general, in the present invention, in particular, the closer the line connecting the center values of the effective energy to the vertical line, the lower the energy side, that is, 50 keV or less in FIG. It will be appreciated that the dose can be cut, the morbidity of radiation damage believed to be caused by low energy X-ray irradiation can be reduced, and human injury can be effectively suppressed.

[0035]

According to the above-mentioned X-ray imaging method of the present invention, it is possible to realize imaging with high resolution and sufficiently contribute to accurate medical diagnosis and the like, and particularly, to significantly reduce the irradiation dose. Therefore, the radiation dose to the patient, the doctor, the operator, or the like is greatly reduced, and the effects such as the occurrence of radiation damage can be effectively suppressed.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an overall configuration of an X-ray imaging method according to the present invention.

FIG. 2 is an X-ray spectrum distribution diagram in the case of using the imaging method shown in FIG.

3A and 3B are X-ray spectrum distribution diagrams in an imaging method not according to the present invention, respectively, shown in contrast to FIG.

FIG. 4 is a schematic diagram showing the relationship between the depth of focus of X-rays and the thickness of the imaging target, in contrast to the case according to the present invention.

FIG. 5 is a schematic diagram showing the relationship between the depth of focus of X-rays and the gradient of an imaging target in comparison with the case according to the present invention.

FIG. 6 is a graph showing the relationship between the thickness of the imaging target and the effective energy in the X-ray imaging method of the present invention.

FIG. 7 is a graph showing the relationship between the thickness of the imaging target and the effective energy in the X-ray imaging method not according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 System 11 X-ray source 12 Rotary filter disk 13a ... 13n Filter member 14 Rotation drive member 15 X-ray controller 16 Filter controller 17 Table

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-103552 (JP, A) JP-A 62-36704 (JP, U) JP-A 54-36625 (JP, Y2) supervised by Hirokazu Kimura Recent medical image diagnostic equipment ”Asakura Shoten Co., Ltd. 1988.6.25 p127-p128 Yoshinori Iwai“ CT Scanner-X-ray Computer Tomography Apparatus-”Corona Corporation S54.2.20 p35- p37

Claims (3)

(57) [Claims] 1. Beam hardening in a medical X-ray imaging system comprising an X-ray source, a filter disposed on the X-ray of the X-ray source, and imaging means for realizing high-resolution X-ray imaging of an object. A method for reducing the phenomenon, comprising: a) providing a uniform reference object and a plurality of filter members having a thickness gradually increasing from a zero value to a predetermined maximum value; and b) providing a low energy distribution of radiated X-rays. X-rays are passed through one of the filter members selected to cut the energy-side portion; c) the center of the effective energy of the energy portion of the X-rays passing through the filter member and the reference object relative to the reference object; D) comparing the effective energy centers of the energy portions obtained for different thickness portions of the reference object to determine a difference between each effective energy center corresponding to various thicknesses of the object; e. ) Standard target Selecting a particular filter member from the plurality of filter members in which the difference between the effective energy centers in the entire range of different thicknesses is within 10% of the effective energy center value for the minimum thickness of the reference object. b)
F) repeating the X-ray imaging using the specific filter member. 2. The method of claim 1, wherein the imaging means comprises a multiplier tube camera, an image processing means, and a cathode ray tube. 3. The method of claim 1, wherein the imaging means comprises a film cassette.