Radiant energy – Source with recording detector
Reexamination Certificate
2000-11-03
2002-05-21
Hannaher, Constantine (Department: 2878)
Radiant energy
Source with recording detector
C250S306000, C250S458100, C250S483100, C250S472100, C378S098800, C378S098900, C378S098300
Reexamination Certificate
active
06392248
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a novel method and apparatus for color radiography applied to medical diagnosis or various kinds of non-destructive inspections, and color light emission sheet therefor.
2. Description of the Related Art
In radiography used for medical diagnosis or industrial non-destructive inspection, it is usual to use a combination of an X-ray film and an intensifying screen to enhance sensitivity of a radiography system. In the radiography, light converted into visible light by irradiating X-rays transmitted through a subject to be inspected on the intensifying screen reduces for instance silver grains on a monochrome X-ray film to blacken, thereby obtaining a transmission image of the subject.
A radiation intensifying screen used in radiography or the like is generally constituted of a support consisting of paper board or plastics, a phosphor layer having a light emission peak corresponding to the X-ray film, and a protective film for protecting the phosphor layer, laminated in this order. Recently, in addition, there is a method where with a light detecting element such as a CCD camera or the like as an imaging system to do without the X-ray film, difference of an amount of transmission of the radiation being digitally detected.
X-radiography for medical diagnosis is applied to various parts of a human body to find out various kinds of foci. In recent years, in order to improve detection sensitivity, a higher contrast X-ray film is main stream. For instance, in mammography due to X-rays (mammography, hereafter), calcification and abnormal soft tissue in a mamma in which difference of X-ray absorption is very scarce have to be radiographed with high resolution and appropriate contrast. To this end, an X-ray tube having a Mo target generating X-rays of approximately 30 kV is used and, in addition, a high contrast X-ray film being used.
In the aforementioned X-radiography, energy of irradiated X-rays and an irradiation period have to be optimized according to the subject, thereby a radiogram of an appropriate film density being obtained. Conditions for radiography are determined further based on a dynamic range (latitude) of the X-ray film, parts to be radiographed of a human body that is a subject and individual difference.
Optimization of the radiographing conditions necessitates a lot of experiences to result in depending on individual technician's skill. Accordingly, depending on the technician's skill, the conditions may deviate from the optimum ones to result in poor X-ray exposure (black radiograph) or excessive X-ray exposure (blank radiograph). In particular, when an X-ray film of high contrast is used, the range of the optimum conditions is very narrow to be likely to result in the poor exposure or excessive exposure.
That is, the contrast characteristics of an existing X-ray film can be understood from a characteristic curve of a film as shown in FIG.
13
. In
FIG. 13
, ordinate denotes film density when the film is exposed, abscissa denoting logarithmic value of the exposure (relative value). The characteristic curve of the film can be divided into three portions based on its shape. A curve portion A of relatively low exposure is called a leg region and corresponds to a low film density portion of a radiograph to result in a very low contrast image or no contrast image. A curve portion C of relatively high exposure is called a shoulder region. There is an upper limit in film density. Accordingly, exposure variation in the C region does not cause variation in contrast.
The highest contrast region B is located interposed between the aforementioned leg region and the shoulder region. The characteristic curve in the region B has a relatively straight and large gradient. The characteristic curve of the X-ray film is determined dependent on parameters such as a grain diameter of silver compound in an emulsion and a thickness thereof. Accordingly, by controlling these parameters, the films different. in sensitivity and contrast characteristics can be obtained. The high contrast X-ray film is one the gradient of which is large in the region B of the characteristic curve.
The densities of the leg and shoulder regions of the characteristic curve are approximately the same for all films. Accordingly, the larger gradient of the characteristic curve causes a narrower range of exposure (latitude) in the region B. In radiographing, the X-ray exposure is preferable to be set at just midway of the region B. However, when an X-ray film of particularly narrow latitude is used, a slight deviation of the conditions causes an image of an inappropriate density. In the existing X-ray film, a width of latitude is approximately one to two digits.
Furthermore, as in the case of the target subjects being blood and tissue, when element compositions of the target subjects are different, taking X-ray energy to be used and the thickness of the subject into consideration, an irradiation period (exposure period) has to be determined based on much experience. When, as in the case of normal tissue and abnormal tissue such as cancer tissue, the element compositions are approximately the same but the densities are different, the situation is also the same. In setting such conditions, the skill of the technician affects largely. In particular, in recent medical diagnosis, as in the case of early findings of cancer for instance, there is a strong demand for a correct detection of an extremely small abnormal tissue. However, a slight deviation of the radiographing condition may cause a radiograph of an inappropriate film density.
Such problems, without restricting to the radiography for medical diagnosis, also similarly occur in the industrial non-destructive inspection. For instance, when the target subjects are aluminum and iron, due to density difference thereof, the optimum conditions for radiographing are naturally different. In addition to this, the thickness of the target subject has to be considered. Furthermore, when there are contained a plurality of substances as in composite material, many radiographs have to be taken while changing the irradiation condition, handling inconveniences causing many problems.
In the existing radiography, it is general to obtain, with the monochrome X-ray film :as mentioned above, a radiograph of a target subject as a monochrome gray-scale image. In the monochrome gray-scale image, it is difficult to draw information out of a slight density change. To overcome such difficulties, there is proposed color radiography (cf. Japanese Patent SHO 48-6157 Official Gazette and Japanese Patent SHO 48-12676 Official Gazette). In the above color radiography, a fluorescent screen (or intensifying screen) furnished with a plurality of line spectra by means of two or more kinds of phosphors is used, thereby the respective color sensitive layers of color film being independently sensitized.
According to the color radiography, a radiograph in which a color changes in accordance with the difference of an amount of X-rays (color radiograph) can be obtained. In the obtained color radiograph, the low exposure portion is colored in red, as the exposure increases a green color starts to mingle with red, a further increase of exposure causing blue to mingle with red and green. A still further increase of the exposure results in white.
However, how hard trying to draw information only out of color variation on the color radiograph, for instance in the portion where much X-ray is exposed, as a result of addition of green and blue to red, the color becomes whitish to be rather difficult in drawing out the information. Furthermore, in the lower exposure portion, there is no difference from the existing monochrome radiograph until the red color component saturates. Accordingly, for the part of lower contrast in comparison with the existing monochrome radiograph, it is difficult to draw out the information.
As mentioned above, in the existing radiography, in particular when a high contrast X-ray film of which g
Nittoh Koichi
Oyaizu Eiji
Saito Akihisa
Takahara Takeshi
Tamura Toshiyuki
Hannaher Constantine
Israel Andrew
Kabushiki Kaisha Toshiba
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