X-ray or gamma ray systems or devices – Specific application – Fluorescence
Reexamination Certificate
2001-09-25
2004-06-22
Glick, Edward J. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Fluorescence
C378S087000, C378S088000
Reexamination Certificate
active
06754304
ABSTRACT:
BACKGROUND OF THE INVENTIONS
1. Field of the Inventions
The suggested inventions relate to the intra-vision means and are designed for producing visually sensed images of the internal structure of an object, in particular, of a biological object, with X-rays. The preferential applications include defectoscopy and medical diagnostics.
2. Description of the Prior Art
Various methods and devices of the said intended use are known, where traditional principles of projection roentgenoscopy are embodied. In such methods and devices, the visible image of the object's internal structure, for example, tissues of a biological object, is obtained as a shadow projection. Density of the acquired image in each of its points is determined by the total attenuation of X-rays that passed through the object on their way from the source to the detection means. The latter is either a fluorescent screen or an X-ray film, which should be chemically treated to get the image visualized (see Polytechnical Dictionary. Moscow, “Soviet Encyclopedia”, 1976 [1], p.425; Physics of image visualization in medicine. Edited by S. Webb. Moscow, “Mir”, 1991 [2], p. 40-41).
In the above mentioned known methods and devices, the image of a real three-dimensional structure is acquired as the said two-dimensional shadow projection, which interpretation requires from the specialist who carries out object analysis, in particular, technical or medical diagnostics, respective experience and qualification and, in a number of cases, is problematic. The reasons for this are low contrast, poor signal to noise ratio, inevitable overlapping of the images of structural elements, impossibility of quantitative comparison between individual local fragments by density. Sharpness and contrast of the acquired image also decrease under the influence of quanta of the secondary Compton scattered radiation, hitting the detection means.
X-ray computer tomography methods and devices permitting to acquire a two-dimensional image of a thin layer of a three-dimensional object are known (V. V. Piklov, N. G. Preobrazhenskiy. Computational tomography and physical experiment. The progress of physical sciences, v. 141, 3
rd
ed., November 1983, p. 469-498 [3]; see also [2], p. 138-146). Such methods are using multiple irradiation of the object under study from different positions and registration of the radiation that passed through this object by a line of detectors. The obtained tissue density distribution of the object in the cross-section under study (target cross-section) is discrete and achieved through computer-assisted solution of combined equations, the order of which as well as the number of resolution elements correspond to the product of the number of positions, from which irradiation is done, by the number of detectors. Doing irradiation in different cross-sections, one can obtain a three-dimensional image of the object based on a set of two-dimensional by-layer images. Computer tomography means permit in principle to obtain an image of sufficiently high quality, and this image presents the picture of tissues density distribution (in contrast to a picture specific to integral absorption of a substance (for example, biological tissues), located in the path of radiation from the source to this or that element of the observed projection.) But this is achieved through a greater number of positions, from which irradiation is done. In this case, the dose of radiation absorbed by the substance is higher, which is undesirable (and in medical applications, is most frequently inadmissible). Presence of Compton scattered radiation is a nuisance factor in this group of known methods and devices too. Both groups of methods and devices used for medical applications are also characterized by the fact, that tissues and organs, which present no interest in the study but are located in the radiation path (both in front and behind the target area), also suffer from intensive radiation (to a lesser degree in the second group of methods and devices than in the first group of methods and devices because when different positions are selected, different tissues and organs surrounding those that are under study are irradiated).
Higher resolving power in the second group of means, requiring a greater number of irradiations from different positions, is limited, first of all, due to inadmissible growth of the dosage. Technical means for acquiring primary data and further image reconstruction is quite complex due to necessity of using fast computers with special software and high-precision requirements to the mechanical structural elements, which must guarantee correct localization of one and the same resolution elements in the target area during their irradiation from different positions. The latter is caused by the fact that the image reconstruction calculations must use the actual data obtained from different irradiation cycles but referring to one and the same resolution elements.
The second above mentioned group of methods and devices, where discrete data on the density of each of the resolution elements is obtained, is the closest one to what is suggested.
SUMMARY OF THE INVENTIONS
The technical result, which the suggested inventions are aimed at, consists in higher accuracy of determining relative indices of the object's substance density in the acquired image together with avoided use of complex and expensive technical means. When the suggested inventions are used for diagnostic purposes in medicine and other investigations related to the action on biological objects, the achieved result consists also in reduced dosage of radiation of tissues surrounding the tissues under study.
To obtain the said types of technical results, in the suggested X-ray method of producing the image of the internal structure of an object, the X-rays are concentrated in a zone, which is located inside the area under study (which area is hereinafter referred to as the target area) of the object. Secondary radiation (scattered Compton coherent and non-coherent, fluorescent radiation), excited in this zone, is transported to one or more detectors. Scanning of the target area of the object is done by way of moving the zone of concentration. The results of measurement at each current position of the zone of concentration (X-rays concentration zone) are attributed to one of the points inside this zone. Movement of the zone of concentration during scanning is followed by simultaneous determination and fixation of coordinates of this zone. Judgment on the density of the object's substance in this point is made based on the population of intensity values of the secondary radiation, which are obtained with the help of one or more detectors and which are determined simultaneously with the coordinates of the said current point. The obtained values, recognized as the density indices of the object's substance, together with respective values of coordinates, are used for building up a picture of the substance density distribution in the object's target area. Movement of the X-ray concentration zone for scanning the object's target area is done by way of relative movement of the object under study and the X-ray sources, which relative position between themselves remains stable, together with the X-ray concentration means, means for secondary radiation transportation to the detectors, and the detectors themselves.
A common feature for the known from ([2], pp. 138-146, [3], pp. 471-472) and suggested methods is the action on the object under study with X-rays during relative movement of the object under study and the X-ray optical system including X-ray sources together with their control units and detectors.
One of the differences of the suggested method consists in the presence of the operation of concentrating X-rays in the zone covering the current point, in which it is required to determine a density value (a current point, to which the measurement results are attributed). Scanning, which presence is a c
Glick Edward J.
Ho Allen C
Holt William H.
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