Radiant energy – With charged particle beam deflection or focussing – With target means
Patent
1975-03-27
1976-08-10
Smith, Alfred E.
Radiant energy
With charged particle beam deflection or focussing
With target means
178DIG5, 250510, G03B 4116
Patent
active
039743861
ABSTRACT:
Differential X-ray images are produced in order to improve the visibility of a contrast medium, such as iodine or xenon, having a K absorption edge at a predetermined X-ray energy. Such differential images are produced by combining first, second and third X-ray images which are individually produced by using first, second and third X-ray spectra at first, second and third X-ray energy levels. The first energy level is below the K edge energy, while the second energy level is above the K edge energy. The third energy level is above the second energy level. The second X-ray image is combined subtractively with the average of the first and third X-ray images to produce a differential X-ray image in which any image elements due to soft tissue and bone are largely cancelled out, while image elements due to the contrast medium are enhanced. In one preferred method, two versions of the second image are combined additively, and the first and third images are combined subtractively therewith. The first, second and third X-ray spectra may be produced by using a single X-ray source with first, second and third X-ray filters. When the contrast medium is iodine, such filters may contain iodine, cerium and lead, respectively. The X-ray source is preferably operated with first, second and third anode voltages when the first, second and third filters are used. The intensity level of the X-ray source may also be changed to provide three different intensity levels for the three different filters. The three X-ray images are preferably converted into television images which are combined electronically to produce the differential X-ray images. Three different gain levels may be employed in the television system for the three filters. The television system may include first and second image storage tubes to provide two stages of image subtraction. The first storage tube may be arranged to produce the differences between successive images in a four image system, in which two versions of the second X-ray image are used alternately with the first and third images. The difference signals produced by the first tube are then selectively written positively or negatively on the second tube in such a manner as to enhance and integrate the image elements due to the contrast medium, while largely cancelling out the image elements due to the soft tissue and bone.
In the television system, it is highly advantageous to provide logarithmic video amplification, so that except for constant terms the video images will be proportional to the absorption coefficients. With such logarithmic amplification, the greatest degree of cancellation of the image elements due to bone and soft tissue is achieved.
REFERENCES:
patent: 3588502 (1971-06-01), Greenfield
patent: 3854049 (1974-12-01), Mistretta et al.
Kelcz Frederick
Mistretta Charles A.
Grigsby T. N.
Smith Alfred E.
Wisconsin Alumni Research Foundation
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