Patent GB-1432088-A (GB)
Title: Differential enhancement of periodically variable means
IPC: G21K4/00
Filed: 1974-05-28
Abstract: 1432088 X-ray apparatus WISCONSIN ALUMNI RESEARCH FOUNDATION 28 May 1974 [14 June 1973] 23591/74 Heading H4F The differential features of periodically variable X-ray or other images are enhanced as to contrast and visibility by using a television system to convert the images into video signals, which are then processed through two successive stages of video subtraction preferably utilizing two different types of video storage devices and displayed. The second stage of video subtraction also involves integration of the differential features so that the contrast and visibility of the features can be built up over a multiplicity of cycles. In the disclosed embodiment, first and second specifically different X-ray images are obtained by producing the X-ray images under different conditions, as by interposing different filters, e.g. containing cerium and iodine, in the path of the X-rays, switching between two different X-ray sources or by energizing an X-ray source with two different voltages to produce different energies. Alternatively the differential features in the X-ray images may be time-dependent, e.g. caused by the heart beat or respiration of a subject. By means of an intensification screen and television camera, the X-ray images are converted into first and second video image signals, which are successively supplied to a video difference detector. Such detector preferably utilizes a video storage tube capable of storing video images in the form of electrical charges distributed over a dielectric layer on a conductive target backplate. The first and second video images are supplied sequentially to the storage tube, which produces a first differential video signal corresponding to the difference between the first and second video signals. The first differential video signal is then supplied to a second integrating and subtracting storage device preferably utilizing a second storage tube capable of storing video images in the form of electrical charges on a mosaic of dielectric islands on a conductive backplate. The first differential video signal is written positively on the target of the second storage tube. The first storage tube is then employed to develop a second differential video signal corresponding to the difference between the second and first video image signals. The second differential video signal is written negatively on the target of the second storage tube. In this way, the differential features of the first and second differential video signals are integrated and enhanced, while the identical or non-differential features of the first and second differential video signals are combined subtractively so as to cancel them from the target of the second storage tube. To obtain the maximum enhancement of the differential features, this cycle of subtraction and integration is repeated so that a multiplicity of cycles are completed. The enhanced image on the target of the second storage tube is then read and reproduced as a visible display on a television monitor. By this system, differential features amounting to only a fraction of 1% of the full contrast range of successive X-ray images can be enhanced to full contrast so that such differential features will be clearly visible.