An Improved Technique for Enhancing Small Periodic Contrast Changes in Television Fluoroscopy

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Abstract
A highly accurate electrical subtraction technique has been developed for detecting and imaging very small periodic contrast changes in a video signal. The process uses two electrical-in electrical-out vidicon-like cathode ray tubes. The first tube puts out a video difference signal only when there is a change in the input video signal. The second, a silicon target storage tube, is used for integrating the difference signal. This storage tube is alternately operated above and below the first crossover point on the secondary emission characteristic for increased common mode rejection in the integrated difference signal. Periodic signals occupying .06 percent of the full scale video scene have been detected. This represents a factor of 10 increase in sensitivity over previously reported results.' The technique has been successfully used for detecting and imaging very small concentrations of non-radioactive iodine and xenon in x-ray phantoms using a conventional television fluoroscopy system. The details of the image subtraction electronics will be described.

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