EVALUATION OF A COMPUTER-RETRIEVED RADIOGRAPHIC IMAGE.

Abstract

A review of the radiologic literature reveals no existing system which performs a digital retrieval (and computer analysis) of scanned radiographic images. The authors' fundamental belief in the potential power and utility of pattern recognition technics in digital computer analysis of radiographs led them to proceed with a pilot study which has convinced them: 1. That the present state of the electronic and mechanical scanning art is entirely adequate to effect analog signal representation of radiographs. 2. That currently available analog-to-digital and digital-to-analog converters and interfaces for digital computers are also entirely adequate. For this pilot study the electronic system was designed and built by one of the authors, Hal C. Becker. Method With a low-resolution system, 35-mm. reproductions of radiographs, and also 2 × 2-in. cutouts from radiographic film itself, were electronically scanned, using a standard Tektronix type 535-A oscilloscope as a flying spot scanner raster source. The light from the scanning raster, after transilluminating the 35-mm. slide and∕or 2 × 2-in. cutout of an original radiograph, was collected by a photomultiplier to develop a video signal which was d.c.-amplified and fed to an analog-to-digital converter. This analog-to-digital unit, loaned by IBM Corporation, provided 500 samples per horizontal scan line, each sample containing 2 digits—the digits ranging from 00 through 99. This digital information was sensed by an IBM 1401 digital computer through its Serial Input-Output Adapter and the elements of each horizontal line (380 lines) were then transferred to digital magnetic tape. We have taken the directional derivatives digitally with the 1401 computer in the +X direction, and the +Y direction. The absolute values of these derivatives were summed for each area element, and this new image matrix, which we shall call the composite derivative of the original image, was written on digital magnetic tape. This composite derivative matrix is now being used in a computer analysis program for scanned radiographic images. We have retrieved both the original image and also the derivative image in two ways: (a) on the IBM 1403 printer, using various characters of the 1403 to produce a gray scale; (b) with a simple digital-to-analog converter operating from the Serial I∕O Adapter of the IBM 1401 computer into an amplifier which modulated the Z axis of a cathode-ray tube in a standard oscilloscope with a long persistence (P7) screen—for visual observation. The oscilloscope screen was photographed with a Polaroid camera in order to produce permanent retrieved photographs of the original image and also of the derivative image.