Contrast enhancement of scanning procedures by high-speed digital computer.

One of the great boons to the scanning process has been the development of contrast enhancement. It has permitted the visualization of clinically significant differences in counting rates not detectable with density:count-rate ratios of 1:1. It has also proved to be one of its greatest curses. At the beginning of a scan, one is unaware of the optimal contrast for the need at hand. In order to overcome this disadvantage a number of efforts involving analog data presentations are undertaken. These include closed-circuit television en hancement by Bender and Blau (1) and color scanning initially by Kakehi and co-workers (2). However useful these efforts at enhancement appear, they share the common faults of the presentation of data in analog form by not allowing retrieval and mathematical manipulation of the data. These problems are sum marized in Table I. Color scans share a number of specific faults with black-and-white presenta tions. Without the capability of data storage, re-scanning at more nearly optimal contrast levels is not possible. Film development is still necessary and is even more cumbersome and expensive if full-size reproductions are desired. Scallop ing not only is still present in color scans but is even intensified in its effect to the point that further efforts in increasing resolution will not prove fruitful until scalloping can be minimized. Beyond the pulse height analyzer in the circuitry of the scanner, even more complex electronic and mechanical apparatus is neces sary for the color scanner.