Automatic Exposure Control in General Radiography

Abstract

SUMMARY An adequate system of automatic exposure control can be used with satisfying results to improve the general film quality in routine radiography. When short exposure times (less than 0.02 sec. = approximately 0.04 sec. setting‐up time) are necessary, a three‐phase generator with automatic current selection ionometric control is essential. Both photometric and ionometric methods combined with other systems of rectification are satisfactory where extremely short exposure times are not necessary. The least satisfactory method is the attachment of either ionometric or photometric sensing devices to generators without falling load characteristics. Radiographers skilled in the aspects of patients' positioning and conversant with the technical processes involved in automatic exposure control are necessary for success of the system in general radiography. When considering automatic exposure control equipment, particular enquiry should be made as to the switching method employed and the minimum exposure times available.

Clinically Acceptable Tolerance of Roentgen Generator Exposure Parameters

“…Hence, the clinically acceptable tolerance was found to be quite large, more than plus or minus one scale step. This was expected, since the smallest density change which the human eye can observe is of the same magnitude (9). Results from calculations made at probability levels from 60 per cent to 100per cent are presented in Fig.…”