ANALYSIS OF VARIATIONS IN CONTRAST DETAIL MEASUREMENTS PERFORMED ON IMAGE INTENSIFIER TELEVISION SYSTEMS

The magnitude of the observer variations intrinsic to contrast-detail measurements were found to be independent of the type of image used in their determination. The two sources of variation identified, within-observer and between-observer variation, were deduced to be 0.115 and 0.111, respectively (variations expressed as a relative standard deviation). When using the Leeds fluoroscopy test objects, an uncertainty on the measured threshold contrasts of 16% for one observer and 11% for two observers may be anticipated when each observer makes one independent reading. This then implies that a change of one perceived disc on the T010 test object (in which the contrast step between discs is approximately 40%) for one independent measurement made by one observer will be significant within two standard deviations. A further implication is that a more sensitive contrast-detail test object could be developed (with approximately 20% contrast steps between discs), provided that the test object is viewed by two or more observers.