A QUALITY-CONTROL TEST FOR ELECTRONIC PORTAL IMAGING DEVICES

A quality control (QC) test suitable for routine daily use has been de veloped for video based electronic portal imaging devices. It provides an objective and quantitative test for acceptable image quality on th e basis of the high contrast spatial resolution and the contrast-to-no ise ratio (CNR). The test uses a phantom consisting of five sets of hi gh-contrast rectangular bar patterns with spatial frequencies of 0.1, 0.2, 0.25, 0.4, and 0.75 1p/mm. Data obtained during a one month calib ration period were used to determine a critical frequency f(c) for the relative square wave modulation transfer function and a critical cont rast-to-noise ratio (CNR(c)). Subsequent measurements indicating signi ficant deviations from these critical values result in warning message s to the operator indicating potential problems in system performance. Measurements over a period of two years show that the QC test provide s a sensitive indication of imaging performance. (C) 1996 American Ass ociation of Physicists in Medicine.