Viewing angle performance of medical liquid crystal displays

Abstract

Cathode-ray tube (CRT) and liquid crystal display (LCD) are currently two main technologies for displaying medical images. LCDs possess a number of advantages, but their performance varies as a function of viewing angle. Our purpose in this study was to characterize the angular response performance of five medical-grade LCDs, and to substantiate their impact on their compliance with the DICOM gray scale display function (GSDF). Furthermore, the study aimed to test a framework to define an angular acceptance range for medical LCDs based on the recent AAPM TG18 guidelines. Measurements were made on five calibrated dual-domain LCDs, including two 3 megapixel monochrome LCDs, two 5 megapixel monochrome LCDs, and one 9 megapixel color LCD. The luminance performance of each display device was measured as a function of the viewing angle at 17 discrete levels using TG18-LN test patterns and a Fourier-optics-based luminance meter. The luminance data were analyzed according to the AAPM TG18 methodology. The displays showed notable variation in luminance and contrast performance as a function of the viewing angle, particularly in diagonal viewing orientations. Overall, the luminance ratio remained greater than 175 within ±20° and ±33° viewing angle cones (β175 =20°-33°). Aiming to maintain a maximum deviation from the GSDF contrast less than 0.3, i.e., κ17 ≤0.3, acceptable viewing angle cones of ±22° and ±35° were indicated (α0.3=22°-35°). The findings demonstrate the significant impact of angular response on image contrast, and the utility of α0.3 and β175 quantities for defining the viewing angle cones within which a medical LCD device can be effectively utilized. © 2006 American Association of Physicists in Medicine.