In-field assessment of display resolution and noise: Performance evaluation of a commercial measurement system

Abstract

— Two key metrics of image quality for high-fidelity displays, including medical displays, are resolution and noise. Until now, these properties have been primarily measured in laboratory settings. For the first time, a system consisting of a CCD camera and analysis software has been made commercially available for measuring the resolution and noise of medical displays in a clinical setting. This study aimed at evaluating this new product in terms of accuracy and precision. In particular, the project involved the measurement of the modulation transfer function (MTF) and the signal-to-noise ratio (SNR) of two medical imaging displays, one cathode-ray tube (CRT) display and one liquid-crystal display (LCD) using this camera/software system. To assess the system's precision, measurements were made multiple times at the same setting. To check for accuracy, the results were compared with published values of the MTF and noise for the same displays. The performance of the system was also ascertained as a function of the focus setting of the camera. The results indicated that for the LCD, when the camera is focused within ±0.6 mm of the optimum focus setting, the MTF values lie within approximately 14% of the best focus MTF at the Nyquist frequency and 11% of the optimum overall sharpness (∫ MTF2 df). Similar results were obtained in the horizontal and vertical directions. For the CRT, this focus produced vertical and horizontal MTF values at the Nyquist frequency within 15.2% and 61.2% of the optimum focus MTF, respectively. The figures in terms of overall sharpness were 3.0% and 0.7%. The results for the noise measurements showed a repeatability of 3% for the LCD and 13% for the CRT and a relative (but not absolute) magnitude of the noise between the two displays reflective of prior measurements. Overall, the measurement system yielded reasonably precise resolution and noise results for both display devices. The accuracy was traceable to published results only for the MTF and for relative level of display noise with differences in the absolute magnitude of noise between current and prior measurements attributed to variations in the non-standard techniques applied for display noise measurements.