Temporal response of medical liquid crystal displaysa)

Abstract

Displays based on liquid crystal technology suffer from slow temporal response due to the dynamics of the molecular rearrangement in response to a pixel voltage change. A slow display can affect the visualization by the human observer of subtle contrast in dynamic presentation of volumetric image datasets or real-time image sequences. In this paper, we describe a measurement method for the characterization of the temporal response of medical liquid crystal displays (LCDs). The ratio of luminance difference to noise at the gray levels of concern determines the reliability of measurements. Coefficients of variations are used to represent the measurement reliability. We optimized the repeatability of most response time measurements to less than 10%. However, poor repeatability is encountered for the response of adjacent gray levels. 256 X 255 inter-gray-level transition time matrices were measured for four medical displays and one high-definition TV LCD display. Response times range from below 20 ms to above 150 ms. For each display, response times are not uniformly distributed, with a faster response for large gray-level transitions. Transition times are smaller when the starting gray level is between 10 and 20 for a target between 25 and 150. The difference could be over 100 ms for different transitions within a display. For transitions with poor temporal response, the luminance after 1, 3, and 5 frames reaches only 12, 45, and 75% of the target value, respectively. We also found that LCD response time depends on temperature, with 1 h warm-up reducing the response time by a factor of 2.