Detectability of the diagonal direction in the assessment of medical images using a high-brightness liquid crystal display monitor

Liquid crystal display (LCD) monitors show a homogenous quadratic pattern in the number of pixels, size, and dimensions. However, their modulation transfer function (MTF) has a non-isotropic effect in the vertical, horizontal, and diagonal directions on the screen from the shape and pattern of arrangement of pixels. Moreover, the MTF of the human eye differs in spatial frequency response directivity among individuals. In this study, the high-brightness LCD monitor detectability was physically simulated and visually examined throughout the system, including the imaging system. Furthermore, the influence of anisotropy of the LCD monitor was evaluated. The MTF of the LCD monitor was measured by acquiring a bar pattern using a digital camera with sufficiently small pixels in the vertical, horizontal, and diagonal directions and by performing interpolation processing through waveform reproduction and frequency analysis. The detectability of the LCD monitor was verified throughout the system, including the imaging system. Radiographs of the rectangular wave chart (0.5–10 LP/mm) were obtained in the vertical, horizontal, and diagonal (45°) directions to assess the perceivable limit of the human eye (LP/mm). The spatial resolution of the LCD monitor in the diagonal direction was higher than that in the vertical or horizontal direction, which was in good agreement with the results of the profile analysis and visual evaluation.