Novel MTF Measurement Method for Medical Image Viewers Using a Bar Pattern Image

摘要

A novel MTF(modulation transfer function) measurement method using a bar pattern image for medical image viewers such as DICOM viewer was developed. A bar-pattern image produced by a personal computer was displayed on a cathode-ray-tube (CRT) display and was imaged with a high resolution single-lens reflex digital camera equipped with a close-up lens. The discrete blurred square-waveform data acquired from the imaged bar patterns were interpolated using the waveform reproduction technique with Fourier analysis in order to obtain interpolated wave curves. All of the measured pixel values in this process were converted into luminance data. The MTF was calculated from the amplitude values of the extracted basic frequency components in the square-waveform, in which an aliasing error was excluded. Actual measurements were performed with two models of medical image viewer equipped with monochrome displays. Horizontal and vertical MTFs at the central position of display area were measured up to Nyquist frequency. Resultant MTFs clearly indicated the difference in resolution for two viewers, as well as visual evaluation did. The standard deviations of MTF values of 5 measurements at Nyquist frequency were 0.004 and 0.01 for horizontal and vertical directions, respectively. Employment of a commercial single-lens reflex digital camera enabled easy and correct focusing and simple data handling. In conclusion, our method may be useful in the medical field due to good reproducibility and easy operativity.