The dependency of pixel size on calcification reproducibility in digital mammography

The purpose of this study is to determine the relative effect of MTF, DQE, and pixel size on the shape of microcalcifications in mammography. Two original images were obtained by a) scanning the film that accompanies an RMI-156 phantom at a resolution of 25 mu m per pixel, b) creating an image with various shapes on a computer. Simulated images were then obtained by changing MTF, adding noise to simulate DQE effects, and changing the resolution of the original images. These images were visually evaluated to determine the recognition of the shape. In the evaluation of 400 mu m microcalcifications on the RMI-156 phantom, we found that shape recognition is maintained with a pixel size of 50 mu m or less regardless of MTF. However, at resolutions over 50 mu m, recognition was insufficient even when MTF was increased. Adding noise decreased visibility but did not affect shape recognition. The same results were obtained using computer-created shapes. The effect of pixel size on the recognition of the shape of microcalcifications was shown to be greater compared to MTF and DQE. It was also found that increasing MTF does not compensate for information lost because of enlarged pixel size.