Structural inhomogeneity in mammography quality control phantoms detected by refraction-enhanced synchrotron radiation imaging.

Synchrotron radiation imaging with the refraction-enhancement mode visualized structural inhomogeneities in phantoms used for image quality control of mammography. Eight phantoms were examined, all of which were manufactured in the United States and approved by the American College of Radiology as dedicated phantoms. In addition to fiber- and mass-mimicking test objects, each phantom has 5 groups of calcification specks of various sizes. Synchrotron radiation (SR) imaging was performed at Spring-8, a synchrotron radiation facility in Japan. Images were obtained with monochromatic 20-keV x-ray beams, a radiation field of 15 mm X 26 mm at a sample plane, a CCD camera with a resolution of 6 micrometers as a detector, and a sample-to-detector distance of 10 to 11 m. Two hundred and forty specks were evaluated in total in the SR images, and the surrounding area of each speck was also included. Evaluation of the images showed that 14 crack-like structures were depicted near specks, and there were 62 specks with attached void(s) or air bubble(s). Refraction-enhanced SR imaging sensitively detected structural inhomogeneities and abnormalities in phantoms which were implicitly agreed to have a homogeneous matrix and test objects without foreign substances. A possible manufacturing-dependent quality issue was identified. The effect of inhomogeneities detected by SR imaging on visual scoring of specks could not be identified in the tested phantoms; this should be assessed on images of other phantoms in a future study.