COMPUTER-ANALYSIS OF MAMMOGRAPHY PHANTOM IMAGES (CAMPI) - AN APPLICATION TO THE MEASUREMENT OF MICROCALCIFICATION IMAGE QUALITY OF DIRECTLYACQUIRED DIGITAL IMAGES

The purpose of this investigation was to apply the recently developed CAMPI (computer analysis of mammography phantom images) method to a Fi scher Mammotest Stereotactic Digital Biopsy machine. Another aim was t o further elucidate the nature of the empirically introduced CAMPI mea sures. Images of an American College of Radiology (ACR) accreditation phantom centered on the largest two speck groups were obtained on this machine under a variety of x-ray conditions. An additional measure, a lternative SNR (ASNR) is introduced which is complementary to the SNR measure. Analyses of the Mammotest images revealed that the mAs and kV p dependencies of the CAMPI measures could be understood from basic im aging physics principles. It is shown that: (1) the measures reflect t he expected linearity of the digital detector and Poisson photon stati stics; (2) under automatic exposure control (AEC) conditions the signa l (SIG) measure is proportional to subject contrast; and (3) under AEC conditions the noise (NOI) measure is proportional to the square root of the average absorbed photon energy. Correspondence with basic imag ing physics principles shows that the measures are significantly free of artifacts. Precision of the CAMPI measures exceeds that of human ob servers by orders of magnitude. CAMPI measures are expected to be mere relevant to clinical mammography than Fourier metrics as the measurem ents are done on objects of arbitrary shape and size that were designe d by the manufacturer to resemble Various detection tasks in mammograp hy. It is concluded that CAMPI can perform objective and highly precis e evaluations of phantom image quality in mammography. It could be use d as a sophisticated quality control tool, as a replacement for the cu rrent ACR/MQSA phantom evaluation program, and to evaluate the rapidly evolving digital mammography technology. (C) 1997 American Associatio n of Physicists in Medicine.