Application of Computer Analysis of Mammography Phantom Images (CAMPI) methodology to the comparison of two digital biopsy machines

The objective of this research was to compare a Fischer MammoVision/MammoTest and a LoRad DSM digital biopsy machine using the Computer Analysis of Mammography Phantom Images (CAMPI) methodology. This study reports on analysis of the 4 largest microcalcification groups (M1, M2, M3 and M4) and the largest nodule (N1) in a mammography accreditation phantom on images acquired at 26 kVp and different mAs values on the two machines. Both machines were linear in response but the MammoTest was more sensitive (i.e., it yielded a larger gray-scale value for a given x-ray technique). However, even after correcting for this difference, the CAMPI noise measure was substantially smaller for the LoRad than the MammoTest over the range of mAs values studied. Similarly, the CAMPI signal-to-noise-ratio and correlation measures were higher for the LoRad than the MammoTest over the same range of mAs, especially for the larger objects (M1/M2 and N1). For the smaller specks in M3/M4 somewhat closer performance was observed. The overall differences are attributed to better contrast/noise performance of the LoRad which appear to outweigh its lesser resolution capability. Our results are in agreement with earlier physical and psychophysical measurements using different methodologies. This work also describes better predictive models (i.e., fits) to describe the variation of all CAMPI measures with mAs at constant kVp. For example, the noise measure was fitted to a function that included physically reasonable sources of noise e.g., dark noise and detector gain fluctuations, in addition to the usual quantum noise. These fits can be used to summarize machine performance and to predict dependencies on other variables (e.g., exposure or dose) that are related to the mAs.