Microcalcifications as elastic scatterers under ultrasound: implications for medical imaging

Microcalcifications are small crystals of calcium phosphates which form in human tissue through a number of mechanisms. The size, morphology, and distribution of microcalcifications (MCs) are important indicators in the mammographic screening for and diagnosis of various carcinomas in the breast. Current ultrasound methodology is not considered reliable at detecting MCs in the size range of clinical interest. The authors are investigating the imaging of MCs under ultrasound in the interest of extending the capabilities of ultrasound. We present an analysis of the acoustic properties of MCs modeled as elastic spheres which considers the predicted complex spectra and spatial coherence of echoes from MCs. We compare the findings of the model to actual echoes from suspected MCs in vivo, and discuss the implications of these findings for medical imaging. We also present preliminary in vivo measurements of phase aberration and the backscatter coefficient of breast tissue, and discuss the ramifications of these results for MC visualization