A statistical model for the ultrasonic backscattered echo from tissue containing microcalcifications

Microcalcifications, generally seen in B-mode breast images as bright spots, often point to the presence of malignancies. Currently, statistical models to describe the signal strengths from tissue containing microcalcifications rely on the Rician or Nakagami densities. Because the Nakagami density requires the existence of randomly located scatterers with random cross sections, microcalcifications manifesting as isolated strong scatterers in the scattering volume makes it less suitable. Additionally, the absence of any regularly spaced scatterers also makes the Rician density less suitable. In this work, it is proposed that a 3-parameter McKay density with heavier tails than the Nakagami density, and hence more severe intensity fluctuations (speckle), might be a better fit to describe echo from tissue containing microcalcifications. This density is developed using a physical description of scattering and its characteristics are explored through random number simulation. Results demonstrate that the McKay densities have higher levels of speckle quantified through the speckle factor than the corresponding gamma densities (Nakagami for the envelope). Some preliminary analysis of tissue-mimicking phantoms modified to include microcalcification-like regions shows that higher speckle factors (seen with the McKay density) can be used to isolate and display microcalcifications. It is expected that this novel approach based on the McKay density will lead to newer and simpler means to detect and identify microcalcifications in ultrasonic B-scans.