Ultrasonic backscatter techniques are being developed to detect changes in the porosity of cancellous bone caused by osteoporosis. Cancellous bone is surrounded by a thin layer of cortical bone (the cortex) that can produce errors in backscatter measurements, especially for non-normal angles of incidence. The goal of this study was to develop a theoretical model to predict power loss in the backscatter signal caused by reflection and attenuation by the cortex. Predictions of the model were tested using a polymer foam to simulate cancellous bone with one surface embedded in a ∼3 mm layer of epoxy to simulate cortical bone. Measurements were made with a 3.5 MHz transducer for angles of incidence ranging from 0 to 30 deg relative to the normal. Good agreement was observed between the theoretical predictions and experimental results.
Hoffmeister et al. (Tue,) studied this question.