Ultrasonic reflection and attenuation by the bone cortex—Implications for backscatter measurements of cancellous bone

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.