Spectral ratio method to estimate broadband ultrasound attenuation of cortical bones in vitro using multiple reflections.

Broadband ultrasound attenuation (BUA) is commonly measured by the spectral ratio method. Conventionally BUA is measured in transverse transmission mode where ultrasound signal is recorded with and without the sample. The spectral ratio method was extended to estimate nBUA (BUA normalized by thickness) in axial transmission mode using spectral amplitudes of the primary reflection and multiple reflection, which echoes more than once between the material interfaces within a layer. We performed three experiments. First, reflections were numerically simulated to verify the accuracy of the method. We then applied the method to estimate attenuation of silicon rubber and the cortex of a bovine femur. The center frequency of the transducers is 2.25 MHz. We obtained 93% accuracy for a simulated data set with 10% random noise after bandpass filtering. For the silicon rubber, 15 measurements were collected and the mean attenuation was 6.33 +/- 0.19 dB MHz(-1) cm(-1). For the bovine bone, eight measurements were performed in the middle portion of the femur. The mean attenuation was 4.91 +/- 0.65 dB MHz(-1) cm(-1) and compared well with those reported in the literature. The results demonstrate that the proposed method has the potential to provide a quick, reliable and robust cortical attenuation assessment in vivo.