Two ultrasound longitudinal waves in cancellous bone acquired using a fast decomposition method with a phase rotation parameter for bone quality assessment

Ultrasound signal passing through cancellous bone consists of two longitudinal waves: fast and slow waves. Accurate decomposition of the fast and slow waves is supposed to be highly beneficial in order to determine the characteristics of cancellous bone. We applied a fast decomposition method using adaptive beamforming technique with a phase rotation parameter to ultrasound signals that passed through bone specimens with various bone volume to total volume (BV/TV) ratios in a simulation study. The decomposition method accurately characterized the two waves with the normalized residual intensity of less than −19.5 dB when the specimen thickness ranged from 4 to 7 mm and the BV/TV ratio was from 0.144 to 0.226. The ratio of the peak envelope amplitude of the fast wave to that of slow wave increased monotonically as BV/TV ratio increased. The result also indicates a strong relationship between the phase rotation value and BV/TV ratio, where the variation of the phase rotation value increased as specimen thickness increased. These findings show that the decomposition method using adaptive beamforming technique with a phase rotation parameter has the high potential in estimating the BV/TV ratio in cancellous bone.