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Application of Dynamic Time Warping Technique to Evaluate Microstructures of Cancellous Bones

Osteoporosis is a systemic skeletal disease, which is characterized by the deterioration of microstructures and the decrease of bone mineral density (BMD). Ultrasonic backscatter technique has a promising potential to evaluate microstructures and BMD of cancellous bone for the diagnosis of osteoporosis. The dynamic time warping (DTW)algorithm, measuring the similarity between two signals, has been widely used in speech and image recognition. The purpose of this study is to investigate the feasibility of the DTW algorithm in extracting features from ultrasonic backscatter signals and estimating the microstructure of cancellous bones. Ultrasonic backscatter measurements were performed on twenty-six bovine cancellous bone specimens using an ultrasonic backscatter bone diagnostic system with a focused broadband transducer, which has a center frequency of 1.04 MHz. The dynamic time warped distance (DTWD)feature was extracted from the cost matrix between the ultrasonic backscatter signals and the reference signal. The associations between ultrasonic backscatter features (including DTWD)and trabecular microstructures (i.e., the average trabecular number (Tb. N)and the average trabecular bone spacing (Tb. Sp)), and BMD were analyzed using the simple Pearson's correlations and Partial correlations. The results showed that the DTWD significantly correlated with the Tb.N (R = −0.86±0.09, p <0.01), the Tb. Sp (R = +0.71±0.12, p <0.01)and the BMD (R = −0.86±0.08, P <0.01). After adjustment for the effect of BMD, the microstructure (i.e., Tb. N and Tb. Sp)still yield significant correlations with the DTWD (R = −0.51±0.15, and R = +0.42±0.15, p <0.01). This study demonstrated that the dynamic time warping technique might have the potential to evaluate the bone microstructure. Ultrasonic backscatter provides a potential measurement for the microstructures of the cancellous bone. Our future work will involve more samples to investigate the efficacy of DTW both in vitro and in vivo.