Identification and analysis of multimode guided waves in tibia cortical bone.

The hollow cylinder model filled with viscous-liquid is performed to simulate tibial bone shape in this paper. Short time Fourier transform (STFT) was applied to identify and analyze guided wave modes of a series of ultrasonic signals acquired at various transmitter-receiver positions for a fixed transmitter. Experimental results were compared with theoretical simulation. The high correlation values for group velocity were obtained between results of experiment and theory for L(0,2) (r=0.89, p<10(-5)), and L(0,3) (r=0.87, p<10(-5)). The experimental group velocities correlated strongly with cortical thickness (cortTh) for L(0,2) (r(2)=0.79, p<10(-5)) and L(0,3) (r(2)=0.74, p<10(-5)) at 0.5 MHz center frequency. The results showed that the STFT is an effective method to identify the propagating modes and derive dispersion information. The experimental results were in good agreement with theoretical predictions. This study suggests that the guided wave L(0,2) mode is a promising mode to assess change in cortical thickness.

Combined spectral estimator for phase velocities of multimode Lamb waves in multilayer plates.

A novel combined spectral estimate (CSE) method for differentiation and estimation the phase velocities of multimode Lamb waves whose wave numbers are much close or overlap one another in multiplayer plates is presented in this paper, which based on auto-regressive (AR) model and 2-D FFT. Simulated signals in brass plate were processed by 2-D FFT and CSE. And experiments are performed by using two conventional angle probes as emitter and receiver on the same surface of three-layered aluminum/xpoxy/aluminum plates, which include symmetrical and unsymmetrical plates. The multimode Lamb waves are excited in these laminates, and the received signal is processed by 2-D FFT and CSE, respectively. The results showed that the phase velocities of multimode signals whose wave numbers are much closed cannot be differentiated by 2-D FFT, but CSE has strong spatial resolution. Compared the measured phase velocities with the theoretical values, the error is smaller than 2% on the whole. It promises to be a useful method in experimental signals processing of multimode Lamb waves.

Predict ultrasonic backscatter coefficient in cancellous bone by theory and experiment.

The scattering mechanism of ultrasound in cancellous bone is investigated theoretically. The relationship of backscatter coefficient (BSC) in cancellous bone with frequency is analyzed in theoretical and experimental. The results of theory and experiment for cancellous bone of bovine tibiae, human calcaneus in vitro and in vivo showed that BSC is a non-linear function of frequency, increasing with frequency. In general, all curve of BSC can be divided into three sections with different slope. The slopes of the first and third section have a large value, and the slope of second section is flat. A good agreement was obtained in the averaged BSC of experiment and cellular model. Those results suggest that the backscatter signal and BSC have a particularly important action in assessment of cancellous bone status and diagnosis of osteoporosis.

Measurement of spectral maximum shift of ultrasonic backscatter signals in cancellous bone.

The feasibility of assessing cancellous bone from the Spectral Maximum Shift (SMS) of the backscattered ultrasonic signal is investigated. And the SMS of backscatter signals from bovine tibiae cancellous bone in vitro were measured and discussed. The spectral maximum of the backscattered signal downshift with increases of the apparent density of cancellous bone. When the bone suffered from osteoporosis, the density will reduce. Therefore, compared with the backscattered signal spectrum in the normal cancellous bone, the osteoporotic cancellous bones have small SMS of backscattered signal. According to the size of SMS, the status of cancellous bone and the degree of osteoporotic fracture risk may be assessed. On the other hand, techniques based on ultrasonic backscatter offer the advantage that only one ultrasonic transducer rather than two transducers is required to perform measurements. The operation of measurement is convenient and simple in assessment of cancellous bone status and diagnosis of osteoporosis.