Correlation reflected fast and slow waves with various cancellous bone models using pulse-echo ultrasound technique

Abstract

Attenuation and velocity of an ultrasound wave parameter can be analyzed to estimate the quality of the bone. However, the bone quality evaluation using ultrasound is still not comparable with X-ray densitometry. Considering the parameters of the fast and slow waves perhaps develop the measurement accuracy of the ultrasound. Currently, fast and slow waves measured using through transmission (TT) technique. Nonetheless, this technique applied two transducers, which limited to certain parts of the skeletal structure. Based on pulse-echo (PE) technique which is much easier to use due to single transducer uses and analyse fast and slow waves might be able to solve the problems. Therefore, the objective of this study is to conduct simulation and experiment of the PE technique to study the correlation between fast and slow waves with various porosities and thicknesses of two-dimentional cancellous models and bone phantom (polyurethane (PU) foam) and comparing the result obtained to the result of the TT technique and previous works. The ultrasound wave measurement was done based on TT and PE technique for both simulation and experiment. The measurement also was repeated for every porosity and thickness. The “incident” and “reflected” waves then separated using bandlimited deconvolution method by estimating the time threshold between transfer function of the fast and slow waves. Then, the parameters for mix, fast and slow waves were calculated, plotted against porosity for several thicknesses and compared in terms of their correlation coefficient. There are two types of bone models orientation (parallel and perpendicular) and two types of materials in the simulation (bone and PU – to compare with experiment). The result showed some of the fast and slow waves were in good agreement with previous work in terms of the behaviour of the wave parameters against porosity for every thickness. Moreover, the bone orientations (simulation), frequency spectral content and domination of the wave can influence the behaviour of the fast and slow waves. The thickness factor influences the parameters of fast and slow waves. Nonetheless, the reaction varied depending on the porosity level. Based on the phase velocity parameters, the separation of the fast and slow waves are easier for the thicker samples for PU materials (simulation and experiment) but the same for bone materials. The overall correlation coefficient of the amplitude and signal loss parameters for the reflected wave was slightly lower compared to incident wave due to suffering additional propagation loss. Nevertheless, for the attenuation parameters, most incident and reflected fast and slow waves shows a consistent trends and good correlation coefficient for simulation and experiment (Bone – R2ßI/Rfast = 0.52/0.50average and R2ßIslow = 0.67average) (PU – R2ßI/Rfast = 0.86/0.61max) (Experiment – R2ßIfast = 0.88max and R2ßRfast = 0.58average, R2ßIslow = 0.65max and R2ßRslow = 0.70average). This indicates that, the reflected fast and slow wave showed similar behaviour as the incident fast and slow wave and feasible to be applied in PE measurement technique. The result from simulation (PU materials) was also in good agreement with the experiment. The overall result shows, considering reflected fast and slow waves especially the attenuation parameter to estimate bone quality, might be able to improve the measurement accuracy for PE technique.