Ultrasound Characterization of Structure and Density of Materials Modeling Trabecular Bone
Yurong Sun
MS Thesis, Dept. of Electrical and Computer Engineering, Worcester Polytechnic Institute, July 12, 2000.
SUMMARY
This thesis investigates new ultrasound approaches to the detection of osteoporosis by utilizing coral samples in original and decalcified density stages, thus mimicking trabecular bone at different levels of osteoporosis. The measurement system utilizes two 0.5 MHz transducers, operating in transmission mode. Nine cylindrical coral samples were separated into 3 groups with 3 different microstructure growth axes in each group. The density of 2 out of the 3 groups is changed by decalcification. The received signal was observed to contain two waves: the fast and the slow wave.
COMPLETE ABSTRACT
This thesis investigates new ultrasound approaches to the detection of osteoporosis by utilizing coral samples in original and decalcified density stages, thus mimicking trabecular bone at different levels of osteoporosis. The measurement system utilizes two 0.5 MHz transducers, operating in transmission mode. Nine cylindrical coral samples were separated into 3 groups with 3 different microstructure growth axes in each group. The density of 2 out of the 3 groups is changed by decalcification. The received signal was observed to contain two waves: the fast and the slow wave.
The density and the microstructure characterize the coral samples physically. The density is determined by dual-energy x-ray absorptiometry (DEXA) and the coral sample dry weight. Three ultrasound parameters are extracted from the received signal: (1) Broadband Ultrasound Attenuation (BUA) as a function of the coral sample rotation angle and decalcification level; (2) analytic signal of the coral sample impulse response as a function of the sample rotation angle and decalcification level, and as a function of the receiving transducer rotation angle and decalcification level and (3) analytic signal of the angular decorrelation, as a function of decalcification level.
The BUA and the fast wave impulse response exhibit angular periodicity. The mean BUA value and the amplitude of the impulse response increase at the intermediate density level and then decrease when the coral sample is heavily decalcified. Finally, the angular decorrelation broadens with reduced density and becomes narrower after heavy decalcification. The results indicate that these ultrasound parameters may be useful in detecting changes in both bone mass density and the microstructure of trabecular bone.
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