Factors influencing the speed of sound through the proximal phalanges.
The amplitude-dependent speed of sound (AD-SOS) in the proximal phalanges is reported to be sensitive to osteoporotic changes. We investigated the influence of bone thickness and cortical thickness on AD-SOS. Phantoms made of Perspex were designed to simulate different bone width (11-16 mm) and cortical thickness (3-7.5 mm). The phantoms were designed with two opposing flat and cylindrical surfaces. The effect of cortical thickness was examined by drilling holes (simulating the medullary canal) of different diameters (1-7 mm) in the middle of the Perspex cylinders. The effect of sample thickness was investigated on solid Perspex phantoms of varied lengths. The standardized precision errors of AD-SOS measurement in vivo and in vitro on volunteers and phantoms were 2.8 and 0.9%, respectively. AD-SOS was influenced by the bone width, cortical thickness, and location along the phalanx. A decrease in either cortical width or cortical thickness resulted in a decrease in AD-SOS. The effect is dependent on whether the contact surface is curved or flat. It is possible that a curved surface has a focusing effect on the wave through the porous core, whereas for a flat surface, the path of the waves might not pass through the center. When cortical thickness and bone width were expressed as a ratio, there was a linear relationship between this ratio and AD-SOS through the phantoms. AD-SOS was independent of thickness for samples greater than 11 mm.
Njeh
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Osteoporosis and Arthritis Research Group, UCSF, San Francisco, CA 94117-1349, USA. Christopher.njeh@oarg.ucsf.edu
Richards
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A
Boivin
C M
CM
Hans
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D
Fuerst
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Genant
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D000328:Adult; D001842:Bone and Bones / Q000000981:diagnostic imaging*; D005260:Female; D005385:Fingers / Q000000981:diagnostic imaging*; D006801:Humans; D008297:Male; D010024:Osteoporosis / Q000000981:diagnostic imaging; D019047:Phantoms, Imaging; D014465:Ultrasonics; D014463:Ultrasonography