Development and Application of Ultrasound Backscatter Methods for the Diagnostics of Trabecular Bone

In osteoporosis, changes in tissue structure and composition impair the mechanical strength of bone and increase the risk of fractures. Osteoporosis causes millions of bone fractures annually worldwide. It is commonly diagnosed by means of dual energy X-ray absorptiometry (DXA), a technique that provides information on areal bone mineral density (BMD, g/cm2). However, most of the low trauma fractures occur in people with normal BMD values. Quantitative ultrasound (QUS) propagation and scattering depend on both the material and structural properties of bone. Thus, ultrasound measurements provide a method for osteoporosis diagnosis. As ultrasound devices are portable, cheap and do not apply ionizing radiation, they might be suitable for osteoporosis screening. In the present thesis work, the composition of trabecular bone and its calcified matrix was analysed and compared experimentally, and by using numerical analyses, to ultrasound speed, attenuation and backscattering parameters. In addition, the diagnostic potential of a point-like ultrasound measurement and that of quantitative ultrasound imaging were compared. Further, the effect of overlying soft tissue on the measurement of human trabecular bone was investigated at various ultrasound frequencies. Finally, a novel dual frequency ultrasound technique (DFUS) was evaluated for the soft tissue correction of bone ultrasound measurements. Bone quantity was the strongest determinant of ultrasound parameters (r = 0.64-0.84, p < 0.01). Ultrasound backscattering was also significantly related (r = -0.66, p < 0.01) to the content of calcified matrix collagen. Variation in ultrasound parameter values within the region of interest was seen to relate with the ultimate strength of trabecular bone (r = -0.82, p < 0.01). Soft tissues overlying the bone induced significant errors (4% 127%) in the ultrasound measurements. This effect increased with the ultrasound frequency. After correction with the DFUS technique, the magnitude of errors induced by soft tissue on ultrasound backscattering diminished significantly, typically to one tenth. QUS parameters of trabecular bone are related to both the quantity and quality of trabecular bone. In addition, measurement of the variation in QUS parameters within the area of interest significantly improves the prediction of bone mechanical strength. The present findings together with the novel DFUS method may enable reliable QUS measurements of trabecular bone at various clinically relevant sites. This could have a significant clinical value. Universal Decimal Classification: 534-8 National Library of Medicine Classification: QT 34, QT 36, WE 200, WE 250, WN 208 Medical Subject Headings: Osteoporosis/diagnosis; Bone and Bones; Bone Matrix; Ultrasonics; Biomechanics; Tissues; Collagen; Numerical Analysis, Computer-Assisted To Hanna and Elviira