Ultrasound measurements of overlying soft tissue thickness at four skeletal sites suitable for in vivo x-ray fluorescence.

Due to signal attenuation in overlying soft tissue, development of x-ray fluorescence systems to measure low atomic number elements, such as strontium, in human bone required a search for a skeletal site with thin overlying tissue. This paper reports ultrasound measurements of overlying tissue on 10 subjects, at four anatomical sites. The average tissue thickness at the finger was (2.9+/-0.7) mm. The average tissue thicknesses were (3.6+/-0.7) mm, (4.8+/-2.0) mm, and (8.4+/-1.7) mm at forehead, tibia and heel, respectively. Additionally, both parametric and nonparametric approaches to the relationship between body mass index (BMI) and tissue thickness suggest that there is a significant linear correlation between the subject's BMI and overlying tissue at the finger and heel bone. These correlations might be used as a criterion to perform XRF measurements, however a larger data set is required to address these correlations more clearly.