FACTORS AFFECTING THE IN-VIVO PRECISION OF BROAD-BAND ULTRASONIC-ATTENUATION

The in vivo precision of broad-band ultrasonic attenuation (BUA) was m easured in one normal male volunteer over periods of one day and six w eeks and in a group of 10 volunteers over a period of two weeks using a Walker Sonix UBA 1001 bone mineral analyser in which the foot is imm ersed in a water tank. Coefficients of variation ranged from 1-3% and, in general, there was no difference in BUA variance between right and left feet. However, right foot BUA values were consistently greater t han those of the left, but there was no difference between mediolatera l and lateromedial transmission. The use of preboiled water improved p recision and reduced measurement time. In addition, factors affecting BUA precision were investigated in the individual volunteer. Equipment stability and conditions of immersion (immersion time, water depth, w ater temperature and concentration of a detergent wetting agent) had c omparatively little effect on BUA values. On the other hand, the effec ts of foot positioning were more pronounced: rotation about the long a xis of the foot, translation across the water tank and foot movement i n the dorsal-plantar direction each contributed a maximum of 1.5-2.0% variation in BUA. However, both rotation about the long axis of the le g and foot movement in the heel-toe direction could change BUA by as m uch as 9%. It is likely that foot positioning will limit the precision achievable with this technique.