Ultrasound measurement on the calcaneus: Influence of immersion time and rotation of the foot

The aim of this study was to evaluate the influence of immersion time and r otation of the heel around the leg axis on the reproducibility of measureme nts using an ultrasound bone imaging scanner (UBIS) with a temperature-cont rolled water bath. Measurements were obtained in 10 men, 11 premenopausal w omen and 10 postmenopausal women. The right foot of all subjects was scanne d 12 times with an interval of 3 min between each scan. The first 10 measur ements, performed to study the effect of immersion time, were taken without intermediate repositioning. Measurements 11 and 12 were also taken without removing the foot, but the calcaneus position was varied by an angle of +/ -2.5 degrees with respect to the reference position used during the first 1 0 measurements. Prolonged immersion of the heel led to a decrease in the va riations of quantitative ultrasound (QUS) parameters between successive mea surements. Following rapid variations with immersion time, the QUS paramete rs reached a plateau. The effect of immersion time on measurement error rem ained significant until the first two or three scans for broadband ultrasou nd attenuation (BUA) and until the sixth or seventh scans for speed of soun d (SOS). The variation in BUA was more pronounced (p <0.05) for the group o f postmenopausal women (20.7% change in BUA between the first and tenth sca ns; p <0.005) than for the group of premenopausal women (6.8% change in BUA between the first and tenth scans; p <0.005). The variations in SOS were s imilar in the two groups (0.8% variation; p <0.005). The impact of immersio n time was smaller for men than for women [2.5%, (p <0.01) and 0.3% (p <0.0 05) of the change between the first and tenth scans for BUA and SOS respect ively]. On the whole, the measurement errors due to rotation of the heel we re lower than those caused by immersion time. The variations were significa nt only in men and premenopausal women. Both immersion time and rotation of the heel may play a role in the precision of QUS and should be carefully s tandardized, particularly for longitudinal studies. In addition, following these results we have adopted a standardized protocol to derive the techniq ue reproducibility in groups of premenopausal and postmenopausal women. The coefficients of variation were 1.1% for BUA and 0.1% for SOS in premenopau sal women, and 1.4% for BUA and 0.13% for SOS in postmenopausal women.