Validity and reliability of a gel-coupled ultrasound scanning system in assessing bone mass in healthy subjects

To determine the reliability and validity of a new ultrasound bone densitometry instrument, we studied 41 healthy volunteers (27 females and 14 males, mean age 33.8 yrs, range 22-45 yrs), who underwent ultrasound measurements with QUS-2 (Metra Biosystems Instrument [Quidel]). The measurements were repeated three times in the same visit (mean coefficient of variation 3.4%, range 0.64-10.87%). Fifteen of these subjects repeated the three measurements in two subsequent visits, 7 days apart from each other. There was a significant variability between subjects (p = 0.0001) and within subjects (p = 0.004). To compare the measurement performed with the new equipment with that of the gold standard, 19 subjects underwent a bone mass measurement by dual X-ray photon absorptiometry (DXA, Hologic QDR 4500A). The broadband ultrasound attenuation correlated with the total femur and femoral neck bone mineral density (r = 0.61, p = 0.005; r = 0.4, p = 0.09, respectively), but not with lumbar spine r = 0.34, p = 0.15). The mean coefficient of variation of the three ultrasound measurements performed in each of the subjects was 3.4% (range 0.64-10.87%). QUS-2 Metra Biosystems ultrasound densitometer does not seem at the moment a useful tool to assess bone mass in clinical setting, because of its high coefficient of variation and its high intra- subject variability.