PERIPHERAL QUANTITATIVE COMPUTED-TOMOGRAPHY IN HUMAN LONG BONES - EVALUATION OF IN-VITRO AND IN-VIVO PRECISION

Despite the excellent performance in clinical practice and research, t he dual-energy X-ray absorptiometry is restricted by the inherent plan ar nature of the measurement and the inability to discriminate between trabecular and cortical components of bone. Recently, a new periphera l tomographic scanner (Norland/Stratec XCT 3000) was introduced for ve rsatile measurements of human long bone characteristics in vivo, inclu ding trabecular and cortical density (TrD and Coo, respectively), resp ective cross-sectional areas (TrA and CoA), bone strength index (BSI), and bone mineral content (BMC). We evaluated the technical performanc e of the scanner using different phantoms and determined the in vivo p recision of the above-noted applications by measuring twice several si tes of upper and lower limbs of 19 and 36 volunteers aged 23-60 years. The bone scans were performed, with intermediate positioning of the s ubject, at two different anatomic sites of the forearm, three sites of the upper arm, three sites of the shank, and two sites of the thigh, with the respective skeletal sites representing different bone composi tions and sizes. According to phantom measurements, the XCT 3000 appea red to be a highly linear, stable, and precise (coefficient of variati on [CV] about 0.2%) system in vitro. The soft tissue thickness, howeve r, had a linear effect on density values and a nonlinear effect on BMC , whereas the effect on cross-sectional area was marginal. The in vivo root mean square CV (CVrms) values for the long bone ends ranged from 0.9% (distal tibia) to 2.7% (distal femur) for TrD, from 1.8% (distal femur) to 7.6% (distal radius) for TrA, from 2.0% (distal tibia) to 6 .8% (proximal tibia) for CoD, from 1.8% (distal femur) to 4.9% (proxim al tibia) for CoA, and from 4.2% (distal tibia) to 7.7% (distal radius ) for BSI. The corresponding CVrms values for the long bone shafts ran ged from 0.5% (midshaft of humerus) to 1.4% (midshaft of fibula) for C oD, from 1.7% (midshaft of tibia) to 4.6% (proximal shaft of humerus) for CoA, and from 2.5% (midshaft of tibia) to 7.5% (proximal shaft of humerus) for BSI. There was no interoperator effect on precision. This study provided, for the first time, independent precision data for th e new XCT 3000 peripheral quantitative computed tomography (pQCT) scan ner in various applications of human long bones (radius, ulna, humerus , tibia, fibula, and femur) and gave practical guidelines and procedur es on how to employ this versatile method in clinical and research app lications. The technical performance of the tested system was excellen t and it allowed, with a low radiation dose, precise in vivo evaluatio n of trabecular and cortical density, cross-sectional area, and BMC of selected skeletal sites. The potential effect of the soft tissue thic kness on density and mineral content values need to be recognized. The pQCT measurement seems to be useful in supplementing the integral, pl anar DXA data and obviously opens new possibilities for clinical pract ice and research.