Peripheral quantitative computed tomography at the distal radius: cross-calibration between two scanners

Peripheral quantitative computed tomography (pQCT) is an important technique to study the interaction between the muscle and bone systems. We have recently established pQCT reference ranges for children, adolescents and young adults using a recent version (XCT 2000) of the Stratec scanners (Stratec Inc., Pforzheim, Germany). However, the previous version of this type of scanner (XCT 900) is still widely used and cross-calibration is needed to use these reference data. Therefore, both distal radii of 19 healthy subjects (age 21 to 59 years; 11 women) were analyzed at the "4% site" using both the XCT 900 and the XCT 2000. Cross-sectional area, total and trabecular bone mineral density (BMD), total bone mineral content (BMC) and polar Strength-Strain Index (SSI) results from the two scanners were compared using linear regression analysis. To achieve scanner calibration we used the intercept and slope of the correlations. The correlation coefficients between the two devices were 0.82 for the cross-sectional area, 0.81 for total BMD, 0.97 for trabecular BMD, 0.99 for total BMC and 0.86 for polar SSI. In conclusion, these data allow for the conversion of XCT 900 results at the distal radius to XCT 2000 values and vice versa.