Multicenter Bone Imaging Protocol

Of the 1690 attending one of the six CRFs, 1658 had a DXA bone scan; of these, 1350 also had a pQCT scan of the nondominant radius (distal 4% and diaphyseal 50% sites) at one of five CRFs where this equipment was provided. All the sites used QDR 4500 Discovery (Hologic Inc., Bedford, MA, USA) and XCT 2000 (Stratec, Pforzheim, Germany) DXA and pQCT scanners, respectively. For consistency and optimization in scan acquisition, a detailed training protocol booklet and illustrative CD were prepared, for each center, on subject and phantom scanning. For cross calibration the European Spine Phantom [ESP]; number 04–22013 (link)), which has three trabecular BMD value (50, 100, 200 mg/cm³) inserts, was scanned at each center at the start and end of the study period. The “known” BMD values of each ESP vertebral body were plotted against the “measured” BMD values and coefficients from the line of best fit were recorded14 (link) and used to calculate standardized BMD (sBMD). The European forearm phantom (EFP)14 (link) similarly was scanned 10 times on each pQCT scanner at the beginning and end of the study in each center and differences between scanners were tested for total and trabecular vBMD and total area of section 1 to 3; cortical vBMD was tested for section 4 only. No cross-calibration was necessary for pQCT measurements.14 (link) For quality assurance (QA) the phantoms provided by the scanner manufacturer were scanned daily and the results were sent to the bone coordinating center monthly for scrutiny. All data were centrally analyzed and scrutinized by author JEA’s laboratory.
The pQCT scans at the distal 4% site provided measures of trabecular and total vBMD and distal CSA, and at the 50% site provided CSA of the diaphysis and the medullary cavity (medullary CSA), and cortical vBMD and polar SSI (mm³)15 (link) were extracted.
The DXA measures included in this analysis were aBMD for the lumbar spine (L₁–L₄) and total hip. Information on prescribed oral glucocorticoids, aromatase inhibitors, and all medications taken for osteoporosis was obtained.