Cancellous and cortical bone mineral density (BMD) of the fourth and fifth lumbar vertebrae were determined using quantitative computed tomography (QCT). Each vertebral segment was placed in a Norland Stratec bone densitometer (Orthometrix, Inc., White Plains, NY) and positioned uniformly on a support so that the instrument-scanning plane was perpendicular to the longitudinal axis of the vertebral body. Scout views were obtained to determine the midpoint of the vertebral body. Three measurements for each vertebra were performed at a resolution of 70 μm/voxel 1 mm apart from this point. The cancellous area of the bone was defined as 45% of the total bone cross-sectional area at the midpoint of the proximal vertebral body, the remaining fraction cortical. The instrument was set to use the threshold contour mode (soft-tissue threshold set at 220 mg/cm3) and a concentric peel algorithm (55% peel-off). Scans were made at 50 kV and 0.3 mA.
