We assessed bone mineral density and body composition
(percentage of body fat) by using dual-energy x-ray
absorptiometry at baseline and at 6, 12, and 24 months.
All sites used a Hologic (Bedford, Massachusetts) Delphi
or Discovery model bone densitometer. Whole-body, posteroanterior
lumbar spine (L1 to L4), and left proximal
femur scans were acquired according to manufacturer
guidelines for participant positioning. We cross-calibrated
scanners by using the same Hologic anthropomorphic
spine and whole-body phantom set before data collection.
Long-term calibration was monitored at each site with a
spine phantom scanned daily and a whole-body phantom
scanned 3 times a week. Based on these phantoms, the
long-term precision was less than 1% for spine bone mineral
density and less than 2% for percentage of body fat. Asingle technician analyzed all scans centrally by using Hologic
software, version 11.2, and one investigator independently
reviewed for scan and analysis quality. We excluded
poor-quality scans (movement artifacts and improper position)
from the analysis (0.7% for spine; 3.9% for hip; and
3.1% for whole body).
We assessed bone mineral density and body composition
(percentage of body fat) by using dual-energy x-ray
absorptiometry at baseline and at 6, 12, and 24 months.
All sites used a Hologic (Bedford, Massachusetts) Delphi
or Discovery model bone densitometer. Whole-body, posteroanterior
lumbar spine (L1 to L4), and left proximal
femur scans were acquired according to manufacturer
guidelines for participant positioning. We cross-calibrated
scanners by using the same Hologic anthropomorphic
spine and whole-body phantom set before data collection.
Long-term calibration was monitored at each site with a
spine phantom scanned daily and a whole-body phantom
scanned 3 times a week. Based on these phantoms, the
long-term precision was less than 1% for spine bone mineral
density and less than 2% for percentage of body fat. Asingle technician analyzed all scans centrally by using Hologic
software, version 11.2, and one investigator independently
reviewed for scan and analysis quality. We excluded
poor-quality scans (movement artifacts and improper position)
from the analysis (0.7% for spine; 3.9% for hip; and
3.1% for whole body).
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