Vertebral morphometry: Repeat scan precision using the lunar Expert-XL andthe hologic 4500A. A study for the 'WISDOM' RCT of hormone replacement therapy

On radiation safety grounds there is concern about the morbidity attributab le to routine radiographs of the spine for the identification of new fractu res in large-scale trials of fracture prevention. However, the role of the potentially safer low-radiation-dose technique of vertebral morphometry per formed by third generation dual-energy X-ray absorptiometry equipment requi res evaluation for use in clinical trials. We have therefore investigated t he short-term inter-scan imprecision as well as the imprecision attributabl e to different-day analyses by the same operator and differences in analyse s by different operators. The volunteer subjects were participants in a pil ot study for a randomized controlled trial of hormone replacement therapy ( Women's International Study of long Duration Oestrogen after Menopause, WIS DOM), Each subject had two morphometric X-ray analysis scans separated by 2 -4 weeks. Exclusions were women with densitometrically defined osteoporosis , as defined by the WHO criterion, and women with a body mass index exceedi ng 30.9 kg/m(2). On average, the women were 58.7 years of age and had bone mineral density values in the lumbar spine which were about 0.7 SD units hi gher than a reference US female age-matched population. Scans were assessed from vertebrae T7 through L4. In the study there were no clinically signif icant differences in performance between the Hologic QDR 4500A and the Luna r Expert XL equipment. Between-scan imprecision was significantly worse tha n imprecision attributable to reanalysis of the same scan by a different op erator or the same operator after an interval. Vertebral level had an effec t on measurement uncertainty, especially at the level of the diaphragm and at T7. Coefficients of variation, expressed as percentages of mean values, were better for absolute height measurements than for height ratios, rangin g from 1.75% to 3.40% for the three heights measured on three separate mach ines and from 2.34% to 4.11% for the two height ratios. These results compa red favorably with the equivalent figures from a parallel study of morphome try precision undertaken using standard lateral radiographs of the thoracic and lumbar spine (3.1-3.6% and 3.8-3.9%, respectively). We conclude that i n trials of prevention therapy in women (or men) selected for not having os teoporosis, low-dose vertebral morphometry using the Hologic 4500A, the Lun ar Expert XL or similar equipment is preferable on safety grounds to the cl assical technique based on standard radiographs, although conventional radi ology may still be required in those with prevalent or incident deformities to exclude causes other than osteoporosis. The place of this low-dose tech nique in trials performed on patients with osteoporosis requires further st udy.