HOLOGIC QDR-2000 WHOLE-BODY SCANS - A COMPARISON OF 3 COMBINATIONS OFSCAN MODES AND ANALYSIS SOFTWARE

This study reports on the short-term in vivo precision and absolute me asurements of three combinations of whole-body scan modes and analysis software using a Hologic QDR 2000 dual-energy X-ray densitometer. A g roup of 21 normal, healthy volunteers (11 male and 10 female) were sca nned six times, receiving one pencil-beam and one array whole-body sca n on three occasions approximately 1 week apart. The following combina tions of scan modes and analysis software were used: pencil-beam scans analyzed with Hologic's standard whole-body software (PB scans); the same pencil-beam analyzed with Hologic's newer ''enhanced'' software ( EPB scans); and array scans analyzed with the enhanced software (EA sc ans). Precision values (% coefficient of variation, %CV) were calculat ed for whole-body and regional bone mineral content (BMC), bone minera l density (BMD), fat mass, lean mass, %fat and total mass. In general, there was no significant difference among the three scan types with r espect to short-term precision of BMD and only slight differences in t he precision of BMC. Precision of BMC and BMD for all three scan types was excellent: <1% CV for whole-body values, with most regional value s in the 1%-2% range. Pencil-beam scans demonstrated significantly bet ter soft tissue precision than did array scans. Precision errors for w hole-body lean mass were: 0.9% (PB), 1.1% (EPB) and 1.9% (EA). Precisi on errors for whole-body fat mass were: 1.7% (PB), 2.4% (EPB) and 5.6% (EA). EPB precision errors were slightly higher than PB precision err ors for lean, fat and %fat measurements of all regions except the head , although these differences were significant only for the fat and % f at of the arms and legs. In addition EPB precision values exhibited gr eater individual variability than PB precision values. Finally, absolu te values of bone and soft tissue were compared among the three combin ations of scan and analysis modes. BMC, BMD, fat mass, %fat and lean m ass were significantly different between PB scans and either of the EP B or EA scans. Differences were as large as 20%-25% for certain region al fat and BMD measurements. Additional work may be needed to examine the relative accuracy of the scan mode/software combinations and to id entify reasons for the differences in soft tissue precision with the a rray whole-body scan mode.