title: Factors influencing short-term precision of dual X-ray bone absorptiometry (DXA) of spine and femur.
abstract: In this study we analyzed the effect of variations in bone area size, baseline soft tissue composition represented by the R-value, and bone region of interest positioning on the precision in vivo of bone mineral density (BMD) and content (BMC) as measured by dual X-ray absorptiometry (DXA). The posterior-anterior (PA) spine, decubitus lateral, and femur modes were evaluated. Eleven (PA-spine), 9 (dec-lat), and 14 (femur) postmenopausal women were scanned twice on a Norland XR-26 with repositioning to determine short-term precision of BMD, BMC, AREA, and the R-value. Phantom precisions (CV[%] of 10 consecutive scans) for BMD (BMC) were PA spine: 0.66% (0.57%), neck: 1.1% (1.2%), and trochanter: 0.55% (1.0%). Precisions in vivo (CV[%]; two consecutive scans averaged over all patients) were PA spine: 0.9% (1.0%), dec-lat: 7.1% (18%), neck: 1.3% (1.9%), and trochanter: 2.5% (4.9%). BMD precision could be fully explained by BMC and AREA variations. However, BMC alone was a particularly poor predictor of BMD in the dec-lat (r2 = 0.05) and in the neck (r2 = 0.13) modes. AREA was a strong predictor for BMC precision explaining between 41% and 88% of the BMC changes. Changes in soft tissue composition contributed significantly in explaining the BMC changes in the dec-lat projection. A higher dependence of BMC changes on AREA changes resulted in a larger difference between BMC and BMD precision.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Radiology, University of California at San Francisco 94143, USA.
authors.forename: K
authors.initials: K
authors.lastname: Engelke
authors.forename: C C
authors.initials: CC
authors.lastname: Glüer
authors.forename: H K
authors.initials: HK
authors.lastname: Genant
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods* / Q000706:statistics & numerical data; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D015519:Bone Density; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging* / Q000378:metabolism*; D006801:Humans; D008593:Menopause / Q000378:metabolism; D008875:Middle Aged; D008961:Models, Structural; D015663:Osteoporosis, Postmenopausal / Q000000981:diagnostic imaging / Q000378:metabolism; D013131:Spine / Q000000981:diagnostic imaging* / Q000378:metabolism*