EVALUATION OF DUAL-ENERGY X-RAY ABSORPTIOMETRY BONE-MINERAL MEASUREMENT COMPARISON OF A SINGLE-BEAM AND FAN-BEAM DESIGN - THE EFFECT OF OSTEOPHYTIC CALCIFICATION ON SPINE BONE-MINERAL DENSITY

Dual energy X-ray absorptiometry (DXA) using a single-beam (SB) design is a well-established procedure for measuring bone mineral area densi ty (BMD). Recently, fan beam (FB) techniques have become available to measure BMD. We evaluated the QDR1000 and QDR2000 densitometers with r egard to precision and cross-compared values using single beam (SB) an d FB techniques. To study the effect of osteoarthritic changes on bone measurement (BMC in g) and bone mineral area density (BMD in g/cm(2)) , both parameters were measured in patients with and without osteophyt ic calcifications (OC) of the lumbar spine. Precision errors for BMD i n vitro over 1 and 6 months using the QDR2000 were 0.4% and 0.6% for S B and 0.5% and 0.7% for the three FB modes. For QDR1000 only SB is ava ilable. Using this scan mode, the BMD difference (delta = 0.1%) in vit ro between QDR1000 and QDR2000 was not significant. The short-term (sa me day) reproducibility of BMD in vivo was 0.85% for SB mode and 1.1% for FB scan mode (n = 33). The midterm (1 month) precision errors were 0.9% for SB and 1.5% for FB (n = 11). The spine BMD of 751 patients f rom our outpatient clinic and department of rheumatology was 1.7% lowe r with FB than with SB (0.878 +/- 0.137 versus 0.888 +/- 0.146 g/cm(2) ). Lower (1.8%) BMD values were also found in the hip with FB compared to SB (0.805 +/- 0.111 versus 0.821 +/- 0.111 g/cm(2)). There was a h ighly significant (P < 0.00001) correlation between SB and FB on the s pine (r = 0.99) and hip (r = 0.98) using the QDR2000. Correlations fou nd QDR1000 and QDR2000 were lower on the spine (r = 0.97) and hip (r = 0.93). In contrast to hip BMD, spine BMD was significantly higher in women (n = 78) with OC (FB: 0.894 +/- 0.134 g/cm(2), SB: 0.900 +/- 0.1 40 g/cm(2)) than in normals (n = 148) (FB: 0.844 +/- 0.130 g/cm(2), SB : 0.865 +/- 0.140 g/cm(2)) (P < 0.05). The FB mode provides reproducib le data in vitro and in vivo, though not as precise as SB. FB results in vivo are 1-2% lower than FB results, even with identical results in vitro. Women with OC present with higher BMD values in spine scans th an normals.