Bouyoucef S E, Cullum I D, Ell P J
Institute of Nuclear Medicine, University College Medical School, London, UK.
Br J Radiol. 1996 Jun;69(822):522-31. doi: 10.1259/0007-1285-69-822-522.
This study describes the cross-calibration of two Hologic bone densitometers, one using a fan-beam X-ray source (QDR4500/A) and the other a pencil-beam source (QDR1000/W). The QDR4500/A allows spine and hip measurements to be made at three principal speeds. Results from two spine phantoms and 154 patients showed no significant difference in the absolute values or precision between speeds. The middle speed (taking 1 min to scan an adult lumbar spine) was used for the comparison between the instruments. The two densitometers were compared using two spine phantoms and 182 patients. In vivo measurements were made of all lumbar spine, hip, forearm and whole body sites. Regression lines, constrained to pass through the origin, were calculated. Slopes for total bone mineral density (BMD) for each scan type ranged between 0.994 and 1.029, the best value being found for forearm (1.000). Scatter graphs of the individual points were generated and showed results slightly worse than would be expected from repeat measurements on a single machine (79-88% fell within the expected 2 SD range). A trend for the QDR4500/A to overestimate BMD at low values and underestimate it at high values was seen in the femoral neck. The trend was more significant in the lumbar spine. There was an overestimate of total hip BMD throughout the range. Slopes of the regression lines for area and bone mineral content (BMC) were used to improve cross-calibration between the systems on a site-to-site basis, after which the results improved to a level consistent with repeat measurements on a single machine (81-94% within 2 SD). At present only global, rather than site-specific, correction factors can be employed for the spine and hip and no overall improvement in cross-calibration was possible. We conclude that although global correction factors allow adequate cross-calibration to be achieved, improvements could be made by the use of scan-site-specific factors.
本研究描述了两台Hologic骨密度仪的交叉校准情况，一台使用扇形束X射线源（QDR4500/A），另一台使用笔形束源（QDR1000/W）。QDR4500/A能够以三种主要速度进行脊柱和髋部测量。来自两个脊柱模型和154名患者的结果显示，不同速度下的绝对值或精密度没有显著差异。中等速度（扫描成人腰椎脊柱需1分钟）用于仪器之间的比较。使用两个脊柱模型和182名患者对这两台骨密度仪进行了比较。对所有腰椎、髋部、前臂和全身部位进行了活体测量。计算了通过原点的回归线。每种扫描类型的总骨矿物质密度（BMD）斜率在0.994至1.029之间，前臂的最佳值为1.000。生成了各点的散点图，结果显示略逊于在单台机器上进行重复测量的预期结果（79 - 88%落在预期的2标准差范围内）。在股骨颈处，观察到QDR4500/A在低值时高估BMD而在高值时低估BMD的趋势。这种趋势在腰椎更为显著。在整个范围内，全髋BMD均被高估。在逐部位基础上，使用面积和骨矿物质含量（BMC）回归线的斜率来改善系统之间的交叉校准，之后结果提高到与在单台机器上进行重复测量一致的水平（81 - 94%在2标准差范围内）。目前，对于脊柱和髋部只能采用全局而非特定部位的校正因子，交叉校准无法整体改善。我们得出结论，尽管全局校正因子能够实现充分的交叉校准，但使用特定扫描部位的因子可能会有所改进。
