Calibration of dual-energy X-ray absorptiometry for bone density

Abstract

Bone Mineral Content (Bmc, G) Using Dexa (Lunar Dpx) Was Measured On Known Hydroxyapatite Samples In A Water Bath In The Presence Of Uniform And Nonuniform Coverings Of Fat-Equivalent Materials. Selective Placement Of Paraffin Over Bone Had A Greater Effect Than Lard In Reducing Apparent Bmc, And Polycarbonate Plastic Had A Lesser Effect. Measured Bmc Was 100.1 ± 1.1% Of Actual Hydroxyapatite Weight When (1) Fat Over Bone Was About Twice The Mass Of Hydroxyapatite, And (2) The Surrounding Soft Tissue Was 15–30% Fat. There Was A Linear Relationship Between Observed And Expected Bmc, Area (Cm²), and bone mineral density (BMD, g/cm²) measured on an aluminum phantom using either the Lunar DPX or the Hologic QDR-1000. The measured area with the two densitometers was identical, but BMC differed. For both an anthropomorphic phantom and human subjects, use of a constant-threshold (0.2 g/cm²) edge-detection algorithm excluded less low-density bone from the transverse processes than the standard DPX edge-detection algorithm. Differences in edge detection could influence the results obtained with phantoms and in vivo and make system intercomparison difficult.