Calibration of dual-energy x-ray absorptiometry for bone density.
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 covering 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.
Mazess
R B
RB
Lunor Corporation, Madison, Wisconsin.
Trempe
J A
JA
Bisek
J P
JP
Hanson
J A
JA
Hans
D
D
D015502:Absorptiometry, Photon; D000465:Algorithms; D015519:Bone Density; D002138:Calibration; D006801:Humans; D006882:Hydroxyapatites / Q000737:chemistry*; D008055:Lipids; D008961:Models, Structural; D010232:Paraffin; D011076:Polycarboxylate Cement
D006882:Hydroxyapatites; D008055:Lipids; D011076:Polycarboxylate Cement; C005506:polycarbonate; D010232:Paraffin