Vertebral bone density evaluated by dual-energy X-ray absorptiometry and quantitative computed tomography in vitro

Abstract Vertebral bone density is evaluated mainly by dual-energy X-ray absorptiometry (DXA) or quantitative computed tomography (QCT). Densitometry is used as an estimator of bone strength and forms the basis for choice of treatment. DXA expresses bone density in grams per square centimeter (area density) and QCT expresses bone density in milligrams per cubic centimeter (volumetric density). The aim of this study was to identify the differences between the two techniques, DXA and QCT, when applied to a group of female and male subjects over a wide age range. The data consisted of 221 lumbar vertebral bodies (L3 and L4) excised at autopsy. There were 90 females with a mean age of 65.6 (range 18–94) years and 131 males with a mean age of 62.0 (range 21–94) years. The vertebrae were scanned en bloc in demineralized water in Plexiglas containers with both DXA and QCT. DXA was performed using posteroanterior (PA) and lateral projection. QCT was performed in the center of each vertebra with 1 cm slice thickness. Both methods showed decreasing bone density with age. Lateral DXA showed a decrease in bone density with age from approximately 0.8 g/cm 2 to approximately 0.4 g/cm 2 . QCT showed a decrease in bone density with age from approximately 180 mg/cm 3 to approximately 30 mg/cm 3 . Lateral DXA bone mineral densities (BMD) were correlated with QCT densities in both females ( r 2 = 0.68, p r 2 = 0.53, p 3 ) were significantly correlated, with r 2 = 0.64 ( p r 2 = 0.61 ( p