Ma. Sabin et al., THE ACCURACY OF VOLUMETRIC BONE-DENSITY MEASUREMENTS IN DUAL X-RAY ABSORPTIOMETRY, Calcified tissue international, 56(3), 1995, pp. 210-214
New developments in dual x-ray absorptiometry (DXA) allow the performa
nce of high precision anteroposterior (AP) and lateral scans of spinal
bone mineral density (BMD, units: g/cm(2)) without the patient moving
from the supine position. Data from both projections may be combined
to give an estimate of the true volumetric bone mineral density (VBMD,
units: g/cm(3)) of the lumbar vertebral bodies. This report presents
a cadaver study designed to validate DXA measurements of volumetric bo
ne density. Sections of whole lumbar spine were scanned in AP and late
ral projections in a water tank to simulate soft tissue. Individual ve
rtebrae were then divided to separate the vertebral body from the neur
al arch, and vertebral body volume was measured using the displacement
of sand. The bone mineral content (BMC) of vertebral bodies and neura
l arches was measured by ashing at 250 degrees C for 60 hours followed
by 500 degrees C for a further 24 hours. The results showed that DXA
scanning systematically underestimated ashing data by 14% for AP BMC,
33% for vertebral body BMC, 23% for vertebral body volume, and 12% for
VBMD. Despite these significant systematic errors, the DXA measuremen
ts and ashing values were highly correlated (r = 0.979-0.992). The res
ults suggested that after allowing for the systematic errors, lateral
DXA parameters related closely to true BMC, volume, and VBMD.