Lunar DPX-IQ, Operator'S Manual, Page: 157 / 166

DPX-IQ Operator’s Manual J-3 Precision and Accuracy
J.2 Accuracy
The LUNAR DPX-IQ accurately measures BMC and BMD (figures J-1 and J-2). The
BMC and BMD of three standard annuli containing bone equivalent material (made
by Radiation Measurements of Middleton, Wisconsin) were calibrated at the
University of Wisconsin Bone Mineral Laboratory against the ash-weight of known
bone sections. These same three annuli were used for evaluation of the LUNAR DP3
and DP4 scanners using conventional Gd
153
sources. The BMC and BMD values
obtained with the DPX were almost identical to the calibrated values. There was a
high degree of linearity (r>0.99) with a regression slope of 1 and a zero intercept.
Accuracy for vertebral area was further validated by comparing the measured areas of
three vertebral bodies (L2-L4) in nine encapsulated spine phantoms using the DPX.
Figure J-1. Actual vs. measured BMD of annuli scanned on DPX
Figure J-2. Actual vs. Measured BMC of Annuli Scanned on DPX
The spine phantoms were radiographed and the projected area of the vertebrae was
measured by image digitization to get an actual area. The area measured with the DPX
correlated highly with the radiographic area (r=0.97) and gave a value that was about
1% higher than the radiographic area. Results for BMD also were closely correlated
(r~0.98) with those obtained on spine and femur phantoms and in vivo using
conventional radionuclide DPA.
1.1
1.0
0.9
0.8
0.7
0.6
Measured BMD
0.6
0.7 0.8
0.9
1.0 1.1
r => 0.99
Actual BMD
45
40
35
30
25
20
Measured BMC
20
25
30 35
40 45
r => 0.99
Actual BMC