EFFECT OF POSITIONING OF THE ROI ON BMD OF THE FOREARM AND ITS SUBREGIONS

Abstract

Inconsistent positioning of patients and region of interest (ROI) is known to influence the precision of bone mineral density (BMD) measurements in the spine and hip. However it is unknown whether minor shifts in the positioning of the ROI along the shaft of the radius affect the measurement of forearm BMD and its subregions. The ultradistal (UD), mid-, one-third (1/3), and total radius BMDs of 50 consecutive clinical densitometry patients were acquired. At baseline the distal end of the ROI was placed at the tip of the ulnar styloid as usual, and then the forearm was reanalyzed 10 more times, each time shifting the ROI 1 mm proximally. The data were normally distributed, and mean values at the various distances from baseline were compared using a paired t-test. No corrections for multiple comparisons were necessary since the differences that were significant were significant at p<0.0001. The UD forearm BMD increased as the ROI was shifted proximally; the increase was significant when shifted even 1 mm proximally (Figure 1a, p<0.0001). These same findings held true for the mid- and total radius bone density, though the percent increase with moving proximally was significantly greater for the UD radius than for the other subregions. However, there was no significant change in the 1/3 radius BMD when shifted proximally 1-10 mm (Figure 1b). Since the one-third radius is the only forearm region usually reported, proximal shifts of the ROI of up to 10 mm should not influence forearm BMD results significantly.