Figure 1: Original DXA scan results from another facility.
Figure 2: Repeat DXA of the forearm at our facility.
Case Description:
The patient underwent a DXA scan of the left forearm on a Hologic scanner, and there was a large discordance in T-scores between regions (Figure 1). Review of the image revealed that the regions of interest labeling appeared to be reversed with the ultra-distal region overlying the forearm diaphyses, and the 1/3 distal region overlying the radial carpal junction. Because the peak BMD of the 1/3 radius is 36% higher than the peak BMD of the ultra-distal radius, (0.694 g/sq.cm. vs 0.443 g/sq.cm respectively) with similar population standard deviations (0.060 g/sq.cm vs 0.058 g/sq.cm respectively) this results in a T-score difference of more than 4 standard deviations when the scanner applies the incorrect normative databases to the results.
This mislabeling can occur if the left forearm is scanned using the right forearm acquisition mode. Alternatively, this could be due to scanning the left forearm with the patient supine with her head at the head of the table. This appears to be the case in this instance as the radius and ulna are reversed from their expected location in the image in addition to the mislabeling. The Hologic manual allows supine left forearm imaging, but the patient’s head must first be positioned at the foot end of the table. As a result of the inverted scan image, the machine software assigned the global ROI and the regional ROIs inappropriately.
Repeat imaging (Figure 2) shows the correct acquisition of the image in right orientation, proper global and regional ROI assignment, and more concordant T-scores between regions.
Credit:
Hazem Bilbeisi MBBS, FRCPS, CCD (Basma Medical Center), Bardees Abu Seriyah (Jordan Hospital) Amman, Jordan.
References:
Hologic Horizon W operator’s manual.