The Alara Metriscan phalangeal densitometer: evaluation and triage thresholds

The Metriscan (Alara Inc, CA) is a compact digital radiographic absorptiometry device capable of determining phalangeal bone mineral density in arbitrary units (BMD(au)) from the second phalanges of the middle three digits. We have examined the utility and the in vitro and in vivo performances of the Metriscan, and established triage thresholds based on the UK's National Osteoporosis Society guidelines on peripheral densitometry. 170 white female participants (70 osteoporotic and 100 non-osteoporotic at the hip or spine) aged between 55 years and 70 years were recruited from patients attending for routine dual X-ray absorptiometry (DXA) examination. All participants underwent two scans of the non-dominant hand (with repositioning) and one of the dominant hand. An additional 10 participants were excluded owing to finger or hand deformities. Radiation exposure to the patient per scan was <0.1 microSv, and a controlled area of 1 m was established around the device. Phantom-based in vitro short-term precision (%CV) was 0.17% without, and 0.22% with, repositioning. Long-term in vitro precision was 0.31% over a 6-month period. In vivo short-term precision was 1.42% for the group as a whole, and 1.30% and 2.23% for the non-osteoporotic and osteoporotic groups, respectively. Triage thresholds for reassurance/referral or referral/treatment were 54.30 BMD(au) and 46.89 BMD(au), respectively, for the non-dominant hand, and 55.02 BMD(au) and 48.73 BMD(au) for the dominant hand. The dominant side proved superior for triage purposes, with a triage referral rate of 44%, compared with 48% for the non-dominant hand. The Metriscan is suitable for use on post-menopausal women in a community-based setting preferably in a triage role as an adjunct to axial BMD.