Axial and total-body bone densitometry using a narrow-angle fan-beam

We assessed a new dual-energy bone densitometer, the PRODIGY, that uses a n arrow-angle fan-beam (4.5 degrees) oriented parallel to the longitudinal ax is of the body (i.e., perpendicular to the usual orientation). High-resolut ion scans across the body can be stepped at 17 mm intervals. The energy-sen sitive array detector uses cadmium zinc telluride, which allowed rapid phot on counting. Spine and femur scans required 30 s, and total-body scans requ ired 4-5 min; the dose was only 3.7 mrem and 0.04 mrem respectively, or abo ut 5 to 10 times lower than conventional fan-beam densitometry. We found on ly a small influence of soft-tissue thickness on bone mineral density (BMD) results. There was also a small ( +/- 1%) influence of height above the ta bletop on BMD results. A software correction for object height allowed a fi rst-order correction for the large magnification effects of position on bon e mineral content (BMC) and area. Consequently, the results for BMC and are a, as well as BMD, with PRODIGY corresponded closely to those obtained usin g the predecessor DPX densitometer, both in vitro and in vivo; there was a generally high correlation (r = 0.98-0.99) for BMD values. Spine and femur values for BMC, area and BMD averaged within 0.5% in vivo (n = 122), as did total-body BMC and BMD (n = 46). PRODIGY values for total-body lean tissue and fat also corresponded within 1% to DPX values. Regional and total-body BMD were measured with 0.5% precision in vitro and 1% precision in vivo. T he new PRODIGY densitometer appears to combine the low dose and high accura cy of pencil-beam densitometry with the speed of fan-beam densitometers.