Determination of bone structural parameters from multiple projection DXA images

To more precisely measure and monitor bone health, The Johns Hopkins University Applied Physics Lab and School of Medicine have developed the Advanced Multiple Projection Dual-Energy X-Ray Absorptiometry (AMPDXA) scanner. This system provides improvements over conventional DXA scanners in image resolution and multiple projection capability. These improvements allow us to determine structural information about the bone in addition to the standard bone mineral density (BMD) measurements. Algorithms and software were developed to process data acquired from the AMPDXA scanner and to determine important structural parameters, such as the center of mass axis in three dimensions and cross-sectional moments of inertia. The analysis operates on three projections about 15 degrees apart, calculates BMD for each projection, and then combines the data into a three dimensional coordinate system. By knowing the patient position in three dimensions, bone structural parameters are calculated more precisely. Using repeated testing of cadaver bones, the precision of determining these structural parameters is approximately the detector pixel size of 0.127 mm. Data on artificial bone cylinders indicate accuracy of about 3%. Comparisons between bone structural parameters derived from AMPDXA and CT scans show very similar results.