A Multiple-projection DXA Scanner for Improved Accuracy and Precision in the Measurement of Bone Cross-sectional Geometry and Body Composition
Osteoporosis and a number of other diseases and conditions alter the mechanical strength of the skeleton such that bones fracture easily. A number of treatments exist that can mitigate the loss of bone strength, hence accurate diagnosis and assessment of the effects of treatment are critical. Bone-weakening conditions are most commonly assessed and diagnosed with a dual energy x-ray absorptiometry (DXA) scanner that can measure mass of bones by their mineral content. Bone mass measurements most commonly are expressed as an estimate of bone density based on the observation that elderly bones that fracture easily have reduced densities. The problem with density measures is that they do not describe a specific mechanical condition and cannot be directly used to assess mechanical strength. Research in our lab has led to techniques for deriving mechanical properties from DXA scans so that changes in structural strength can be measured directly using engineering principles. We have applied the method to DXA scans from various bone research studies around the world and have shown that structural parameters better describe altered mechanical strength and are far superior to crude density measures. The problem with our methods is that current DXA scanners are not designed to measure structure hence precision and accuracy is less than ideal for clinical use. The main limitations of current scanners is that 1) bones are three dimensional, and only two-dimensional information can be acquired from conventional DXA images. This mainly constrains precision so that if the patient is not positioned consistently over time (typically years between scans), the projected dimensions and the geometry computed from them are not consistent. 2) DXA scans typically have poor image quality. 3) Structural properties are strongly dependent on patient size so some means of to determine strength appropriate for body size is needed. The invention is a DXA scanner that is specifically designed to measure structural properties and to address the specific limitations of current DXA scanners in this regard. The design incorporates innovations in data acquisition, scanning protocols and software. To address the positioning problem, the scanner derives data from multiple different projections effectively acquiring in 3D so that scanning precision becomes independent of patent positioning. To improve image quality detector configuration provides higher spatial resolution and a SNR independent of patient size. The scanner will be able to measure the skeleton and body composition in the entire body, or in any subregion of the skeleton. Specific scanning protocols will be used to measure skeletal size for scaling of bone geometry measurements independent of body size. Engineering designs for the device have been produced, and proof-of-principal work using a more advanced clinical prototype is under way under NASA funding. The entire design uses no advanced fabrication methods, the detectors have been constructed, and other components are commercially available. Description (Set) Proposed Use (Set) Many instruments measure some skeletal property and provide indirect inferences of fracture risk based on statistical construct using comparisons with normal and abnormal individuals. The result is often confusing and arely definitive. The invention will provide a noninvasive capability for directly measuring skeletal structural strength in engineering terms so that fracture risk can be estimated with engineering principles, not statistical inference. The production cost of the instrument will be comparable to those of current whole body capable DXA scanners.
Beck, Thomas J.
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