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Proc SPIE Int Soc Opt Eng. 2013 Mar 29;8672:867203.

Peripheral Quantitative CT (pQCT) Using a Dedicated Extremity Cone-Beam CT Scanner.

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Department of Biomedical Engineering, Johns Hopkins University, Baltimore MD.
Russell H. Morgan Department of Radiology, Johns Hopkins University, Baltimore MD.
Carestream Health Inc., Rochester NY.
Divisions of Rheumatology, Allergy and Clinical Immunology, Department of Medicine, Johns Hopkins University, Baltimore MD.
Curtis National Hand Center, Union Memorial Hospital, Baltimore MD.
Department of Biomedical Engineering, Johns Hopkins University, Baltimore MD ; Russell H. Morgan Department of Radiology, Johns Hopkins University, Baltimore MD.



We describe the initial assessment of the peripheral quantitative CT (pQCT) imaging capabilities of a cone-beam CT (CBCT) scanner dedicated to musculoskeletal extremity imaging. The aim is to accurately measure and quantify bone and joint morphology using information automatically acquired with each CBCT scan, thereby reducing the need for a separate pQCT exam.


A prototype CBCT scanner providing isotropic, sub-millimeter spatial resolution and soft-tissue contrast resolution comparable or superior to standard multi-detector CT (MDCT) has been developed for extremity imaging, including the capability for weight-bearing exams and multi-mode (radiography, fluoroscopy, and volumetric) imaging. Assessment of pQCT performance included measurement of bone mineral density (BMD), morphometric parameters of subchondral bone architecture, and joint space analysis. Measurements employed phantoms, cadavers, and patients from an ongoing pilot study imaged with the CBCT prototype (at various acquisition, calibration, and reconstruction techniques) in comparison to MDCT (using pQCT protocols for analysis of BMD) and micro-CT (for analysis of subchondral morphometry).


The CBCT extremity scanner yielded BMD measurement within ±2-3% error in both phantom studies and cadaver extremity specimens. Subchondral bone architecture (bone volume fraction, trabecular thickness, degree of anisotropy, and structure model index) exhibited good correlation with gold standard micro-CT (error ~5%), surpassing the conventional limitations of spatial resolution in clinical MDCT scanners. Joint space analysis demonstrated the potential for sensitive 3D joint space mapping beyond that of qualitative radiographic scores in application to non-weight-bearing versus weight-bearing lower extremities and assessment of phalangeal joint space integrity in the upper extremities.


The CBCT extremity scanner demonstrated promising initial results in accurate pQCT analysis from images acquired with each CBCT scan. Future studies will include improved x-ray scatter correction and image reconstruction techniques to further improve accuracy and to correlate pQCT metrics with known pathology.


bone mineral density; bone morphometry; cone-beam CT (CBCT); joint morphology; joint space analysis; osteoarthritis; osteoporosis; peripheral quantitative computed tomography (pQCT); rheumatoid arthritis

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