title: Peripheral Quantitative CT (pQCT) Using a Dedicated Extremity Cone-Beam CT Scanner.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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).
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors: Department of Biomedical Engineering, Johns Hopkins University, Baltimore MD.
authors: A A
authors: AA
authors: Muhit
authors: Department of Biomedical Engineering, Johns Hopkins University, Baltimore MD.
authors: S
authors: S
authors: Arora
authors: Department of Biomedical Engineering, Johns Hopkins University, Baltimore MD.
authors: M
authors: M
authors: Ogawa
authors: Department of Biomedical Engineering, Johns Hopkins University, Baltimore MD.
authors: Y
authors: Y
authors: Ding
authors: Department of Biomedical Engineering, Johns Hopkins University, Baltimore MD.
authors: W
authors: W
authors: Zbijewski
authors: Department of Biomedical Engineering, Johns Hopkins University, Baltimore MD.
authors: J W
authors: JW
authors: Stayman
authors: Russell H. Morgan Department of Radiology, Johns Hopkins University, Baltimore MD.
authors: G
authors: G
authors: Thawait
authors: Carestream Health Inc., Rochester NY.
authors: N
authors: N
authors: Packard
authors: Carestream Health Inc., Rochester NY.
authors: R
authors: R
authors: Senn
authors: Carestream Health Inc., Rochester NY.
authors: D
authors: D
authors: Yang
authors: Carestream Health Inc., Rochester NY.
authors: J
authors: J
authors: Yorkston
authors: Divisions of Rheumatology, Allergy and Clinical Immunology, Department of Medicine, Johns Hopkins University, Baltimore MD.
authors: C O
authors: CO
authors: Bingham
authors: Curtis National Hand Center, Union Memorial Hospital, Baltimore MD.
authors: K
authors: K
authors: Means
authors: Russell H. Morgan Department of Radiology, Johns Hopkins University, Baltimore MD.
authors: J A
authors: JA
authors: Carrino
authors: Department of Biomedical Engineering, Johns Hopkins University, Baltimore MD ; Russell H. Morgan Department of Radiology, Johns Hopkins University, Baltimore MD.
authors: J H
authors: JH
authors: Siewerdsen
keywords: bone mineral density; bone morphometry; cone-beam CT (CBCT); joint morphology; joint space analysis; osteoarthritis; osteoporosis; peripheral quantitative computed tomography (pQCT); rheumatoid arthritis