title: Dual-Energy Imaging of Bone Marrow Edema on a Dedicated Multi-Source Cone-Beam CT System for the Extremities.
abstract: OBJECTIVE
  Arthritis and bone trauma are often accompanied by bone marrow edema (BME). BME is challenging to detect in CT due to the overlaying trabecular structure but can be visualized using dual-energy (DE) techniques to discriminate water and fat. We investigate the feasibility of DE imaging of BME on a dedicated flat-panel detector (FPD) extremities cone-beam CT (CBCT) with a unique x-ray tube with three longitudinally mounted sources.
  
  
  METHODS
  Simulations involved a digital BME knee phantom imaged with a 60 kVp low-energy beam (LE) and 105 kVp high-energy beam (HE) (+0.25 mm Ag filter). Experiments were also performed on a test-bench with a Varian 4030CB FPD using the same beam energies as the simulation study. A three-source configuration was implemented with x-ray sources distributed along the longitudinal axis and DE CBCT acquisition in which the superior and inferior sources operate at HE (and collect half of the projection angles each) and the central source operates at LE. Three-source DE CBCT was compared to a double-scan, single-source orbit. Experiments were performed with a wrist phantom containing a 50 mg/ml densitometry insert submerged in alcohol (simulating fat) with drilled trabeculae down to ~1 mm to emulate the trabecular matrix. Reconstruction-based three-material decomposition of fat, soft tissue, and bone was performed.
  
  
  RESULTS
  For a low-dose scan (36 mAs in the HE and LE data), DE CBCT achieved combined accuracy of ~0.80 for a pattern of BME spherical lesions ranging 2.5 - 10 mm diameter in the knee phantom. The accuracy increased to ~0.90 for a 360 mAs scan. Excellent DE discrimination of the base materials was achieved in the experiments. Approximately 80% of the alcohol (fat) voxels in the trabecular phantom was properly identified both for single and 3-source acquisitions, indicating the ability to detect edemous tissue (water-equivalent plastic in the body of the densitometry insert) from the fat inside the trabecular matrix (emulating normal trabecular bone with significant fraction of yellow marrow).
  
  
  CONCLUSIONS
  Detection of BME and quantification of water and fat content were achieved in extremities DE CBCT with a longitudinal configuration of sources providing DE imaging in a single gantry rotation. The findings support the development of DE imaging capability for CBCT of the extremities in areas conventionally in the domain of MRI.
authors.affiliation: Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD USA 21205.
authors.forename: W
authors.initials: W
authors.lastname: Zbijewski
authors.affiliation: Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD USA 21205.
authors.forename: A
authors.initials: A
authors.lastname: Sisniega
authors.affiliation: Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD USA 21205.
authors.forename: J W
authors.initials: JW
authors.lastname: Stayman
authors.affiliation: Russell H. Morgan Department of Radiology, Johns Hopkins University, Baltimore, MD USA 21287.
authors.forename: G
authors.initials: G
authors.lastname: Thawait
authors.affiliation: Carestream Health Inc., Rochester NY.
authors.forename: N
authors.initials: N
authors.lastname: Packard
authors.affiliation: Carestream Health Inc., Rochester NY.
authors.forename: J
authors.initials: J
authors.lastname: Yorkston
authors.affiliation: Russell H. Morgan Department of Radiology, Johns Hopkins University, Baltimore, MD USA 21287.
authors.forename: S
authors.initials: S
authors.lastname: Demehri
authors.affiliation: Russell H. Morgan Department of Radiology, Johns Hopkins University, Baltimore, MD USA 21287.
authors.forename: J
authors.initials: J
authors.lastname: Fritz
authors.affiliation: Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD USA 21205 ; Russell H. Morgan Department of Radiology, Johns Hopkins University, Baltimore, MD USA 21287.
authors.forename: J H
authors.initials: JH
authors.lastname: Siewerdsen
keywords: bone marrow edema; bone mineral density; cone-beam CT; dual-energy imaging; extremities imaging