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Session: Dual Energy and Spectral CT and CBCT [Return to Session]

Quantitative Dual-Energy Imaging of Bone Composition On Multisource Cone-Beam CT with Model-Based Artifact Corrections

S Liu*, G Shi, G Osgood, J Siewerdsen, J Stayman, W Zbijewski, Johns Hopkins University, Baltimore, MD


TH-E-TRACK 3-4 (Thursday, 7/29/2021) 3:30 PM - 4:30 PM [Eastern Time (GMT-4)]

Purpose: The recently introduced extremity Cone-Beam CT (CBCT) with a three-source x-ray unit enables single-rotation dual energy (DE) imaging by operating the x-ray tubes at different potential. We investigate the application of this novel DE acquisition mode for Bone Mineral Density (BMD) measurements in extremities with and without metal implants.

Methods: The extremity CBCT implements three x-ray tubes arranged longitudinally (parallel to the long axis of the extremity). For DE imaging, the peripheral sources were operated at 70 kVp (low energy, LE) and the central source was operated at 100 kVp (high-energy, HE) in an alternating sequence. This yielded 105 views for each of the peripheral LE sources and 210 views for the central HE source; the total CTDI scan dose was ~10 mGy. Experimental studies involved a 16 cm water cylinder with BMD inserts (50 mg/mL, 100 mg/mL, 200 mg/mL) surrounding a Titanium tibial nail. Image domain DE decomposition was applied to estimate BMD (Calcium concentration). LE reconstruction for the decomposition was generated by weighted Filtered-Backprojection of the two peripheral source datasets. Scatter was estimated using accelerated Monte Carlo simulations (107 photons/view+denoising) from preliminary HE and LE reconstructions. To mitigate metal artifacts, constrained three-material decomposition (Ca, Ti and water) was first performed to obtain a model of the implant. The model was used to interpolate projection values behind the metal. Standard two-material DE decomposition was then applied to estimate BMD.

Results: With the proposed artifact correction framework, the BMD estimation errors were comparable for phantoms with and without metal: ~30% for the 50 mg/mL insert, ~16% for the 100 mg/mL insert, and ~12% for the 200 mg/mL insert.

Conclusion: Single-scan DE imaging has been implemented on the multisource extremity CBCT. Model-based artifact corrections enabled accurate BMD estimation even in the presence of metal hardware.



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