TH-E-218-01: Dual-Energy CBCT Imaging for Metal Artifact Reduction and Contrast Enhancement

Purpose: To develop dual-energy CBCT imaging techniques for potential applications in metal artifact reduction and contrast enhancement. Methods: Metal artifact reduction using virtual monochromatic (VM) technique was evaluated with a bench-top CBCT system. Low- and high-energy projections were acquired at 80kVp and 150kVp (with an additional 0.8mm tin filtration). These projections were then decomposed into acrylic and aluminum basis material projections to synthesize VM projections. VM projections were then reconstructed to generate VM CBCTs. The effect of VM CBCT on the metal artifact reduction was evaluated with an in-house titanium-BB phantom. Optimal energy to maximize contrast-to-noise ratio (CNR) in VM CBCT was determined using a water phantom containing two iodine concentrations.The effect of contrast enhancement using linearly-mixed-image technique was evaluated using a kV on-board imager at 80kVp and 125kVp. The dose partitioning between low- and high-energy CBCTs was varied while keeping total dose approximately equal to single-energy CBCTs, measured using an ion chamber. Noise level and CNR for six tissue types were investigated for dual-energy CBCTs in comparison with single energy CBCTs at 100kVp. Results: Metal artifacts were substantially reduced using VM CBCT and quantitative analysis showed about 70% improvement in CNR in the titanium-BB phantom study. Optimal energy selection to maximize CNR was 50keV for both iodine concentrations. A maximum noise reduction of 4% was achieved for linearly-mixed dual-energy CBCTs compared with that of equivalent-dose single-energy CBCTs. Linearly-mixed CBCTs showed an improvement of CNR ranging from 3-14% when 60% and 80% dose was partitioned to low-energy projections. Conclusions: Dual-energy CBCT imaging techniques were developed and shown to be effective in metal artifact reduction. Linearly-mixed dual-energy CBCT has the potential to improve noise and CNR depending on the dose-partitioning scheme compared with single-energy CBCT with equivalent dose. This work is partially supported by a research grant from Varian Medical Systems.