Author: Theodore Higgins Arsenault, Kenneth W. Gregg, Lauren E Henke, Rojano Kashani, Christian Erik Petersen, Alex T. Price, Atefeh Rezaei, Runyon C. Woods 👨🔬
Affiliation: University Hospitals Seidman Cancer Center 🌍
Purpose: CBCT is subject to more artifacts due to increased photon scatter, especially in areas of increased tissue heterogeneities compared to fan-beam CTs (FBCTs). Improved imaging panels combined with advanced iterative reconstruction techniques may reduce artifacts seen with CBCT. This investigation will characterize in-vivo image quality within the brain using an advanced C-arm linac imaging CBCT solution.
Methods: Images were acquired for five patients with either a brain or head and neck malignancy on a TrueBeam equipped with the HyperSight CBCT solution. CBCT protocols utilized a full-fan geometry and reconstruction using iterative Acuros with metal artifact reduction (iCBCT-MAR) algorithms. These images were registered to the patients’ FBCTs, and quantitative metrics such as artifact index (AI), non-uniformity, contrast-to-noise ratio (CNR), and average Hounsfield-unit (HU) difference were calculated within spatially consistent points of various structures across four of the patients’ two types of CT scans. These points were located at the four lobes and center of the brain, in addition to an area of increased artifact. The remaining patient was evaluated only for three areas of increased artifact caused by a metal implant.
Results: The median AI across the four main patients was 6.4 [0 to 13.5] in the 4 lobe regions + center, and went up to 16.8 [8.9 to 42.3] in the increased artifact areas. The median non-uniformity in the four lobe regions + center was 2.1 [1.9 to 4.4] for CBCT and 1.4 [1.2 to 1.6] for FBCT. CNR for the FBCT scans was 0.5 [0.0 to 2.0], and the CBCT scan was 0.6 [0.1 to 2.9]. The median difference in HU values was -7.4 [-18.0 to 17.8].
Conclusion: Image quality metrics were comparable between the FBCT and advanced CBCT images. Isolated artifacts that may impact local image quality were observed.