Contrast Enhanced Cone Beam CT Capabilities of Halcyon with Hypersight
Abstract
Purpose
Dynamic contrast enhanced CT (DCE-CT) is a functional imaging method used to measure vascular perfusion with high resolution and clinical value. DCE cone beam CT (DCE-CBCT) has been prevented by low image quality and lengthy acquisition, however, enhanced image quality and rapid scan times of imaging solution HyperSight equipped on the Halcyon or TrueBeam is a potential enabler to DCE-CBCT. This provides the possibility for CBCT-based functional measurements during adaptive radiotherapy.
Methods
A contrast enhancement phantom, containing capsules of varying diameter and orientation mimicking different iodine contrast levels, was used to characterize image quality, spatial resolution, and partial volume averaging on a CTSim scanner, Halcyon (HyperSight-CBCT), TrueBeam (HyperSight-CBCT), and TrueBeam (CBCT). Capsule CT number and volume was computed across variable mAs, kV, scan modes, slice thickness, reconstruction algorithms and phantom positioning to generate a comprehensive set of metrics. HU consistency, uniformity and accuracy, volume accuracy, and modulation transfer function (MTF) curves were calculated.
Results
Across mAs, mean CT number (10mm 1.56 g/cm3 capsules) varied by less than 0.3% for CT and TrueBeam (HyperSight-CBCT), 0.6% for Halcyon, and 0.8% for TrueBeam (CBCT); across phantom positions, variation was less than 1% for CT, 3% for Halcyon, 5% for TrueBeam (HyperSight-CBCT), and 8% for TrueBeam (CBCT). Averaged across orientations, volume percent error was less than 2% for CT and TrueBeam (HyperSight-CBCT), 0.2% for Halcyon, and 1% for TrueBeam (CBCT). HU uniformity and percent error were similar across modalities (less than 13% coefficient of variation, less than 3% variation, respectively). CBCT displayed lower 10% MTF values and decreased CT numbers than HyperSight-CBCT.
Conclusion
HyperSight-CBCT displayed greater HU consistency, volume accuracy and spatial resolution, and less partial volume averaging than CBCT, demonstrating potential for assessment of contrast enhancement. Future work will involve acquisitions with a flow phantom to investigate the temporal resolution of HyperSight-CBCT.