Deformable motion correction for interventional cone-beam CT

Cone-beam CT (CBCT) is a valuable tool for guiding interventional procedures, including embolization and ablation of soft-tissue targets. However, long scan times (5-30 s) make CBCT susceptible to artifacts arising from involuntary motion. This work reports a method to estimate deformable motion from scan data without additional patient monitoring. A motion vector field (MVF) is computed that minimizes a gradient entropy objective function for image sharpness. MVFs describing deformable motion were estimated as a spatial interpolation of M rigid motion trajectories, each with temporal motion modeled by an N-point spline. Abrupt changes were penalized via spatial-temporal regularization, and a modified 3D filtered backprojection approach was used for motion-corrected image reconstruction. The method was evaluated in digital simulation, cadaver, and retrospective clinical studies. Sharpness of edges at soft-tissue boundaries improved by 75% (4.4±1.1 to 1.1±0.1 mm), 77% (2.2±0.1 mm to 0.5±0.0 mm), and 33% (0.9±0.1 to 0.6±0.1 mm), respectively. These initial studies demonstrate feasibility of correcting deformable organ motion, which will increase the utility and precision of CBCT guidance.