Volume-of-interest imaging using multiple aperture devices

Volume-of-interest (VOI) imaging is a strategy in computed tomography (CT) that restricts x-ray fluence to particular anatomical targets via dynamic beam modulation. This permits dose reduction while retaining image quality within the VOI. VOI-CT implementation has been challenged historically by a lack of hardware solutions for tailoring the incident fluence to the patient and anatomical site as well as challenges involving interior tomography reconstruction of truncated projection data. In this work, we propose a general VOI-CT imaging framework using multiple aperture devices (MADs), an emerging beam filtration scheme based on two binary x-ray filters. Location of VOI is prescribed using two scout views at anterior-posterior (AP) and lateral perspectives. Based on a calibration of achievable fluence field patterns, MAD motion trajectories designed using an optimization objective that seeks to maximize the relative fluence in the VOI subject to minimum fluence constraints. A modified penalized-likelihood method is developed for reconstruction of heavily truncated data using the full-field scout views to help solve the interior tomography problem. Physical experiments were con- ducted to show the feasibility of non-centered and elliptical VOI in two applications - spine and lung imaging. Improved dose utilization and retained image quality is validated with respect to standard full-field protocols. Compared with full-field scans at reference dose, the MAD-VOI scans reduced total dose by 80% while retaining image quality. We observe that the contrast-to-noise ratio is 30% higher compared with low-dose full-field scans at the same dose usage.