Breathing-speed quantitative motion imaging using radial acquisition and motion-subspace reconstruction

Motivation: Motion-resolved MRI relies on the navigation technique and can miss motion peaks or baseline drifts since it reconstructs a composite motion cycle without localized temporal information. Goal(s): To develop a quantitative motion imaging at breathing speed (temporal resolution <450ms) for robust characterization of motion. Approach: A combination of highly undersampled radial acquisition (3 spokes/frame) and motion subspace reconstruction was employed to achieve <450ms of temporal resolution. The motion sub-space was computed directly from the data. The diaphragm position was quantified automatically using a position-tracking algorithm. Results: True motion information at breathing speed can be obtained, outperforming state-of-the-art motion-resolved MRI that uses motion sorting. Impact: Direct measurement of motion at the speed of breathing can enable the extraction of functional information and improve motion characterization for radiotherapy planning.