自動呼吸および体動補正（ACROBATIC）フリーランニング心臓全周5次元磁気共鳴画像法

Free-running five-dimensional (5D) whole-heart magnetic resonance imaging (MRI) simplifies image acquisition by eliminating the need for external gating, breath-holding, and prospective scan planning. However, it remains vulnerable to patient movement in pediatric populations, which may require sedation or general anesthesia. We present a retrospective motion correction approach using the automatic respiratory and bulk patient motion correction (ACROBATIC) framework to detect, estimate, and correct for bulk motion, thereby improving image quality in pediatric cardiac MRI.

Free-running Ferumoxytol-enhanced three-dimensional (3D) radial gradient-echo (GRE) data from 210 pediatric patients were manually categorized by the amount of bulk motion within each acquisition, based on retrospective reconstructions. From this cohort, 25 cases with the highest and 25 with the lowest detected bulk motion were selected, forming the moving and reference cohorts, respectively, for subsequent analysis and evaluation of the proposed framework. Respiratory motion was estimated using focused navigation. Bulk motion events were automatically detected from the variation in repeated radial readouts. The data were divided into four-dimensional (4D) arrays with timepoints spanning single respiratory cycles and reconstructed into retrospective real-time images using compressed sensing. Bulk motion was corrected via 3D rigid registration and poorly aligned images were excluded using an outlier-rejection algorithm. Final reconstruction was performed using a previously established 5D cardiac and respiratory motion-resolved compressed sensing approach. ACROBATIC's performance was evaluated by a Dice coefficient (automatic detection), sharpness metrics at the blood-myocardium interface and within the pulmonary vessels, as well as qualitative grading by two expert reviewers.

The ACROBATIC framework successfully differentiated between moving and non-moving patients relative to manual evaluation (Dice = 0.96). Image sharpness significantly improved after motion correction, for analyses of the blood-myocardium interfaces and pulmonary veins. Expert evaluations supported the quantitative findings with average grade improvements of 0.44 and 0.54, respectively for Reviewer 1 and Reviewer 2.

The ACROBATIC framework effectively reduces motion-related artifacts in pediatric cardiac MRI, particularly in patients with significant movement. This method supports the broader goal of achieving high-quality, dynamic whole-heart imaging in children without the need for sedation or general anesthesia.