Accelerating PREFUL MRI: Comparison of Registration Methods and Impact of Time Series Reduction.

The purpose of this study is to evaluate whether accelerated registration and reduced acquisition times preserve the robustness of phase-resolved functional lung (PREFUL) MRI, thereby improving clinical feasibility by facilitating integration into tight time slots and enabling faster turnaround of results. PREFUL MRI at 1.5 T was retrospectively analyzed in 28 patients with chronic obstructive pulmonary disease (COPD) and 56 healthy volunteers. Image registration was performed using Advanced Normalization Tools (ANTs) and Forsberg. Time series (TS) were truncated from 55 to 45, 30, and 15 s per slice. The 55-s variant was evaluated twice to assess potential nondeterministic effects; the first served as the reference. PREFUL parameters, including regional ventilation, quantified perfusion (QQ), flow volume loop correlation metric (FVL-CM) and corresponding defect percentages, were compared across registration methods and TS lengths using Wilcoxon tests, Pearson correlations, intraclass correlation coefficients (ICC), and regional overlap analysis. Forsberg reduced computation time by ~20-fold (3 vs. 58 min per slice) while maintaining trends and repeatability. Although functional values were slightly lower and defect scores higher, correlations between registrations exceeded 90% for most parameters, with regional overlap ≥ 97% in healthy volunteers and ≥ 80% in COPD patients. Shortening the TS to 30 s introduced minor deviations but preserved overlap (≥ 79%) and strong correlations (≥ 77%) compared with 55 s, except for QQ. Larger deviations occurred primarily at 15 s. Repeatability remained moderate to high (ICC ≥ 68%) for all parameters, except QQ, down to 30 s, with the FVL-CM, perfusion defect percentage and amount of nondefect regions in COPD being most stable (ICC ≥ 72%). Forsberg provides results comparable to ANTs at a fraction of the processing time, enabling PREFUL analysis within a practical timeframe. Acquisition for each slice may be reduced to 30 s without compromising robustness, supporting more efficient protocols, although caution is warranted for QQ.