Short and long-term breathing irregularities in MR navigator and bellow surrogates and enhancement of external-internal motion correlation

Motivation: Breathing irregularities affect respiratory-correlated 4D-imaging quality with assumed periodic respiration and external-to-internal motion prediction. Goal(s): To assess the variety of breathing irregularities and predictability of internal motion. Approach: External bellows and concurrent internal navigator waveforms were collected during two 50-minute MRI scans for three subjects. Data analysis included breathing periodicity index (BPI), external-internal correlation, and correlation enhancement by phase-shift correction. Results: BPI decreases as subjects transition from awake to semi-asleep stages. The mean correlation between external and internal BPI is 0.55 across 12 scans in three subjects. The native external-internal correlation (c=0.75±0.01) is enhanced to c=0.88±0.01 with phase-shift correction. Impact: Both short-term and long-term respiratory irregularities were characterized. Keeping subjects awake through communication reduced irregularities and increased gating efficiency. Additionally, phase-shift correction improved the external-internal motion correlation, suggesting a higher fidelity in 4D-imaging surrogates and better internal motion prediction.