Ultrafast fMRI Detects Age-Related Changes in Harmonics of Cardiac Pulsations in the Brain at 7 T

PURPOSE: Aging impacts pulsatility of blood vessels in the brain, reflecting vascular health. Resolving characteristics of cardiac pulsatility requires faster acquisitions than traditional fMRI. An ultrafast fMRI method was developed and applied to sample several harmonics of cardiac pulsations at 7 T. METHODS: Leveraging partial separability, an ultrafast fMRI method (TR = 65 ms) was applied at 7 T with full brain coverage at 2 mm isotropic resolution and concurrent pulse plethysmographic (PPG) recordings in 28 healthy adults, 22 of whom had acceptable PPG and MRI data. The reliability of the pulsation was assessed for each voxel through even/odd splitting of heartbeats. The PPG was used to retrospectively temporally align signals across heartbeats, and analysis was performed on amplitudes of harmonic frequencies to explore age- and sex-related differences. Reliable measures of four harmonics of the heartbeat were characterized along with the ratios of the harmonics to the primary harmonic. RESULTS: High reliability of the pulsation was found near major arteries, tested by Spearman correlation between the first harmonic and a vessel atlas (p < 0.0001). Consistent with previous literature, older adults exhibited higher harmonic amplitudes with the strongest result in the second harmonic in gray matter with FDR-corrected q = 0.020. In addition, males had a higher third-to-first harmonic ratio. CONCLUSION: Ultrafast fMRI can reliably resolve several harmonics of cardiac pulsations in the brain in and around blood vessels. This may provide a way to characterize vascular health throughout the brain during aging.