Ultrafast fMRI detects age-related changes in harmonics of cardiac pulsations in the brain at 7 T.

Purpose: To develop and apply an ultra-fast fMRI acquisition at 7 T to measure the pulsatile signals in the brain with full brain coverage and detect age-related differences. Pulsatile signals' parameters provide information about the health status of the cerebrovascular system. This new acquisition provides a good mix of spatial coverage, image resolution, and temporal resolution for observing physiological signals. Methods: A partial separability MRI acquisition and reconstruction approach was used to collect 3D data acquired at 7 T with TR = 65 ms in 28 healthy adults. 8 young subjects and 14 older subjects (10 male and 12 female) had acceptable pulse plethysmography and MRI data. With full-brain coverage and 2 mm isotropic resolution, the reliability of the pulse signal (even/odd heartbeat as test/retest) within each brain voxel was computed across subjects. Within voxels of high pulse reliability, the average magnitude within 0.15 Hz of the 4 heartbeat harmonic frequencies were compared within CSF, GM, and WM between young/old and between male/female participants. Results: Increased first harmonic magnitude in older adults compared to young adults was detected in regions with reliable cardiac pulsations, which overlap major arteries and CSF pools. There was also a greater magnitude of the third harmonic normalized to the first in males. Brain maps of the pulse frequency and the harmonics were formed for visualization of regions of high pulsatility. Conclusion: This new approach captures the pulsatile signal with BOLD fMRI with high spatiotemporal resolution and can be sensitive to age- and sex-related differences.