Next Generation 7 Tesla Arterial Spin Labeling With Rotated Spiral Acquisition Enables Mesoscale Resolution in 3D Brain Perfusion and Functional MRI

PURPOSE: To achieve high resolution (≤ 1 mm isotropic) whole-brain perfusion imaging at 7 T with next generation ASL pulse sequence, reconstruction algorithm, and MRI hardware. METHODS: We capitalized on three major innovations: (1) FLASH-based pseudo-Continuous ASL (pCASL) sequence with rotated golden-angle stack-of-spirals (rGA-SoS) sampling; (2) dynamic compressed sensing (CS) reconstruction with high spatiotemporal resolution and motion-resolved self-navigation; and (3) high density array coil and high-performance Impulse gradient of the NexGen 7 T scanner. Whole-brain laminar perfusion imaging was validated by correlation with histological data of microvascular and cell body density, as well as through finger-tapping (FT) and working memory (WM) fMRI tasks. RESULTS: The proposed rGA-SoS sequence achieved a 3.3-fold SNR and 2-fold higher intraclass correlation coefficient (ICC) compared to matched Cartesian sampling at 7 T, enabling up to 0.8 mm isotropic spatial resolution and/or a temporal resolution of 14 s at 1 mm isotropic. Resting-state perfusion showed strong correlations with microvascular and cell body density. Laminar perfusion fMRI revealed a two-peak activation in the primary motor cortex induced by FT, and distinct laminar profiles for task-positive and task-negative networks during WM task. CONCLUSION: This method offers a noninvasive imaging tool to bridge the gap between mesoscopic MRI with microscopic cellular imaging, as well as to investigate neural excitation and inhibition underlying positive and negative fMRI activations.