Multi-slice passband bSSFP fMRI at ultra-high field

TL;DR

This study develops a multi-slice passband bSSFP fMRI method at ultra-high fields, achieving non-distorted activation maps in human and rat brains with performance comparable to or better than traditional methods.

Contribution

It introduces a multi-slice bSSFP acquisition with Cartesian read-out that preserves signal characteristics and enables high-quality, distortion-free fMRI at ultra-high fields.

Findings

Human 7T fMRI with 2D-bSSFP matches 3D-bSSFP temporal SNR.

Rat 14T fMRI shows similar sensitivity to GE-EPI with fewer distortions.

Potential for improved mouse fMRI at ultra-high fields.

Abstract

Balanced steady-state free precession (bSSFP) can be used as an alternative to gradient-echo (GE) EPI for BOLD functional MRI when image distortions and signal drop-outs are severe such as at ultra-high field. However, 3D-bSSFP acquisitions have distinct drawbacks on either human or animal MR systems. On clinical scanners, 3D imaging is suboptimal for localized fMRI applications, and also results in distortions, blurring, and increased sensitivity to motion or physiological noise. On pre-clinical systems, 3D acquisitions have low temporal resolution due to limited acceleration options, while single slice offers insufficient coverage. The aim of the present study was to implement a multi-slice bSSFP acquisition with Cartesian read-out to obtain non-distorted BOLD fMRI activation maps in the human and rat brain at ultra-high field. We show that the bSSFP signal characteristics are preserved in a new pseudo-steady-state. In the human brain at 7 Tesla, we demonstrate that both task- and resting-state fMRI can be performed with 2D-bSSFP, with a temporal SNR that matches that of 3D-bSSFP, resulting in - at least - equal performance. In the rat brain at 14 Tesla, we show that the multi-slice bSSFP protocol has similar sensitivity to gradient-echo EPI for task fMRI, while benefitting from much reduced distortions and drop-outs. The advantages of passband bSSFP at 14 Tesla in comparison with GE-EPI are expected to be even more marked for mouse fMRI.