Concurrent CBF and BOLD FMRI with dual-echo spiral simultaneous multi-slice acquisitions at 7T

Area of Science:

• Neuroimaging
• Magnetic Resonance Imaging
• Functional Magnetic Resonance Imaging (fMRI)

Background:

• Arterial Spin Labeling (ASL) offers specific measurement of cerebral blood flow (CBF) for neural activation.
• ASL faces challenges with low signal-to-noise ratio (SNR) and limited coverage/resolution.
• Ultra-high field (UHF) strengths improve ASL's SNR, but single-echo acquisition compromises optimal echo time (TE) for concurrent CBF and BOLD contrasts.

Purpose of the Study:

• To implement and validate a dual-echo spiral out-in ASL sequence with simultaneous multi-slice (SMS) readout for fMRI.
• To assess the capability of this sequence for concurrent acquisition of optimal TE BOLD and non-BOLD (CBF) contrasts at UHF.
• To compare the performance of the dual-echo spiral ASL sequence against conventional Cartesian EPI acquisitions.

Main Methods:

• Development of a dual-echo spiral out-in ASL sequence incorporating SMS readout.
• Acquisition of fMRI data using the developed sequence and conventional Cartesian EPI with matched parameters.
• Validation using a visuomotor task paradigm.
• Analysis of cerebral blood flow (CBF) and Blood-Oxygen-Level-Dependent (BOLD) contrast maps.

Main Results:

• The dual-echo spiral ASL sequence successfully generated robust CBF and BOLD activation maps.
• Measured absolute and relative CBF changes aligned with prior literature and Cartesian acquisitions.
• BOLD response amplitude was higher with the spiral sequence due to a more optimal TE.
• Simultaneous multi-slice (SMS) readout increased coverage without compromising temporal resolution.

Conclusions:

• Dual-echo spiral out-in SMS acquisition is a promising technique for simultaneous BOLD and non-BOLD contrast acquisition at UHF.
• This method overcomes TE compromise issues inherent in single-echo ASL acquisitions.
• The sequence offers improved BOLD signal and robust CBF measurements with no loss in temporal resolution, enhancing fMRI capabilities.