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High-resolution Functional Magnetic Resonance Imaging Methods for Human Midbrain
Published on: May 10, 2012
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Ultra-high spatial resolution BOLD fMRI in humans using combined segmented-accelerated VFA-FLEET with a recursive RF
Avery J L Berman1,2, William A Grissom3,4, Thomas Witzel1,2
1Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts, USA.
Magnetic Resonance in Medicine
|July 25, 2020
Summary
This study introduces a new functional MRI (fMRI) technique, VFA-FLEET-SLR, which significantly reduces ghosting artifacts for ultra-high-resolution imaging. This advancement enables clearer BOLD signal detection at resolutions previously unattainable.
Area of Science:
- Neuroimaging
- Magnetic Resonance Imaging (MRI)
- Biomedical Engineering
Background:
- Single-shot echo-planar imaging (EPI) faces spatial encoding limitations in functional MRI (fMRI).
- Multi-shot segmented EPI reduces readout duration but suffers from intermittent ghosting due to long inter-segment acquisition times.
- Existing methods like VFA-FLEET-Sinc show inconsistent slice profiles and ghosting, hindering fMRI applications.
Purpose of the Study:
- To develop a multi-shot segmented EPI technique for ultra-high-resolution fMRI with reduced ghosting artifacts.
- To improve inter-segment fidelity and maximize signal for fMRI using a novel segment ordering and variable flip angle progression.
- To enable fMRI at previously inaccessible spatial resolutions by minimizing motion and respiration-induced artifacts.
Main Methods:
- Developed Variable Flip Angle-FLEET (VFA-FLEET) with a novel FLEET segment ordering.
- Designed a recursive Shinnar-Le Roux (SLR) radiofrequency (RF) pulse for VFA-FLEET-SLR to ensure consistent slice profiles and signals.
- Compared VFA-FLEET-SLR against conventional-segmented EPI and VFA-FLEET-Sinc at 3T and 7T, assessing temporal stability and image quality.
Main Results:
- VFA-FLEET-SLR demonstrated significant reductions in both intermittent and stable ghosting compared to conventional methods.
- Achieved 0.6-mm isotropic acquisition at 7T using VFA-FLEET-SLR combined with acceleration, enabling reliable blood oxygenation level-dependent (BOLD) response detection.
- Simultaneous multi-slice VFA-FLEET-SLR was successfully implemented to counteract increased repetition time, using RF-encoded controlled aliasing.
Conclusions:
- VFA-FLEET with recursive RF pulse design (VFA-FLEET-SLR) significantly reduces artifacts and spatial blur in fMRI.
- This technique enables fMRI acquisitions at unprecedented spatial resolutions within a full-brain field of view.
- The developed method supports ultra-high-resolution fMRI, improving the detection of neural activity with enhanced image quality.
