Multi-echo balanced SSFP with a sequential phase-encoding order for functional MR imaging at 7T.

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Neuroimaging
• Biophysics

Background:

• Balanced steady-state free precession (bSSFP) is a powerful MRI technique.
• Accelerated imaging is crucial for functional MRI (fMRI) to capture rapid brain activity.
• Existing methods like Echo Planar Imaging (EPI) can suffer from distortions, particularly at high magnetic field strengths like 7 Tesla (7T).

Purpose of the Study:

• To develop and evaluate a novel 2D multi-echo passband balanced SSFP (bSSFP) sequence with sequential phase-encoding for fast functional brain imaging at 7T.
• To assess the performance of this sequential multi-echo bSSFP in terms of image quality and functional activation compared to conventional methods.

Main Methods:

• A 2D multi-echo passband balanced SSFP (bSSFP) sequence with sequential phase-encoding was developed.
• A GRAPPA-based reconstruction method was implemented to mitigate ghosting artifacts inherent in multi-echo bSSFP.
• Image quality was compared between multi-echo bSSFP and conventional single-echo bSSFP.
• Submillimeter-resolution fMRI experiments were conducted using a checkerboard visual stimulus to compare activation characteristics.

Main Results:

• Multi-echo bSSFP with a shorter echo train length (ETL=3) demonstrated higher structural similarity to single-echo bSSFP.
• Multi-echo bSSFP (ETL=3) achieved higher temporal signal-to-noise ratio (tSNR) than GRAPPA-accelerated single-echo bSSFP (R=2).
• Functional imaging with multi-echo bSSFP (ETL=3) approached the speed of accelerated EPI without tSNR penalty, yielding comparable activation patterns and virtually distortion-free images.

Conclusions:

• Sequential multi-echo bSSFP (ETL=3) is well-suited for high-speed, submillimeter fMRI at 7T.
• This method provides an effective way to accelerate bSSFP imaging without compromising tSNR, unlike traditional parallel imaging techniques.
• It offers a valuable alternative for distortion-free functional imaging, preserving activation patterns observed with conventional bSSFP.