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High-resolution Functional Magnetic Resonance Imaging Methods for Human Midbrain
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Highly accelerated submillimeter resolution 3D GRASE with controlled blurring in -weighted functional MRI at 7
Suhyung Park1,2, Salvatore Torrisi1,3, Jennifer D Townsend1,3
1Helen Wills Neuroscience Institute, University of California, Berkeley, CA, USA.
Magnetic Resonance in Medicine
|November 24, 2020
Summary
This study introduces an advanced functional MRI technique for highly accelerated submillimeter resolution imaging. The new method significantly improves signal-to-noise ratio and reduces blurring, enhancing BOLD activations for detailed brain imaging.
Area of Science:
- Neuroimaging
- Magnetic Resonance Imaging (MRI)
Background:
- Gradient and Spin Echo (GRASE) imaging offers potential for functional MRI but faces limitations like k-space modulation causing blurring and signal-to-noise ratio (SNR) loss with variable flip angles (VFA).
- Improving spatial resolution and temporal SNR (tSNR) is crucial for advanced functional MRI applications, particularly at high field strengths like 7T.
Purpose of the Study:
- To develop a highly accelerated, submillimeter resolution, T2*-weighted functional MRI technique at 7 Tesla.
- To overcome the limitations of conventional GRASE imaging by enhancing the point spread function (PSF) and tSNR through controlled blurring and optimized encoding.
Main Methods:
- Implementation of a three-dimensional GRASE sequence with inner-volume selection and variable flip angles (VFA).
- Design of a VFA scheme to balance SNR and blurring for optimal functional sensitivity.
- Development of a novel GRASE-optimized random encoding considering T2* and T2 decay for incoherent aliasing and constrained reconstruction.
Main Results:
- Achieved 0.8 mm isotropic resolution in T2*-weighted functional MRI.
- Expanded the excited volume to 36 slices, reducing PSF by 52%-68% compared to conventional and VFA-GRASE.
- Demonstrated a 2- to 3-fold improvement in mean tSNR, leading to enhanced Blood-Oxygen-Level-Dependent (BOLD) activations.
Conclusions:
- Successfully demonstrated the feasibility of the proposed accelerated GRASE method for T2*-weighted functional MRI at 7T.
- The developed technique shows significant promise for enabling cortical layer-specific functional MRI due to its high resolution and improved sensitivity.
