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Accelerated spin-echo functional MRI using multisection excitation by simultaneous spin-echo interleaving (MESSI)
SoHyun Han1,2, Congyu Liao1,2, Mary Kate Manhard1,2
1Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts.
Purpose:
Spin-echo functional MRI (SE-fMRI) has the potential to improve spatial specificity when compared with gradient-echo fMRI. However, high spatiotemporal resolution SE-fMRI with large slice-coverage is challenging as SE-fMRI requires a long echo time to generate blood oxygenation level-dependent (BOLD) contrast, leading to long repetition times. The aim of this work is to develop an acquisition method that enhances the slice-coverage of SE-fMRI at high spatiotemporal resolution.
Theory And Methods:
An acquisition scheme was developed entitled multisection excitation by simultaneous spin-echo interleaving (MESSI) with complex-encoded generalized slice dithered enhanced resolution (cgSlider). MESSI uses the dead-time during the long echo time by interleaving the excitation and readout of 2 slices to enable 2× slice-acceleration, while cgSlider uses the stable temporal background phase in SE-fMRI to encode/decode 2 adjacent slices simultaneously with a "phase-constrained" reconstruction method. The proposed cgSlider-MESSI was also combined with simultaneous multislice (SMS) to achieve further slice-acceleration. This combined approach was used to achieve 1.5-mm isotropic whole-brain SE-fMRI with a temporal resolution of 1.5 s and was evaluated using sensory stimulation and breath-hold tasks at 3T.
Results:
Compared with conventional SE-SMS, cgSlider-MESSI-SMS provides 4-fold increase in slice-coverage for the same repetition time, with comparable temporal signal-to-noise ratio. Corresponding fMRI activation from cgSlider-MESSI-SMS for both fMRI tasks were consistent with those from conventional SE-SMS. Overall, cgSlider-MESSI-SMS achieved a 32× encoding-acceleration by combining Rinplane × MB × cgSlider × MESSI = 4 × 2 × 2 × 2.
Conclusion:
High-quality, high-resolution whole-brain SE-fMRI was acquired at a short repetition time using cgSlider-MESSI-SMS. This method should be beneficial for high spatiotemporal resolution SE-fMRI studies requiring whole-brain coverage.
Insights
This study introduces a new method for spin-echo functional MRI (SE-fMRI) that significantly improves slice coverage and resolution. This advancement enables high-quality, whole-brain SE-fMRI at faster speeds for better neuroscience research.
Area of Science:
- Neuroimaging
- Magnetic Resonance Imaging
Background:
- Spin-echo functional MRI (SE-fMRI) offers superior spatial specificity compared to gradient-echo fMRI.
- Acquiring high spatiotemporal resolution SE-fMRI with extensive slice coverage is challenging due to long repetition times required for Blood Oxygenation Level-Dependent (BOLD) contrast.
Purpose of the Study:
- To develop an advanced acquisition technique that enhances slice coverage for SE-fMRI while maintaining high spatiotemporal resolution.
Main Methods:
- Developed a novel acquisition scheme named multisection excitation by simultaneous spin-echo interleaving (MESSI) combined with complex-encoded generalized slice dithered enhanced resolution (cgSlider).
- MESSI utilizes dead time during long echo periods to interleave excitation and readout of two slices, achieving 2x slice acceleration.
- cgSlider encodes and decodes adjacent slices simultaneously using phase constraints, further accelerated with simultaneous multislice (SMS) imaging.
- The combined cgSlider-MESSI-SMS approach achieved 1.5-mm isotropic whole-brain SE-fMRI with 1.5s temporal resolution at 3T.
Main Results:
- The cgSlider-MESSI-SMS technique provides a 4-fold increase in slice coverage compared to conventional SE-SMS at equivalent repetition times, with similar temporal signal-to-noise ratios.
- fMRI activation patterns observed with cgSlider-MESSI-SMS were consistent with conventional SE-SMS for sensory stimulation and breath-hold tasks.
- An overall 32x encoding acceleration was achieved by combining in-plane acceleration, multi-band (MB), cgSlider, and MESSI techniques.
Conclusions:
- High-quality, high-resolution whole-brain SE-fMRI can be acquired with significantly reduced repetition times using the cgSlider-MESSI-SMS method.
- This technique is highly beneficial for studies demanding high spatiotemporal resolution and comprehensive whole-brain coverage in SE-fMRI.
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