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Segmented spin-echo pulses to increase fMRI signal: repeated intrinsic diffusional enhancement
A W Song1, H Mao, R Muthupillai
1Brain Imaging and Analysis Center, Duke University, Durham, North Carolina 27710, USA. allen.song@duke.edu
Magnetic Resonance in Medicine
|September 30, 1999
Summary
This study introduces a novel spin-echo functional MRI (fMRI) technique to improve signal detection. The method enhances sensitivity to blood oxygenation level dependent (BOLD) changes, particularly in challenging brain regions.
Area of Science:
- Neuroimaging
- Magnetic Resonance Imaging
Background:
- Gradient-recalled acquisition in functional magnetic resonance imaging (fMRI) suffers from signal loss in critical brain areas like the medial temporal lobe and basal ganglia.
- These methods are also prone to artifacts from large veins and cerebrospinal fluid (CSF), leading to potential false-positive results.
- Spin echoes address some drawbacks but have reduced sensitivity to blood oxygenation level dependent (BOLD) susceptibility changes.
Purpose of the Study:
- To present a novel method for enhancing spin-echo fMRI signal.
- To increase the participation of spins in the dynamic BOLD process for improved functional signal detection.
Main Methods:
- A modified spin-echo technique was developed, segmenting the T2 weighting period.
- Extra free diffusion time blocks were incorporated, with spins restored to the longitudinal axis to prevent transverse relaxation.
- This approach increases spin availability for detecting BOLD field gradients.
Main Results:
- The enhanced method increases the functional signal by recruiting more spins modulated by the capillary BOLD field gradient.
- This leads to a greater functional signal compared to conventional spin-echo techniques.
Conclusions:
- The proposed spin-echo enhancement method improves fMRI signal sensitivity.
- This technique, applied to spin-echo echo-planar imaging (EPI), shows promise for fMRI studies in anatomically challenging, inhomogeneous regions, such as air/tissue interfaces.