Spin-echo and gradient-echo EPI of human brain activation using BOLD contrast: a comparative study at 1.5 T

Area of Science:

• Neuroimaging
• Magnetic Resonance Imaging (MRI)
• Functional MRI (fMRI)

Background:

• Blood Oxygenation Level Dependent (BOLD) contrast is a key technique in functional magnetic resonance imaging (fMRI) for detecting brain activity.
• Spin-echo (SE) and gradient-echo (GE) echo-planar imaging (EPI) sequences are commonly used for BOLD fMRI, but their relative sensitivities differ.

Purpose of the Study:

• To compare the sensitivity of spin-echo and gradient-echo echo-planar sequences for detecting human brain activation using BOLD contrast at 1.5 T.
• To quantify the differences in signal changes and relaxation rates (R2 and R2*) between SE and GE sequences during motor cortex activation.

Main Methods:

• Collected time-course BOLD fMRI data from the primary motor cortex during rest and finger movement using both SE and GE EPI sequences at 1.5 T.
• Acquired images at various echo times (TE) to measure resting and active state signal intensities, R2 (1/T2), and R2* (1/T2*) values.
• Calculated the ratio of activation-induced signal changes between GE and SE sequences at optimal TEs for each sequence.

Main Results:

• Brain activation resulted in an average R2 change of -0.16/s and an average R2* change of -0.55/s.
• The average delta R2*/delta R2 ratio was 3.52, indicating a stronger effect on R2*.
• The gradient-echo sequence demonstrated a 1.87-fold greater signal change compared to the spin-echo sequence for maximal BOLD contrast.

Conclusions:

• Gradient-echo sequences offer superior sensitivity for BOLD signal detection in fMRI compared to spin-echo sequences.
• Understanding these differences is vital for optimizing fMRI acquisition parameters and interpreting results in neuroscience research.
• The findings support the use of gradient-echo sequences for enhanced detection of neural activity via BOLD contrast.