Hadamard-encoded sub-slice fMRI for reduced signal dropout

Area of Science:

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

Background:

• Susceptibility-induced field gradients in fMRI cause image distortion and signal dropout near air interfaces.
• Reducing slice thickness improves signal dropout but decreases signal-to-noise ratio (SNR).

Purpose of the Study:

• To develop a novel fMRI acquisition technique to mitigate susceptibility artifacts.
• To improve the detection of brain activation in challenging regions with minimal SNR loss.

Main Methods:

• Simultaneous excitation of subslices with alternating Hadamard-encoded radiofrequency pulses.
• Incoherent addition of subslices to reduce through-plane dephasing.
• Acquisition using a sensory task and hypercapnic challenge with breathholding (BH).

Main Results:

• The proposed method demonstrated improved brain activation detection compared to conventional acquisition.
• Average T-scores in the BH task increased by 16% (P<.0003).
• Significant improvements in BH activation extent and T-scores were observed in frontal brain regions.

Conclusions:

• The novel fMRI technique effectively reduces susceptibility-induced artifacts, improving brain activation detection.
• This method offers a trade-off between temporal resolution and SNR, allowing for optimized acquisition parameters.
• The findings suggest potential for enhanced neuroimaging studies in regions prone to signal dropout.