Block-interleaved segmented echo-planar imaging for improved activity detection in submillimeter high-resolution functional MRI at 7 T.

Purpose: Isotropic submillimeter high-resolution functional MRI (fMRI) facilitates noninvasive investigation of neuronal activities at the mesoscale level, including cortical columns and laminae. However, the task-evoked functional activity becomes less detectable when using single-shot echo planar imaging (EPI) with parallel imaging techniques such as generalized autocalibrating partially parallel acquisitions (GRAPPA), owing to a reduction in temporal signal-to-noise ratio (tSNR). Although conventional multishot EPI (msEPI) enhances tSNR, it reduces temporal resolution, making it less suitable for fMRI studies involving short-duration stimuli. To overcome this problem, a novel msEPI-based fMRI acquisition and reconstruction method, called block-interleaved segmented EPI (BISEPI), was proposed.

Methods: This technique uses timing information of a block design paradigm during acquisition and reconstruction to preserve both temporal resolution and tSNR. Furthermore, a k-space-based motion correction method is incorporated to mitigate head motion artifacts.

Results: Results from human studies showed that the proposed method reduced g-factor penalties typically observed in GRAPPA-accelerated EPI. It provided high tSNR, improved motion robustness, and enhanced sensitivity to blood oxygen level-dependent signal responses.

Conclusion: The proposed method circumvents both conventional msEPI-related and GRAPPA-related problems and enables the detection of blood oxygen level-dependent signal responses at submillimeter spatial resolution. It is effective for paradigms using short-duration, low-power stimuli at 0.7-mm isotropic resolution, and standard-power stimuli at 0.4-mm isotropic resolution.