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For our Winter 2020 Spotlight on Basic Research, Wei-Tang Chang, PhD, has written the below update on his investigative scope at UNC’s Biomedical Research Imaging Center. Dr. Chang’s basic science imaging interests include the development of advanced MR imaging techniques, such as ultrahigh-resolution and ultrafast MR acquisitions.

The hippocampus is the earliest and most severely affected structure in neurodegenerative disorders such as Alzheimer’s disease (AD). The hippocampal-subfield volumetry has been shown to reveal structural abnormalities in AD, but the subfield volumetry is not specific to AD, and the sensitivity is still inconclusive. Network-based approaches for hippocampal-subfield taking into account the brain-wide functional connectivity rather than local structural change could potentially enhance the sensitivity of AD biomarkers. Given the width of hippocampal subfields can be as small as ≤1 mm, high resolution functional MRI (fMRI) with temporal resolution of ~2s and whole-brain coverage is needed but very technically challenging due to intrinsically-low signal-to-noise ratio (SNR) and hardware limitation. As a result, the functional mapping of hippocampal-subfield networks in the human brain remains poorly understood.

To address these challenges, we developed two novel MR sequences, namely partition-encoded simultaneous multi-slab (PRISM) and multiband 3D (MB3D), to achieve ultrahigh spatial resolution and whole-brain coverage with a temporal resolution of 2sec. For the MR scanners without the capability of ultra-thin slice excitation, the PRISM sequence offered the required through-plane resolution with the cost of ~7% SNR loss at the slab boundary. For the MR scanners that can perform with ultra-thin slice excitation, MB3D sequence provided comparable performance compared to PRISM without the slab-boundary artifact. With the enhanced imaging capability, we aimed to investigate the age-dependent alterations of not only the local hippocampal organization, but also the global functional connectivity associated with different hippocampal subfields. In 2019, an NIH National Institute on Aging (NIA) R21 award began funding our investigation – “Ultrahigh-resolution fMRI of age-altered hippocampal subfield-cortical interactions” (PI: W-T Chang) — at UNC’s Biomedical Research Imaging Center.