Abstract
Ultra-high field 7-Tesla (7 T) MRI has the potential to advance our understanding of neuropsychiatric disorders, including major depressive disorder (MDD). To date, few studies have quantified the advantage of resting state functional MRI (fMRI) at 7 T compared to 3-Tesla (3 T). We conducted a series of experiments that demonstrate the improvement in temporal signal-to-noise ratio (TSNR) of a multi-echo multi-band fMRI protocol with ultra-high field 7 T MRI, compared to a similar protocol using 3 T MRI in healthy controls (HC). We also directly tested the enhancement in ultra-high field 7 T fMRI signal power by examining the ventral tegmental area (VTA), a small midbrain structure that is critical to the expected neuropathology of MDD but difficult to discern with standard 3 T MRI. We demonstrate up to 300% improvement in TSNR and resting state functional connectivity coefficients provided by ultra-high field 7 T fMRI compared to 3 T, indicating enhanced power for detection of functional neural architecture. A multi-echo based acquisition protocol and signal denoising pipeline afforded greater gain in signal power compared to classic acquisition and denoising pipelines. Furthermore, ultra-high field fMRI revealed mood-related neurocircuit disturbances in patients with MDD compared to HC, which were not detectable with 3 T fMRI. Ultra-high field 7 T fMRI may provide an effective tool for studying functional neural architecture relevant to MDD and other neuropsychiatric disorders.
Highlights
Introduction In the past30 years, functional magnetic resonance imaging (MRI) has provided unprecedented insight into the neural mechanisms of neuropsychiatric disorders in humans, including major depressive disorder (MDD)
We report improved signal power across the brain with ultra-high field 7 T functional MRI compared to 3 T that is boosted by multi-echo based denoising
Functional connectivity coefficients between diverse brain regions relevant to MDD and other neuropsychiatric disorders was significantly enhanced at 7 T compared to 3 T, including of ventral tegmental area (VTA), a small midbrain structure that is limited by poor temporal SNR (TSNR) at lower clinical field strength
Summary
Introduction In the past30 years, functional magnetic resonance imaging (MRI) has provided unprecedented insight into the neural mechanisms of neuropsychiatric disorders in humans, including major depressive disorder (MDD). Higher field strengths produce more B0 inhomogeneities and susceptibility artifacts, which lead to geometric distortion, signal dropout and signal pile-up[6]. Ventral portions of the brain, including subcortical and midbrain structures important for mood regulation, are affected by susceptibility distortions and signal drop-out due to their proximity to bone and sinuses[11,12]. These limitations have led to concerns regarding the utility of ultra-high field MRI for examining ventral regions relevant to neuropsychiatric disorders. We have developed and implemented an ultra-high field 7 T functional MRI scanning protocol with multiple TE’s, thin slices, multiband acquisition and TE-dependent physiological denoising methods to improve signal power detection and temporal SNR (TSNR) for in vivo imaging
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