7T-fMRI: Faster temporal resolution yields optimal BOLD sensitivity for functional network imaging specifically at high spatial resolution

Peter E Yoo; Sam E John; Shawna Farquharson; Jon O Cleary; Yan T Wong; Amanda Ng; Claire B Mulcahy; David B Grayden; Roger J Ordidge; Nicholas L Opie; Terence J O'Brien; Thomas J Oxley; Bradford A Moffat

doi:10.1016/j.neuroimage.2017.03.002

7T-fMRI: Faster temporal resolution yields optimal BOLD sensitivity for functional network imaging specifically at high spatial resolution

Neuroimage. 2018 Jan 1:164:214-229. doi: 10.1016/j.neuroimage.2017.03.002. Epub 2017 Mar 8.

Authors

Affiliations

¹ Melbourne Brain Centre Imaging Unit, Department of Anatomy and Neuroscience, The University of Melbourne, Kenneth Myer Building 30 Royal Parade, Parkville, Victoria, Australia; Vascular Bionics Laboratory, Melbourne Brain Centre, Department of Medicine, The University of Melbourne, Victoria, Australia.
² Department of Electrical & Electronic Engineering, The University of Melbourne, Victoria, Australia; Vascular Bionics Laboratory, Melbourne Brain Centre, Department of Medicine, The University of Melbourne, Victoria, Australia; The Florey Institute of Neuroscience and Mental Health, 30 Royal Parade, Parkville, Victoria, Australia.
³ Melbourne Brain Centre Imaging Unit, Department of Anatomy and Neuroscience, The University of Melbourne, Kenneth Myer Building 30 Royal Parade, Parkville, Victoria, Australia; Imaging Division, Florey Institute of Neuroscience and Mental Health, Melbourne Brain Centre, 245 Burgundy Street, Heidelberg, Melbourne, Victoria, Australia.
⁴ Melbourne Brain Centre Imaging Unit, Department of Anatomy and Neuroscience, The University of Melbourne, Kenneth Myer Building 30 Royal Parade, Parkville, Victoria, Australia.
⁵ Department of Electrical and Computer Systems Engineering, Monash University, Clayton, VIC 3800, Australia; Department of Physiology, Monash University, Clayton, VIC 3800, Australia; Biomedicine Discovery Institute, Monash University, Clayton, VIC 3800, Australia.
⁶ Department of Electrical & Electronic Engineering, The University of Melbourne, Victoria, Australia; Vascular Bionics Laboratory, Melbourne Brain Centre, Department of Medicine, The University of Melbourne, Victoria, Australia; Center for Neural Engineering, The University of Melbourne, Victoria, Australia.
⁷ Departments of Medicine and Neurology, Melbourne Brain Centre at The Royal Melbourne Hospital, The University of Melbourne, Melbourne, Victoria, Australia.
⁸ Vascular Bionics Laboratory, Melbourne Brain Centre, Department of Medicine, The University of Melbourne, Victoria, Australia; The Florey Institute of Neuroscience and Mental Health, 30 Royal Parade, Parkville, Victoria, Australia; NeuroEngineering Laboratory, Department of Electrical &Electronic Engineering, The University of Melbourne, Melbourne, Victoria, Australia; Departments of Medicine and Neurology, Melbourne Brain Centre at The Royal Melbourne Hospital, The University of Melbourne, Melbourne, Victoria, Australia.
⁹ Melbourne Brain Centre Imaging Unit, Department of Anatomy and Neuroscience, The University of Melbourne, Kenneth Myer Building 30 Royal Parade, Parkville, Victoria, Australia. Electronic address: bmoffat@unimelb.edu.au.

PMID: 28286317
DOI: 10.1016/j.neuroimage.2017.03.002

Abstract

Recent developments in accelerated imaging methods allow faster acquisition of high spatial resolution images. This could improve the applications of functional magnetic resonance imaging at 7 Tesla (7T-fMRI), such as neurosurgical planning and Brain Computer Interfaces (BCIs). However, increasing the spatial and temporal resolution will both lead to signal-to-noise ratio (SNR) losses due to decreased net magnetization per voxel and T₁-relaxation effect, respectively. This could potentially offset the SNR efficiency gains made with increasing temporal resolution. We investigated the effects of varying spatial and temporal resolution on fMRI sensitivity measures and their implications on fMRI-based BCI simulations. We compared temporal signal-to-noise ratio (tSNR), observed percent signal change (%∆S), volumes of significant activation, Z-scores and decoding performance of linear classifiers commonly used in BCIs across a range of spatial and temporal resolution images acquired during an ankle-tapping task. Our results revealed an average increase of 22% in %∆S (p=0.006) and 9% in decoding performance (p=0.015) with temporal resolution only at the highest spatial resolution of 1.5×1.5×1.5mm³, despite a 29% decrease in tSNR (p<0.001) and plateaued Z-scores. Further, the volume of significant activation was indifferent (p>0.05) across spatial resolution specifically at the highest temporal resolution of 500ms. These results demonstrate that the overall BOLD sensitivity can be increased significantly with temporal resolution, granted an adequately high spatial resolution with minimal physiological noise level. This shows the feasibility of diffuse motor-network imaging at high spatial and temporal resolution with robust BOLD sensitivity with 7T-fMRI. Importantly, we show that this sensitivity improvement could be extended to an fMRI application such as BCIs.

Keywords: 7T, fMRI, sensitivity, temporal resolution; BCI; Classification; Physiological noise.

Publication types

Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

Adult
Brain / diagnostic imaging*
Brain Mapping / methods*
Female
Humans
Image Processing, Computer-Assisted / methods*
Magnetic Resonance Imaging / methods*
Male
Nerve Net / diagnostic imaging*
Young Adult