ISMRM 24th Annual Meeting & Exhibition • 07-13 May 2016 • Singapore

Scientific Session: fMRI Physiology

Wednesday, May 11, 2016
Room 334-336
16:00 - 18:00
Moderators: Nicholas Blockley, Kevin C. Chan

Detection and modeling of 0.75 Hz neural oscillations using rapid fMRI at 7 Tesla
Laura Lewis1,2, Kawin Setsompop2,3, Bruce R Rosen2,3, and Jonathan R Polimeni2,3
1Society of Fellows, Harvard University, Cambridge, MA, United States, 2Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Boston, MA, United States, 3Department of Radiology, Harvard Medical School, Boston, MA, United States
            Recent work has suggested that fMRI can detect neural activity on faster timescales than previously thought. We tested the temporal limits of fMRI using oscillating visual stimuli to generate an oscillatory neural response in human visual cortex. Using rapid (TR=227 ms) fMRI acquisition at 7 Tesla, we were able to detect 0.75 Hz oscillations in visual cortex that were an order of magnitude larger than predicted by canonical linear models. Using the balloon/Windkessel model we show that continuous and rapidly varying neural activity can generate larger fMRI signals than expected. We conclude that fMRI can be used to measure oscillations of up to at least 0.75 Hz, and suggest alterations to hemodynamic response models for experiments studying continuous and rapidly varying neural activity.

Validation and Optimization of Calibrated fMRI from oxygen-sensitive Two-Photon Microscopy of the mouse brain
Louis Gagnon1,2,3, Sava Sakadzic4, Frederic Lesage2, Philippe Pouliot2, Anders M Dale5, Anna Devor5, Richard B Buxton5, and David A Boas3
1Department of Medicine, Laval University, Quebec, QC, Canada, 2Department of Electrical Engineering, Ecole Polytechnique Montreal, Montreal, QC, Canada, 3Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, United States, 4Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Chalestown, MA, United States, 5Department of Radiology and Neuroscience, UCSD, La Jolla, CA, United States
Calibrated fMRI allows to estimate relative changes in the Cerebral Metabolic Rate of Oxygen Consumption (rCMRO2) from combined BOLD and ASL measurements during a functional task. Here, we improved the accuracy of the approach by using Two-Photon microscopic measurements of the cortical microvasculature together with first principle Monte Carlo simulations of proton diffusion across the two-photon volumes. Our method allowed (1) to validate Calibrated fMRI from the microscopic point of view and (2) to optimize the free parameters of the biophysical model assumed, therefore increasing the accuracy of this method to estimate rCMRO2.

Graded hypercapnia-calibrated BOLD: Beyond the iso-metabolic hypercapnia assumption
Ian D Driver1, Richard G Wise1, and Kevin Murphy1
1CUBRIC, School of Psychology, Cardiff University, Cardiff, United Kingdom
We propose a method for correcting for bias introduced by an iso-metabolic assumption in hypercapnia calibrated BOLD studies. A graded hypercapnia design and an assumption of linear CMRO2 dependence on hypercapnia level are used to separate the calibration parameter M from CMRO2 changes during hypercapnia. This method avoids intra-subject and experimental variability introduced by making a prior assumption of iso-metabolism or a CMRO2 decrease with hypercapnia based on literature values. We implement this method using two distinct levels of hypercapnia, measuring lower M values than when making the iso-metabolic assumption, with a significant dose-wise reduction in CMRO2 with hypercapnia level.

The acute effects of caffeine on brain oxygen metabolism: a dual calibrated FMRI study
Alberto Merola1, Michael A Germuska1, Esther AH Warnert1, Sharmila Khot1,2, Daniel Helme2, Lewys Richmond2, Kevin Murphy1, and Richard G Wise1
1CUBRIC, Cardiff University, Cardiff, United Kingdom, 2Department of Anesthesia and Intensive Care Medicine, Cardiff University, Cardiff, United Kingdom
Caffeine acute effects on oxygen metabolism are not well characterized across the brain with MRI. We aim at measuring these in a double-blind, crossover, placebo-controlled study on sixteen healthy, moderate caffeine consumers using a dual calibrated fMRI approach and a novel forward estimation model. Results show spatial variations in OEF0, CBF, CVR, venous CBV and CMRO2 across grey matter at different levels of resolution (grey matter, ROI and voxel), in agreement with most of the literature findings. Therefore we propose this approach as the first viable method to assess the effects of drugs on brain metabolism with a voxel-wise resolution.

Visual cortical responses to auditory stimulation during deep isoflurane anesthesia: an fMRI study - Permission Withheld
Celia M. Dong1,2, Patrick P. Gao1,2, Leon C. Ho1,2, Alex T.L. Leong1,2, Russell W. Chan1,2, Xunda Wang1,2, and Ed X. Wu1,2
1Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Hong Kong, China, People's Republic of, 2Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong, China, People's Republic of
Anesthesia is needed in many neuroscience studies but its effect on brain network response properties has not been fully understood. In particular, how it modulates crossmodal sensory responses remains largely unknown. This study investigated the brain responses to auditory stimulation at different isoflurane levels using large-view BOLD fMRI. Robust responses to multiple pure tone sound stimuli were detected in the bilateral visual cortex at 2.5% isoflurane but not at 1.0% isoflurane level. These results revealed the broad and profound modulation effects of anesthesia on brain crossmodal response properties during external sensory stimulation. 

Resting state and stimulus evoked fMRI in awake, head-posted and habituated rats.
Pei-Ching Chang 1, Daniele Procissi2, Maria Virginia Centeno1, and Vania Apkarian1
1Physiology, Northwestern University, Chicago, IL, United States, 2Radiology, Northwestern University, Chicago, IL, United States
fMRI in rodents is a major tool for basic neuroscience research. It allows investigation of brain networks in different animal models of disease and injury using translational methods with clinical relevance. In many instances it is essential to image animals in an awake condition (i.e. without anesthesia).  While several have shown it is possible to image animals in the awake condition they nearly all require initial anesthesia and forced restraint. In this study we describe a strategy to image rats trained to be "comfortably" restrained and head posted and show how it is possible to enhance the performance of the fMRI experiments. 

Concurrent fMRI and intrinsic optical imaging spectroscopy with high resolution at ultra high field (14.1T)
Matthias F. Valverde Salzmann1, Klaus Scheffler1, and Rolf Pohmann1
1High-field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany
A setup for concurrent functional MRI and intrinsic optical imaging spectroscopy inside a 14.1 T animal scanner was developed, based on a magnetic field proof camera and optics. fMRI and optical imaging were simultaneously performed on rats with electrical forepaw stimulation, resulting in excellent signals for both BOLD and optical reflectance in two wavelengths (red and green). Only minor interactions between both modalities were observed. The combination of these two techniques can be used to investigate the origins of the BOLD effect and to open up novel ways of exploring brain function.

Resting-state BOLD local synchrony as a strong proxy of glucose uptake and as a biomarker of aging using functionally-driven gray matter parcelization
Michaël Bernier1, Étienne Croteau2, Christian-Alexandre Castellano2, Stephen C Cunnane2, and Kevin Whittingstall3
1Nuclear medecine and radiobiology, Université de Sherbrooke, Sherbrooke, QC, Canada, 2Research center of aging, Université de Sherbrooke, Sherbrooke, QC, Canada, 3Diagnostic radiology, Université de Sherbrooke, Sherbrooke, QC, Canada
Currently, PET is the primary imaging modality used to infer energy metabolism in the brain. It is also known to be a reliable biomarker of aging and cognitive diseases.  However, the cost and invasive nature of PET limits its use in basic research.  There is therefore great interest in developing alternative less invasive approaches for estimating brain glucose metabolism.  Using resting state fMRI metrics such as regional local homogeneity (ReHo), amplitude of low-frequencies fluctuations (ALFF) and regional global connectivity (closeness) we found that both regional- and subject-variations in ReHo strongly correlate with brain glucose uptake in healthy young and aging participants.

The association between cerebrovascular reactivity and resting-state fMRI connectivity in healthy adults
Ali Golestani1, Jonathan Kwinta1,2, Stephen Strother1,2, Yasha Khatamian1, and Jean Chen1,2
1Rotman Research Institute at Baycrest, Toronto, ON, Canada, 2Medical Biophysics, University of Toronto, Toronto, ON, Canada
Changes in the cerebrovascular reactivity (CVR) in known to alter the amplitude of the task-based blood oxygenation level dependent (BOLD) fMRI signal. The effect of CVR on resting-state functional connectivity however is still unknown. In this study, we altered within-individual CVR by manipulating the end-tidal CO2 (PETCO2) level, and in each PETCO2 level we calculated CVR and resting-state connectivity in the motor and executive control networks. rs-fMRI connectivity is significantly influenced with CVR, irrespective of neural function. The strength of this association varies between motor and executive control networks. This study stresses the importance of vascular measurements to remove biases in interpreting rs-fMRI connectivity.

Cortical Laminar Resting-State Fluctuations Scale with Hypercapnic Response
Maria Guidi1, Laurentius Huber2, Leonie Lampe1, and Harald E. Möller1
1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, 2NIMH, Bethesda, MD, United States
Cortical layer-dependent fMRI can investigate effective connectivity of the brain. However, in order to obtain layer-dependent activity information, the unspecific fMRI sensitivity to draining veins must be accounted for, e.g., with calibrated BOLD methods.  Regional variations of resting-state fMRI signal fluctuations have been suggested to resemble features of baseline physiology, such as venous blood volume and vascular reactivity. In this study, we investigate the possibility to use resting-state signal fluctuations to normalize/calibrate layer-dependent fMRI task-responses. In calibration studies with induced hypercapnia, we validate the new approach to obtain cortical profiles of vascular reactivity by comparisons with the established M-value.

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