Mario G. Báez-Yáñez¹, Jeroen Siero^1,2, and Natalia Petridou^1
1Department of Radiology, Center for Image Sciences, UMC Utrecht, Utrecht, Netherlands, ²Spinoza Centre for Neuroimaging Amsterdam, Royal Netherlands Academy of Arts and Sciences, Amsterdam, Netherlands

In order to quantify the hemodynamic contributions to the BOLD fMRI signal in humans, it is necessary to adopt a computational model that resembles the cortical vasculature and mimics hemodynamic changes triggered by neurovascular coupling. Moreover, simulation of the local magnetic disturbance induced by the geometry, hemodynamic changes, and the biophysical properties of the tissues can provide accurate insights on the physiological fingerprint of the BOLD fMRI signal. In this work, based on a realistic 3D computational approach of the human cortical vasculature, we simulate the biophysical effects produced by hemodynamic changes to compute a dynamic BOLD fMRI signal response.

Klaus Scheffler

James Mester, Paolo Bazzigaluppi, Matthew Rozak, Bojana Stefanovic

This lecture will review recent work characterizing neurovascular coupling on the microscopic level and underscore the significance of studying network-level behaviour.

Joerg Peter Pfannmoeller¹, Louis Gagnon², Avery Berman¹, and Jonathan Polimeni^1
1Imaging, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Boston, MA, United States, ²Physics, Engineering Physics and Optics, Laval University, Quebec, QC, Canada

The brain’s physiology may fundamentally limit the achievable spatial and temporal specificity of gradient-echo fMRI. Even if the physiology does not pose such a limitation a better understanding would allow for data analysis techniques that improve the spatial specificity. Microscopy allows for highly detailed investigations of local physiological mechanism and provides a growing knowledge from which fMRI may benefit profoundly. A current challenge is the transition from focal mechanisms to their consequence on the mesoscopic scale of BOLD examinations. In this abstract we present our recent work on this transition using simulations of the BOLD effect.

 

Ratnamanjuri Devi¹, Toralf Mildner¹, Torsten Schlumm¹, Jöran Lepsien ¹, and Harald E. Möller ^1
1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany

Measurement of functional CBF is challenging due to inherently low SNR and signal amplitudes, especially in regions of negative BOLD response. Here, multi-echo center-out EPI is introduced which allows for simultaneous measurement of functional changes in CBF and T2* with improved sensitivity. Using a visual stimulus inducing positive and negative BOLD responses, a linear relationship between absolute changes in CBF and T2* along both positive and negative directions was found with similar coupling ratios. Negative absolute functional CBF changes were found to be almost independent of the baseline CBF, in agreement with previous work on the positive BOLD response.

Aneurin J Kennerley¹, Benedikt A Poser², Frida H Torkelsen¹, Rainer Goebel², Amanda Kaas², and Laurentius Huber^2
1Chemistry, University of York, York, United Kingdom, ²Maastricht Brain Imaging Centre, Maastricht University, Maastricht, Netherlands

With recent advances in ultra-high-field MRI hardware and sequence mechanisms, it has become possible to capture CBV-weighted fMRI signal across cortical layers. However, the exact contrast mechanisms of layer-dependent VASO has not been fully validated with gold-standard pre-clinical methods. 

Phillip G D Ward^1,2,3, Edwina R Orchard^1,2,3, Stuart Oldham³, Aurina Arnatkevičiūtė³, Francesco Sforazzini¹, Alex Fornito³, Gary F Egan^1,2,3, and Sharna D Jamadar^1,2,3
1Monash Biomedical Imaging, Monash University, Melbourne, Australia, ²Australian Research Council Centre of Excellence for Integrative Brain Function, Melbourne, Australia, ³Turner Institute for Brain and Mental Health, Monash University, Melbourne, Australia

The BOLD signal detects changes in relative concentrations of oxy/deoxy-haemoglobin. Thus, individual blood haemoglobin levels may influence the BOLD signal-to-noise ratio in a manner independent of neural activity. In this study, we emulate group-differences in haemoglobin by performing a median split on 524 healthy elderly individuals based on individual measurements of haemoglobin. When compared, the two haemoglobin subgroups showed no differences in cognitive measures, however, significant differences in linear relationships between cognitive performance and functional connectivity were observed in four cognitive tests. Our findings confirm that haemoglobin levels are an important confounding variable in BOLD-fMRI-based studies in the elderly.