ISMRM23 - Demystifying the fMRI Signal & Its Biophysical Origins I: fMRI Biophysical Signal Origin & Modeling

ISMRM & ISMRT Annual Meeting & Exhibition • 03-08 June 2023 • Toronto, ON, Canada

Demystifying the fMRI Signal & Its Biophysical Origins I: fMRI Biophysical Signal Origin & Modeling

Sunrise Course

ORGANIZERS: Natalia Petridou, Rita Schmidt

Monday, 05 June 2023

716A/B

07:00 - 08:00

Moderators: Nikos Priovoulos & Noam Shemesh

Skill Level: Basic to Intermediate

Session Number: S-M-08

CME Credit

Session Number: S-M-08

Overview
This is a sunrise educational course on the fMRI signal and its biophysical origins. The course will describe the fMRI biophysical signal origin and modeling, followed by analysis of the systematic and physiological components of the fMRI signal. In addition, the course will connect the fMRI signal to other modalities, including intra-cranial measurements and spectroscopy.

Target Audience
Scientists and clinicians interested in learning/refreshing their knowledge of the biophysical origins of the fMRI signal.

Educational Objectives
As a result of attending this course, participants should be able to:
- Describe the biophysical origins and biophysical models of the fMRI signal;
- Recognize the systematic and physiological noise contributions to the fMRI signal and review data acquisition methods to characterize the noise;
- Describe how the fMRI signal relates to intra-cranial measurements in animals and electrophysiological measurements in humans; and
- Explain relationships between the fMRI signal and underlying metabolic process, and review combined fMRI and spectroscopy data acquisition approaches.

07:00		Biophysical Origins of the fMRI Signal View Presentation Video Kamil Uludag Keywords: Neuro: Brain function, Neuro: Brain connectivity, Contrast mechanisms: fMRI I will describe the physiological processes underlying BOLD signal and discuss the generative biophysical model and its time course properties: It primarily results from changes in oxygen metabolism, cerebral blood flow, and volume, which affect paramagnetic deoxygenated hemoglobin. The physiological origin of BOLD signal transients, such as the initial overshoot, steady-state activation, and post-stimulus undershoot, will be explored. Incorrect physiological assumptions in the generative model of the BOLD signal can lead to incorrect inferences about local neuronal activity and effective connectivity between brain regions. The author also introduces the recent laminar BOLD signal model.
07:30		Biophysical Modeling of the fMRI signals View Presentation Video Jonathan Polimeni Keywords: Contrast mechanisms: fMRI, Neuro: Brain function This educational lecture will review classic and modern biophysical models of the fMRI signals, with a focus on models of the BOLD response. We will consider the “balloon” model framework, which seeks to model the BOLD response within a single voxel and its nonlinearities, as well as extensions such as hierarchical models based on mass balance inspired by newly-available high-resolution fMRI that account for the coupling of hemodynamics between adjacent voxels sampling across cortical depths. We will conclude with newer approaches based on realistic Vascular Anatomical Network or VAN models informed by optical imaging measurements of microvascular anatomy and dynamics.