Contrast Mechanism: Modelling from the Ground Up
Weekend Course
ORGANIZERS: Weitian Chen, Flavio Dell'Acqua, Shaihan Malik, Marco Palombo, Cristian Tejos
Saturday, 10 May 2025
316C
13:00 -
17:00
Moderators:
All Sections: Elizabeth Powell & Dan Wu
Skill Level: Intermediate to Advanced
Session Number: WE-12
No CME/CE Credit
Session Number: WE-12
Overview
How do you model? Molecular dynamics and microstructure: connections between relaxation, diffusion, MT. Underlying physics and biology.
Target Audience
Intermediate or advanced researchers or clinicians, including trainees (students and fellows) who wish to learn about the physical models behind MRI contrast mechanisms.
Educational Objectives
As a result of attending this course, participants should be able to:
• Describe physical origins of relaxation, diffusion, exchange and susceptibility contrasts;
• Construct analytic and numerical models for these contrasts; and
• Discuss fundamental connections between these contrasts and how to create unified models.
| | Part I |
| 13:00 | | Physics of Relaxation Dmitriy Yablonskiy |
| 13:25 | | Physics of Diffusion Rafael Henriques Keywords: Contrast mechanisms: Diffusion, Physics & Engineering: Physics, Image acquisition: Reconstruction This talk introduces the fundamental physics of diffusion. Key concepts such as random walks, the diffusion averaged propagator, Gaussian vs non-Gaussian diffusion, and time-dependent effects will be explored. The presentation will also highlight how structural disorder and exchange influence diffusion. Understanding these concepts will provide essential background for building biophysical models in diffusion MRI and prepare participants for the subsequent lectures in the educational session “Contrast Mechanism: Modelling from the Ground Up”. |
| 13:50 | | Physics of MT/Exchange Andreea Hertanu Keywords: Contrast mechanisms: CEST & MT, Contrast mechanisms: Microstructure This lecture covers the fundamental principles of magnetization transfer (MT)-based techniques, starting with the binary spin-bath model and its associated Bloch-McConnell mathematical framework. We will delve into the key factors influencing MT, including the lineshape of free and bound protons, as well as on-resonance and dipolar order effects. Building on this foundation, we will explore advanced strategies for modeling the MT signal, addressing proton compartmentalization and strategies to enhance specificity in the context of myelin imaging. |
| 14:15 |  | Physics of Susceptibility Emma Biondetti Keywords: Contrast mechanisms: Susceptibility, Neuro: Brain, Neuro: Cerebrovascular This talk will introduce the physics of magnetic susceptibility. It will also describe three important sources of magnetic susceptibility in the brain: (1) non-haem iron in the form of ferritin, (2) myelin, and (3) haem-iron found in haemoglobin. It will then describe the magnetic field perturbation generated by a bulk magnetic susceptibility distribution, which is essential to understand processing methods such as $$$B_0$$$ field mapping, susceptibility-weighted imaging (SWI) or quantitative susceptibility mapping (QSM). |
| 14:40 | | Break & Meet the Teachers |
| 15:10 | | Biophysical Models & Analysis of Relaxation & Susceptibility TBD |
| | Part II |
| 15:35 | | Microstructural Models & Analysis of Diffusion Marco Pizzolato Keywords: Contrast mechanisms: Diffusion, Contrast mechanisms: Microstructure The diffusion MRI signal can be modeled in various ways, but each involves different assumptions and various degrees of approximation. Nevertheless, modeling has provided valuable insights into tissue properties. While all models aim to characterize the diffusion process, some go further by inferring specific geometrical features of tissue microstructure, while others are tailored to particular tissue types or data acquisition designs. This talk explores increasing levels of complexity in microstructure modeling, offering a comprehensive and up-to-date overview. Organized around key advancements in modeling, it integrates theoretical insights and highlights current challenges and future possibilities. |
| 16:00 | | Biophysical models of relaxation and susceptibility Anders Sandgaard Keywords: Contrast mechanisms: Susceptibility, Contrast mechanisms: Microstructure, Contrast mechanisms: Relaxometry In this lecture, we introduce biophysical models for estimating magnetic susceptibility from MRI signal phase and transverse relaxation. Magnetic susceptibility is an intriguing contrast mechanism as it offers potential insights into the chemical composition and microstructural organization of tissue, which may be crucial for studying neurodegenerative diseases. However, estimation requires explicit modeling of both tissue microstructure and magnetic properties to faithfully recover susceptibility from the MRI signal. Here we present recent models and discuss the opportunities and open challenges in susceptibility MRI. |
| 16:25 | | From the Top Down: Inferring Parameters from Complex Models Eleftherios Garyfallidis |