Advanced Physics and Analysis: MR Relaxation: From Molecular Dynamics To Quantitative Imaging Biomarkers

Magnetic resonance relaxation encodes rich information about tissue microstructure, molecular dynamics, and biochemical environment, making it a powerful source of contrast for quantitative imaging. This lecture will provide a conceptual and practical overview of MR relaxation. We will begin with the physical mechanisms that drive relaxation and its theoretical description, shifting from a classical to a quantum mechanical description of relaxation (from Bloch to Redfield theory). We will then discuss why relaxation parameters such as T1 and T2, are highly sensitive to tissue composition and pathology, highlighting their clinical relevance. The second part of the lecture will focus on how relaxation is measured in practice, covering conventional and accelerated relaxation mapping sequences, followed by a quick introduction to advanced approaches such as MR fingerprinting and nonconventional contrast mechanisms. Together, these topics will illustrate how relaxation-based MRI bridges fundamental spin physics and modern quantitative imaging applications.