Hai-Ling Cheng

Keywords: Contrast mechanisms: Relaxometry, Contrast mechanisms: Perfusion, Contrast mechanisms: Diffusion

MRI is unique amongst imaging modalities for its rich variety of contrast mechanisms. In this talk, we explore the breadth of MRI contrast available, from the most basic contrast derived from differences in T₁/T₂/T₂* relaxation times to more advanced methods based on water diffusion, chemical shift, and chemical exchange saturation transfer (CEST). We also discuss how these same contrast mechanisms that arise from the molecular and biochemical properties of tissue can be exploited in understanding and measuring tissue physiology and function – as in perfusion imaging, blood oxygenation level-dependent (BOLD) imaging of brain function, and elastography of tissue stiffness.

Xiaojuan Li

Jia Guo

Keywords: Contrast mechanisms: Flow, Contrast mechanisms: Diffusion, Contrast mechanisms: Perfusion

Contrast mechanisms in MRI are versatile, including not only the information from static properties of tissues, but also the information from the spins that are moving. This educational lecture will cover some of the basic principles of the contrast generation mechanisms that are based on the movement of spins, from microscopic (diffusion) to macroscopic (bulk blood flow) levels. Emphasis will be given on understanding the very physics of how the spin displacement information is used for such contrast in MRI, with examples showcasing their applications.

David Thomas

Antonio Chiarelli

Keywords: Contrast mechanisms: fMRI

Functional MRI (fMRI) refers to techniques that detect changes in the resonance signal associated with modulation in brain activity. Blood-oxygen-level-dependent (BOLD) fMRI is the most used and powerful tool to measure brain function non-invasively, but it is a surrogate measure of brain activity reflecting an interplay of local changes in metabolism and hemodynamics. This lecture will primarily discuss metabolic and vascular effects of brain activity and how they are probed by BOLD fMRI. Alternative fMRI techniques to quantify physiological changes in the activated brain are also discussed with an additional introduction on emerging techniques proposed to directly probe neuronal activity.

Meng Yin

Jinyuan Zhou

Keywords: Contrast mechanisms: CEST & MT, Contrast mechanisms: Molecular imaging, Neuro: Brain

Chemical exchange-dependent saturation transfer (CEST) imaging is a molecular MRI technique that can detect exogenous or endogenous chemicals in biological tissue (such as proteins, glutamate, and glucose) indirectly using the water signal. This lecture will review its basic imaging principles, theory, various quantification methods, nomenclatures, key types, and potential applications. As an example, we will explore protein-based amide proton transfer (APT) imaging of glioma and assess its added clinical value in identify active tumor when it is incorporated into a standard MRI protocol. The lecture will conclude with a discussion about CEST technical limitations, controversies, and pitfalls.