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Séminaire Yi Wang

23 juin 2017

Magnetic resonance imaging (MRI) - basic concepts and applications to transport processes

Séminaire Yi Wang, Cornell University - Professeur invité à l’IMFT

Ce séminaire vise un public intéressé vers les concepts de base et l’application aux phénomènes de transport

Vendredi 30 Juin à 14 h 00

Amphithéâtre Nougaro

This lecture aims to provide an MRI tutorial to the IMFT community with general interests in using MRI to study transport processes. With the assumption that the audience are fluent with Fourier transform and electromagnetism, MRI is described using largely the classical torque equation as proton spin responses to various magnetic fields, which consist of the engineered fields and the intrinsic fields. The engineered fields include 1) the main field that is uniform in space and constant in time ; 2) the programmable gradient field that varies linearly in space ; and 3) the programmable radiofrequency (RF) field. The intrinsic fields include dipole fields from neighboring protons under thermal fluctuation that cause relaxations, and fields from molecular electron clouds that cause susceptibility/chemical shift. Protons do the signal-generating spin procession under the main field, which is really needed to bring a small spin order over thermal fluctuation. The RF field is used to pump energy against relaxation-caused signal decay. The invention of MRI is the gradient field, which is used to provide spatial encoding for image formation, and to provide motion encoding for studying flow and diffusion. Currently, MRI of flow in large vessel (magnetic resonance angiography, MRA) and MRI of diffusion (diffusion weighted imaging (DWI), diffusion tensor imaging (TDI)) have been commonly used in clinical practice. MRI of flow in arterioles, capillaries and venioles (MR perfusion imaging) has also been used largely as a perfusion weighted imaging (PWI), but accurate perfusion quantification remains a challenge for critical medical problems such as ischemic stroke and heart attack.