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What Can MRI Do for You?

What Can MRI Do for You?. Noninvasive imaging cellular /macromolecular contents molecular magnetism transport processes. Yi Wang. Transport processes. This category of MRI contrast mechanisms is useful for assessing live tissue functions: Flow Perfusion, convection, permeability

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What Can MRI Do for You?

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  1. What Can MRI Do for You? • Noninvasive imaging • cellular/macromolecular contents • molecular magnetism • transport processes Yi Wang

  2. Transport processes This category of MRI contrast mechanisms is useful for assessing live tissue functions: • Flow • Perfusion, convection, permeability • Diffusion (tensor)

  3. Diffusion – incoherent motion Diffusion increase in tumor (bright) Isotropic Restricted Diffusion decrease in acute ischemia (dark) Fiber tractography

  4. Perfusion & flow – coherent motion Reduced perfusion (yellow) Coherent Flow (vessel blocked in left) Ischemic stroke

  5. Molecular magnetism This category of MRI contrast mechanisms is useful to assess molecular properties and their changes in metabolism (oxygen metabolism, iron metabolism): • Electron cloud response – chemical shift at molecule nuclei, diamagnetic field outside molecule • Unpaired electrons – strong paramagnetic field outside molecule

  6. Tissue magnetism An external magnetic field puts force/torque on electrons. Protons are too heavy to respond. B M Unpaired e- Spin response (torque): Magnetic moment parallel to B paramagnetic Orbital response (Lorentz force): Magnetic moment opposing B Diamagnetic Chemical shift at nucleus

  7. Chemical shift – NMR spectroscopy

  8. Iron paramagnetism – fMRI, QSM Electronic configuration fMRI Iron metabolism

  9. Relaxation (T1, T2) This category of contrast mechanism is useful to examine macromolecular/cellular contents in water. • T2 is very sensitive to cellular content change, a must in all MRI protocols in clinical practice. • T1 is sensitive to tissue global or “lattice” environment, used with contrast agents.

  10. cellular contents: T2 relaxation Pure water: Zero contents 1/T2 small, T2 long, 2 sec Normal tissue: Lots of contents 1/T2 large, T2 short, 75 msec Edema/lesion: Median amount 1/T2 median, T2 median, 200 msec

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