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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

What Can MRI Do for You?

  • Noninvasive imaging
  • cellular/macromolecular contents
  • molecular magnetism
  • transport processes

Yi Wang

transport processes
Transport processes

This category of MRI contrast mechanisms is useful for assessing live tissue functions:

  • Flow
  • Perfusion, convection, permeability
  • Diffusion (tensor)
diffusion incoherent motion
Diffusion – incoherent motion

Diffusion increase in tumor (bright)

Isotropic

Restricted

Diffusion decrease in acute ischemia (dark)

Fiber tractography

perfusion flow coherent motion
Perfusion & flow – coherent motion

Reduced perfusion (yellow)

Coherent

Flow (vessel blocked in left)

Ischemic stroke

molecular magnetism
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
tissue magnetism
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

iron paramagnetism fmri qsm
Iron paramagnetism – fMRI, QSM

Electronic configuration

fMRI

Iron metabolism

relaxation t1 t2
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.
cellular contents t2 relaxation
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