sLecture

↳ Topic 3: Magnetic Resonance Imaging

Excerpt from Prof. Bouman's Lecture

Accompanying Lecture Notes

Magnetic Resonance Imaging (MRI)

Definition

• Can be very high resolution
• No exposure to ionizing radiation
• Very flexible and programmable
• Tends to be expensive, noisy, and slow

Fig 1: The exterior of an MRI scanner

Fig 2: MRI scan of a patient

MRI Attributes

• Based on magnetic resonance effect in atomic species
• Does not requires any ionizing radiation
• Numerous modalitites
  • Conventional anatomical scans
  • Functional MRI(fMRI)
  • MRI Tagging
• Image formation
  • RF excitation of magnetic resonance modes
  • Magnetic field gradients modulate resonance frequency
  • Reconstruction computed with inverse Fourier transform
  • Fully programmable
  • Requires an enormous (and very expensive) superconducting magnet

Magnetic Resonance

Fig 3: Precession of atom in the presence of a magnetic field

• Atom will precess at the Lamor frequency
  

$ \omega_0 = LM \ $
where
$ M $ is the magnitude of the ambient magnetic field
$ \omega_0 $ is the frequency of precession in radians per second
$ L $ is the Lamor constant and its value depends on the choice of atom

The MRI Magnet

Fig 4: The MRI magnet

• Large superconducting magnet
  • Uniform field within bore
  • Very large static magnetic field

References

• C. A. Bouman. ECE 637. Class Lecture. Digital Image Processing I. Faculty of Electrical Engineering, Purdue University. Spring 2013.

• G. Francis. Psy 200. "Introduction to Cognitive Psychology". Class Lecture Notes. Faculty of Psychological Sciences, Purdue University. Spring 2013.

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