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Basics of MRI

Basics of MRI. 42-431: Introduction to Biomedical Imaging and Image Analysis. Gustavo K. Rohde. References. Joseph P. Hornak, The Basics of MRI http://www.cis.rit.edu/htbooks/mri/ Online MRI simulator (brainweb) http://www.bic.mni.mcgill.ca/brainweb/

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Basics of MRI

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  1. Basics of MRI 42-431: Introduction to Biomedical Imaging and Image Analysis Gustavo K. Rohde

  2. References • Joseph P. Hornak, The Basics of MRI • http://www.cis.rit.edu/htbooks/mri/ • Online MRI simulator (brainweb) • http://www.bic.mni.mcgill.ca/brainweb/ • Hobbie, Roth, Intermediate physics for medicine and biology.

  3. History • Block, Purcell (Nobel prize winners 1952) credited with discovering nuclear magnetic resonance (NMR) phenomenon in 1946. • Between 1950~1970, NMR was used mostly in chemical and molecular analysis. • In 1973 P. Lauterbur (Nobel prize 2003) demonstrated MRI on test tube samples.

  4. MRI machine

  5. Magnetic Resonance Imaging Sequence of 2D slices 3D rendering

  6. MRI signal • Protons (mostly in hydrogen atoms in H2O) have spin which can be though of as a small magnetic field • MRI aims to reconstruct the magnetization (mean magnetic moment of nuclear spin per unit volume) function of each spatial coordinate. dipole Strength of dipole: A m2

  7. MR signal B Time-domain signal Frequency spectrum

  8. frequency encoding Precession in spatially constant field Precession in spatially varying field

  9. phase encoding Precession in spatially varying field Turn field off

  10. In 2D

  11. In 2D After phase encoding gradient

  12. In 2D With frequency encoding gradient

  13. Example 1 Original image Raw data FT in freq. direction FT in phase direction to get an image

  14. Example 2 Original image Raw data FT in freq. direction FT in phase direction to get an image

  15. Example 3 Original image Raw data FT in freq. direction FT in phase direction to get an image

  16. Final Image Usually the absolute value of the DFT of the raw data is taken as the pixel intensity value.

  17. Imaging a “slice”

  18. RF excitation

  19. A “Pulse” sequence

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