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MRI

MRI. DRAFT 5-12-09. Principles of MRI . Sectional Anatomy Provides anatomic and physiologic info Non- invasive No radiation Magnetic fields and Radio waves. Sectional No superimposition Can resolve small contrast differences Uses magnets instead of x-rays. Flat image

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MRI

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  1. MRI DRAFT 5-12-09

  2. Principles of MRI • Sectional Anatomy • Provides anatomic and physiologic info • Non- invasive • No radiation • Magnetic fields and Radio waves

  3. Sectional No superimposition Can resolve small contrast differences Uses magnets instead of x-rays Flat image Superimposed structures Can only distinguish air, at, soft tissue, bone and metal Most organs can only be seen with contrast Uses radiation MRI vs. Conventional Radiography

  4. Xray vs. MRI

  5. Signal Production • MRI depends on nucleus • Hydrogen • Most commonly used • Most common element in body • Creates a strong signal • Nucleus is a single proton

  6. Hydrogen • Contains • 1 proton • 1 orbiting electron

  7. Precession • Protons in random directions • With magnet attempt to line up • Do not line up precisely • They rotate about the direction of the magnetic field • Protons • Absorb energy when RF is applied • Absorption is called resonance • Radiowaves and nuclear precession are at the same frequency

  8. 1.5 tesla 1 telsa 0.5 telsa 0.2 telsa 63MHz 42 MHz 21 MHz 8 MHz Field Strength and Frequency

  9. Precession • http://mrsrl.stanford.edu/~brian/mri-movies/resonance.mpg

  10. Spin Control • http://images.google.com/imgres?imgurl=http://www.magnet.fsu.edu/education/tutorials/magnetacademy/mri/images/mri-scanner.jpg&imgrefurl=http://www.magnet.fsu.edu/education/tutorials/magnetacademy/mri/&usg=__7QaxmAuglPxgvYqzlBDl4yatfQc=&h=300&w=390&sz=33&hl=en&start=1&tbnid=iCrVIzxgDH1sFM:&tbnh=95&tbnw=123&prev=/images%3Fq%3Dresonance%2B%252B%2BMRI%26gbv%3D2%26hl%3Den

  11. The Wonder of Waves • http://images.google.com/imgres?imgurl=http://www.magnet.fsu.edu/education/tutorials/magnetacademy/mri/images/mri-scanner.jpg&imgrefurl=http://www.magnet.fsu.edu/education/tutorials/magnetacademy/mri/&usg=__7QaxmAuglPxgvYqzlBDl4yatfQc=&h=300&w=390&sz=33&hl=en&start=1&tbnid=iCrVIzxgDH1sFM:&tbnh=95&tbnw=123&prev=/images%3Fq%3Dresonance%2B%252B%2BMRI%26gbv%3D2%26hl%3Den

  12. Gradient Coils

  13. MRI Slices of Brain

  14. Equipment Console Computer Room Magnet Room

  15. Console and Computer Room

  16. Magnet Room • Must be LG enough for magnets and antennas • Coils are antennas wound up in shape of body part • 3 types of magnets (strength measured in Gauss or Tesla) • RESISTIVE • Not to exceed 0.15 telsa • 10 tons • LG amount of current through coils • Fringe field in all directions • SUPERCONDUCTIVE or Cryogenic • High field strengths • 10 tons • Cooled with liquid helium • Fringe field in all directions • PERMANENT • Not to exceed 0.3 telsa • 100 tons • Smaller fringe field

  17. Body Coils…Antennas

  18. Significance of Signal • Signal strength is converted to different shades of gray • White is strong signals • Black is weak signals • Three properties affect signal strength • Nuclear Density • Relaxation rates • Flow phenomena

  19. Relaxation Rates:T1 and T2

  20. MRA and Flow Phenomena

  21. Contrast Media • No Oral Contrast • Gadolinium • IV injected • Lower toxicity • Low side effects • Less than IV in CT and conventional radiography • Many new contrasts being developed but none approved for clinical use yet

  22. Lawsuits and Gadolinium • In May 2007 FDA issued a public warning about Gadolinium increasing the incidence of Nephrogenic Systemic Fibrosis • For those with impaired kidney function • Development of excessive scar tissue and thick, hardened and tight areas of skin which often cover the joints, resulting in severe limitations on movement. • Can lead to confinement to a wheelchair, bed or death.

  23. Contraindications • Objects containing metal • Scissors, O2 tanks, and gurneys • Metallic prosthesis • Aneurysm clips • Hearing aids • Slivers of metal in eyes • Electronic equipment • Claustrophobia

  24. Imaging Planes • Images can be obtained in many planes • Coronal • Transverse • Oblique • Equal resolution for any plane • Loss of detail if reconstructed • 3D block of tissue can be obtained instead of slices

  25. Coronal Thorax

  26. Sagittal Thorax

  27. 3D Imaging

  28. Closed MRI

  29. Open MRI

  30. Sitting MRI

  31. Extremity MRI

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