MRI

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

14. Gradient Coils

15. MRI Slices of Brain

16. Equipment Console Computer Room Magnet Room

17. Console and Computer Room

18. 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

19. Body Coils…Antennas

23. 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

24. Relaxation Rates:T1 and T2

25. MRA and Flow Phenomena

27. 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

28. 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.

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

30. 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

31. Coronal Thorax

32. Sagittal Thorax

33. 3D Imaging

34. Closed MRI

35. Open MRI

36. Sitting MRI

37. Extremity MRI