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Magnetic Resonance Imaging

Dr Mohamed El Safwany, MD. Magnetic Resonance Imaging. Intended learning outcome. The student should learn at the end of this lecture MRI basics. Oxygen, hydrogen, carbon, nitrogen elements constitute 96 % of human body mass.

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Magnetic Resonance Imaging

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  1. Dr Mohamed El Safwany, MD. Magnetic Resonance Imaging

  2. Intended learning outcome The student should learn at the end of this lecture MRI basics .

  3. Oxygen, hydrogen, carbon, nitrogen elements constitute 96 % of human body mass. • Oxygen is 65 % of body mass; carbon is 18.5 %, hydrogen 9.5 %, nitrogen 3.2 %. • Let us ignore all elements but Hydrogen.

  4. Simplest element with atomic number of 1 and atomic weight of 1 • When in ionic state (H+), it is nothing but a proton. • Proton is not only positively charged, but also has magnetic spin (wobble)! • MRI utilizes this magnetic spin property of protons of hydrogen to elicit images!! • We are magnets!

  5. The protons (i.e. Hydrogen ions) in body are spinning in a hap hazard fashion, and cancel all the magnetism. That is our natural state! • We need to discipline them first

  6. Magnetic field strength: 0.3 – 7 T (2500 times more than earth’s magnetic field). Average field strength – 1.5 T • Open magnet – less field strength, less claustrophobic • Closed magnet – more field strength, claustrophobic

  7. Proton alignment • Compass aligns with the earth • In a similar fashion, • Our body protons (hydrogen) align with this external magnetic field. • Now, we are disciplined (spinning in line with each other!)

  8. Radio frequency pulses in resonance push the aligned protons (H+) to a higher energy level.

  9. Radio Frequency pulse • Same as Radio waves – high wavelength, low energy electromagnetic waves • Radiofrequency coils • Act as transmitter and receiver • Different types of coils

  10. The higher energy gained by the protons is retransmitted (NMR signal)

  11. T1WI T2WI PDWI DWI ADC GE Perfusion images fMRI BOLD images MRA MRV Post-Gd images Volumetric images MR arthrograms FLAIR STIR Etc etc etc Images

  12. T1-weighted contrast

  13. T2-weighted contrast

  14. Tissue Appearance

  15. sequence exercise

  16. Which sequence is it? T2

  17. Which sequence is it? T1

  18. Which sequence is it? FLAIR

  19. Which sequence is it? DWI

  20. Which sequence is it? ADC

  21. Which sequence is it? GE

  22. Which sequence is it? PostGd

  23. Which sequence is it? MRV

  24. Which sequence is it?, 3D MRV

  25. Which sequence is it? MRA

  26. Which sequence is it? T2

  27. Which sequence is it? T1

  28. Which sequence is it? STIR

  29. Which sequence is it? MR arthrogram

  30. Before entering tunnel, there is a checklist! • No mobiles, no credit cards, please! • Known potential safety concerns due to large static magnetic field: • Internal cardiac pacemakers • Steel cerebral aneurysm clips (ferromagnetic) • Small steel slivers embedded in eye • Cochlear implants • Stents anywhere in the body

  31. Clinical Aspects of MRI

  32. Advantages of MRI No ionizing radiation & no short/long-term effects demonstrated Variable thickness, any plane Better contrast resolution & tissue discrimination Various sequences to play with to characterise the abnormal tissue Many details without I.V contrast

  33. Disadvantages of MRI • Time consuming • Not easily available (long waiting list)

  34. MRI has limitations: • Bone • Air • Time consuming

  35. Faster Less expensive Less sensitive to patient movements Easier in claustrophobics Acute haemorrhage Calcification Bone details Foreign body No ionising radiation Greater details, hence more sensitive and more specific Any plane scanning Contrast less allergic No beam hardening artefact MR CT

  36. Anatomy Congenital anomalies Hereditary and metabolic diseases Infections Demyelination Vascular event Tumours Trauma Dementia Hydrocephalus Cranial nerves Arteriograms Venograms Skull base Pituitary gland Indications (almost everything)

  37. Vascular MRI • Peripheral vascular arteriogram with or without I.V contrast • Aortogram • Dissection • Pulmonary arteriogram • When CT is contraindicated

  38. Cardiac MRI • Coming in a big way • Very useful in congenital heart diseases, cardiomyopathies • Evidence is emerging in the evaluation of myocardial infarction

  39. Breast MRI • Problem solving • Breast implants • Recurrence • Multifocal disease

  40. Foetal MRI • Assessment of congenital anomalies • Placental abnormalities • Twin assessment

  41. Text Book David Sutton’s Radiology Clark’s Radiographic positioning and techniques

  42. Assignment Two students will be selected for assignment.

  43. Question Define differences between CT and MRI?

  44. Thank You

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