MRI

• Source in MRI:

  • high-intensity magnetic field
  • helium-cooled superconducting magnets are used today
  • Non-ionizing
  • gradient coils turn radiofrequency pulses on/off.
• 2 sources inside the gantry: natural magnet and superconducting magnets
• natural magnet: let machine align with magnetic field of the earth
• superconducting magnets:

  • image-forming magnet
  • produce 3D images in MRI
  • we can turn on and off
• detector in MRI: phased array receiver coils (RF coil) capable of acquiring multiple channels of data in parallel
• The gantry of an MRI machine contains 3 different materials: natural magnet, gradient coils, radiofrequency coil/receiver coil
• Gradient coils: will define the intensity of the magnet that will be received by the patient (gives dose)
• RF coils/receiver coils: acts as transceiver wherein the magnet produced from the machine will pass through RF coils, and also receives the bounced back magnet from the patient
• MRI produces images of the body by utilizing the magnetic properties of certain nuclei, predominately hydrogen (H+) in water and fat molecules
• The response of magnetized tissue when perturbed by an RF pulse varies between tissues and is different for pathological tissue as compared to normal.
• MRI was originally called nuclear magnetic resonance (NMR) but because the word ‘‘nuclear’’ was associated with ionizing radiation, the name was changed to emphasize the modality’s safety
• MRI can image in any plane
• MRI has excellent soft tissue contrast detail
• MRI visualizes blood vessels without contrast; no bony artifact since no signal from bone
• MRI is particularly useful in neurological, cardiovascular, musculoskeletal, and oncological imaging.
• MRI has high purchase and operating costs
• MRI has a lengthy scan time
• MRI is more difficult for some patients to tolerate because it is lengthy, loud, instances of claustrophobic patient
• MRI has poor images of lung fields
• MRI is unable to show calcification
• MRI is contraindicated in patients with pacemakers or metallic foreign bodies
• CT scan

  • uses CT scan for scanning of bone
  • diagnosing chest and lung problems
  • widely used because scanning time is less than 5 minutes
• MRI

  • uses MRI machine to visualize soft tissue in ligaments, tendon injuries, spinal cord injuries, brain tumor
  • scanning takes more than 30 minutes and it is very costly
  • safer compared to CT scan