imagine the nervous system 2

• CT or Computerised Axial Tomography (CAT)


  uses x rays

  • x ray rotates 360 degrees around patient
  • x ray detector rotates in opposite direction

  x rays absorbed in different amounts in different tissue

  • Higher density tissue create a whiter image
  • Good for bones, haemorrhages and blood vessels

  
• tomography

  takes a series of 2D images through body

  • 2D images can be reconstructed into a 3D image
• contrast CT

  used contrast agents which are iodine rich

  good for blood vessels

  • Computerised tomography angiography (CTA)
  • Morphology
  • Perfusion (blood flow and blood volume)

  
• Magnetic Resonance Imagining (MRI)


  uses magnetic field and radio frequency waves

  mag. field generated by very strong magnets

  • some atoms have magnetic properties called nuclear spin
  • body made up of 60% water
  • MRI primarily measuring water
• MRI - how image is generated

  magnetic field aligns protons (H) in water molecules

  PROTONS IN 2 SPIN STATES:

  • spin up = aligned parallel to magnetic field
  • spin down = aligned anti- parallel

  
• MRI - how image is generated 2

  radio frequency pulse applied

  • frequency depends on strength of magnet = RESONANCE
  • protons absorb this energy = shifts nuclear spin to different position
  • radiofrequency pulse then turned off and protons release this energy and relax into original positions
  • Different protons are affected differently depending on the tissue they are found in
  • Energy released is detected by the imaging system
• types of images

  T1 weighted

  • H20 appears black
  • high fat content appears white
  • ventricles black

  T2 weighted

  • H2O appears white
  • high fat black
  • ventricles white

  
• MRI imaging

  Good for bones and soft tissue

  Can take a series of images
• contrast enhanced MRI

  for blood vessels = angiography

  • morphology
  • perfusion(blood flow and blood volume)

  uses Gadolinium as contrast agent

  • strong magnetic properties = strong MRI signal
• Diffusion weighted MRI

  measures water mobility within tissue

  Aids in the determination of acute ischemic stroke

  • Water would be less likely to diffuse across regions that have sustained ischemic damage due to cytotoxic oedema (swelling)
  • This generates a hyperintense signal relative to surrounding tissue
• Diffusion tensor imaging (DTI)

  measures water molecules that can only diffuse in one direction

  • good to detect white matter in brain

  RED - GREEN - BLUE CODE

  • red = right to left
  • green = anterior to posterior
  • blue = dorsal to ventral

  Colour intensity = magnitude of diffusion

  
• Functional MRI (fMRI)

  BOLD imaging = blood oxygenation level dependent

  Oxyhaemoglobin and deoxyhaemoglobin have different magnetic properties

  BOLD measures changes in the levels of these forms of hemoglobulin

  Areas of increased activity = increased blood flow, in particular increased oxyhaemoglobin

  Low resolution BOLD image combined with high resolution MRI image
• Positron Emission Tomography (PET)

  uses short lived radioactive isotopes injected into the blood stream

  • show up in areas where cells are more active
  • as the isotopes decay they emit positrons (positive electrons)
  • Positrons collide with electrons in the tissue forming photons
  • Scintillation crystals in the scanner cameras around the patient detect the photons
  • 3D image of radioactivity constructed
• Fluorodeoxyglucose (FDG)

  Areas of increased activity = increased glucose metabolism

  FDG = glucose tagged with radioactive fluorine atom

  Taken up by cells but not metabolised

  Accumulates in areas of increased activity