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MRI, LOCALISATION OF THE SIGNAL - Coggle Diagram

- - - - Complex malformations
      - Cardiac function
      - Myocardial viability
      - Valvular disease
      - Congenital heart disease
  - - - Visualise the bilary and pancreatic ducts
        
        Non contrast technique
        
        Relies on relatively stationary nature of bile (compared to blood)
        
        Allows us to depict fluid-filled pancreatic ducts and biliary tree
        
        Heavily T2 weighted pulse sequence
        
        Ideal for static or slow moving fluid
        
        Shows high signal!
        
        With low signal of surrounding tissue
        
        WITH BREATH HOLD
      - Mostly for postoperative patients and biliary abnormality patients
    - - ERCP
        Endoscopic retrograde cholagniopancreatography
        
        Combines Endoscopy and Fluoroscopy
        
        To diagnose and treat biliary tree and pancreatic problems
        
        Mostly for therapeutic purposes
        
        Stent placement, stone extraction, stricture dilatation
  - - - Nephrogenic systemic fibrosis
        
        Rare fibrotic disorder that affects the skin, joints and other organs
      - Gadolinium contraindication: GFR <30
        
        Chronic severe kidney disease is also a contraindication
  - - - In brain
        
        Brains tumours, Alzheimers disease, strokes, seizures, depression
      - Muscles
        
        Normal MRI (NMR) is used to measure intramyocellular lipids
- - - - Million of protons in the body have an inherent spin, with a vector pointing along the axis of spin. These vectors point in random directions
        
        The MRI machine uses a strong magnetic field
        
        The magnet causes proton vectors to align and precess (along the direction of the magnet). Either parallel or antiparallel
        
        Vector does not align perfectly with the applied magnetic field, it rotates around the magnetic field vector = PRECESSION
        
        Frequency of precession = Larmour frequency
        
        Parallel = low energy state, more stable
        
        Antiparallel = high energy state, less stable
        
        Short Radio-wave frequency pulse (EM radiation) is sent
        
        This pulse matches the Larmour frequency of precession of the protons
        
        The protons absorb the energy and resonate
        
        Now all protons:
        
        are in the high energy state
        
        they precess
        
        they precess IN PHASE
        
        3 more items...
        
        Protons in the lower energy state (parallel) will flip to high energy state
        
        1.5 - 3 Tesla: Common magnetic field strength
    - - Giving protons angular momentum and thus creating a magnetic field around it.
        
        The spin is actually a vector - where the direction of the vector point along the axis of the spin
- - - - Brightens structures on T1 images
        
        Due to the interaction between tissue hydrogen protons and the unpaired electron of gadolinium
- - - - Different tissues relax at different rates
        
        Watery tissue: long relaxation time
        Tumours: Intermediate
        Fatty tissue: Short relaxation time
      - TYPES
        
        T1
        
        Relaxation time it takes for protons to align parallel to the magnetic field (in lower energy state)
        
        i.e the protons reorient themselves -> leads to recovery of longitudinal magnetisation ("recovery of longitudinal orientation")
        
        Fat = light
        CSF = dark
        
        Only proteinaceous fluid is bright.
        Some aged hemorrhages
        
        Shorter T1 = brighter T1WMRI image
        
        = spin-latice and longitudinal relaxation time
        
        T2
        
        Relaxation time it takes for the protons to align perpendicular to the magnetic field
        
        Protons dephase and lose transverse magnetisation ("recovery from transverse magnetisation")
        
        Fat = light
        CSF and all fluid = light
        
        Shorter T2 = darker T2WMRI
        
        Spin-spin and transverse relaxation time
        
        FLAIR
        
        Fluid attenuation inversion recovery
        
        A T2 weighted image
        
        BUT: CSF fluid is SUPPRESSED
        
        CSF = dark
        
        1 more item...
- - - - Applying a pulse equal to the larmour frequency of the feet will cause only these protons to precess in phase. Only this part of the body will produce a signal
      - This is why MRI takes so long. The RF pulse must be changed according to each slice along the gradient magnet