9/6 Neuroimaging - Basak Flashcards Preview

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basic principle

helical CT

computed tomography

  • highly collimated xray beam that rotates around patient
  • shows differential rate of absorption depending on substance passed through → density values for every point 


helical CT combines continuous rotating xray with table movement


air < fat < water < csf < white / gray matter < blood (60-100) < bone


most effective uses of CT

  • intracranial hemorrhage
  • acute trauma
  • stroke imaging
  • fractures
  • sinusitis
  • bone lesions
  • dental imaging
  • myelography
  • CT angiography
  • CT perfusion
  • temporal bone


contrast vs noncontrast CT


when would you give contrast

when would you NOT

don't want to give contrast if you're looking for blood

  • CONTRAINDICATED when intracranial hemorrhage is the concern (esp subarachnoid)
  • hard to tell the diff between contrast in a blood vessel and a hemorrhage


why give contrast?

  • tumor, infection/abscess, CTA/CTV to look at arteries/veins



why is infarction dark?

infarct = edema = fluid = hypodense = dark


properties of protons relevant to MRI

1. spin

  • proton spinning around axis induces magnetic field (mag moment)
  • in presence of strong mag field, these magnetic moments align

2. precession

  • proton in external magnetic field develops secondary spin/"wobble" aka precession
  • frequency of precession is directly related to strength of main mag field




how it works

intensity: determinants

magnetic resonance imaging

use magnets and radiofreq waves → measure H nuclei

  • use magnetic field to align nuclei, then use radio pulse from an electric coil to disturb equilibrium → pushes protons into higher energy state
  • when the pulse stops, protons realign and give off energy, which is measured

key terms: hypointensity, hyperintensity → intensity determined by water (hypo) and fat (hyper)


T1W images vs T2W images vs FLAIR images vs DWI



why do each?

T1W good for anatomy

  • water/csf, edema: hypo
  • white matter (fat): hyper
  • gray matter: iso

T2W good for pathology

  • water/csf, edema: hyper
  • white matter (fat/myelin) = hypo
  • gray matter: iso

FLAIR: fluid attenuation inversion recovery : good for pathology

  • similar to T2W images except csf is hypointense
    • allows for eval of white matter adj to ventricles (i.e. multiple sclerosis → white matter tracts around ventricles)

DWI: diffusion weighted image

  • primary seq for detection of acute/subacute infarct (up to 14d old)
  • hyper signal is ABNORMAL


MRI contrast

gadolinium-based agents → produce hyperintensity in vessels and areas of bbb breakdown




adv vs disadv

  • exquisite delineation of anatomy
  • sensitive to pathology
  • posterior fossa: much clearer than in CT
  • in utero imaging


  • long exam
  • issues: claustrophobia, pacemaker/metallic foreign bodies, expensive


most effective uses of MRI

  • intracranial tumor, tia/stroke, infection, demyelination
  • seizure/epilepsy
  • dementia
  • pituitary
  • hearing
  • CN abnormalities


MR angiography

aims to create intensity diffs between flowing blood in vessels and stationary tissues

  • signals depend on velocity and imaging parameters
  • used to image intracranial vessels, carotic vasculature, vertebral arteries, venous anatomy of neck


MRI adv techniques

1. magnetic resonance spectroscopy

  • measures brain nt and biochemicals via noninvasive survey of chemical environment (a.a.s, lipid, lactate, NAA, choline, creatine, myoinositol)
  • aids in eval of brain tumors, radiation necrosis, inf, metab disease

2. diffusion tensor imaging

  • assessment of white matter tracts based on water diffusion chars along tracts of axons
  • eval of neurodegen disease, epilepsy, traumatic brain injury, MS
  • role in preop eval of brain tumors

3. functional MRI (fMRI)

  • assesses brain metabolic activity (indirect measure of neuronal discharge) → specific areas of function during an activity/stimulus
  • blood oxygen level dependent imaging (BOLD) : looks at converstion of oxyHb → deoxyHb and utilization of glucose
  • role in preop eval


catheter angiography


catheter in through femoral a → aorta under fluoroscopy

iodinated contrast helps visualize vasculature


interventional radiology

minimally invasive treatment options for conditions of brain, head/neck, spine

  • microcatheters, microguidewires, balloon catheters, embolic material, stents


stroke management/tx, epistaxis, preop embolization for tumor vasc, vertebroplasty


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