9/6 Neuroimaging - Basak Flashcards
CT
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
MRI
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
intensities
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
MRI
adv vs disadv
- exquisite delineation of anatomy
- sensitive to pathology
- posterior fossa: much clearer than in CT
- in utero imaging
- NO RADIATION
disadvantages
- 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
INVASIVE!
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
