Neuroimaging Flashcards
How does CT work
- xrays emitted in a beam and detected on the opposite side
- creates 2d slices that can be visualized into 3D by scrolling through
- Bone/calc = bright white
- Air = black
- Soft tissue = grayscale (Hornsfield)
What is CT the most sensitive/specific for
SAH, SDH, EDH, abscesses, masses
What are some limitations of CT
poor differentiation of soft tissue (Can miss inflammatory changes and ischemia)
How does contrast work in CT
- iodine contrast media blocks passage of xrays
- helps distinguish enhanced tissues from background
- timing of contrast admin determines what lights up
- renally excreted
What does CT contrast help highlight
vascular and inflamed tissues (also malignancy, abscess)
- typically not as good as MRI if it is available
How to interpret a CT
- identify pt
- identify plane (axial and soft tissue is good to start with)
- scroll superior to inferior
- blood, cisterns, brain, ventricles, bones (blood can be very bad)
Where is the blood
epidural
where is the blood
subdural
where is the blood
intracerebral
Where is the blood
intraventricular
where is the blood
subarachnoid (cisterns/circle of willis)
What to check when evaluating cisterns on CT
are they open and do they have blood in them
What to look for when evaluating the brain parenchyma on CT
- symmetry
- grey-white differentiation
- shift
- hyper/hypodensity
What to look for when evaluating the ventricles on CT
should be open, symmetrical, without blood
What to look for when evaluating bone on CT
- switch software to bone window
- look for fractures, step-offs, gaps (compare to other side)
What is CTA head/neck
CT angiography of head and neck vessels to assess for vascular cut-offs/occlusions, or high risk stenoses
What are the indications for CTA head/neck
- TIA
- vertebral/carotid artery dissection
- dense/cortical strokes (large vessel occlusion)
- aneurysm detection and operative planning
Describe brain MRI mechanism of action
best for viewing soft tissue
- harnesses natural tendency of hydrogen ions to align in magnetic field (alignment and relaxation)
- different tissues realign at different intensities
- T1, T2, FLAIR, STIR, DWI, ADC
Describe the difference between T1 and T2 view
T1 highlights tissue (fat) and T2 highlights mostly water
Describe FLAIR
Fluid attenuated inversion recovery
- nullifies signal from CSF
- helps find subtle problems near CSF rich areas, pre-infarct edema, demyelinated MS lesions
Describe STIR
- nullifies signal from tissue
- good for finding subtle problems in fat-rich areas, fracture, osteomyelitis
Describe DWI and ADC
(Diffusion weighted imaging, apparent diffusion coefficient)
Helpful for identifying stroke within minutes of happening
- combines T2 and water enhancement
- ADC is a superimposed sequence to control quality (DWI can appear too bright)
What contrast is used in MRI
Gadolinium: a rare earth metal that interacts with H+ ions in a magnetic/pulsing field
- contraindicated in pregnancy
- need renal panel (predisposition to nephrogenic systemic fibrosis)
**- enhances arteries and vascularly abnormal tissues (tumors, abscess)
What is the likely diagnosis in this MRI with contrast
Tumor: lit up because it is vascularized
If it was an abscess it would be dark because it wouldn’t be vascularized
