Neuroimaging Flashcards
how do CT scans work?
computed tomography: x-ray beam rotates around patient, amount of absorption depends on density of tissue traversed
acquired data reconstructed mathematically to produce density values for every point
density expressed in Hounsfield Units (HU) from -1000 to +1000 —> air = -1000, water = 0, calcification = +1000
what are the advantages and disadvantages of CT scans?
advantages: fast, less costly than MRI, very sensitive to hemorrhage, great imaging of calcium and bone
disadvantage: radiation dose, not as sensitive to small lesions or anatomical detail as MRI, artifact from metal can be significant
when should contrast be used with brain CT scans?
contrast contains iodine, hyperdense in vessels or where there is breakdown of BBB, indicated for tumor, infection, CTA
do NOT use contrast in setting of acute trauma (acute intracranial hemorrhage)
how does acute cerebellar infarct appear on CT scan?
usually caused by thromboembolic events —> ischemic stroke
this causes cytotoxic edema (increased water in cell) —> low density CT
low density takes 4-6 hours to develop, edema peaks 3-7 days
what are the basic steps of how an MRI works?
- patient placed in main magnet
- radio frequency wave sent in from coil
- radio frequency wave turned off
- tissues emit a signal, as energy from protons is emitted and detected by coil
- emitted signals used for reconstruction of image
what is the difference between/ use of T1 vs T2 weighted brain MRIs?
T1W is best for anatomy: water (CSF)/edema is hypointense, gray matter is isointense, white matter (fat/myelin) is hyperintense
T2W is best for pathology: water (CSF)/edema is hyperintense, gray matter is isointense, white matter (fat/myelin) is hypointense
what is a FLAIR brain MRI?
FLAIR = fluid attenuation inversion recovery, best for pathology
similar to T2W images (water/edema = hyperintense) BUT CSF is hypointense - allows for detailed evaluation of white matter adjacent to ventricles, such as in multiple sclerosis!
what type of MRI imaging is used for ischemic brain infarcts?
diffusion weighted image (DWI) - shows hyperintensity with acute or subacute infarcts (up to 14 days old)
what is used for intravenous contrast in MRI?
gadolinium (rare earth element) - produces hyperintensity in vessels and areas of BBB breakdown
what are the advantages and disadvantages of MRI?
advantages: great detail of anatomy, very sensitive to pathology (edema, small lesions), excellent for evaluation of posterior fossa structures (brainstem, cerebellum), in utero imaging, no radiation
disadvantages: lengthy, claustrophobia, pacemaker contraindication and metallic foreign bodies, expensive
how does HSV-1 encephalitis appear on MRI?
abnormal signal and enhancement in medial temporal and inferior frontal lobes
bilateral but asymmetric
what can magnetic resonance spectroscopy (MRS) do?
measures brain NT and biochemicals - amino acids, lipids, lactate, choline, creatine, etc
aids in evaluation of brain tumors, radiation necrosis, infections, metabolic disease
what can diffusion tensor imaging (DTI) do?
Allows assessment of white matter tracts based on water diffusion characteristics along these tracts of axons
diffusion sequence used to create 3D image
used for evaluation of neurodegenerative diseases, epilepsy, TBI, MS
describe the procedure of catheter angiography
invasive procedure -
1. Catheter inserted via femoral artery and directed into Aorta under fluoroscopy
2. Iodinated contrast material injected to visualized vasculature
