mri notes

order MR if question about age of hemorrhage

(classically in child abuse cases)

hemorrhage on CT

white 2/2 Hgb/protein concentratino ~56 HU, anemic patient may appear isodense

hyper acute blood 0-72 hyperdense

Early subacute 3 days 1 week still hyperdense

Late subacute hypodense 1 week to months

MRI

2 factors affect MR: oxygenation state of hemoglobin, lysi of initially intact RBC

hyperacute 3-6hours - contains oxyhemoglobin (diamagnetic) - will not see it on GRE/SWI

acute 8-72 hrs - ^ deoxyhemoglobin (paramagnetic) will see on SWI/GRE

chronic hemorrhage - months to years, iron atoms deposited and cannot exit

hyper acute

oxy - isointense T1, bright on T2

acute 1-3 days

deoxy - iso on T1 dark on T2

subacute )3-7days)

bright on TI, dardk on T2

late 7-14 days bright bright - extracellular methemoglobin

chronic >14 days - dark dark T1T2

intracranial vasculature

digital subtractio angiography - gold standard, catheter angiography

do each vessel individually

bolus injection 100ml at 4-6ml/sec

large bore 18guage antecubital to get good cta

MRA/V

TOF - no contrast - moving spins experience different excitations (flow related), slow flow may appear as if vessel is occluded - can see >1.5mm on 1.5T

2D limitations - need adequate flow, aneurysms poorly visualized, underestimated because of slow moving spins

Phase contrast -

TRICKS - time resolved iagin of contrast kinetics: needs contast -time resolved imaging of contrast

giant aneurysm >2.5cm presents w/mass effect

http://www.youtube.com/watch?v=_OJ5qnErsTc&NR=1