Scout

Can show anatomy and findings not included on the other sequences

Can also be helpful for susceptibility as may be one of few GRE sequences performed.



T1

Good for anatomy


Bright on T1:


In addition to the T1-bright subcutaneous fat, there is T1-hyperintense extra-axial something adjacent to the right occipital lobe (arrow), in this case representing subacute subdural hematoma, which was not visible on CT.


T2


Best for general pathology - edema is bright

Also good for anatomy

Flow voids

Sinuses, orbits



How do you tell if an image is T1- or T2- weighted?


The easiest way is to look at the fluid. Most images have fluid - e.g. brain ventricles, or spinal canal CSF.

Water bright ==> T2 weighting

Water dark ==> T1 weighting

**exception: certain sequences specifically FLAIR suppresses fluid/water



FLAIR (T2 with water suppression)

follow-up:

How do you tell if a brain image is T1 or T2FLAIR?

Flair T1
T2 FLAIR T1

CSF is dark on both, so that won't help. BUT the white and gray matter look different. Specifically, white matter has myelin (you can think of it as being like fat) so looks brighter on T1.



FLAIR:

Good for picking out lesions, increasing conspicuity

caveat - less senstiive in the posterior fossa



Periventricular, pericallosal, callosal white matter lesions due to multiple sclerosis in this patient.



Fat Sat & Gado


T1fsw T1
T1 with fat saturation and with
intravenous gadolinium contrast
T1





Sag



Midline structures





Susceptibility

Susceptibility (SWI) exagerrates the magnetic effects which causes loss of signal around blood products (hemosiderin). This is useful to evaluate for prior hemorrhage.


Look for black spots, but also compare for conventional T1/T2 signal and head CT (if available) differentials of acute blood rather than old hemosiderin, calcification


Diffuse axonal injury manifested as numerous foci of susceptibility artifact. The patient had a history of trauma with motor vehicle collision reportdly occuring at 100 miles per hour.



SWI - dark spot from hemosiderin
from this cavernous malformation ("cavmal")

T2 - still some dark signal but
not as exagerrated
T1 - also some brightness from blood product
T1 post - hard to tell on signle slice
but there is a small associated
enhancing developmental
venous anomaly (DVA)




Diffusion-weighted imaging

Diffusion-weighted images (DWI) are often thought as most useful for ischemic stroke, but actually other things can also be bright - some neoplasms (e.g. medulloblastoma, lymphoma),


Ischemia

DWI - brightness can be restricted diffusionADC - if dark, confirms diffusion is restricted




by Sean Novak




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