Neuroimaging

Question 1

Hounsfield Units (HU)

air, fat, water, brain, bloood, calcification

Answer 1

Air: -1000
Fat: -100
Water: 0
Brain: 30-40
Blood: 50-100
Calcification: 1000

Question 2

Match: MRI and CT with the words (intensity and density)

Answer 2

CT: density
MRI: intensity

Question 3

What are the intensities of T1W images of the following:

Water
Edema
White matter (fat)
Grey matter

Answer 3

CSF = dark

Water: hypointense
Edema: hypointense
White matter (fat): hyperintense
Grey matter: isointense

Question 4

What are the intensities of T2W images of the following:

Water (CSF)
Edema
White matter (fat)
Grey matter

Answer 4

CSF = bright

Water: hyperintense
Edema: hyperintense
White matter (fat): hypointense
Grey matter: isointense

Question 5

What is FLAIR?

Answer 5

“fluid attenuation inversion recovery”

• T2 weighted but CSF is hypointense
• allows for exquisite evaluation of white matter adjacent to ventricles (ie as in multiple sclerosis)

Question 6

Diffusion Weighted Image

Answer 6

-primary sequence for detection of acute or subacute infarcts (up to 14 days old)

Question 7

MRI Contrast: what element is used and why do we do it?

Answer 7

What: Gadolinium (IV)
Why: produces hyperintensity in vessels and areas of BBB breakdown

Question 8

Why do an MRI?

Answer 8

To see the extend of damage (ie: infarct) more clearly; it’s sensitive and specific

-very small amts of blood can be picked up in MRI vs CT

Think: MRI for soft tissue. CT for bone.