Neuroradiology

Question 1

CT pros and cons:

Answer 1

Pros:

1.

Question 2

CT brightness scale:

Answer 2

• Bright/hyperdense: Bone/calcium; Acute blood; contrast
• Gray: white matter is darker than gray matter.
• Dark/hypodense: edema; encephalomalacia; CSF; air, stroke

Question 3

When to get a CT:

Answer 3

o	Head Trauma
o	Fresh hemorrhage
o	Speed needed
o	Skull fracture
o	Calcified lesion
o	Claustrophobic or obese
o	Pacemaker or metallic fragments

Question 4

When to get an MRI:

Answer 4

o Subtle area of tumor/infarct/demyelination
o Brainstem lesion
o Old Hemorrhage
o Anatomical detail needed

Question 5

CTA (CT Angiogram)

Answer 5

• fast, high resolution
• iodine contrast
• high sensitivity for aneurysms >4mm

Question 6

MRI T1:

Answer 6

Good for visualizing anatomic details.
Dark: Fluid (CSF); Gray matter
Bright: Fat; Marrow; Contrast; proteinaeous fluid; White matter

Question 7

MRI T2:

Answer 7

Good for visualizing pathology: Gray matter is brighter than white matter.
Dark: Calcification, Deoxyhemoglobin, Blood vessels, Melanin.
Bright: Fat, Fluid (CSF), Lesions (edema, infarct, tumor).

Question 8

MRI FLAIR (FLuid Attenuation Inversion Recovery)

Answer 8

Like T2 but with CSF turned dark.
White matter is gray. Gray matter is light. Lesions are bright.
Microvascular damage around ventricles shows up as hyperintensities.

Question 9

When do strokes show up on FLAIR?

Answer 9

Show up after 6-12hrs and stay forever as hyperintense.

Question 10

MRI DWI (Diffusion Weighted Imaging):

Answer 10

Used for visualizing stroke (confirm w/ ADC).
Images are grainy.
Dark: Brain, CSF.
Bright: Restricted diffusion, stroke.

Question 11

When do acute strokes show up on DWI?

Answer 11

Acute strokes show up bright within minutes and remain 10-14 days.
T2 hyperintensities can “shine through” to DWI.

Question 12

Not all restricted diffusion on DWI is an acute stroke:

Answer 12

o	T2 shine through.
o	Acute MS lesions.
o	Some tumors.
o	Some abscesses.
o	Beware the artifact!

Question 13

MRI ADC (apparent diffusion coefficient)

Answer 13

Used to confirm stroke as source of restricted diffusion
Used to help rule out T2 shine through. Can be calculated even if it is not filmed. Acute stroke is hypointense (dark) on an ADC map.
Dark: True diffusion, restriction.
Bright: CSF, confirm stroke.

Question 14

MRI T1 post gadoliniem contrast:

Answer 14

• Acute strokes gently enhance after a week, and continue to enhance for about 6 months.
Tumors and abscesses tend to enhance more intensely.

Question 15

Gadolinium contrast: (used in MRI versus iodine in CT)

Answer 15

1. For contrasted images, only areas of contrast enhancement will be bright. Typically this is done by using a T1 weighted image with fat saturation.
2. MRI contrast (gadolinium) is contraindicated for any patient with a GFR

Question 16

MRA and MRV

Answer 16

Noninvasive, requires gadolinium.
Take thin slices and then stack.
MRV requires contrast.