Tobias chapter 28 – imaging of the neurologic system

Question 1

What is T1W vs T2W good for? What is the exception?

Answer 1

T1W: anatomic detail
T2W: pathology

Exception: pathology involving fat or methemoglobin

Question 2

What are each of these sequences good for?
T1 FLAIR
T2 FLAIR
STIR

Answer 2

T1 FLAIR: similar to T1 with better contrast to noise ratio
T2 FLAIR: help distinguish high protein fluid (edema) from normal fluid (CSF)
STIR: good contrast for fluid or fluid Rich tissues against fat background. Similar to T2. Should not be used with contrast.

Question 3

What MRI sequence would you use to search for blood?

Answer 3

T1W

Question 4

What MRI sequence would you use to look for edema or necrosis?

Answer 4

T2W

Question 5

What contrast medium is used with CT? Why? What is the dose?

Answer 5

Iodine based contrast (metal)
400 to 800 mg of iodine/kilogram

Question 7

What MRI sequence would you use to look for demyelination?

Answer 7

T2W

Question 9

What contrast medium is used with MRI? What does it enhance in the CNS?

Answer 9

Gadolinium
Enhances meningitis, choroid plexus, pituitary gland

Question 10

What does meningitis look like in a T1 weighted MRI image following gadolinium?

Answer 10

Hyper intense (increased perfusion)

Question 11

Does contrast agent (gallium) penetrate the brain? Why?

Answer 11

No, the blood brain barrier prevents penetration, therefore only the meninges, chloride plexus and pituitary (highly vascular areas) will contrast enhance

Question 12

What does vasogenic edema look like on noncontrast CT, T1 weighted MRI or T2 weighted MRI?

Answer 12

CT: hypoattenuating
T1: hypointense
T2: hyper intense (remember – T2 is great for protein, rich fluid).

Question 13

Our brain tumors typically hypo or hyper attenuating on CT contrast? Why?

Answer 13

Typically, hypERattenuating due to breakage of the blood brain barrier

Question 14

What is the typical appearance of an in fact on MRI ((T1 W) or CT contrast?

Answer 14

Ring appearance due to necrotic center [core hypoattenuating/hypo intense) with a ring of hyper attenuating/hyper intense tissue (perfused).

Question 15

What are the three types of cerebral edema? How are they identified on MRI (features of each)

Answer 15

1) Vasogenic: causes hypointensity on T1W and a hypERintensity on T2W
2) Interstitial: transependymal migration of CSF into periventricular white matter
3) cytotoxic: results in ischemia

Question 16

What are the three types of secondary hydrocephalus that can be observed on MRI? What are their causes?

Answer 16

1. Non-communicating – obstruction of flow from ventricles to subarachnoid space.
2. Communicating – reduced absorption by the arachnoid villi or increased production of CSF.
3. Compensatory – from loss of cerebral parenchyma.

Question 17

Describe the four steps to classify CNS pathology. Include the meaning of the acronym MIIND.

Answer 17

1. Intra-axial or extra-axial? (inside or outside the neuroparencha)
2. Location
3. Solitary, multifocal or diffuse.
   - if multifocal, classify symmetrical versus random, as symmetrical = neurodegenerative (metabolic or toxic disorder)
4. Size, shape, margination, attenuation/intensity, contrast, enhancement pattern.
   MIIND: Malformations, inflammation, injury, neoplasia, degeneration