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ACVS Phase I Master Deck *Use This* > Chapter 28: Imaging of the CNS > Flashcards

Chapter 28: Imaging of the CNS Flashcards

1
Q

Which form of imaging has the highest spatial resolution?

A

Radiography

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2
Q

Which imaging modality has the highest contrast resolution?

A

MRI

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3
Q

What structure provides contrast within the vertebral canal?

A

The epidural fat

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4
Q

When may MRI be more beneficial for the imaging of bone than CT?

A

Infiltrative disease

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5
Q

What is the difference in MPR image acquisition in CT and MRI?

A
  • With CT, sagittal and dorsal planes are reformatted/reconstructed after acquisition of transverse images
  • With MRI, images for each anatomical plane are obtained using seperate acquisition

The spatial resolution of MRI sagittal and dorsal images may therefore be better than CT

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6
Q

What modality is usually considered the first line of imaging in trauma? Why?
What is the exception to this rule?

A
  • CT as is it very good for identifying hemorrhage and fractures
  • The exception may be in cases of TBI as MRI findings can be used to prognosticate
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7
Q

What are the commonly used contrast agents for CT and MRI?

A
  • CT: iodinated contrast
  • MRI: gadolinium-based contrast
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8
Q

What are the terms (-suffix) used to describe the level of brightness in radiography, CT and MRI?

A
  • Radiographs = opacity
  • CT = attenuation or density
  • MRI = intensity
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9
Q

What are the Hounsfield units of air, fat, water, brain, acute to subacute clotted blood, mineral and bone, metal?

A

air: -1000
fat: -100
water: 0
brain: 30-40
acute to subacute clotted blood: 60-100
mineral and bone: variable 100 to >1000
metal: variable 100 to >3000

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10
Q

List some causes of hypoattenuation on CT scan:

A
  • Cystic or fluid-filled
  • Necrosis
  • Edema
  • Fatty infiltration
  • Gas
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11
Q

List some caused of hyperattenuation in CT

A
  • Hemorrhage
  • Mineral
  • Metal
  • Densely cellular/fibrotic
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12
Q

What produces the signals in MRI?

A

Mobile hydrogen atoms within the tissue (protons/spins) that spin on their axis to create a small magnetic field

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13
Q

Define pulse sequencing?

A

A series of timed events by which a radiofrequency pulse is used to create a signal
T1 is good anatomic detail
T2 is more sensitive to pathology

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14
Q

Which are the pulse sequences upon which all others are built?

A
  • Spin echo (considered the work-horse of clinical MRI and is used to produce T1W, T2W and proton density-weighted images
  • Gradient echo
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15
Q

What is FLAIR?
Why is it useful?

A

FLuid-Attenuated Inversion Recovery
- Suppresses the signal from fluid
- Gives the ability to distinguish pure fluid structures (nulled signal) from solid, but high-water content lesions such as edema within tissue (high signal)
- Improved conspicuity of hyperintense lesions compared with spin echo T2W image

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16
Q

What are STIR sequences?
Why is it useful?

A

Short Tau Inversion Recovery
- suppresses fat signal
- Allows assessment of high water content fluid or soft tissues against a background of suppressed fat
- Useful for vertebral and paravertebral soft tissue pathology

17
Q

What are T2* sequences used for?

A

Useful for identifying hemorrhage or blood clots

18
Q

What sequence is particularly useful for radiation planning?

A

spoiled gradient echo - because it’s fast and able to image a lot of area quick.

Spoil their plans!

19
Q

What lesions is fat suppresion useful for?

A
  • Lesions within fatty cancellous bone
  • Lesions involving the meninges
  • Nerve sheath tumours
  • To discriminate between other structures which may be hyperintense on T1W and T2W images
20
Q

What MRI sequences can perform angiography without the need for IV contrast?

A
  • Time-of-flight (for rapid arterial flow)
  • Phase-contrast MRA (slow venous or CSF flow)
21
Q

What is MRI spectroscopy?

A

A physiological MR technique that evaluates brain chemistry and metabolism

22
Q

List the structures with high signal intensity on T1W and T2W images

A

T1: Fat Men are PIGs, Ma
Fat/methemoglobin/protein/ions/gadolinium/melanin
T2: “DECeNCy”
Demyelination/Edema/CSF/Necrosis/Cellular infiltration

23
Q

What are the dose ranges for IV contrast for CT and MRI?

A

CT: Iodinated contrast 400 - 800mg iodine/kg
MRI: Gadolinium - 0.1-0.15mmol/kg

24
Q

What is normally enhanced on post-contrast imaging of the CNS?

What are two options for imaging after contrast injection?

A
  • Normally enhanced: Meninges, choroid plexus, pituitary gland
  • Can obtain images immediately after injection to evaluate vasculature and after a delay of a few minutes to evaluate distribution or leakage
25
Q

How does vasogenic edema appear on CT, T1W and T2W MRI?

A

CT: hypoattenuating
T1W: hypointense
T2W: hyperintense

Typically migrates along the white matter tracts

26
Q

What are the minimum sequences recommended to be acquired for brain MRI?

A

T1W before and after gadolinium contrast
T2W
T2 FLAIR
T2*

27
Q

What are some age-expected normal variants on brain MRI?

A

Enlargement of ventricles and subarachnoid space with advancing age
Signal intensity reversal of white and grey matter in neonates (until about 16wk when myelination has progresses)
Appearance of bones in neonates

28
Q

What are some secondary changes associated with alteration in CSF flow?

A
  • Ventriculomegaly
  • Syringohydromyelia
  • Spinal cord (presyrinx) edema
29
Q

List the three forms of secondary hydrocephalus:

A
  • Noncommunicating (obstruction of flow)
  • Communicating (decreased resorption by arachnoid villi or increased production
  • Compensatory (loss of brain parenchyma)
30
Q

List some ways of categorizing primary pathology of the brain

A
  • Intra vs extraparenchymal
  • Solitary, multifocal or diffuse
  • Symmetric or random distribution
31
Q

What is the mnemonic for general categories of neuro disorders?

A

MIIND
- malformations
- inflammation
- injury
- neoplasia
- degenerative

32
Q

What are the recommended volumes of contrast for CT myelogram?

A
  • Using nonionic contrast media (iohexol or iopamidol) administer 0.45ml/kg (full spine) or 0.3ml/kg (regional)
  • NO MORE than 8ml total (seizures)
33
Q

What are the main lesion localizations within the vertebral column?

A
  • Extradural
  • Intradural-extramedullary
  • Intramedullary

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