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Tobias full > Imaging of the CNS > Flashcards

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 haemorrhage 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 denstiy
  • MRI = intensity
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9
Q

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

A
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10
Q

List some causes of hypoattenuation on CT scan

A
  • Cystic or fluid-filled
  • Necrosis
  • Oedema
  • Fattu infiltration
  • Gas
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11
Q

List some caused of hyperattenuation in CT

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

What produces the signals in MRI?

A

Mobile hydrogen atoms within the tissue

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13
Q

Define pulse sequencing

A

A series of timed events by which a radiofrequency pulse is used to creaste a signal

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14
Q

Which are the only 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
  • Give the ability to distinguish pure fluid structures (nulled signal) from solid, but hihgh-water content lesions such as oedema within tissue (high signal)
  • Improved conspicuity of hyperintense lesions compared with spin echo T2W images
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16
Q

WHat are STIR sequences?
Why is it useful?

A
  • Short Tau Inverstion Recovery - supresses fat signalling
  • Allows assessment of high water contect fluid or soft tissues against a background of suppressed fat
  • Useful for vertebral and paravertebral soft tissue pathology
17
Q

Whar are T2* sequences used for?

A

Useful for identifying haemrrhage or blood clots

18
Q

What sequence is particularly useful for radiation planning?

A

spoiled gradient echo

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 rapis arterial flow)
  • Phase-contract 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
23
Q

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

A
  • Iodinated contrast 400 - 800mg iodine/kg
  • Gadolinium - 0.1-0.15mmol/kg
24
Q

What is normally enhanced on post-contract 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 vasculater and after a delay of a few minutes to evaluate distribution or leakage
25
Q

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

A
  • CT: hypoattenuating
  • T1W - hypointense
  • T2W - hyperintense

Typically migrates alson the white matter tracts

26
Q

What are are minimum sequences recommened to be acquired for brain MRI?

A
  • T1W before and after gadolinium contrast
  • T2W
  • T2 FLAIR
  • T2*
27
Q

What are come age-expected normal varients 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 cahnges associated with alteration in CSF flow?

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

List the three forms of secondary hydrocephalus

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

List some ways of categorising 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 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 localisation within the vertebral column?

A
  • Extradural
  • Intradural-extramedullary
  • Intramedullary

Tobias full (110 decks)

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