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Neurosurgery > Imaging > Flashcards

Imaging Flashcards

1
Q

Does CT or MRI have better spatial and contrast resolution?

A

CT has better spatial resolution, MRI has better contrast resolution

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2
Q

What is contrast resolution?

A

The ability to discriminate tissues of differing composition

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3
Q

What is spatial resolution?

A

The ability to resolve fine detail

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4
Q

Which imaging modality has the highest spatial resolution?

A

Radiographs, then CT, then MRI.

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5
Q

What are the disadvantages of use of a myelogram for assessment of the spinal cord?

A

Invasive and associated with adverse effects (including worsening of neurologic signs).

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6
Q

What provides normal contrast within the vertebral canal on CT?

A

The epidural fat. Loss of the epidural fat can result in loss of contrast. Myelography can be used to overcome this issue.

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7
Q

Is bone hypointense or hyperintense on MRI?

A

Hypointense (black) due to the absence of hydrogen protons

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8
Q

What contrast medium is typically used in MRI studies?

A

Gadolinium based contrast media

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9
Q

What is functional MRI

A

The provision of physiologic information through the use of specialized pulse sequences

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10
Q

What are the Hounsfield units for various structures viewed on CT scan?

A
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11
Q

What terms are used to describe image brightness on various modalities?

A

Radiography: Opacity
CT: Attenuation or density
MRI: Intensity

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12
Q

Is a wide or narrow window width of CT used for evaluation of neuroparenchyma?

A

Narrow window width to apply shades of grey to soft tissues only, improving their discrimination.

Wide window widths are required for evaluation of the lungs or bone to encompass the wide range of tissues in these organs.

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13
Q

What is responsible for production of the signal in an MRI?

A

Mobile hydrogen atoms (extremely abundant in the tissues in the form of water and lipid molecules).

Hydrogen atoms precess when exposed to a strong magnet align and precess around the magnetic field. Applied radiofrequency pulses disrupt this, and cause a downward spiralling of the atoms. When the radiofrequency pulse is removed the change in magnetic field generates an electrical voltage that is detected by the MRI unit.

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14
Q

What are MRI FLAIR sequences typically used for?

A

Suppression of fluid signal.

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15
Q

What are MRI STIR sequences typically used for?

A

Suppression of fat signal.

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16
Q

How can T2 FLAIR sequences distinguish fluid types?

A

Pure fluid with little to no protein content such as cerebrospinal fluid is nulled, whereas edema is hyperattenuated

17
Q

What is the primary difference between spin echo and gradient echo MRI sequences?

A

Spin echo corrects for signal loss caused by static inhomogeneities in the field, whereas gradient echo does not.

18
Q

What is the main difference between T1W and T2W MRI images?

A

T1W images provide good anatomic detail, T2W images are considered to be more sensitive to pathology

19
Q

What are gradient echo (T2*W) sequences most useful in detecting?

A

Hemorrhage - shown as signal voids

20
Q

What are some fat suppression techniques that can be used with MRI?

A
  1. Spectral fat suppression.
  2. Dixon technique (in-phase, or out-of-phase).
  3. STIR (cannot be used following contrast, and is more similar to a T2W than T1W image).
21
Q

What is spectral fat saturation?

A

Suppression of the MRI fat signal. Can be used to better delineate lesions within the fatty cancellous bone, lesions involving the meninges, and in discriminating between structures that may be hyperintense on T1W and T2W images.

Particularly useful on T1W images post-contrast as it can suppress the normally hyperintense fat signal, making delineation of the contrast enhancement more apparent.

22
Q

Describe the substances that are hyperintense on T1W and T2W images

A
23
Q

Is cerebrospinal fluid hypointense or hyerintense on T1W and T2W images?

A

Hyperintense on T2W, hypointense on T1W.

Edema is also T2W hyperintense, T1W hypointense (due to prolongation of T1 and T2 relaxation times).

24
Q

Is white or gray matter more or less hyperintense on T1W and T2W images?

A

White matter more hyperintense than gray matter on T1W images, reverse for T2W

25
Q

Are protein bound fluids such as in mucin or marked cerebrospinal fluid inflammation more or less hyperintense on T1W and T2W images?

A

More hyperintense on T1W images (as compared to edema which is more hyperintense on T2 images)

26
Q

What CNS structures are normally enhanced on MRI with the administration of contrast?

A

Meninges, choroid plexus, pituitary.

27
Q

How can syringohydromyelia be differentiated from spinal cord edema?

A

Syringohydromyelia will be suppressed on T2W flair sequences.

28
Q

What occurs secondary to disruption of the blood/brain barrier?

A

Vasogenic edema, that typically migrates along white matter tracts. It is hypoattenuating on noncontrast CT, hypointense on T1W images, and hyperintense on T2W images.

29
Q

Is T1W or T2W more useful for evaluation post-contrast images?

A

T1W. Contrast will be seen as hyperintense. Lesion may be surrounded by hypointense region if associated vasogenic edema.

30
Q

What routine MRI sequences should be performed for evaluation of the brain?

A

Pre- and post-contrast T1W, T2W, T2 FLAIR, T2*W +/- spectral fat saturation following contrast administration to help identify subtle lesions.

31
Q

Is asymmetry and enlargement of the ventricles a normal finding in some patients?

A

Yes - highlights the importance of the neurologic examination in assessing the importance of MRI findings.

32
Q
A
33
Q

What are some signs on MRI that suggest an extraparenchymal intracranial lesion?

A

Displacement of subadjacent neural tissue, broad base, contiguous dural enhancement, or dural tail, hyperostosis/remodelling of the skull, CSF between the mass and brain.

34
Q

What are the classifications of abnormalities involving the spinal cord based MRI/CT?

A

Extradural, intradural-extramedullary, intramedullary

35
Q

What does the MIIND pneumonic stand for when assessing potential causes of neurologic disease?

A

Metabolic.
Inflammatory.
Injuries.
Neoplasia.
Degenerations.

36
Q

What does the ‘golf tee sign’ indicate on spinal MRI imaging?

A

Intradural extramedullary location of mass (see image pg 384 Tobias)

Neurosurgery (11 decks)

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