Neuroradiology & Anatomy - Strottmann Flashcards Preview

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Flashcards in Neuroradiology & Anatomy - Strottmann Deck (16):
1

What type of electromagnetic wave does CT use? MRI?

CT: X-rays

MRI: Radio waves & Magnetic fields

2

Describe the difference in the size of a CT machine vs. an MR imager.

  • CT is a circular gantry (donut)
    • Not overly deep
  • MRI is a cylindrical magnet (coffin)
    • Add in the head restraints typically used to prevent motion blur in imaging, and one can see how claustrophobia can be an issue for some patients

3

Contrast CT and MRI in terms of time needed for a typical set of scans.

  • CT: Fast. A few minutes.
  • MRI: Slower. Several minutes, perhaps up to half an hour
    • May present trouble regarding certain patients; e.g. psychotic, drunk, etc.

4

Compare CT and MRI in terms of the radio-contrast that can be used.

CT: Iodine

MRI: Gadolinium

5

How do CT and MRI compare in terms of expense?

MRI is more expensive than CT.

6

What anatomic planes does CT scan in?

What about MRI?

  • CT: Scan is in axial plane
    • Images in other planes are generated digitally from axial data
  • MRI: Scans in multiple planes: axial, coronal, sagittal (& oblique)

7

Compare CT and MRI in terms of how multiple image data sets are generated.

  • CT: A single scan is done (maybe two, if contast is given). From there, digital manipulation of the data is used to generate various "windows" (brightness & contrast settings) that are useful for visualizing different structures.
  • MRI: A seperate scan (3 to 8+) is done for each set of images.
    • Multiple planes
    • Various pulse seqeunces
    • Each image set is viewed with only one window.

8

When viewing axial images, what should you always remember that your perspective is?

  • Pt laying on their back
  • You're standing at the foot end of the table
  • You're looking up at the undersurface of the anatomic slide in question

9

Compare the strengths of CT vs. MRI in terms of which tissues each is useful for looking at.

  • CT
    • Bone
    • Hemorrhage
    • Trauma
    • Fluid (e.g. CSF)
    • +/- soft tissue
  • MRI
    • Soft tissues
      • Includes bone marrow
    • Better contrast enhancement

10

Rank the follow tissue types in order of brightest to darkest when looking at a CT image:

  • CSF
  • Air
  • Gray matter
  • White matter
  • Hemorrhage
  • Fat
  • Bone

From brightest to darkest on CT:

  1. Bone (bright white)
  2. Hemorrhage
  3. Gray matter
  4. White matter
  5. CSF
  6. Fat
  7. Air (black)

Note that gray matter is (unintuitively) slightly brighter than white matter on CT.

11

Rank the follow tissue types in order of brightest to darkest when looking at a T1W1 MRI image:

  • CSF
  • Air
  • Gray matter
  • White matter
  • Fat
  • Bone

From brightest to darkest on T1W1 MRI:

  1. Fat (white)
  2. White matter
  3. Gray matter
  4. CSF
  5. Air & cortical bone (black)

Note that white matter is slightly brighter than gray matter on T1W1 MRI.

12

Rank the follow tissue types in order of brightest to darkest when looking at a T2W1 MRI image:

  • CSF
  • Air
  • Gray matter
  • White matter
  • Fat
  • Bone

From brightest to darkest on T2W1 MRI:

  1. CSF (bright)
  2. Fat
  3. Gray matter
  4. White matter
  5. Air & cortical bone (black)

Note that grey matter is (unintuitively) slightly brighter than white matter on T1W1 MRI.

13

While looking at an axial slice image of a patient's head, you note a bright ring encircling the brain. What would you conclude this ring to be if you were looking at:

  • A CT image?
  • An MRI image?

  • CT: The skull
    • Bone is brighest on CT!
  • MRI: The subcutaneous fat of the head (not the skull!)
    • Fat is bright on MRI!

14

What is the Diffusion Weighted Imaging form of MRI most useful for detecting in terms of neurological pathology?

Early identification of ischemic stroke

15

How can you find the central sulcus on an axial image?

Look for an "omega-shaped" (hook-like) sulcus extending from each lateral edge of the brain about mid-way along the ventral-dorsal axis. The central sulci typically should not reach the midline of the brain.

16

What is a major contraindication for CT? For MRI?

  • CT: Anaphylactic reaction to iodine contrast
    • Mild allergies can be coutneracted with a short course of immunosuppression using antihistamines and prednisone prior to administration of iodine
  • MRI: Metal implant / pacemaker etc.
    • Gadolinium anaphylaxis and allergies are much rarer than those to iodine