Neuroradiology Basics

Question 1

What is a potential downfall of head CT for suspected ischemic stroke in the first 6 hrs after presentation?
What is the main utility of CT imaging this early?

Answer 1

• Low sensitivity for ischemia in first 6 hrs

- Rule out hemorrhagic stroke

Question 2

What are six potential markers of ischemia seen on head CT in a stroke patient?

Answer 2

1) Midline shift due to edema
2) Loss of cortical sulci
3) Hyperdense MCA sign
4) Insular ribboning
5) Darker (hypointense) lentiform nuclei (i.e. caudate and putamen)
6) Blurring of grey-white matter junction

Question 3

In hyperacute ischemic stroke what specific type of CT imaging proves useful and why?

Answer 3

CT perfusion imaging. Allows visualization of infarct core and penumbra, with the latter being the region of potentially reversible damage.

Question 4

How is CT perfusion conducted and how can features like CBF and CBV be measured?

Answer 4

IV contrast is given and changes the density of blood. By visualizing slices over time we can measure CBF, CBV, and MTT.

Question 5

How should the infarct core and penumbra appear on CBF and CBV scans during CT perfusion? Why?

Answer 5

CBF: Both infarct core and penumbra should have decreased flow
CBV: Infarct core should have low volume BUT penumbra should appear like normal brain tissue

Since penumbra contains area of reversible damage it still has capability to autoregulate and dilate cerebral vessels to receive more volume thus it appears similar to normal brain tissue.

Question 6

When viewing mean transit time (MTT) on CT perfusion which color represents normal transit and which represents delayed? How should the infarct core and penumbra appear?

Answer 6

Blue is normal MTT
Orange-yellow is delayed MTT

Infarct core and penumbra are delayed thus orange-yellow

Question 7

What is the fundamental difference in CT angiography and CT perfusion in terms of image acquisition?

Answer 7

Both involve contrast but CTA images the ENTIRE brain over time and CT perfusion images a few slices over time

Question 8

What is the procedural difference in CTA and cerebral angiography?

Answer 8

CTA involves contrast given peripherally
Cerebral angiography involves contrast being given through a catheter fed through the femoral artery and passed up to the region of interest (e.g. aortic arch, ICA, vertebral arteries)

Question 9

What is the gold standard for diagnosis of aneurysms and AVMs?

Answer 9

Cerebral angiography (because if identified then they can be treated interventionally if catheter remains in place)

Question 10

How can you distinguish an A-P view of ICA and lateral view of vertebral artery on cerebral angiography?

Answer 10

A-P ICA will swing lateral to medial

Lateral vertebral will go from anterior to posterior

Question 11

What is the type of cerebral angiography performed when a pre-contrast image is taken?

Answer 11

Digital Subtraction Angiography (DSA)

Question 12

Define fluoroscopy

Answer 12

Multiple X-ray images recorded over time when a contrast bolus is being given (lots of radiation exposure)

Question 13

How do the following appear on T1 weighted MRI?

CSF
Grey matter
White matter

Answer 13

CSF: Dark
Grey matter: Grey
White matter: White

Question 14

How do the following appear on T2 weighted MRI?

CSF
Grey matter
White matter

Answer 14

CSF: Bright
Grey matter: Grey
White matter: Dark

Question 15

Why must you caution the use of gadolinium contrast in patients with renal disease?

Answer 15

Risk of neprhogenic systemic fibrosis

Question 16

A patient presents with head trauma after a welding accident in his shop. You are considering an MRI. What precaution do you take first?

Answer 16

X-ray imaging of head to rule out possibility of metal fragments embedded which can lead to further damage if he received an MRI immediately

Question 17

What are situations when MRI is contraindicated?

Answer 17

Pacemaker, Metal, DBS placed, Non-MRI compatible vascular clips, Foreign bodies, Severe claustrophobia

Question 18

How does ischemia appear on DWI?

Answer 18

Anything with decreased diffusion will appear bright

Question 19

How does ischemia appear on ADC?

Answer 19

Anything with decreased diffusion will appear dark

Question 20

What does diffusion tensor imaging visualize?

What is anisotropy?

Answer 20

• Visualizes direction of water movement

- Anisotropy: directional diffusion of water

Question 21

How does white matter appear on DTI? CSF?

Why are they different?

Answer 21

White matter: Bright
CSF: Dark

Water moves in one direction along axon in WM and thus gives off one signal. In CSF water is moving in all directions so the signals cancel each other out.

Question 22

What is DTI tractography?

Answer 22

Takes individual voxels from DTI and connects them to understand anatomical relationship of WM tracts.

Question 23

What is the difference between MRA and inflow angiography (TOF)?

Answer 23

• MRA uses contrast and is very similar to CTA in scope
• Inflow angiography (Time-of-flight; “TOF”) does NOT use contrast; it is an ordinary MRI with special settings to allow blood to appear brighter to image vasculature