Flow Phenomena

Question 1

What do you mean by phase change?

Answer 1

We can use special sequences in MRI only to only observe the phase of the spins (not magnitude or frequency)

Question 2

What is normal pressure hydrocephalus (NPH)?

Answer 2

an abnormal increase in cerebrospinal fluid within the brain cavities due to a blockage in the flow of CSF

Question 3

What are the steps to scanning the CSF flow?

Answer 3

1. Make sure patient is comfortable (tape the patient’s head to prevent motion if needed)
2. Place the pulse-ox on the patient’s finger
3. Set up traditional scans that you will use later for scouts
4. Set the acquisition window for retro-pulse gating and adjust it to pass the full cardiac cycle
5. If aliasing occurs increase your venc

Question 4

What does a good NPH study result in?

Answer 4

the aqueduct going from white to black in intensity (in phase images)

Question 5

In a NPH study, if you don’t see that the aqueduct is greyish all through the cycle you need to:

Answer 5

drop the venc from 20 to 10 and rescan

Question 6

In a NPH study, if no flow is seen, how do you fix it?

Answer 6

do a sag flow and send the axial (venc-10) and sag flow to PACS

Question 7

What is a third ventriculostomy?

Answer 7

When patients have an obstructed cerebral aqueduct, surgeons make a hole at the bottom of the third ventricle to re-establish the CSF flow

Question 8

What does flow compensation or MGN (magnetic gradient nulling) do?

Answer 8

adds (or modifies) the reading gradient in such a way that the flow related dephasing is cancelled