Frequently Asked Questions

1. What is VENC?

a.  Velocity Encoding
b.  Measured in cm/s
c.  A parameter that should be chosen to encompass the highest
    velocities likely to be encountered within the vessel of
    interest.

2. Where is the highest velocity in a blood vessel?

a.  Highest is in the center, lowest is on the outside, along the
    vessel wall

3. How do I know what the VENC on a PC image is?

a.  In ImageJ or Horos: Draw an ROI around a vessel with aliasing
    and the min and max velocity in the ROI is your VENC
b.  Measure velocity of air (black and white dots) to find min and
    max

4. What are the units of velocity?

a.  Distance/Time
b.  Cm/S

5. What are the units of flow?

a.  Volume/Time mL/s

6. What is aliasing?

a.  An instantaneous transition from voxel to voxel where + to -- or
    -- to +, where you don't believe that is happening.
b.  When the peak velocity of flow exceeds the VENC

7. What criteria do I use to judge whether a flow in a vessel is aliased?

a.  By comparing the complex difference and phase images you can see
    where the vessels are in each image. If pixels within the ROI on
    both images are dark but should be light, there is aliasing.

8. What is special about how we record the values?

a.  Magnitude images- Like the years, counted
b.  PHASE image- Like hours, goes around and around

9. What is the average velocity in the tissue and what is it in the background?

a.  Velocity in the tissue (parenchyma):
    i.  Zero
    ii. Looks solid grey (in a phase image)
b.  Velocity in the background (air):
    i.  Velocity here is as high/low as possible
    ii. Looks like black and white static (in a phase image)

10. What is the SD in the image vs the air?

a.  SD, or standard deviation, is how far away from the mean the
    values are

11. What do we expect the velocity to be in a vein vs an artery?

a.  Vein: - (Negative Velocity)
b.  Artery: + (Positive Velocity)

12. What is the use of a complex difference vs phase?

a.  Complex difference image gives the best overall idea of the
    anatomy of the vessel and margins of the ROI
b.  Phase image helps to refine the ROI