Reviews on TOF, Bright & Dark Blood, etc.

Question 1

What is the Time-of-Flight (TOF) Phenomena used for?

Answer 1

used to visualize desired vascular structures

Question 2

When does the TOF happen?

Answer 2

happens when acquiring normal MRI images.

Question 3

What is the TOF based on the timing of?

Answer 3

pulse sequence
slice thickness
flow’s speed

Question 4

TOF with Spin Echo (SE)

Answer 4

longer time between RF excitation and RF refocusing pulse
flowing protons are not present within the slice for both pulses
vessels appear DARK

Question 5

TOF with Gradient Echo (GRE)

Answer 5

shorter time from RF excitation and gradient rephasing
flowing protons are present within the slice for both pulses
vessels appear BRIGHT

Question 6

What are the 2 parts of a vessel?

Answer 6

vessel wall (endothelium)
lumen (where blood flows)

Question 7

Factors that can alter speed/patterns of blood flow

Answer 7

size
shape
tortuosity of vessel
beating of heart
disease state

Question 8

4 basic blood flow patterns groups

Answer 8

laminar flow
vortex flow
spiral flow
turbulent flow

Question 9

Laminar flow

Answer 9

most common flow, parallel to the vessel wall

Question 10

Does blood flow faster or slower in the center of the vessel?

Answer 10

fast due to less resistance

Question 11

Does blood flow faster or slower to the wall of the vessel?

Answer 11

slower due to friction

Question 12

What happens when vessels are bifurcating?

Answer 12

vessels change in size/direction

Question 13

Vortex flow

Answer 13

stagnant/slow-moving, complex flow
counter-flow

Question 14

Spiral flow

Answer 14

turbulent flow pattern changes velocities randomly/rapidly
most difficult type of flow to image

Question 15

What is Flow-Related Enhancement (FRE)?

Answer 15

a phenomenon in MRI where flowing blood appears bright on an image

Question 16

Why does Flow-Related Enhancement occur?

Answer 16

occurs because the pulse sequence timing allows flowing blood to avoid saturation, while stationary tissues become saturated

Question 17

What is Flow-Related Signal Loss (FRSL)?

Answer 17

FRSL occurs when flowing blood appears dark on an image due to the timing of the pulse sequence

Question 18

What is Time-of-Flight (TOF) MRA?

Answer 18

Produces flow-related enhancement
Can use both 2D and 3D acquisitions
This imaging works best when slices are PERPENDICULAR to the flow of blood

Question 19

What is CE-MRA?

Answer 19

a technique that uses a contrast agent to improve the visibility of blood vessels

Question 20

What is Phase Contrast MRA?

Answer 20

a technique that measures the velocity and direction of blood flow

Question 21

What is Bright Blood MRA?

Answer 21

a type of MRI technique that uses a specific pulse sequence to visualize flowing blood

Question 22

How does Bright Blood MRA work?

Answer 22

by using short TR and TE values, Bright Blood MRA saturates stationary tissues but allows flowing blood to remain unsaturated, making it appear bright on the image

Question 23

2D TOF

Answer 23

ideal for large, slow flow, and the anatomy to be imaged covers a large area
2D TOF, used in carotids, iliac arteries, and femoral arteries
lower SNR

Question 24

3D TOF

Answer 24

ideal for tortuous vessels
fast-moving flow (in the brain)
higher resolution
higher SNR
better for visualizing smaller vessels

Question 25

Spatial Saturation Bands

Answer 25

to minimize venous signal appearing bright on MRAs suppress venous signal

Question 26

MOTSA

Answer 26

multiple Overlapping Thin Slice Acquisition

Question 27

What does MOTSA reduce?

Answer 27

the saturation effect in 3D TOF acquisitions

Question 28

TE (Bright Blood Imaging)

Answer 28

shorter TE = quicker signal is recorded flowing protons receive both RF excitation pulse and refocusing gradient Good for stationary tissues

Question 29

TR (Bright Blood Imaging)

Answer 29

shorter TR = more saturation the flow is low, the flow might be saturated as well

Question 30

reasons for DARK BLOOD on Bright Blood Imaging

Answer 30

changes in flow patterns saturation flow is not perpendicular to imaging plane

Question 31

Dark Blood Imaging

Answer 31

flow-related signal loss using SE, uses both RF excitation and at least 1 RF refocusing pulse

Question 32

3 ways to achieve DARK BLOOD

Answer 32

SE is preferred spatial saturation band placement inversion recovery techniques

Question 33

reasons for BRIGHT BLOOD on Dark Blood Imaging

Answer 33

post-contrast imaging imaging parameters flow being parallel to the imaging plane

Question 34

What happens when the flow is very slow and is exposed to both RF excitation and RF refocusing pulse?

Answer 34

Bright Blood on Dark Blood imaging

Question 35

Timing bolus

Answer 35

injecting a small amount of contrast and seeing how long the contrast takes to arrive at the area of interest this timing is used to set the delay from the administration of contrast to start the image

Question 36

Automatic Bolus Detection

Answer 36

uses a Region of Interest (ROI) placed on the desired part of the anatomy that will track the change in signal intensity

Question 37

Real-time Bolus Tracking

Answer 37

"Fluoro-triggering" A technique that images a specific area of interest in real time Tech can visualize the arrival of contrast to the area of interest

Question 38

Dynamic CE-MRA Acquisition

Answer 38

rapidly and repeatedly imaging the same area of interest over and over again image acquisition and administration start at the same time 4D or time-resolved angio

Question 39

What is the purpose of Flow Encoding Gradients?

Answer 39

to reduce artifacts, image, and even measure the speed of flowing tissues

Question 40

Gradient Moment Nulling

Answer 40

"Flow compensation" a technique used to reduce the artifact from flowing tissues

Question 41

Intra-voxel dephasing

Answer 41

a loss of signal amplitude within a voxel due to flowing blood and stationary tissues being out of phase with one another

Question 42

What is GMN used for?

Answer 42

to reduce intra-voxel dephasing by rephasing the protons within flowing tissues

Question 43

3 gradients for basic GMN implementation

Answer 43

Initial flow encoding gradient (+ polarity) 2nd flow encoding gradient ( - polarity at double strength) 3rd flow encoding gradient (+ polarity)

Question 44

Is flow direction crucial for GMN?

Answer 44

yes

Question 45

Which flow encoding gradient does Phase Contrast enhanced MRA use?

Answer 45

bi-polar flow encoding gradient (two lobes, 1 positive and 1 negative)

Question 46

Where does phase shift happen when the bi-polar gradient is turned on?

Answer 46

1st positive lobe

Question 47

Where do the stationary protons recover the phase shift and go back to where they started?

Answer 47

the negative lobe

Question 48

What doesn't the negative lobe do?

Answer 48

rephrasing the flowing protons

Question 49

What does Phase Contrast Imaging produce?

Answer 49

a difference in signal and phase info. between the stationary and flowing protons

Question 50

What does Phase Contrast Imaging measure?

Answer 50

the speed and direction of protons in flowing tissues, great for visualizing and quantify blood and CSF flow

Question 51

How does PC Imaging correct phase shift from an inhomogeneous field?

Answer 51

a 2nd set of flow-encoding bipolar gradients is applied w/ the same strength but opposite polarity

Question 52

Velocity Encoding (VENC)

Answer 52

the parameter that adjusts phase contrast angiography/venography to image certain blood vessels flowing at a certain speed

Question 53

Which parameter controls the flow encoding gradient?

Answer 53

VENC

Question 54

Low VENC = __________ High VENC = _____________

Answer 54

Low VENC = aliasing High VENC = poor contrast