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MRI Physics 2 > Reviews on TOF, Bright & Dark Blood, etc. > Flashcards

Reviews on TOF, Bright & Dark Blood, etc. Flashcards

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1
Q

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

A

used to visualize desired vascular structures

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2
Q

When does the TOF happen?

A

happens when acquiring normal MRI images.

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3
Q

What is the TOF based on the timing of?

A

pulse sequence
slice thickness
flow’s speed

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4
Q

TOF with Spin Echo (SE)

A

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

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5
Q

TOF with Gradient Echo (GRE)

A

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

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6
Q

What are the 2 parts of a vessel?

A

vessel wall (endothelium)
lumen (where blood flows)

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7
Q

Factors that can alter speed/patterns of blood flow

A

size
shape
tortuosity of vessel
beating of heart
disease state

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8
Q

4 basic blood flow patterns groups

A

laminar flow
vortex flow
spiral flow
turbulent flow

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9
Q

Laminar flow

A

most common flow, parallel to the vessel wall

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10
Q

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

A

fast due to less resistance

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11
Q

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

A

slower due to friction

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12
Q

What happens when vessels are bifurcating?

A

vessels change in size/direction

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13
Q

Vortex flow

A

stagnant/slow-moving, complex flow
counter-flow

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14
Q

Spiral flow

A

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

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15
Q

What is Flow-Related Enhancement (FRE)?

A

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

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16
Q

Why does Flow-Related Enhancement occur?

A

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

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17
Q

What is Flow-Related Signal Loss (FRSL)?

A

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

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18
Q

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

A

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

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19
Q

What is CE-MRA?

A

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

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20
Q

What is Phase Contrast MRA?

A

a technique that measures the velocity and direction of blood flow

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21
Q

What is Bright Blood MRA?

A

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

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22
Q

How does Bright Blood MRA work?

A

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

23
Q

2D TOF

A

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

24
Q

3D TOF

A

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

25
Q

Spatial Saturation Bands

A

to minimize venous signal appearing bright on MRAs
suppress venous signal

26
Q

MOTSA

A

multiple Overlapping Thin Slice Acquisition

27
Q

What does MOTSA reduce?

A

the saturation effect in 3D TOF acquisitions

28
Q

TE (Bright Blood Imaging)

A

shorter TE = quicker signal is recorded

flowing protons receive both RF excitation pulse and refocusing gradient
Good for stationary tissues

29
Q

TR (Bright Blood Imaging)

A

shorter TR = more saturation

the flow is low, the flow might be saturated as well

30
Q

reasons for DARK BLOOD on Bright Blood Imaging

A

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

31
Q

Dark Blood Imaging

A

flow-related signal loss

using SE, uses both RF excitation and at least 1 RF refocusing pulse

32
Q

3 ways to achieve DARK BLOOD

A

SE is preferred
spatial saturation band placement
inversion recovery techniques

33
Q

reasons for BRIGHT BLOOD on Dark Blood Imaging

A

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

34
Q

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

A

Bright Blood on Dark Blood imaging

35
Q

Timing bolus

A

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

36
Q

Automatic Bolus Detection

A

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

37
Q

Real-time Bolus Tracking

A

“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

38
Q

Dynamic CE-MRA Acquisition

A

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

39
Q

What is the purpose of Flow Encoding Gradients?

A

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

40
Q

Gradient Moment Nulling

A

“Flow compensation”

a technique used to reduce the artifact from flowing tissues

41
Q

Intra-voxel dephasing

A

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

42
Q

What is GMN used for?

A

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

43
Q

3 gradients for basic GMN implementation

A

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

44
Q

Is flow direction crucial for GMN?

A

yes

45
Q

Which flow encoding gradient does Phase Contrast enhanced MRA use?

A

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

46
Q

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

A

1st positive lobe

47
Q

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

A

the negative lobe

48
Q

What doesn’t the negative lobe do?

A

rephrasing the flowing protons

49
Q

What does Phase Contrast Imaging produce?

A

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

50
Q

What does Phase Contrast Imaging measure?

A

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

51
Q

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

A

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

52
Q

Velocity Encoding (VENC)

A

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

53
Q

Which parameter controls the flow encoding gradient?

A

VENC

54
Q

Low VENC = __________
High VENC = _____________

A

Low VENC = aliasing
High VENC = poor contrast

MRI Physics 2 (3 decks)

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