Pcc Winter Term Physics Unit 1 Flow Compensation

Front 1

What are the 4 types of flow?

Back 1

Laminar
Vortex
Turbulent
Spiral

Front 2

Which type of flow can be compensated for?

Back 2

Laminar (first order laminar flow - because it has a constant velocity)

Front 3

Time of Flight phenomenon - what is it

Back 3

flowing nuclei in the slice do not receive a rephasing pulse by the time they flow out of the slice. this creates a signal void.

Front 4

What parameter affects what type of signal is seen in respect to flow phenomena?

Back 4

TE. A longer TE increases signal void.

Front 5

A longer TE ____ (increases/decreases) signal void.

Back 5

increases.

Front 6

What is entry slice phenomenon (AKA inflow effect)?

Back 6

Nuclei flowing PERPENDICULAR to the slice enter as "fresh", because they were not present during saturation of the surrounding tissue. The signal they produce appear brighter. This is most prominent in the first slice of a stack.

Front 7

As TR increases, entry slice phenomenon ___.

Back 7

Increases

Front 8

As TR decreases, entry slice phenomenon ___.

Back 8

decreases.

Front 9

As slice thickness increases, entry slice phenomenon ___.

Back 9

decreases.

Front 10

As slice thickness decreases, entry slice phenomenon ___.

Back 10

increases.

Front 11

As flow velocity increases, entry slice phenomenon ___.

Back 11

increases.

Front 12

As flow velocity decreases, entry slice phenomenon ___.

Back 12

decreases.

Front 13

Does counter-current flow increase or decrease entry slice phenomenon?

Back 13

Increases.

Front 14

Describe this Flow Compensation type: Even-Echo rephasing. What kind of weighted image is this used in?

Back 14

Used in reducing intra-voxel dephasing in T2 weighted images. The basic principle is that the 2nd echo is a multiple of the first echo (40ms, 80ms, etc). Reduces intravoxel dephasing because flowing nuclei that are out of phase at the first echo are in phase at the second echo as long as the nuclei are given exactly the same amount of time to rephase as they were given to dephase.In other words, if at the first TE of 40ms they were out of phase, 40ms later (at 80ms) they will be in phase again.

Front 15

What is Gradient Moment Rephasing/Nulling (a type of flow compensation technique) most effective on?

Back 15

**This is the MOST effective on 1st order laminar (venous) flow!!!!!***

Front 16

What part of the pulse sequence performs Gradient Moment Nulling?

Back 16

Slice select and/or the readout gradient.

Front 17

What artifact does GMN predominantly reduce?

Back 17

Intra-voxel dephasing.

Front 18

Flowing nuclei in GMN sequences appear ___ (bright/dark)

Back 18

Bright. This is because the signals from the flowing nuclei add constructively to the surrounding vessel wall - the spins are in phase.

Front 19

GMN is most effective on ___ slow/fast laminar flow.

Back 19

Slow laminar flow. This is because the slower flow has a more constant velocity than fast turbulent flow (venous rather than arterial).

Front 20

What are 3 ways to compensate for flow artifacts?

Back 20

1. Even Echo Rephasing
2. Gradient Moment Nulling
3. Spatial Pre-Sat (Chem Sat, and SPIR)

Front 21

What's another term for GMR/GMN?

Back 21

Flow comp

Front 22

What's another term for Chem Sat?

Back 22

Fat Sat

Front 23

What are the 2 types of spatial saturation?

Back 23

Chem sat and Spatial Inversion Recovery (SPIR)

Front 24

Chemical saturation is a type of spatial pre-saturation RF pulse that suppresses ___ and ___.

Back 24

Fat and water.

Front 25

SPIR is a type of spatial pre-saturation RF pulse that can suppress ___.

Back 25

Gadolinium

Front 26

Utilizing a gradient moment nulling technique will do what to your TE?

Back 26

It will increase the TE if it is turned on. It will decrease the TE if turned off.

Front 27

What is the main parameter that gradient moment nulling/rephasing affects?

Back 27

TE

Front 28

Gradient moment nulling is also called ___.

Back 28

Flow Comp

Front 29

Why does using Flow Comp (GMN/GMR) make your scan times longer?

Back 29

It needs more time because there's an extra gradient that is being used. The TE needs to be increased, which increases time.

Front 30

Sat Band is also known as ___

Back 30

REST slabs (spatial pre-saturation). An extra RF pulse is used.

Front 31

Spatial Pre-Saturation is also known as ___ or ___.

Back 31

SAT bands, or REST slabs. An extra RF pulse is used.

Front 32

Fat Sat is also known as

Back 32

Chemical Sat

Front 33

What are the precessional freq. differences between fat and water? What is this called?

Back 33

This difference is called "Chemical Shift"

1.0T = Fat is 147Hz slower than Water
1.5T = Fat is 220Hz slower than Water
3.0T = Fat is 294 Hz slower than water.

Front 34

SPIR (Spatial Inversion Recovery) techniques uses what kind of pulses?

Back 34

Uses a 180 deg pulse instead of a 90 degree pulse.

An RF pulse at the precessional freq. of fat is applied to the imaging volume but inlike chemical pre-saturation this has a magnitude of 180 degrees. A 90 degree pulse is applied after a time TI (corresponding with the null point of fat). This nulls the signal from fat. This technique combines fat sat and inverting mechanisms.

Front 35

STIR sequences rely on what parameter to null signal from fat?

Back 35

They totally rely on T1 recovery time or fat to null signal rather than precessional frequency of fat, like SPIR sequences do - this means they are less susceptible to field inhomogeneities than fat saturated methods like SPIR or chem/fat sat.

Front 36

In ___ (STIR/SPIR), gadolinium may be nulled along with fat.

Back 36

STIR. This is because using gadolinium shortens the T1 of any tissue that "takes up" the contrast, which means gadolinium-enhanced tissues would have shorter T1 times, and would recover longitudinal magnetization faster, so if the echo is later, there will be a signal void..

Front 37

____ (STIR or SPIR) sequences may be used to null the signal from fat by selectively nulling the signal from fat, leaving gadolinium untouched (thereby NOT nulling gadolinium).

Back 37

SPIR. It selectively singles out fat and nulls it.

Front 38

(STIR / SPIR) must NEVER be used post-gad.

Back 38

STIR. The signal from fat isn't singled out and nulled..

Front 39

Which direction does chemical shift happen in (phase or freq?

Back 39

Frequency

Front 40

Does chemical shift vary with different field strengths?

Back 40

YES. As field strength increases, so does the differences in precessional frequences.

1.0T = 110Hz slower than H20
1.5T = 220Hz slower than H20
3.0T = 294Hz slower than H20

Front 41

Co-Current flow appears ___ (dark/bright).

Back 41

Bright. The flowing spins will be excited several times, and so they will have signal. Counter-current flow will not have as much signal, if any.

Front 42

Which of the following increase the entry-slice phenomena?

A. co-current flow
B. thick slices
C. thin slices
D. longer TR
E. counter-current flow
F. A and B only
G. A, C and D only
H. C, D and E only

Back 42

H. C, D and E only

Front 43

True or False: Increasing the TE will result in an increase of signal seen within the vessel.

Back 43

False

Front 44

Gradient Moment Rephasing will produce:
A. white blood
B. black blood

Back 44

A. White blood

Front 45

Spatial Pre-saturation would produce:
Student Response
A. white blood
B. black blood
C. no change in vessel appearance

Back 45

B. Black Blood

Front 46

What is the difference in the precessional frequency between fat versus water at 1.0 T?

Back 46

147 Hz slower

Front 47

What is the difference in the precessional frequency between fat versus water at 1.5 T?

Back 47

220 Hz slower

Front 48

What is the difference in the precessional frequency between fat versus water at 3.0 T?

Back 48

294 Hz slower

Front 49

What is the type of flow that can be affected by compensation techniques?

A. turbulent
B. spiral
C. vortex
D. laminar

Back 49

D. Laminar

Front 50

True or False: The gradient rephasing pulse used in "flow comp" excites the entire body part within the coil.

Back 50

True

Front 51

True or False: The excitation pulse used in forming the image is slice selective.

Back 51

True

Front 52

True or False: A long TR increases the rate of RF pulses which would decrease the magnitude of entry slice phenomena.

Back 52

False. A longer TR increases the magnitude of entry slice phenomena.

Front 53

True or False: A STIR sequence can be used following a Gadolinium injection.

Back 53

False. You may use a SPIR sequence with a T1. Never STIR. It will saturate out the gad because it nulls signal from CSF.

Front 54

True or False: A SAT band placed just outside the medial border of the scan FOV on a coronal shoulder sequence would suppress flow artifacts from venous blood flow.

Back 54

False.

Front 55

True or False: A SAT band placed just outside the superior margin of an axial scan of the abdomen would suppress venous flow artifacts.

Back 55

False

Front 56

True or False: A SAT band placed just outside the inferior margin of an axial scan of the neck would suppress venous flow artifacts.

Back 56

True

Front 57

True or False: A SAT band placed just anterior to the vertebral bodies on a sagittal scan of the C-Spine would suppress arterial flow artifacts and motion artifacts from swallowing.

Back 57

True

Front 58

How does increasing TE affect the type of signal void when considering TOF phenomenon?

Back 58

Increasing TE allows the flowing nuclei that have been excited to exit the slice before the rephasing pulse is applied. This causes a signal void.

Front 59

How do vessels appear in when using "flow comp" - bright or dark?

Back 59

Bright

*remember T2 flow problems when flow comp is not used in peds*

Front 60

How do vessels appear when using "sat pulses" - bright or dark?

Back 60

Dark.

Front 61

Describe spatial pre-saturation

Back 61

Spatial pre-sat bands are placed outside the FOV on tissue, so when the 90 deg pulse is delivered any flowing nuclei is phased. Another 90 deg pulse is applied when the nuclei enters the slice. This saturates the nuclei and creates a signal void.