Physics: Mri (Sequences 2)

Front 1

Spoiled GE acronyms

Back 1

Front 2

What is the effective TE

Back 2

The contrast in fast spin echo is modified in relation to a standard spin echo sequence. As the echoes are received at different echo times, the echoes corresponding to the central k-space lines are the ones that will determine image contrast. The moment at which theses echoes are acquired is called effective TE

Front 3

What limits the echo train length in T1 sequences

Back 3

In T1 weighted sequences, the need to choose a short TR limits echo train length

Front 4

When is fast spin echo commonly used

Back 4

This type of sequence is very commonly used in T2 weighting, namely in pelvic imagery.

Front 5

Why does fast spin echo cause fat to be brighter than standard T2 sequences

Back 5

Within lipid molecules a spin-spin coupling (J coupling) occurs between the atomic nuclei. This coupling shortens relaxation time T2. Fast repetition of 180° pulses in fast spin echo sequences will perturb J coupling, causing fat T2 to lengthen.
Thus, fat has a higher T2 signal in fast spin echo than in standard spin echo, the latter respecting J coupling.

Front 6

What is a delayed interval echo train used for

Back 6

A DIET (Delayed Interval Echo Train) sequence is a fast SE sequence where the delays between 180° pulses are designed to respect J coupling: as a result, the fat maintains an appearance closer to that observed in a standard SE sequence

Front 7

How fast is fast SE sequences

Back 7

fast around 10 seconds

Front 8

Are fast SE susceptible to magnetic susceptibility and magnetic field heterogeneities

Back 8

less than normal T2

Front 9

Why are the parameters (TR, effective TE, echo train length) of fast SE sequences limitied

Back 9

The risk of artifacts and the large quantity of radiofrequency energy deposited by 180° pulses

Front 10

Fast spin echo can be combined with the technique developed for multi-echo sequences to obtain images faster with different contrasts in the same zone of interes

Back 10

yes

Front 11

What are the acronymns for ultrafast SE

Back 11

Front 12

What does a generic diagram of ultrafast spin echo look like

Back 12

Front 13

What is awseme about ultrafast echo sequences

Back 13

The echo train technique can be pushed to the limit to fill the entire Fourier plane with a single 90° pulse

Front 14

How long is TR in ultrafast echosequences

Back 14

as long as is needed

Front 15

Why are ultrafast spin echo sequences sometimes called single shot

Back 15

These so-called « single-shot » sequences require the successive application of as many 180° pulses as there are k-space lines to fill.

Front 16

What is the arrangement of the phase encoding gradients before and after the 180 pulses

Back 16

Front 17

Are the latest echos (ones that create K spaces at the bottom) in an ultrafast spin echo alway acquired

Back 17

no, The sequence can be further accelerated, avoiding the need to register the latest echoes (whose signal is much reduced by T2 relaxation) by partial k-space acquisition

Front 18

How many K space lines are actually aquired in an ultrafast spin echo

Back 18

Just over half the k-space lines are actually acquired

Front 19

How are the remaining K spaces filled in

Back 19

the missing lines are calculated using k-space symmetry properties.

Front 20

What is the consequence of calculating the K space properties in the bottom half

Back 20

increased signal to noise in ultrafast spin echo

Front 21

Are ultrafast spin echo sequences highly T2 weighted

Back 21

yes

Front 22

How long does it take to make a slice with an ultrafast spin echo sequence

Back 22

under 1 second

Front 23

What is effective TE

Back 23

this is when the echos corresponding to the signals that make up the central K space are acquired

Front 24

What is effective TE

Back 24

Front 25

What is TE time

Back 25

(TE) The echo time represents the time in milliseconds between the application of the 90° pulse and the peak of the echo signal in spin echo and inversion recovery pulse sequences.

Front 26

Does ultrafast spin echo sequences image moving body parts well

Back 26

These sequences are well adapted to imaging non-circulating liquid structures appearing as a T2-weighted hypersignal

Front 27

What to areas of the body does a ultrafast spin echo image well

Back 27

cholangio MRI
Uro MRI

Front 28

What is a negative impact of a long echo time

Back 28

The negative impact of very long echo trains is a decay in signal to noise ratio

Front 29

What are two reasons for a decay in the signal to noise ratio

Back 29

weak signal from later echos

very high effective TE

Front 30

Does ultrafast imaging have a low spatial resolution and blurring in the phase encoding direction

Back 30

yes

Front 31

If you see the acrynomn "ss" what are they talking about

Back 31

ultrafast spin echo

Front 32

If you see HASTE what is it

Back 32

ultrafast spin echo

Front 33

What are the acronymns of IR, STIR and FLAIR

Back 33

Front 34

Do all acroynms of IR have the word 'IR' or TIRM

Back 34

yes

Front 35

Do all acryonyms of STIR have the word STIR

Back 35

yes

Front 36

Do all acrynomn of flair have the word flair

Back 36

yes

Front 37

What is the TI

Back 37

between the initial 180 pulse and first 90 RF pulse

Front 38

What is the purpose of the first 180 pulse in inversion recovery

Back 38

The sequence starts with a 180° RF inversion wave which flips longitudinal magnetization Mz in the opposite direction (negative)

Front 39

What occurs after the magnetization is in the negative longitudinal direction

Back 39

Due to longitudinal relaxation, longitudinal magnetization will increase to return to its initial value, passing through null value

Front 40

What is the TI time

Back 40

The delay between the 180° RF inversion wave and the 90° RF excitation wave is referred to as the inversion time TI.

Front 41

What are inversion recovery sequences weighted in

Back 41

T1

Front 42

Does inversion recovery increase the T1 weighting of spin echo

Back 42

yes

Front 43

What types of sequences can an inversion recovery sequence be used

Back 43

Spin Echo and Gradient echo

Front 44

How does inversion recovery work

Back 44

first 180 degree pulse
then once the longitudinal relaxation of the tissue you are trying to null reaches the transverse plane so a 90 pulse occurs

Front 45

What does the 90 degree pulse do

Back 45

flips the protons into the transverse plane

Front 46

What causes the signal in an inversion recovery sequence

Back 46

A second 180 degree pulse at time TE/2 produces an echo at time TE, which is the
detected signal intensity.

Front 47

What is the inversion recovery dependent on T1 or T2 changes

Back 47

The size of the signal obtained with the readout pulse is strongly dependent on the
value of T1 and TI.

Front 48

Important: When does inverstion recovery occur

Back 48

the begining of the sequence

Front 49

After inversion recovery occurs what type of sequence is if followed by

Back 49

Spin echo (standard but sometimes gradient echo)

Front 50

Once all the tissue types are a hit with the 90 pulse which one does not give a signal

Back 50

the one that was already at 90 degrees and therefore did not move.

Front 51

In an inversion recovery are you measuring T1 or T2

Back 51

this is confusing because spin echo is typically a T2 sequence but this is actually T1 since the signal that is being measure is because of longitudinal relaxation

Front 52

What are the 2 ways that a IR sequences is gray scalled

Back 52

Either signal magnitude (amplitude in relation to 0) used for gray scale display: the more absolute the value of the tissue signal (positive or négative), the stronger it will be.
Or the gray levels will be distributed from the negative signal values to the positive values (with a null signal background that will be gray rather than black): this is the « true » display type.

Front 53

In the magnitude type of gray scale what is black

Back 53

where the signal is null

Front 54

In the magnitude type of gray scale what is more gray

Back 54

the higher the magnitude of the signals (negative or positive)

Front 55

What is the other scale

Back 55

gray levels will be distributed from the negative signal values to the positive values (with a null signal background that will be gray rather than black): this is the « true » display type.

Front 56

Is the null gray or black in the true display type

Back 56

gray

Front 57

What is more black in the true display type

Back 57

negative

Front 58

Why cant a null tisue emit a signal

Back 58

absence of transverse magnetization due to the absence of longitudinal magnetization (dont understand just memorize)

Front 59

If a photon undergoes a 180 pulse and is exactly at the transverse plane can it emit a signal if a 90 degree pulse occurs

Back 59

no

Front 60

How do you make a tissue null

Back 60

by adjusting the TI

Front 61

In order to save time can IR sequences be combined with fast spine echo sequences

Back 61

yes

Front 62

What is emphasized in IR sequences

Back 62

IR emphasizes T1 differences, and tissues with short T1 values produce high-in-
tensity signals.