Mri Physics Pulse Sequences

Front 1

•Using a very long echo trains
•Fill all lines of K space in one repetition (called single shot)
•Gradients switched so many times – this is called blipping
•This is currently fastest acquisition models in MRI
•Real time imaging, Dynamic imaging, Functional imaging, Diffusion weighted imaging (DWI), Perfusion imaging are based on EPI

THESE DESCRIBE WHICH TYPE OF IMAGING?

Back 1

Echo planar imaging (EPI)

Front 2

•Separating FID and MR signal
•TE is longer than TR
•Rephase is initiated by an RF pulse, than with gradient
•True T2 image

Back 2

Steady state free precession

Front 3

•This sequence should be used when T1 weighted images are required

Back 3

Incoherent gradient echo

Front 4

•SSFP is a steady state sequence that obtains images that have a sufficiently long TE and less T2* when using the steady state than other gradient echo pulse sequences.
TRUE OR FALSE?

Back 4

TRUE

Front 5

•Scan time is reduced
•Centric K space filling
•Use for breath – hold, dynamic imaging after contrast
•Gradient echo sequences do not demonstrate true T2 weighting because:
- the TE is never long enough;
-gradient rephasing is so inefficient, that any echo is dominated by T2* effects.
-

Back 5

Incoherent gradient echo

Front 6

• Gradient spoiling is not as efficient as RF spoiling but T2* weighting can also be achieved. Gradient spoiled sequences are therefore more

Back 6

versatile than RF spoiled sequences.

Front 7

• Gradient spoiling involves

Back 7

applying a gradient that dephases the residual transverse magnetization

Front 8

. RF spoiling applies

Back 8

. RF spoiling applies RF excitation pulses at different phases every TR so that the residual transverse magnetization also has different phase values (and is therefore dephased).

Front 9

tissues with long T2 times are not allowed to dominate image contrast but T1/proton density contrast prevails; this is called

Back 9

spoiling

Front 10

•Variable flip angle (same as coherent)
•The steady state is maintained, so that residual transverse magnetization is left from previous repetitions.
•That transverse magnetization from previous excitation is used
This describes which type of pulse sequence?

Back 10

Incoherent gradient echo

Front 11

•These sequences keep this residual magnetization coherent by process known as rewinding.

Back 11

Coherent gradient echo

Front 12

•T2* used for blood pathologies
-Flow effect volume imaging, hemorrhages, angiographic
Advantage: very fast scan time, breath hold possible, increase sensitivity to flow
Disadvantage: poor SNR
This describes what?

Back 12

Coherent gradient echo T2* (use in GE)

Front 13

These are a result of Coherent gradient echo,

Back 13

•These sequences keep this residual magnetization coherent by process known as rewinding.
•MR signal has FID and MR signal

Front 14

•After the echo any residual transverse magnetization that still remains begins to dephase. The gradient used to phase encode at the beginning of the sequence is then

Back 14

switched on with opposite polarity and the same amplitude to the phase encode.

Front 15

•After the echo any residual transverse magnetization that still remains begins to dephase. The gradient used to phase encode at the beginning of the sequence is then switched on with opposite polarity and the same amplitude to the phase encode.
•This results in the residual transverse magnetization rephasing so that it is always in phase and therefore preserved when the next excitation pulse is applied.
WHAT TYPE OF PS IS THIS?

Back 15

Coherent gradient echo

Front 16

The two main types of gradient echo sequence are called:

Back 16

• • coherent or rewind sequences;
• • incoherent or spoiled sequences.

Front 17

•Gradient echo pulse sequences can generally be categorized according to whether they utilize the steady state
TRUE OR FALSE

Back 17

true

Front 18

•Most gradient echo sequences utilize the steady state because - ? -

Back 18

the TRs are so short that the fastest scan times are achievable.

Front 19

residual transverse magnetization affects ?

Back 19

image contrast.

Front 20

•Because the transverse magnetization does not have time to decay, its magnitude DOES WHAT?

Back 20

accumulates over successive TRs. This residual transverse magnetization therefore affects image contrast.

Front 21

•Steady state –
•The energy “in” equals

Back 21

stable condition
the energy “out”

Front 22

•Steady state – stable condition
•The energy “in” equals the energy “out”
•The NMV does not move between repetition times
•This is a situation when the TR is shorter than both the T1 and T2 relaxation times of all the tissues.
WHICH TYPE OF PS IS THIS/

Back 22

The steady state and echo formation

Front 23

•Tissues with long T2 times (mainly water) appear bright. Most gradient echo sequences utilize the steady state because the 1. __ __ _ ___ ___ ___ that the fastest scan times are achievable
•

Back 23

TRs are so short

Front 24

•Parameters:
•T1
•PD
•T2

Back 24

>45
<20
>20, <45

Front 25

•Parameters:
•T1

Back 25

>45

Front 26

Parameters:
•PD

Back 26

<20

Front 27

ParAmeters:
•T2

Back 27

>20, <45

Front 28

•Gradient echo images are more sensitive to external magnetic field
TRUE OR FALSE

Back 28

TRUE

Front 29

•The longer the TE, the more ?

Back 29

•The longer the TE, the more T2 contrast in the image

Front 30

Echo planar imaging (EPI), • This is currently fastest acquisition models in MRI T or F

Back 30

TRUE

Front 31

Echo planar imaging (EPI)

Back 31

1 • Using a very long echo trains
2 • Fill all lines of K space in one repetition (called single shot)

Front 32

• Gradients switched so many times – this is called 1. _____ and is used in whart type of imaging?

Back 32

1 blipping
2 Echo planar imaging (EPI)