Physics In Mri, Week 5, Chapt 5, Pulse Sequences,mri Tech Class

Front 1

Pulse sequences can generally be categorized as

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1. Spin echo pulse sequences (spins are rephased by a 180 degree rephasing pulse):

2. Gradient echo pulse sequences (spins are rephased by a gradient):

Front 2

Spin echo pulse sequences (spins are rephased by a 180 degree rephasing pulse):

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Conventional spin echo
Fast or turbo spin echo
Inversion recovery

Front 3

Gradient echo pulse sequences (spins are rephased by a gradient):

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Coherent gradient echo
Incoherent gradient echo
Steady state free precession
Balanced gradient echo
Fast gradient echo
Echo planar imaging

Front 4

Conventional spin echo pulse sequences are used to produce

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T1, T2 or proton density weighted images and are one of the most basic pulse sequences used in MRI.

Front 5

In a spin echo pulse sequence there is a 90° excitation pulse followed by

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a 180° rephasing pulse followed by an echo

Front 6

After the application of the 90° RF pulse, spins lose

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precessional coherence because of an increase or decrease in their precessional frequency caused by the magnetic field inhomogeneities.

Front 7

The NMV decays in the transverse plane

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and the ability to generate a signal is lost.

Front 8

After the application of the 90° RF pulse, spins lose

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precessional coherence because of an increase or decrease in their precessional frequency caused by the magnetic field inhomogeneities.

Front 9

A180° RF pulse flips the

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dephased nuclei through 180°. The fast edge is now behind the slow edge

Front 10

The NMV decays in the transverse plane

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and the ability to generate a signal is lost.

Front 11

A180° RF pulse flips the

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dephased nuclei through 180°. The fast edge is now behind the slow edge

Front 12

A180° RF pulse flips the dephased nuclei through 180°. The fast edge is now behind the slow edge
The fast edge eventually catches up with the slow edge reforming the NMV. This is called

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rephasing.

Front 13

A180° RF pulse flips the dephased nuclei through 180°. The fast edge is now behind the slow edge
The fast edge eventually catches up with the slow edge reforming the NMV. This is called

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rephasing.

Front 14

The signal in the receiver coil is regenerated and can be measured. This regenerated signal is called an echo and, because an RF pulse has been used to generate it, it is specifically called

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a spin echo.

Front 15

The signal in the receiver coil is regenerated and can be measured. This regenerated signal is called an echo and, because an RF pulse has been used to generate it, it is specifically called

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a spin echo.

Front 16

A single spin echo pulse consists of a single 180° RF pulse applied after the excitation pulse to produce a single spin echo.
1. The TR is the length of time from
2. The TE is the length of time from

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1. one 90° RF pulse to the next 90° RF pulse.

2. the 90° RF pulse that begins the pattern to the mid-point or peak of the signal generated after the 180° RF pulse, i.e. the spin echo.

Front 17

Spin echo sequences are still considered the gold standard in that the contrast they produce is

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understood and is predictable.

Front 18

Spin echo sequences produce T1, T2 and PD weighted images of good quality and may be used in any part of the body for any indication.

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TRUE

Front 19

Advantages OF SPIN ECHO SEQUENCES ?

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Good image quality
Very versatile
True T2 weighting
Available on all systems
Gold standard for image contrast and weighting

Front 20

Disadvantages OF SPIN ECHO SEQUENCES ?

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Long scan times

Front 21

a much faster version of conventional spin echo.

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Fast spin echo (FSE)

Front 22

In spin echo sequences, one phase encoding only is performed during each TR
In fast spin echo what is different?

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more than one phase encoding is performed per TR, reducing the scan time.

Front 23

FSE employs a train of 180° rephasing pulses, each one producing

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a spin echo

Front 24

This train of spin echoes is called

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an echo train.

Front 25

The number of 180° RF pulses and resultant echoes is called the

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echo train length (ETL) or turbo factor.

Front 26

The spacing between each echo is called the

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echo spacing.

Front 27

In FSE , after each 1._______, a phase encoding step is performed and data from the resultant echo are stored in K space.

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1. rephasing

Front 28

In FSE, several lines of K space are filled every TR instead of one line as in conventional spin echo.what is the result?

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As K space is filled more rapidly, the scan time decreases.

Front 29

Typically __,__,__ or __ 180° RF pulses are applied during every TR.

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2, 4, 8 or 16,

Front 30

Typically 2, 4, 8 or 16, 180° RF pulses are applied during every TR. As 2, 4, 8 or 16 phase encodings are also performed during each TR, the scan time is reduced to __, __, __, or
__ of the original scan time.

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1/2, 1/4, 1/8 or 1/16

Front 31

The higher the turbo factor the -?

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shorter the scan time

Front 32

Each echo has a different TE and data from each echo are used to produce one image
. T or F

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True

Front 33

Each echo has a different TE and data from each echo are used to produce one image
And therefore data collected from them have variable weighting T or F

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True

Front 34

In any sequence, each phase encoding step applies a different - ?

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slope of phase gradient to phase shift each slice by a different amount. This ensures data are placed in a different line of K space.

Front 35

When the TE is selected the resultant image must have a weighting corresponding to that TE, i.e. if the TE is set at 102 ms a T2 weighted image is obtained (assuming the TR is long)
1. .T or F and
2. what is this known as?

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True
(known as the effective TE in FSE sequences)

Front 36

FSE produces T1, T2 or proton density scans in a fraction of the time of CSE. Because the scan times are reduced, 1. ____ ____ can be increased to improve spatial resolution.

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1.matrix size

Front 37

FSE is usually used for -?anatony-?

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brains, spines, joints, extremities and the pelvis

Front 38

Two contrast differences between spin echo and fast spin echo:
1.
2.

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1.Fat remains bright on T2 weighted image due to the multiple RF pulses (reduce the effect of spin – spin interaction in fat) it is known as
J Coupling
2. The repeated 180 pulses can increase magnetization transfer effect so that muscles, for example appears darker

Front 39

What may occur at the edges of tissues with different T2 decay values?

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Image blurring

Front 40

Image blurring may occur at the edges of tissues with different T2 decay values
Because each line of K space filled during an echo train contains data from echoes with different TE. T or F

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True

Front 41

Sast or Turbo spin Echo Advantages are:

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Short scan times
High resolution imaging
Increased T2 weighting
Magnetic susceptibility
decreases*
* This can be a disadvantage as well as an advantage, e.g. haemorrhag

Front 42

Disadvantages of Fast or Turbo Spin Echo:

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Some flow artefacts increased
Incompatible with some imaging options
Some contrast interpretation problems
Image blurring possible

Front 43

Single shot fast spin echo (SS-FSE) ;
1.
2.
3.
4.

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All lines of K space are acquired at one TR
Combines a partial Fourier technique with fast spin echo
SNR poor
SAR increased

Front 44

Driven equilibrium Fourier transform = ?

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Modification of FSE

Reverse flip angle is applied at the end of echo train
Drives any transverse magnetization into longitudinal plane – get magnetization ready for next 90 excitation pulse
- Increased signal intensity in fluid based structures

Front 45

Some manufactures call : DRIVE,

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RESTORE or FR – FSE

Front 46

Inversion recovery (IR)

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Inversion recovery is a spin echo sequence that begins with a 180° inverting pulse .

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Inversion recovery is a spin echo sequence that begins with a 180° inverting pulse . This inverts the NMV through 180°. The TR is the time between successive 180° inverting pulses.T or F

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TRUE

Front 48

Inversion recovery is a spin echo sequence that begins with a 180° inverting pulse . Tor F

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True

Front 49

Inversion recovery is a spin echo sequence that begins with a 1 ___ inverting pulse . This inverts the NMV through 2 __. When the pulse is removed the NMV begins to relax back to B0. A3 __ pulse is then applied at time interval TI (time from inversion) after the 180° inverting pulse.
A further 4. __ RF pulse is applied which rephases spins in the transverse plane and produces an echo at time TE after the excitation pulse

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1. 180' 2. 180' 3. 90' 4. 180°

Front 50

What is the main factor that controls weighting in IR sequences.

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The TI (time from inversion)

Front 51

The 1.__ controls the amount of T2 decay. For T1 weighting it must be 2____. for T2 weighting, 3. ___.
The 4.__ must always be long enough to allow full longitudinal recovery of magnetization before each inverting pulse.

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1.TE
2.short
3.long
4.TR

Front 52

Fast inversion recovery is?

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Fast inversion recovery is a combination of inversion recovery and fast spin echo.

Front 53

Fast inversion recovery is a combination of inversion recovery and fast spin echo.
Multiple 180° rephasing pulses are applied to produce multiple echoes which are phase encoded with a different slope of gradient.
TI allows suppression of signal from various tissue types.

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True

Front 54

Short TAU Inversion recovery (STIR) is ?

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STIR (short TI inversion recovery) uses short TIs such as 100– 180 ms, depending on field strength
TIs of this magnitude place the 90° excitation pulse at the time that NMV of fat is passing exactly through the transverse plane. At this point (called the null point) there is no longitudinal component in fat.In this way a fat suppressed image results. The TI required to null the signal from the tissue is 0.69 times its T1 relaxation time

Front 55

Different tissue have different T1 relaxation times: T or F

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True

Front 56

FLAIR stands for ?

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(fluid attenuated inversion recovery)

Front 57

The TI required to null the signal from the tissue is - ? -

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0.69 times its T1 relaxation time

Front 58

which type of pulse sequence uses long TIs such as 1700–2200 ms, depending on field strength, to null the signal from CSF in exactly the same way as the STIR sequence .

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FLAIR (fluid attenuated inversion recovery)

Front 59

Because CSF has a long T1 recovery time, the ___ must be longer to correspond with its null point.

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TI

Front 60

90' - 180' - 90'

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Single Spin Echo pulse sequence

Front 61

90' - 180' - 180' - 90' ETL

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Fast Spin Echo

Front 62

90 180 180 R-90 90 ETL

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Drive

Front 63

Two contrast differences between spin echo and fast spin echo:
1. Fat remains bright on T2 weighted image due to the multiple RF pulses (reduce the effect of spin – spin interaction in fat) it is known as ?

Back 63

J Coupling

Front 64

Two contrast differences between spin echo and fast spin echo:
1. Fat remains bright on T2 weighted image due to the multiple RF pulses (reduce the effect of spin – spin interaction in fat) it is known as
J Coupling
2. The repeated 180 pulses can A).___ ____ ____ ____ so that muscles, for example B). ____ ______.

Back 64

1. increase magnetization transfer effect
2.appears darker