Ch.5 Spin Echo Pulse Sequences

Front 1

Pulse sequences enable us to control?

Back 1

The way in which the system applies pulses and gradients.

Front 2

Definition of pulse sequences is?

Back 2

A series of RF pulses, gradient applications and intervening time periods.

Front 3

Examples of Spin echo pulse sequences are?

(spins are rephased by 180 degree rephasing pulse)

Back 3

- Conventional spin echo

- Fast or turbo spin echo

- Inversion recovery

Front 4

Examples of gradient echo pulse sequences are?

(spins are rephased by a gradient)

Back 4

- Coherent gradient echo

- Incoherent ''

- Steady state free precession

- Balanced gradient echo

- Fast gradient echo

- echo planar imaging

Front 5

RECAP: spin echo uses a 90 degree excitation pulse followed by?

Back 5

One or more 180 degree rephasing pulses to generate a spin echo.

Front 6

If only one echo is generated what kind of image is produced?

Back 6

T1 weighted image using a short TR and TE.

Front 7

For T2 weighted image, two __ rephasing pulses, generating two spin echoes are applied.

Back 7

RF

Front 8

What kind of pathology are T2 images useful for identifying?

Back 8

Tissues that are diseased and generally more edematous and/or vascular. Because they have increased water content and consequently have a high signal on T2 imaging and can therefore be more easily identified.

Front 9

Fast or turbo spin echo reduces scan time how?

Back 9

By performing more than one phase encoding step subsequently filling more than one line of K space per TR.

Front 10

How is this achieved?

(question 9)

Back 10

Achieved by using several 180 degree rephasing pulses to produce a train of echoes or echo train.

Front 11

Conventional spin echo is?

Back 11

A 90 degree excitation pulse id followed by 180 degree rephasing pulse. Only one phase encoding step is applied per TR on each slice. Therefore only 1 line of K space is filled per TR.

Front 12

Each echo is used to produce a separate image

T or F

Back 12

True - usually proton density and T2

Front 13

Definition of Turbo factor or Echo train length?

Back 13

Number of 180 degree rephasing pulses performed per TR corresponds to the number of echoes produced and the number of lines of K space filled.

Front 14

In conventional spin echo 256 phase matrix means?

(assuming 1 NEX has been selected)

Back 14

256 phase encodings must be applied.

256 TR times elapse to complete the scan.

Front 15

In fast spin echo using the same parameters but selecting a TF of 16 means?

Back 15

16 phase encoding steps are performed every TR. scan time is reduced to 1/16 of the original.

Front 16

Effective TE

Back 16

TE is at which operator wishes to weight image. Phase encoding steps so that steep or shallow slopes are applied to various echoes produced.

Front 17

Shallow phase encoding slopes result in an echo that has?

Back 17

Maximum signal amplitude.

Front 18

Shallow slopes are centered over the effective TE. True or False?

Back 18

True - produce max signal

Front 19

Steep slopes produce much smaller amplitude and are placed away from effective TE. True or False?

Back 19

True

Front 20

Data collected around effective TE have more impact on image contrast as they fill the __ __ of K space.

Back 20

Central lines

Front 21

Data from the wrong weighting(other TEs) much less effect of contrast and they fill __ __ of K space.

Back 21

Outer lines

Front 22

Some negative affects of fast spin echo can be?

(one example, others on pg.146)

Back 22

Due to the closely spaced 180 degree pulses - fat remains bright on T2.

Front 23

Advantage of fast spin echo with metal artefacts is?

Back 23

The repeated 180 degree RF pulses compensate for field inhomogeneity.

Front 24

Advantages of fast or turbo spin echo sequences?

Back 24

- Scan times greatly reduced

- high-res matrices and multiple NEX can be used.

- increased T2 information

Front 25

Disadvantages of fast or turbo spin echo sequences?

Back 25

- Some flow and motion affects increased

- Fat bright on T2 weighted imaging

- Image blurring with very long echo trains

Front 26

Single shot fast spin echo (SS-FSE)

Back 26

Technique where all the lines of K space are acquired in one TR.

- half of lines are acquired in one TR the other half is transposed.

Front 27

A couple disadvantages of SS-FSE?

Back 27

SNR penalty, SAR significantly increased - reduction in number of slices.

Front 28

DRIVE, RESTORE or FR-FSE is?

Back 28

Reverse flip angle excitation pulse is applied at the end of the echo train. Drives any transverse mag into longitudinal plane.

Front 29

DRIVE therefore gives a high signal to?

Back 29

Increase signal intensity in fluid based structures like CSF.

Front 30

IR (inversion recovery) is?

Back 30

Sequence begins with a 180 inverting pulse. inverts NMV into full saturation, then a 90 excitation pulse is applied known as TI (time inversion) resultant FID is then rephased by a 180 pulse to produce a spin echo at time TE.

Front 31

IR imaging is weighted how?

Back 31

contrast of imaging depends primarily on the length of the TI. If 90 excitation pulse is applied after transverse recovery- heavily T1 weighted- large contrast difference between fat and water.

Front 32

IR weighted imaging if 90 excitation pulse is applied when NMV reaches full recovery?

Back 32

PD weighted image, as both fat and water have fully relaxed.

Front 33

IR is different form conventional spin echo in what way?

Back 33

Tissues begin recovery from full saturation as opposed to the transverse plane.

Front 34

Is IR sequences good for GAD contrast?

Front 35

IR advantages and disadvantages?

Back 35

- Very good SNR as TR is long

- Excellent T1 contrast

- Long scan times unless used in conjunction with FSE

Front 36

Fast inversion recovery is?

Back 36

180 inverting pulse is followed after the TI time by the 90 excitation pulse and the train of 180 pulses to fill multiple lines of K space as in FSE.

Front 37

Fast inversion recovery is usually used to...?

Back 37

Suppress signal from certain tissues in conjunction with T2 weighting so that water and pathology return a high signal. (STIR and FLAIR)

Front 38

STIR (short tau inversion recovery) is?

Back 38

Time it takes fat to recover from full inversion to the transverse plane so that there is no longitudinal mag corresponding to fat. This is called the null point.

Front 39

Is STIR sequences good with GAD?

Back 39

Should not be used in conjunction with GAD, which shortens T1 times enhancing tissues, making them bright. T1 times of these stuctures are shortened so they approach the T1 time of fat. Therefore in STIR enhancing tissue may be nulled.

Front 40

STIR uses?

Back 40

...Msk bone marrow. Suppresses fat to see lesions in these areas...

Front 41

FLAIR (fluid attenuated inversion recovery) is?

Back 41

Is selecting a TI corresponding to the time of recovery of CSF from 180 to the transverse plane nulls the signal from CSF.

Front 42

FLAIR uses?

Back 42

Suppresses the high CSF signal in T2 weighted images so that pathology adjacent to CSF is seen more clearly. (used a lot in brain and spine)

Front 43

FLAIR especially useful in visualizing..?

Back 43

Multiple sclerosis plaques, acute sub-arachnoid hemorrhage, and meningitis.

Can also be used to select TI time of that corresponds to the null point of white matter in brain to look for abnormalities.

Front 44

IR prep sequences are?

Back 44

Useful in cardiac imaging. black blood- IR prep begins with two 180 inverting sequences which completely nulls the signal in blood, useful when looking at morphology of heart and great vessels.