_____________ contrast parameters are those that cannot be changed because they are inherent to the body's tissue.

21

_____________ contrast parameters are those that can be changed.

21

Some intrinsic contrast parameters are:

22

• T1 recovery time
• T2 decay time
• Proton density
• flow
• apparent diffusion coefficient (ADC)

Some extrinsic contrast parameters are:

22

• TR
• TE
• flip angle
• TI
• turbo factor/echo train length
• b value

A tissue has a high large __________ component of coherent magnetization at time TE.

22

T1 and T2 relaxation depend on three factors:

22-23

• The inherent energy of the tissue
• How closely packed the molecules are
• How well the molecular tumbling rate matches the Larmor frequency of hydrogen.

Generally, the two extremes of contrast in MRI are _______ and _______ .

23

Fat has a high/low inherent energy, slow/fast tumbling rate and can/cannot easily absorb energy into its lattice from hydrogen nuclei.

23-24

Water has a high/low inherent energy, matched/unmatched tumbling rate and can/cannot easily absorb energy into its lattice from hydrogen nuclei.

25

Fat has a short/long T1 and T2 time and appears light/dark on a T2 weighted image. 

24-27

Water has a short/long T1 and T2 time and appears dark on a T1/T2 - weighted image. 

25-26

At 1T, the T1 and T2 times for water is ______ ms.

28

To demonstrate either T1, proton density or T2 contrast, specific values of _____ and _____ are selected for a given pulse sequence.

29

For T1 weighting, the TR must be short/long.

30

For T2 weighting, the TE must be ______.

30

To achieve proton density weighting, the effects of T1 and T2 contrast must be __________ so that proton density weighting can dominate.

30

The TR knob controls the amount of _____ contrast.

31

The TE knob controls the amount of ______ contrast.

31

Turning the TR knob down turns the heat up/down on T1 contrast, meaning the contrast is increased/decreased.

31

Turning the TE knob up turns the heat up/down on T2 contrast, meaning the contrast is increased/decreased.

31

For T1 weighting, turn the heat up/down on T1 and up/down on T2. Both TR and TE should be long/short.

31

For T2 weighting, turn the heat up/down on T1 and up/down on T2. Both TR and TE should be short/long.

31

For PD weighting, turn the heat up/down on T1 and up/down on T2. The TR should be long/short and TE should be long/short.

31

T2* decay is faster than T2 decay because of a combination of two effects:

31-34

• T2 decay itself
• dephasing due to magnetic field inhomogeneities

Whenever the NMV is pushed beyond 90º it is said to be _____________.

33

When the NMV is pushed to a full 180º it is said the be ___________.

33

The ____________ (how far the excitation pulse moves the vectors via resonance) has a significant impact on saturation effects.

34

To measure relaxation times and produce an image with good contrast we need to regenerate the signal. There are two ways to do this:

34-37

• by using an additional 180º RF pulse
• by using gradients

A __________ pulse sequence uses a 180º rephasing pulse to generate an echo.

37

A ____________ pulse sequence uses a gradient to regenerate an echo.

37

______ is the time between each 90º excitation pulse for each slice.

40

______ is the time between the 90º excitation pulse and the peak of the spin echo.

40

The _____ is the time to rephase after the application of the 180º RF pulse and equals the time to dephase when the 90º RF pulse is withdrawn.

40

A spin echo using only one echo can be used to produce a ________ weighted image if a short TR and TE are used.

40

A spin echo using two echoes can be used to produce both __________ and ________ weighted images in the TR time.

42

• proton density
• T2

Typical values of TR and TE:

Long TR -

Short TR -

Long TE -

Short TE -

43

• 2000 ms
• 300-700 ms
• 60 ms+
• 10-25 ms

A ___________ pulse sequence uses an RF excitation pulse that is variable, and therefore flips the NMV through any angle, not just 90º.

46

____________ are generated by coils of wire situated within the bore of the magnet.

47

The ______________ is the center of the bore of the magnet in all planes and remains at the field strength of the magnetic field.

47

The direction of the gradient, i.e. which end is greater than B₀ and which is lower than B₀, is called ________________.

47

When a gradient is switched on, the magnetic field strength along its axis is _______ or ________.

48

As gradients cause nuclei to speed up or slow down, they can be used to either ________ or _________ their magnetic moments.

48

Gradients that dephase are called __________.

49

Gradient echo pulse sequences are usually associated with much longer/shorter scan times than spin echo pulse sequences.

51

The most important disadvantage of gradient echo pulse sequence is that there is no compensation for magnetic field ____________.

51

In gradient echo sequences, the __________ is an extrinsic contrast parameter that is changed to affect image contrast. Its value, combined with the ________ determines whether T1 effects are maximized or minimized.

51

A short _____ produces T1 weighting and never permits a T2 or proton density weighted image to be obtained.

52

To give gradient echo imaging more flexibility, the flip angle is usually reduced to _________.

52

To obtain a T1 weighted image in gradient echo, the differences in the T1 times of the tissues are minimized/maximized and the differences in the T2 times of the tissues are minimized/maximized.

52

To obtain a T2* weighted image in gradient echo, the differences in the T2* times of the tissues are minimized/maximized and the differences in the T1 times are minimized/maximized.

52

To obtain a proton density weighted image in gradient echo, both T1 and T2* processes are minimized/maximized so that the differences in proton density of the tissues can be demonstrated.

52

For T1 weighting using gradient echo, turn the heat up/down on T1 and the heat up/down on T2*.

54

To turn the heat up on T1 contrast using gradient echo, the TR is short/long and the flip angle is low/high.

54

To turn the heat down on T2* using gradient echo, the TE is short/long.

54

For T2* weighting using gradient echo, turn the heat up/down on T2* and the heat up/down on T1.

54

To turn the heat up on T2* using gradient echo, the TE is short/long.

54

To turn the heat down on T1 contrast using gradient echo, the TR is short/long and the flip angle is low/high.

54

For proton density weighting using gradient echo, turn the heat up/down on T1 and the heat up/down on T2*.

54

Typical values in gradient echo imaging:

Long TR -

Short TR -

Short TE -

Long TE -

Low flip angles -

Large flip angles -

56

• 100 ms+
• less than 50 ms
• 1-5 ms
• 15-25 ms
• 5-20º
• 70º +