Chapter 6 Questions

Front 1

Some MRI systems have pulse sequences which utilize flow compensation only along the readout direction or only along the slice direction. If transverse images of the knee are being acquired with a pulse sequence which allows flow compensation in only one direction, in which direction is the flow compensation best applied to reduce motion artifacts from the popliteal artery?

Back 1

In the slice direction
*Although motion atifacts are always displayed in the phase direction,motion COMPENSATION must be applied in the direction of the motion, regardless of the phase direction.

Front 2

Consider a hypothetical study in which a set of images is acquired perpendicular to a vessel with normal flow. Which of the diagrams below depicts the correct appearance of the image and resulting flow artifact if the phase direction of the image is from left to right.

Back 2

B

Hint 2

Front 3

Which of the following is TRUE regarding spectral fat saturation?
1. It increases the SAR of the sequence
2. The homogeneity of the magnet affects the degree and uniformity of fat suppression.
3. The mechanism by which it works relies by which it works relies upon the short T1 relaxation time of fat

Back 3

1. It increases the SAR of the sequence
2. The homogeneitty of the magnet affects the degree and uniformity of fat suppression

Front 4

In an image which does NOT employ flow compensation, which of the following explains the reason for a dark signal in a vessel with normal flow?

Back 4

The signal from the protons in blood is mismapped along the phase encoding direction of the image.

Front 5

Which of the following statements about motion artifact control techniques is FALSE regarding their application to MR angiography?

Back 5

Motion artifact control techniques are not generally used with MR angiography

Front 6

Which of the following statements are TRUE about MR angiography?

Back 6

1. Saturation pulses are often selected to eliminate the venous flow when studying arterial flow.

2. Spectral fat saturation is useful in time of flight angiography in order to reduce the signal of fatty structures and esure that the vascular structures maintain the brightest signal.

3. Gradient moment nulling is applied to time of flight angiography sequences in order to rephase the moving proton's signals and make the flowing blood appear bright.

Front 7

If gradient moment nulling is applied only along the slice direction of a transverse set of brain images, which physical gradient must use extra pulses?

Back 7

Along the Z gradient

Front 8

When gradient moment nulling is added to a pulse sequence and all other parameters are unchanged, the:

Back 8

*With the application of the additional gradient pulses, the shortest possible TE is lengthened compared to other sequences that are not using gradient moment nulling. In short, echo time is increase.

Hint 8

Gradient moment nulling involves additional gradient pulses in order to rephase the phase errors that occur as the protons move during the course of the pulse sequence measurement.

Front 9

Which of the following is TRUE regarding an ECG triggered sequence?

Back 9

ECG triggering will not remove the respiratory artifact on sagittal lumbar spine images.

Front 10

A pulse sequence with a given set of parameters allows a maximum of 20 slices. If 2 saturation pulses are then added, the:

Back 10

Maximum number of slices would decrease

*The application of two saturation pulses will decrease the amount of time available to collect echoes from each slice. The result is that fewer slices can be imaged when applying saturation pulses.

Front 11

If we also want to rephase the signal from protons that have a more complex motion, extra _________ must be added to the standard gradient moment nulling gradient waveform which rephases the signal from protons with a constant velocity.

Back 11

Gradien pulses

Front 12

If a coronal saturationn region is placed anterior to the cervical spine to eliminate motion artifacts from swallowing, which gradient must be turned on during the transmission of the initial saturation 90 degree RF pulse?

Back 12

y- gradient

Front 13

If two saturation regions are applied to a dual contrast fast spin echo study of the lumbar spine, how many 90 degree pulses are applied during a single repetition, for a given slice?

Back 13

2

*Each saturation pulse normally consists of a single 90 degree RF pulse applied simultaneously wiht a gradient which selects the saturation region.

Front 14

The addition of which of the following motion compensation techniques increases the specific absorption rate of the sequence?

Back 14

Saturation pulse

Front 15

The SAR determines what?

Back 15

The maximum amount of energy allowed to be transmitted into the patient before excessive heating of the tissues occurs.

Front 16

Flow compensation adds gradient pulses to rephase the signal of protons, but it ________ ________ add RF energy to the sequence.

Back 16

Does not

Front 17

Does respiratory gating add RF energy to the saturation pulse?

Back 17

No

Front 18

Which of the following would be ineffective at reducing motion artifacts created by blood flowing through the sagittal sinus?
A. Fat saturation
B. Saturation pulses
C. Flow compensation
D. ECG triggering

Back 18

A. fat saturation

Front 19

In which direction must the artifact from motion appear in an image?

Back 19

Phase direction

Front 20

What is the result of the following gradient echo sequences with two perfectly overlapping saturation regions placed in a coronal orientation anterior to sagittaly slices in the cervical spine: 90 degree - spoiler- 90 degree - spoiler - 45 degree echo?

Back 20

Sagittal gradient echo images with a single dark region anterior to the spine, in the area of overlapping saturation pulses.

*Perfectly overlapping saturation regions result in a final saturation region which is equal to the thickness of one of the saturation regions.

Front 21

T/F? : A sequence with gradient moment nulling only rephases moving protons, not stationary protons.

Back 21

False

*In basic sequences that does not feature flow compenstion, only stationary protons will rephase. Flow compensation applies additional gradient pulses to the basic spin echo pulsing scheme and is required in order to rephase moving protons. (Both moving and stationary protons are rephased)

Front 22

In what orientation and position should a saturation region be located in order to eliminate carotid blood flow from transverse images of the cervical spine?

Back 22

Transverse, inferior to the region of interest

Hint 22

In transverse image the blood flow of the carotids is inferiorly.

Front 23

Which of the following techniques has no effect upon scan time?
A. Respiratory triggering
B. Respiratory gating
C. Respiratory compensation
D. the scan time of all three techniques is the same and the patient is dependent

Back 23

Respiratory compensation

*Respiratory compensation does not significantly alter the scan time since it only involves the manipulation of the phase encoding step applie to each echo as it is recorded and reordered in the raw data during the respiratory cylce.

Front 24

T/F? : Respiratory compensation reorders the filling of the rawdata?

Back 24

True

Front 25

The spoiler after a 90 degree saturation pulse __________________ magnetization.

Back 25

Dephases the transverse

The spoiler ensures that the saturation pulse suppresses signal from the protons in the saturation region.

Front 26

Which of the following is a reason that a positive gradient followed by a negative gradient yields a net phase if the protons are moving?

1. The effect of a positive gradient is not equal and opposite to the effect of a negative gradient pulse because the protons are moving.
2. Moving protons will always have a net phase, regardless of the type of gradient pulses applied.
3. Equal and opposite gradient pulses only cancel when separated by a 180 degree RF pulse.

Back 26

# 1 only

*This is because the protons are MOVING. If they were stationary, then the rule will apply that if an equal and opposite gradient is applied then the gradient will be zeroed out.

Front 27

Which of the following logical gradients is not balanced for phase prior to collecting the echo?

A. Readout gradient
B. Slice select gradient
C. Phase gradient
D. All three gradients

Back 27

C. Phase gradient

*Only the gradient whose purpose is specifically to encode phases into the echoes is not balanced for phase before the echo is recorded.

Front 28

What should the thickness of a saturation be?

Back 28

Large enough to cover the region of the anatomy generating motion.

Front 29

Which of the following is a measure of thre amount of RF energy allowed to be transmitted per kilogram of a patient's body weight?
A. transmitter bandwidth
B. Specific absorption rate
C. Duty cycle
D. Receiver bandwidth

Back 29

B. Specific absorption rate

Front 30

If the THICKNESS of a single saturation region is doubled, the specific absorption rate will:

Back 30

Be unaffected

Front 31

If a saturation pulse is applied as shown in the diagram below, of the following is the result of the image from the depicted slice?

Back 31

Venous flow will appear dark

Front 32

Which of the following is TRUE regarding physiological triggering?1. Once the physiological occurance triggers the start of the acquisition, echoes are collected until the TR is completed.2. It synchronizes the pulse sequence to even an irregular physicological cycle.3. It synchronizes the pulse sequence to a multiple of the TE period.

Back 32

#1

Front 33

Which of the following motion artifact control techniques is the most effective at suppressing cardiac motion?A. respiratory compensationB. ECG triggeringC. Fat saturationD. Flow compensation

Back 33

B. ECG triggering

Front 34

Which of the following types of image contrast can be achieved when using spectral fat saturation?1. T1 weighted2. T2 weighted3. Proton Density

Back 34

D. 1, 2 and 3

Front 35

The definition of spectrally selective, as it relates to fat suppression, is selecting the magnetization of protons by its range of:

Back 35

Resonant frequencies

Front 36

When performing a cardiac study during a specific phase of the cardiac cycle, which of the following should be used?A. Pulse triggeringB. Pulse gatingC. ECG gating

Back 36

ECG gating

Front 37

In a gadolinium-enhanced brain study, which of following is the most appropriate technique for reducing fat signal?

Back 37

Spectral fat saturation

Front 38

What is the effect of the extra gradient pulses of a flow compensated pulse sequence for rephasing the signal of protons with a complex motion compared to a flow compensated sequence for rephasing the signal of protons with a constant velocity?

Back 38

The TE will increase*The effect of the additional gradient pulses required to compensate the more complex motion is that the mimimum allowable TE will increase in order to accommodate all of the gradient pulses into the sequence timing.

Front 39

The inversion time that will best null the fat signal on a 0.2T MRI system when running a spectrally selective fat suppressed inversion recovery sequence (the T1 relaxation time of fat is approximately 240ms at 0.2T) is _____ ms.

Back 39

166*The time after the initial 180 degree RF inversion pulse that this zero crossing occurs is equal to 0.693 times the T1 time of the tissue. For a tissue with a T1 of 240 msec the T1 required to put fat at the zero crossing= 0.693 x 240 msec.

Front 40

If two saturation regions are applied during a dual contrast fast spin echo study of the lumbar spine with an echo train length of 4, how many 90 degree RF pulses ar applied during a single repetition, for a given slice.

Back 40

3*The total number of 90 degree pulses used within a TR period of fast spin echo sequence is equal to the initial excitiation pulse plus the number of sat pulses.

Front 41

When gradient moment nulling is used for a T2 weighted cervical spine exam, the CSF appears _______ and the appearance of flow artifacts ________.

Back 41

Bright, decrease