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Physics > Chapter 7 > Flashcards

Chapter 7 Flashcards

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1
Q

In which direction does truncation occur

A

Phase Axis

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2
Q

Which of the following best describes a remedy for cross excitation?

A

Excite alternate slices during the acquisition

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3
Q

Which best describes the appearance of a zipper artifact?

A

A dense line on the image at a specific point.

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4
Q

What unit is used to express the amount of chemical shift?

A

ppm

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5
Q

In which direction does aliasing occur?

A

phase and frequency axis

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6
Q

What is another term for phase ghosting?

A

Phase mismapping

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7
Q

In some circumstances, magnetic susceptibility artifact can be useful in diagnosis. (T or F)

A

true

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8
Q

Which of the following best describes the appearance of chemical shift artifact on an image?

A

Produces a dark edge at the interface between fat and water.

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9
Q

Which of the following is a remedy for aliasing?

A

Using “no phase wrap” software

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10
Q

To reduce chemical shift artifact, ALWAYS use the widest receive bandwidth in keeping with good SNR and the smallest FOV possible. (T or F)

A

true

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11
Q

In which direction does chemical shift artifact occur?

A

Frequency Axis

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12
Q

How can we reduce truncation?

A

Increase the number of phase encoding steps

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13
Q

What is another name for a truncation artifact in a sagital cervical spine?

A

Gibbs

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14
Q

In which direction does phase ghosting occur?

A

Phase Axis

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15
Q

Which of the following is a possible cause of shading artifact?

A

Inhomogeneities in the main magnetic field

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16
Q

Which of the following are methods of reducing phase ghosting

A

Using respiratory compensation techniques
Carefully explain the procedure to the patient
Swap phase and frequency
Use pre-saturation pulses

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17
Q

Which of the following best describes Moire artifact?

A

Black and white banding artifact on the edge of the FOV

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18
Q

remedy for Moire

A

keep anatomy w/in the FOV

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19
Q

remedy for Magic Angle

A

move the body part or change TE

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20
Q

remedy for aliasing

A

use no phase wrap software

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21
Q

remedy for chemical misregistration

A

select a TE that matches periodicity of fat and water

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22
Q

remedy for zipper

A

call an engineer

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23
Q

remedy for cross excitation

A

gap between the slices, alternate slices

24
Q

remedy for chemical shift

A

use lower field strengths, wide RBW

25
Q

remedy for truncation

A

increase the # of phase encoding steps

26
Q

types of gating for EKG, ECG

A

lead wires on the patients chest.used when imaging chest heart and great vessels

27
Q

types of gating for peripheral gating

A

light sensor attached to patients finger to detect pulses thru capillaries. not as accurate

28
Q

types of gating for respiratory compensation

A

bellows around the chest. signal corresponds to max and minimum motion of chest. TR may be reduced

29
Q

types of gating for respiratory triggering

A

times the excitation RF w a certain phase of respiration. increased scan times

30
Q

appearance of phase mismapping artifact

A

produces replications of moving anatomy across image

31
Q

appearance of chemical shift artifact

A

dark edges at edge between fat and water

32
Q

appearance of magnetic susceptibilty

A

large signal voids

33
Q

appearance of cross excitation and cross talk artifact

A

adjacent slices in different image contrast

34
Q

appearance of zipper aritfact

A

dense line across the image

35
Q

appearance of magic angle

A

in tissues that contain collagen at high signal intensity

36
Q

appearance of aliasing

A

anatomy outside the FOV is folded on top of the anatomy inside FOV

37
Q

appearance of moire

A

black and white banding at the edge of FOV

38
Q

Which is true concerning chemical shift?

A

Expressed in parts per million (ppm).

equals 3.5 ppm

39
Q

direction of ghosting

A

phase only

40
Q

direction of aliasing

A

both phase and frequency

41
Q

direction of chemical shift

A

frequency only

42
Q

other name for phase mismapping

A

ghosting

43
Q

other name for aliasing

A

wrap around

44
Q

other name for truncation

A

Gibbs

45
Q

cause of ghosting

A

anatomy moving along the phase direction during pulse sequence

46
Q

cause of aliasing

A

anatomy outside the FOV is mapped inside FOV

47
Q

cause of chemical shift

A

different chemical environments of fat and water

48
Q

cause of truncation

A

undersampling of data

49
Q

cause of magnetic suscpetibility

A

braces, hair pins, implants, etc

50
Q

cause of cross excitation

A

RF pulse not square

51
Q

cause of zipper

A

leakin RF shielding

52
Q

cause of magic angle

A

collage is 55-degree angle to Bo

53
Q

cause of shading

A

inhomogeneities in the main magnetic field

54
Q

direction of zipper

A

frequency only

55
Q

direction of magnetic susceptibility

A

phase and frequency

56
Q

direction of truncation

A

phase only

Physics (15 decks)

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