Chapter 7 Flashcards
In which direction does truncation occur
Phase Axis
Which of the following best describes a remedy for cross excitation?
Excite alternate slices during the acquisition
Which best describes the appearance of a zipper artifact?
A dense line on the image at a specific point.
What unit is used to express the amount of chemical shift?
ppm
In which direction does aliasing occur?
phase and frequency axis
What is another term for phase ghosting?
Phase mismapping
In some circumstances, magnetic susceptibility artifact can be useful in diagnosis. (T or F)
true
Which of the following best describes the appearance of chemical shift artifact on an image?
Produces a dark edge at the interface between fat and water.
Which of the following is a remedy for aliasing?
Using “no phase wrap” software
To reduce chemical shift artifact, ALWAYS use the widest receive bandwidth in keeping with good SNR and the smallest FOV possible. (T or F)
true
In which direction does chemical shift artifact occur?
Frequency Axis
How can we reduce truncation?
Increase the number of phase encoding steps
What is another name for a truncation artifact in a sagital cervical spine?
Gibbs
In which direction does phase ghosting occur?
Phase Axis
Which of the following is a possible cause of shading artifact?
Inhomogeneities in the main magnetic field
Which of the following are methods of reducing phase ghosting
Using respiratory compensation techniques
Carefully explain the procedure to the patient
Swap phase and frequency
Use pre-saturation pulses
Which of the following best describes Moire artifact?
Black and white banding artifact on the edge of the FOV
remedy for Moire
keep anatomy w/in the FOV
remedy for Magic Angle
move the body part or change TE
remedy for aliasing
use no phase wrap software
remedy for chemical misregistration
select a TE that matches periodicity of fat and water
remedy for zipper
call an engineer
remedy for cross excitation
gap between the slices, alternate slices
remedy for chemical shift
use lower field strengths, wide RBW
remedy for truncation
increase the # of phase encoding steps
types of gating for EKG, ECG
lead wires on the patients chest.used when imaging chest heart and great vessels
types of gating for peripheral gating
light sensor attached to patients finger to detect pulses thru capillaries. not as accurate
types of gating for respiratory compensation
bellows around the chest. signal corresponds to max and minimum motion of chest. TR may be reduced
types of gating for respiratory triggering
times the excitation RF w a certain phase of respiration. increased scan times
appearance of phase mismapping artifact
produces replications of moving anatomy across image
appearance of chemical shift artifact
dark edges at edge between fat and water
appearance of magnetic susceptibilty
large signal voids
appearance of cross excitation and cross talk artifact
adjacent slices in different image contrast
appearance of zipper aritfact
dense line across the image
appearance of magic angle
in tissues that contain collagen at high signal intensity
appearance of aliasing
anatomy outside the FOV is folded on top of the anatomy inside FOV
appearance of moire
black and white banding at the edge of FOV
Which is true concerning chemical shift?
Expressed in parts per million (ppm).
equals 3.5 ppm
direction of ghosting
phase only
direction of aliasing
both phase and frequency
direction of chemical shift
frequency only
other name for phase mismapping
ghosting
other name for aliasing
wrap around
other name for truncation
Gibbs
cause of ghosting
anatomy moving along the phase direction during pulse sequence
cause of aliasing
anatomy outside the FOV is mapped inside FOV
cause of chemical shift
different chemical environments of fat and water
cause of truncation
undersampling of data
cause of magnetic suscpetibility
braces, hair pins, implants, etc
cause of cross excitation
RF pulse not square
cause of zipper
leakin RF shielding
cause of magic angle
collage is 55-degree angle to Bo
cause of shading
inhomogeneities in the main magnetic field
direction of zipper
frequency only
direction of magnetic susceptibility
phase and frequency
direction of truncation
phase only
