1st Part Chapter 7

Question 1

Physiological motion

Answer 1

Flow artifact
Ghosting
Remedy is to pre saturate pulse and flow comp

Swap phase to decrease artifact

Question 2

Aliasing wrap around

Answer 2

Object is larger than FOV

The anatomy outside FOV produces a signal

Question 3

Hardware and mechanical artifacts

Answer 3

Truncation (Gibbs)
RF zipper
Herringbone
No uniformity

Question 4

Truncation and remedy

Answer 4

Under sampling nyquist theorem
Multiple rings of duplication at transitions btwn high and low signal intensities

Increase matrix or phase encoding steps

Question 5

Gibbs

Answer 5

Cervical spine area

Question 6

Zipper- cause, image and remedy

Answer 6

Extraneous RF entering room and interfering with signal from patient

Dense line on image possible zebra
Poor shimming

Leak in RF shielding
Call engineer

Question 7

Shading- cause and remedy

Answer 7

Uneven excitation of nuclei within pt due to RF pulses or uneven cool loading

Loss of signal intensity so make sure cool is loaded correctly

Pt is not touching coil

Question 8

Magnetic susceptibility

Answer 8

Metal or substances change local MF for hydrogens causing a difference in frequency

Signal loss and worse with gradient echo

Remove metal

Question 9

Chemical shift what, cause and remedy

Answer 9

Precessional difference btwn fat and water at high fields dark edges

Narrow bandwidth so to fix increase and widen it

Question 10

Chemical misregistration

Answer 10

Ring of dark signal around organs
Fat and water out of phase with each other canceling each other out

Fat and water at different frequencies. Only in phase at certain times

Question 11

Cross talk / excitation

Answer 11

Energy dissipating to adjacent slices.. over excitation if nuclei

Talk= no remedy
Excitation= ensure 30% gap btwn slices