MRI Image Artifacts

Question 1

What does motion artifact look like in MRI?

Answer 1

bright noise or repeating densities oriented in the phase direction

Question 2

How can you reduce motion artifact?

Answer 2

best to speak to patient, make them comfortable, or switch to faster sequences (Blade/propeller)

Question 3

How does a Blade/Propeller sequence work?

Answer 3

K-space is filled so each line will run through the center or the k-space (central intensity information); only works for in-plane motion

Question 4

What is a flow artifact the result of?

Answer 4

motion of blood or csf during acquisition of squence (along phase encoding direction)

Question 5

What are three ways of reducing flow artifacts?

Answer 5

using sat band, flow compensation, and change of phase encoding direction

Question 6

What is the reason and cause of a zipper artifact?

Answer 6

Reason: RF leakage into the receiver circuit
Causes: open scanner door, RF emission from other instruments in the scanner room, hardware/software problems of the MR scanner

Question 7

Why does aliasing/wrap artifact occur?

Answer 7

when the field of view (FOV) is smaller than the body part being imaged

Question 8

How are aliasing/wrap artifacts corrected?

Answer 8

oversampling, increase FOV, change of phase encoding direction, and use of sat bands

Question 9

Phase ambiguity equation

Answer 9

30 = 360 + 30

Question 10

What is a chemical shift artifact?

Answer 10

Dark and white border around where fat and other tissues form borders; the MRI mistakes the frequency differences of fat and water as spatial (positional) difference

Question 11

How can chemical shift be reduced?

Answer 11

eliminated by fat suppression, increasing the receiver BW, and using lower field strength

Question 12

What is susceptibility artifacts the result of?

Answer 12

microscopic gradients or variation in the magnetic field strength; commonly seen surrounding ferromagnetic objects in the body

Question 13

How can susceptibility artifacts by reduced?

Answer 13

using FSE/TSE, parallel imaging, higher resolution, and low fields

Question 14

What are “black boundary” artifacts?

Answer 14

an artifically created black line located at the fat-water interfaces such as muscle-fat interfaces; a result of selecting an echo time (TE) in which the fat and water spins are out of phase

Question 15

What are Gibbs (or truncation) artifacts?

Answer 15

bright or dark lines that are seen parallel and adjacent to border of abrupt intensity change; related to the finte number of encoding steps used by the Fourier transform

Question 16

What are Moire fringes artifacts?

Answer 16

an interference pattern most commonly seen when doing gradient echo images with the body coil; increase shimming to reduce it