Week 3.3 CT and MRI Artifact Flashcards
why might you get artifact
interference, improper operation, external radiation or electromagnetic interference, natural artifact from the body
what does artifact do
obscures pathology, or makes you think there is a pathology that isn’t really there. can misdiagnose a patient
what is noise
CT: statistical error that is random light and dark strips
how can you decrease the noise
combining data from multiple scans
what is beam hardening
CT: dark streaks between 2 high attenuating objects like metal, bone, iodine, barium.
where is CT beam hardening most common
Especially in the posterior cranial fossa with metal implants
how does motion cause artifact
pt breathing, HR, bowel movement, that causes blurring, double images and streaks.
how can you fix motion artifact
with a faster machine and faster rotation
what is CT ring artifact
mis-calibrated detector element, easily fixed with recalibration
what is CT metal artifact
objects or fragments like aneurysm clips, implants, dental, bullets, shrapnel, joint replacements.
what are some other CT artifacts
scatter, pseudo enhancement, cone beam, helical
MRI artifact can come from 4 things, what are they
- Physiologic (breathing, bowel, blood flow, heart beat, patient moves)
- MRI physics like metal and chemical shifts
- MRI hardware and room shielding
- MRI software
what can cause artifact in an MRI
devices, construction and vibration, door isn’t shut all the way
what is phase encoded motion
ghosting in the direction of motion, like from swallowing, breathing, arterial pulsations and patient movement. smear in the phase direction
what is chemical shift artifact
during the frequency encoding of an MRI, this is when fat and H2O oscillate in different directions in the magnetic field. cause a black and bright band at the edges
