MRI artefacts Flashcards
(10 cards)
how can u improve blade/propller artefact
- increase FOV or phase sampling
- adjust blade parameter e.g number of blades
- place sat bands outside FOV in phase encoding direction (nulls signal from tissues outside region)
what is blooming artefact, what does it look like, how to prevent
- found in SWI, signal from blood spreads beyond actual boundary = signal loss = distortion in surrounding structures
- increase bandwidth (reduce magnetic susceptibility), adjust echo time, select SE sequence
whats contrast media artefact, cause and solution
- change in magnetic property of tissue cause by CA (alteration in signal and distortion in imaging seen)
- Contrast media can cause types of artefacts : non-uniformity, chemical shift, susceptibility
what is a dark band artificact, what causes it, how to fic
- magnetic field inhomogeneity = variation in signal intensity = artifact
- looks like a dark band going thru image
- increase bandwidth (reduce effect of inhomogeneity), reduce voxel size, change image plane orientation, increase ETL, shorter TE, SE instead of GRE
what is eddy current artifact, causes and resolution
- interaction of gradient magnetic field with conductive material in patient/ surrounding (as when gradients are turned on and off rapidly, eddy currents induced in conductive material)
- looks like shadow of the anatomy
- proper gradient calibration, proper sequence, ETL optimisation
what is flow artifact, causes and resolution
- signal changes dur to movement of fluid e.g CSF
- cause blurring, ghosting or signal loss
- thicker slices, lower TE, increasing NEX (number of excitation, sat bands, another sequences
what is Gibbs / truncation causes and resolution
- truncation/cut off of high freq info during image recon
- looks like ripples in anatomy
- decrease pixel size by decreasing FOV, smoothing filters, FAT SAT (if boundary is fat), increase matrix size (reducing chemical shift), increase phase encoding step
what is herringbone artifact, causes and resolution
- electromagnetic spikes by gradient coils due to switching on or off rapidly
- disturbance of MRI signal = static/herringbone look on image
- check room doors shut to prevent external RF interference, check cables are secure and for nearby electronics, check for fused bulb filaments in scanner
what is RF overflow artifact, causes and resolution
- RF signal exceeds dynamic range of receiver system leading to signal saturation
- looks like streaks/ fabric pattern over anatomy (not showing underlying anatomy)
- short echo times, reduce transmit power/ smaller flip angle, use advances sequence, use advance artifact correction algorithm
what zipper artefact , causes and resolution
Zipper artifact is a type of artifact in MRI images that appears as a series of bright and dark stripes that run parallel to the phase-encoding direction. It is caused by a timing error in the gradient system that causes the gradient to switch on too early or too late, leading to phase errors in the acquired signals.
- closed door, remove electronic devices/non MRI compatible things or blown bulbs, call engineer if nothing found
