Signal intensity artifacts in clinical MR imaging.
Signal intensity artifacts are often encountered during magnetic resonance (MR) imaging. Occasionally, these artifacts are severe enough to degrade image quality and interfere with interpretation. Signal intensity artifacts inherent in local coil imaging include intensity gradients and local intensity shift artifact. The latter can be minimized but not eliminated with optimal coil design and tuning. Improper coil or patient positioning can produce subtle or, in some cases, severe signal intensity artifacts, and each is easily corrected. Signal intensity artifacts and image degradation can also occur in a perfectly functioning coil if protocols are not optimized. Failure of decoupling mechanisms can produce signal intensity artifacts that will not respond to protocol optimization and will worsen with gradient imaging. Improper coil tuning manifests as a shading artifact that can mimic other findings. Signal-degrading artifacts may be caused by a ferromagnetic foreign body in the imager. Signal intensity artifacts can also result from performing ultrafast imaging with coils that were not designed for this type of imaging or from MR imaging system malfunction. Familiarity with the various causes of signal intensity artifacts is necessary to maintain optimal image quality and should be required as part of any MR imaging quality assurance program.