Optimizing abdominal MR imaging: approaches to common problems.

Abdominal magnetic resonance (MR) imaging involves many challenges and is complicated by physiologic motion not encountered to the same degree in other regions of the body. Problems that uniquely affect abdominal MR imaging include motion artifact (from respiratory, cardiac, gastrointestinal, and voluntary movement), susceptibility artifact, conductive and dielectric effects, and wraparound artifact. Techniques to minimize these artifacts often need to be addressed within the time constraints of a single breath hold. Patient motion during image acquisition is minimized by using physical restraint, respiratory gating, and reduction of acquisition time. Correction of motion-induced dephasing (through gradient moment nulling), signal averaging, and suppression of signal in moving structures all address unavoidable motion (eg, cardiac pulsation). Acquisition time is minimized by obtaining fewer phase-encoding steps, decreasing repetition time, and increasing efficiency with use of parallel imaging and multiecho acquisitions. Adjusting the echo time does not directly affect scanning time, but it does allow more time for section sampling per repetition time interval in multisection acquisitions by means of closer echo spacing and it plays a pivotal role in optimizing image quality. Familiarity with basic MR imaging principles and the ability to minimize the effects of motion and other artifacts are essential to optimizing abdominal MR imaging protocols and improving efficiency.