Clinical application of abdominal echoplanar imaging (EPI): optimization using a retrofitted EPI system.

Abstract

Echoplanar MRI (EPI) with data acquisition times as short as 36 ms has been advocated for imaging body areas where gross physiologic motion degrades images. In this study we investigated the effect of various operator-defined parameters on image quality in EPI of the abdomen using a commercially available scanner. Specifically, we assessed the effect of breathholding, slice thickness, k-space coverage (raw data size), and high resolution EPI in volunteers. The effect of these parameters on signal-to-noise ratio (SNR) and image quality of liver, spleen, kidney, and pancreas was evaluated to propose guidelines for clinical EPI of the abdomen. The requirements for contiguous imaging were analyzed in a phantom experiment. Our study suggests that optimum clinical EPI requires a minimum slice thickness of 7 mm. Breathhold single shot techniques are preferred to avoid spatial misregistrations and to optimize the signal yield for segmented techniques. Maximum k-space coverage at a given TE should be implemented. High resolution techniques (128 x 512) suffer from low SNR and are clinically not useful for routine EPI. Contiguous imaging requires a scan time of > 6 s to eliminate effects of cross-talk. The results suggest that clinical EPI requires careful attention to the choice of imaging parameters. The practical recommendations may help other investigators to optimize their clinical EPI studies.