Pre-excitation gradients for eddy current nulled convex optimized diffusion encoding (Pre-ENCODE).

Purpose: To evaluate the use of pre-excitation gradients for eddy current-nulled convex optimized diffusion encoding (Pre-ENCODE) to mitigate eddy current-induced image distortions in diffusion-weighted MRI (DWI).

Methods: DWI sequences using monopolar (MONO), ENCODE, and Pre-ENCODE were evaluated in terms of the minimum achievable echo time (TE ) and eddy current-induced image distortions using simulations, phantom experiments, and in vivo DWI in volunteers ( ).

Results: Pre-ENCODE provided a shorter TE than MONO (71.0 17.7ms vs. 77.6 22.9ms) and ENCODE (71.0 17.7ms vs. 86.2 14.2ms) in 100 of the simulated cases for a commercial 3T MRI system with b-values ranging from 500 to 3000 s/mm and in-plane spatial resolutions ranging from 1.0 to 3.0mm . Image distortion was estimated by intravoxel signal variance between diffusion encoding directions near the phantom edges and was significantly lower with Pre-ENCODE than with MONO (10.1 vs. 22.7 , ) and comparable to ENCODE (10.1 vs. 10.4 , ). In vivo measurements of apparent diffusion coefficients were similar in global brain pixels (0.37 [0.28,1.45] mm /s vs. 0.38 [0.28,1.45] mm /s, ) and increased in edge brain pixels (0.80 [0.17,1.49] mm /s vs. 0.70 [0.18,1.48] mm /s, ) for MONO compared to Pre-ENCODE.

Conclusion: Pre-ENCODE mitigated eddy current-induced image distortions for diffusion imaging with a shorter TE than MONO and ENCODE.