Fast-spin-echo (FSE) acquisitions are routinely used in clinical MRI, but can be affected by concomitant field (CF)-induced phase errors. The conventional whole-body MR gradient typically employs symmetric design. On such systems only CFs of 2nd-order spatial dependence are significant. These CFs can cause ghosting in large-FOV FSE acquisition, but are typically negligible over a brain scan volume. Recently, a high-performance, asymmetric gradient system was developed whose CF contains additional zeroth and first-order spatially-dependent fields. Here, we investigate the effect of CF in FSE on this system using extended-phase-graphs simulation, and demonstrate a real-time compensation for them.