EPI
Echo-Planar Imaging — ultra-fast MR sequence that acquires the whole 2D image in one excitation by rapid gradient-reversal switching. Single-shot EPI captures a full image in tens of milliseconds; the basis for diffusion-weighted imaging (DWI), functional MRI (fMRI), and diffusion tensor imaging (DTI). Mansfield's 2003 Nobel Prize work.
Why it matters to buyers: Gates fMRI and DWI capability. High gradient strength and slew rate required for clean EPI; not all scanners support robust EPI at clinical quality. Premium 3T platforms (Prisma, Vida, Premier, Ingenia Elition) clearly outperform mid-tier 1.5T on EPI-dependent workflows.
Why it matters to engineers: Susceptible to geometric distortion near air-tissue interfaces (sinuses, ear canals) due to B0 inhomogeneity. Requires good shim and robust gradient performance. Distortion-correction sequences (multi-shot EPI, parallel imaging acceleration, B0 mapping) reduce but don't eliminate the artifact.