Synopsis

Low field and portable scanners have spurred a broad reimagining of spatial encoding in MRI. Many designs still use B0 variation as the primary source of spatial encoding, but these span a broader range of switchable and permanent magnet sources, with both linear and nonlinear spatial variation. In addition, the enormous reduction in SAR at low field has opened many possibilities for RF encoding, including methods based on hardware geometry, complex RF waveforms, and Bloch-Siegert evolution with hardware that allows continuous frequency encoding. Advanced reconstruction methods also play a larger role in low field imaging.