Quadrature Transverse Electromagnetic (TEM) Surface Coils

At high fields (above 4 T) constructing volume coils for human head and body imaging is difficult due to lower efficiency (B1/(P)1/2) and higher power deposition. Alternatively, surface coils, while providing high efficiency due to substantially smaller excitation volume, generate a strongly inhomogeneous B1 field. Half‐volume coils, which provide a compromise between these two types of RF coils, can reduce power deposition while preserving sensitivity and producing reasonable homogeneity. This article describes design and construction of a 4 T half‐volume quadrature head‐sized TEM coil. The coil produces a sufficiently large homogeneous B1 field region for the use as a volume coil. At the same time it provides superior transmission efficiency, resulting in significantly lower total power deposition, as well as greater sensitivity and improved patient comfort and accessibility compared with conventional full‐volume coils. In addition, this coil suppresses the RF penetration artifact that distorts the RF magnetic field profile and alters the intensity in high‐field images recorded with linear surface and volume coils. These advantages make it possible to apply this device as an efficient transmit/receive coil for high field imaging with a restricted field‐of‐view