Depth-focused radio frequency coils for MR imaging

Surface coils improve signal-to-noise ratios by the simple expedient of reducing field of view. The uniformity of response of these coils is poor, since signal reception is weighted toward the surface of the object, which generally is of least interest. Furthermore, whole-section transmitter coils excite the subject uniformly, so that weak signals are detected from far regions. A dual-coil arrangement permits avoidance of these problems by combining the nonuniform excitation and reception characteristics of two surface coils.