The signal-to-noise ratio (SNR) from implanted coils is widely known to be superior to that from surface coils. This article addresses the quantitative aspects of this improvement by explicitly evaluating the magnetic vector potential in a conducting medium of finite extent for both implanted and surface coils. The predictions of the model are tested with actual image data from spin warp experiments on gelatin phantoms. The authors derived a simplified expression that yields the gain in SNR of an implanted coil relative to that of a surface coil and is valid in many practical situations.
