OPTIMIZED RADIOFREQUENCY COILS FOR INCREASED SIGNAL-TO-NOISE RATIO INMAGNETIC-RESONANCE MICROSCOPY

The signal-to-noise ratio (SNR) is a major obstacle to achieving incre ased resolution in magnetic resonance microscopy (MRM). The SNR consid erations for MRM are presented, with particular attention to the role of judicious receiver coil design in maximizing sensitivity and limiti ng noise contributions both from the sample and the coil. We present a number of different coil configurations that have been optimized for particular applications of MRM in the biological sciences. An overview of the literature regarding derivations of the SNR for birdcage-confi guration volume coils, inductively coupled surface coils, and surgical ly implanted coils is presented in a unified fashion. Microscopy coils designed to reduce the total Volume of excitation, thus coupling more closely to a given region of interest, are discussed. The Volume coil is presented in terms of its application to lung imaging in small ani mals at 2 T and imaging of stroke at 7 T. The performance of tradition al surface coils is demonstrated by application to spinal cord imaging in the rat. Finally, implanted coils are examined, as used in studies of the carotid arteries. (C) 1997 John Wiley & Sons, Inc.