DECOUPLING - THEORY AND PRACTICE I - CURRENT METHODS AND RECENT CONCEPTS

Current methods for broadband heteronuclear decoupling are reviewed fr om a historical perspective, The principal concern is that decoupling should be effective over a wide range of chemical shifts without undue radiofrequency heating of the sample, particularly when human patient s are involved, Continuous-wave methods are the least efficient in thi s respect, followed by noise decoupling, Composite pulse schemes offer a more effective use of radiofrequency power, while adiabatic passage methods are the most efficient of all, pi-level decoupling employs a low level of radiofrequency irradiation during the relaxation delay to maintain the nuclear Overhauser effect, with a higher level during si gnal acquisition in order to decouple over a wide frequency band, All decoupling sequences introduce cycling sidebands into the observed spe ctrum, and schemes are described to minimize the intensity of these ar tifacts, In part II, practical applications of decoupling methods are examined in the context of in vivo spectroscopy, where the improvement s in sensitivity and resolution through broadband decoupling can be cr itical for solving clinical problems, Attention is focused on the regu latory limits on power deposition in these experiments, A tabulation o f the existing work on decoupling in biological tissue is presented,ma inly involving P-31 and C-13 spectroscopy in vivo or in vitro. (C) 199 7 John Wiley & Sons, Ltd.