A method for determining B-1 field inhomogeneity. Are the biases assumed in heteronuclear relaxation experiments usually underestimated?

We describe a method allowing the determination of the effective B-1 field amplitude distribution in a high-resolution NMR spectrometer. This method w hich can be adapted to almost any sequence, essentially consists of a nutat ion followed by a purging B-0 gradient pulse. Experimental results obtained with this approach are described in homonuclear and heteronuclear cases. T he experimental distributions are used to estimate the biases induced by B- 1 inhomogeneity, as well as the loss of RF power on heteronuclear transvers e self-relaxation rate determination. In this type of measurement, the expe rimental biases induced on the intensities can be as large as 5% for long m ixing times. (C) 1999 Academic Press.