A Method for Determining B_1 Field Inhomogeneity. Are the Biases Assumed in Heteronuclear relaxation Experiments Usually Underestimated?

摘要

We describe a method allowing the determination of the effective B_1 field amplitude distribution in a high-resolution NMR spectrometer. This method which can be adapted to almost any sequence, essentially consists of a nutation followed by a purging B_0 gradient pulse. Experimental results obtained with this approach are described in homonuclear and heteronuclear cases. The experimental distributions are used to estimate the biases induced by B_1 inhomogeneity, as well as the loss of RF power on heteronuclear transverse self-relaxation rate determination. In this type of measurement, the experimental biases induced on the intensities can be as large as 5% for long mixing times.