  A wide variety of nuclear magnetic resonance experiments rely on the
prediction and analysis of relaxation processes. Recently, innovative
approaches have been introduced where the sample travels through a broad range
of magnetic fields in the course of the experiment, such as dissolution dynamic
nuclear polarization or high-resolution relaxometry. Understanding the
relaxation properties of nuclear spin systems over orders of magnitude of
magnetic fields is essential to rationalize the results of these experiments.
For example, during a high-resolution relaxometry experiment, the absence of
control of nuclear spin relaxation pathways during the sample transfers and
relaxation delays leads to systematic deviations of polarization decays from an
ideal mono-exponential decay with the pure longitudinal relaxation rate. These
deviations have to be taken into account to describe quantitatively the
dynamics of the system. Here, we present computational tools to (1) calculate
analytical expressions of relaxation rates for a broad variety of spin systems
and (2) use these analytical expressions to correct the deviations arising in
high-resolution relaxometry experiments. These tools lead to a better
understanding of nuclear spin relaxation, which is required to improve the
sensitivity of many pulse sequences, and to better characterize motions in
macromolecules.
