nOe-buildup
The mixing time can be adjusted to obtain sufficient signal-to-noise ratio for the cross peaks. The NOE intensity is proportional to the relaxation rate,i.e. the NOE should (per SOLOMON equation) increase linearly with the mixing time. However, the NOE is defined for steady state:
In a transient system : any relaxation and any cross relaxation lead to population changes, and therefore affect in principle the cross-relaxation rate again. As the Solomon equation is only valid for the initial buildup rate of the NOE. In practice: we have to obtain NOE at several mixing times and construct the buildup curve. The NOE can be used/converted into distances as long as the mixing time is in the linear range of the buildup curve. Alternatively, on could simulate the build up curve to obtain the initial buildup rate for tmix =0, which would be the more exact way to determine the correct of the cross relaxation rate.