Development of a 3-D, multi-nuclear continuous wave NMR imaging system

The development of a 3-D, multi-nuclear continuous wave NMR imaging (CW-NMRI) system is described and its imaging capability is demonstrated on a range of materials exhibiting extremely short T2 relaxation values. A variety of radiofrequency resonators were constructed and incorporated into a new gradient and field offset coil assembly, while the overall system design was modified to minimise microphonic noise which was present in an earlier prototype system. The chemically combined 27Al in a high temperature refractory cement was imaged, and the CW-NMRI system was found to be sensitive to small differences in 27Al content in these samples. The penetration of 23Na in salt water into samples of ordinary Portland cement (OPC) was investigated, with enhanced uptake observed for samples with larger pore size distributions. The solid 13C component in a carbonated cement sample was also imaged, as were the 7Li nuclei in a sample of powdered Li2CO3. A spatial resolution of 1 mm was measured in an image of a rigid polymeric material exhibiting a principal T2∗ value of 16.3 μs. Finally, a high-resolution 3-D image of this rigid polymer is presented.