In recent years, an increasing amount of research has been conducted into the application of single-sided portable NMR to medical imaging. Portable NMR is potentially highly complementary to conventional, high-field MRI by being both more mobile and cost-efficient. This makes it an attractive imaging modality in remote-community or away-from-hospital settings, where high-field MRI is not easily available, as well as for routine screening tasks, where high-field MRI may not be cost-efficient.
While the underlying physics of conventional MRI and portable NMR are the same, there are significant practical differences, the most significant being the presence of a strong, permanent magnetic field gradient in single-sided portable NMR instrumentation. Consequently, rather than producing near-ideal 90- or 180-degree radio-frequency pulses, portable NMR yields a spatially dependent distribution of rotation angles at each pulse, meaning that for a CPMG pulse sequence, the measured signal is a composite of various coherence transfer pathways rather than that of the pure spin echo pathway. As a result, for simple imaging phantoms, diffusion coefficients measured from CPMG decays are consistently 20-40% greater than those measured from stimulated echo diffusion measurements.
We will discuss our attempts to identify which of the non-ideal pathways contribute to this bias as well as our attempts to correct for this bias or alternatively to filter these pathways out.