Chapter 25: Rethinking the Detection Scheme: Hyperpolarized Xenon NMR and MRI Signal Amplification by Gas Extraction and Remote Detection

Remote detection of NMR and MRI is an alternative detection modality where the information about a sample of interest is stored as longitudinal magnetization of a fluid. This fluid is then extracted and transported to a detector optimized for sensitivity. Hyperpolarized ¹²⁹Xe gas is ideally suited for this purpose due to its long spin–lattice relaxation time constant, its chemical inertness and the low background signal in the absence of targeted addition of prepolarized gas. The method is described in some detail, with a summary of potential sensitivity advantages and implications of non-ideal fluid transport. The time-of-flight remote detection technique is described to quantify fluid flow and dispersion in a laboratory frame of reference. Different applications are reviewed, including gas flow in rocks, in wood, in microporous materials and in microfluidic devices.