SQUID DETECTED NMR AND MRI AT ULTRALOW FIELDS

摘要

Nuclear magnetic resonance NMR signals are detected in microtesla fields. Prepolarization in millitesla fields is followed by detection with an untuned do superconducting quantum interference device SQUID magnetometer. Because the sensitivity of the SQUID is frequency independent, both signal-to-noise ratio SNR and spectral resolution are enhanced by detecting the NMR signal in extremely low magnetic fields, where the NMR lines become very narrow even for grossly inhomogeneous measurement fields. MRI in ultralow magnetic field is based on the NMR at ultralow fields. Gradient magnetic fields are applied, and images are constructed from the detected NMR signals.