Development of A SQUID-Based Low-Field NMR/MRI System

In the case of most physiological tissues, longitudinal relaxation time (T1) depends on the applied magnetic field strength, and the T1-contrast between different types of tissues can be enhanced at low magnetic fields. Prepolarized SQUID-based MRI could be used to perform T1-weighted imaging at low fields. We aimed to develop a low-field MRI system that can provide clear T1-weighted images. The system consists of five sets of coils for generating magnetic fields required for generating the NMR/MRI signal and a first-order SQUID gradiometer for detecting free induction decay (FID) signals from a sample. We improved the polarizing-field-driving circuit to increase the field, and developed the SQUID-driving electronics to reduce the artifacts in the increased polarizing field. Using this system, we measured T1 of water–oil mixture sample. Clear T1 spectrum of each ingredient of the sample was obtained by CONTIN analysis.