Improved contrast in ultra-low-field MRI with time-dependent bipolar prepolarizing fields: theory and NMR demonstrations

摘要: The spin-lattice (T1) relaxation rates of materials depend on the strength external magnetic field in which occurs. This T1 dispersion has been suggested to offer a means discriminate between healthy and cancerous tissue by performing resonance imaging (MRI) at low fields. In prepolarized ultra-low-field (ULF) MRI, spin precession is detected fields order 10–100 μT. To increase signal strength, sample first magnetized with relatively strong polarizing field. Typically, kept constant during polarization period. However, ULF polarizing-field can be easily varied produce desired time course. paper describes how novel variation duration optimize contrast two types having different dispersions. addition, NMR experiments showing that principle works practice are presented. described procedure may become key component for promising new approach MRI ultra-low