Fig. 1. Comparison of MRI at 47,000 gauss and 21 gauss. (A) Water inside a cylindrical Plexiglas cell at 47,000 gauss. (B) Laser-polarized helium-2 gas inside a cylindrical glass cell at 47,000 gauss. (C) Water inside a cylindrical glass cell at 21 gauss. No image is seen because of the very low 1H spin polarization at low magnetic fields. (D) Laser-polarized helium-3 gas inside a roughly H-shaped glass cell at 21 gauss. (Right) Photograph of the glass "H" cell.
Fig. 2 Example of low-field noble-gas MRI performed with the prototype instrument. Excised rat lungs (photo on left) were filled with laser–polarized helium-3 gas and imaged with MRI at 21 gauss (right). The two-dimensional spatial resolution is 1 mm^2, with a 20 mm slice thickness, and the imaging time was ~ 25 seconds. Conventional, thermally-polarized water proton MRI is impractical at such low magnetic fields.