Scheme: Optically-detected MRI Imaging of Flow in Porous Metallic Materials with Optically-Detected MRI Shoujun Xu, Department of Chemistry, University of Houston, Houston, TX 77204 Optically-detected magnetic resonance imaging (MRI) in the Earth’s magnetic field is uniquely suited for imaging fluids inside porous metallic materials, since audio-frequency radiations have sufficient penetration depth in metals, in contrast to radiofrequency and visible light. High sensitivity is achieved by using atomic magnetometers for detection instead of conventional inductive coils. Atomic Magnetometer Scheme: Optically-detected MRI Two-dimensional imaging of water flow in a porous steel sample (top row) and a void volume (bottom row). Note that water vacates the steel sample much faster than it does in the void volume. Relaxation time of protons as a function of pore size in steel, which are measured under continuous flow. 0.4 s 0.7 s 1.0 s 2.0 s flow A potential molecular probe for pH, Gd(TTHA) has a pH-dependent enhancement on the relaxation of proton nuclear spins. Shown are the results from two low concentrations of Gd(TTHA). flow