Fast spatially-resolved T2 measurements with constant-gradient CPMG

Publication date: Available online 15 September 2018

Source: Magnetic Resonance Imaging

Author(s): Stefan A. Hertel, Daan W. de Kort, Isabelle Bush, Andrew J. Sederman, Lynn F. Gladden, Benjamin Anger, Hilko de Jong, Matthias Appel

Abstract

Speed of acquisition is paramount for the application of magnetic resonance to flow experiments through porous rocks. One popular method for imaging core floods is the spatially resolved T₂ experiment which can separate fluids either by their viscosity contrast or by doping one fluid with a relaxation agent. Existing techniques for spatial-T₂ may suffer from long acquisition times and eddy currents due to the pulsing of magnetic field gradients. Here, we propose a constant gradient method for 1d spatially-resolved T₂ which embraces the speed of frequency encoding techniques and avoids eddy currents by the absence of any gradient ramps during the radio frequency (r.f.) pulse train. We provide the operating envelope for this kind of experiment, which is restricted due to the slice selectivity of the r.f. pulses in the presence of the magnetic field gradient. Additionally, we show that the effects of self-diffusion and the mixing of T₁ and T₂ contributions are manageable. As an illustration, we have applied this technique to an enhanced oil recovery experiment. The two fluid phases were tracked without any doping and with a time resolution of 40 s. In this case, the increased time resolution allowed us to observe dynamic flow phenomena such as fluid fingering and the calculation of the velocity of the fluid displacement fronts.

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