A simplified method for accuracy estimation of nuclear magnetic resonant imaging

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Abstract
Multi-dimensional tomographic-based data sets are now being used to calculate physical properties and transport coefficients. This article presents a method, based upon the propagation of uncertainties, for determining the valid range of values for the property calculated. The example used to demonstrate the method is the application of nuclear magnetic resonance imaging (NMRI) to measure fluid velocity profiles for the calculation of fluid viscosities. The resolution of the velocity data is shown to be the most important factor for implementation of the NMRI-based viscometry technique. Uncertainties in the velocity measurement are propagated through the shear viscosity calculation to estimate the standard deviation of the shear viscosities. Two data sets, experimental velocity resolutions of 0.6 and 1.5 mm/s, demonstrate that when the shear viscosity standard deviation exceeds 30% of the predicted shear viscosity value we observe a discrepancy between the data and viscosities obtained using conventional rheometrical instruments. Removal of those data points with a standard deviation exceeding 30% of the shear viscosity value provided data that agreed to within 6% of conventional rheometry data. The estimation methodology for property uncertainty can be applied prior to experimental measurements to design for accuracy over a specific range of the property to be determined. These findings are not restricted to NMRI and should hold for other tomography-based viscometers