The influence of field strength on the apparent diffusion coefficient of 3He gas in human lungs

The 3He MR diffusion signal is sensitive to lung microstructure, but it is also affected by the presence of background field inhomogeneities induced by the magnetic susceptibility difference at the air-tissue interface. These susceptibility-induced gradients, which are dependent on field strength, have been assumed negligible in theoretical models used to extract airway morphometric information from 3He MR diffusion data at field strengths up to 4.7 T. In this work, the effect of susceptibility gradients on 3He apparent diffusion coefficient is demonstrated with experiments in healthy volunteers at two B0 field strengths: 1.5 and 3 T. Apparent diffusion coefficient values obtained at 3 T were systematically larger than at 1.5 T, demonstrating that susceptibility effects are statistically significant even at clinical field strengths (B0 = 3 T) and introduce biases in the estimates of airway dimensions (e.g., mean linear intercept up to 17% larger at 3 T than 1.5 T). Susceptibility effects should be taken into account in the development of theoretical models of lung 3He MR diffusion and considered when interpreting 3He apparent diffusion coefficients obtained at different B0. Magn Reson Med, 2012. (C) 2011 Wiley Periodicals, Inc.