Assessment of T1 and T effects in vivo and ex vivo using iron oxide nanoparticles in steady state—dependence on blood volume and water exchange

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Abstract
Accurate knowledge of the relationship between contrast agent concentration and tissue relaxation is a critical requirement for quantitative assessment of tissue perfusion using contrast‐enhanced MRI. In the present study, using a pig model, the relationship between steady‐state blood concentration levels of an iron oxide nanoparticle with a hydrated diameter of 12 nm (NC100150 Injection) and changes in the transverse and longitudinal relaxation rates (1/T and 1/T1, respectively) in blood, muscle, and renal cortex was investigated at 1.5 T. Ex vivo measurements of 1/T and 1/T1 were additionally performed in whole pig blood spiked with different concentrations of the iron oxide nanoparticle. In renal cortex and muscle, 1/T increased linearly with contrast agent concentration with slopes of 101 ± 22 s−1mM−1 and 6.5 ± 0.9 s−1mM−1 (mean ± SD), respectively. In blood, 1/T increased as a quadratic function of contrast agent concentration, with different quadratic terms in the ex vivo vs. the in vivo experiments. In vivo, 1/T1 in blood increased linearly with contrast agent concentration, with a slope (T1‐relaxivity) of 13.9 ± 0.9 s−1mM−1. The achievable increase in 1/T1 in renal cortex and muscle was limited by the rate of water exchange between the intra‐ and extravascular compartments and the 1/T1‐curves were well described by a two‐compartment water exchange limited relaxation model. Magn Reson Med 47:461–471, 2002.
Funding Information
  • Swedish Research Council (K2001-04x-06676-19A)