Limits of detection of SPIO at 3.0 T using T2* relaxometry

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Abstract
T2* relaxometry for quantitative MR imaging is strongly hampered by large-scale field inhomogeneities, which lead to signal losses and an overestimation of the relaxation rate R2*. This is of particular importance for the sensitive detection of iron oxide contrast agent distributions. To derive an accurate measurement of T2*, a main field inhomogeneity correction is applied: the main field inhomogeneity is derived from multislice T2* relaxometry data and used as an initial value for an iterative optimization, by which the relaxation signal is corrected for each voxel. These corrected T2* maps show reduced influence of the local field variation and contain information about the local SPIO concentration. The method was tested on phantoms and the limit of detection of SPIO labeled cells using T2* relaxometry was estimated in volunteers to be 120 × 103 cells/mL (2.4 μg Fe/mL) in the brain and 385 × 103 cells/mL (8 μg Fe/mL) in the liver. Magn Reson Med 53:1202–1206, 2005.