Limits of Detection of SPIO at 3.0 T Using T2 Relaxometry

T(2)* 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 R(2)*. This is of particular importance for the sensitive detection of iron oxide contrast agent distributions. To derive an accurate measurement of T(2)*, a main field inhomogeneity correction is applied: the main field inhomogeneity is derived from multislice T(2)* relaxometry data and used as an initial value for an iterative optimization, by which the relaxation signal is corrected for each voxel. These corrected T(2)* 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 T(2)* relaxometry was estimated in volunteers to be 120 x 10(3) cells/mL (2.4 microg Fe/mL) in the brain and 385 x 10(3) cells/mL (8 microg Fe/mL) in the liver.