Improved quantification of SPIO in peripheral tumor xenografts using QSM

The use of MRI relaxometry for super-paramagnetic iron oxide (SPIO) quantification in a murine peripheral tumor xenograft, a frequently performed procedure in drug development research, may result in inaccurate estimates because of the dependence of relaxivity on tissue microenvironment. SPIO complexes conjugated to PET radiotracers have been proposed for more accurate SPIO quantification, but these have disadvantages of a cyclotron requirement, low spatial resolution and confounding tumoricidal effects. We demonstrate that SPIO quantification in peripheral tumor xenografts using new quantitative susceptibility mapping (QSM) algorithms has good agreement with quantification using PET suggesting that QSM may provide value for quantification in drug development research.