Although preliminary clinical trials are ongoing, successful the use of iron-oxide magnetic nanoparticles (IONP) for heatbased cancer treatments will depend on advancements in: 1) nanoparticle platforms, 2) delivery of a safe and effective alternating magnetic field (AMF) to the tumor, and 3) development of non-invasive, spatially accurate IONP imaging and quantification technique. This imaging technique must be able to assess tumor and normal tissue anatomy as well as IONP levels and biodistribution. Conventional CT imaging is capable of detecting and quantifying IONPs at tissue levels above 10 mg/gram; unfortunately this level is not clinically achievable in most situations. Conventional MRI is capable of imaging IONPs at tissue levels of 0.05 mg/gm or less, however this level is considered to be below the therapeutic threshold. We present here preliminary in vivo data demonstrating the ability of a novel MRI technique, Sweep Imaging with Fourier Transformation (SWIFT), to accurately image and quantify IONPs in tumor tissue in the therapeutic concentration range (0.1-1.0 mg/gm tissue). This ultra-short, T2 MRI method provides a positive Fe contrast enhancement with a reduced signal to noise ratio. Additional IONP signal enhancement techniques such as inversion recovery spectroscopy and variable flip angle (VFA) are also being studied for potential optimization of SWIFT IONP imaging. Our study demonstrates the use of SWIFT to assess IONP levels and biodistribution, in murine flank tumors, following intra-tumoral and systemic IONP administration. ICP-MS and quantitative histological techniques are used to validate the accuracy and sensitivity of SWIFT-based IONP imaging and quantification.