Molecular Imaging of Tumors Using a Quantitative T-1 Mapping Technique via Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) of glioblastoma multiforme (GBM) with molecular imaging agents would allow for the specific localization of brain tumors. Prior studies using T-1-weighted MR imaging demonstrated that the SBK2-Tris-(Gd-DOTA)(3) molecular imaging agent labeled heterotopic xenograft models of brain tumors more intensely than non-specific contrast agents using conventional T-1-weighted imaging techniques. In this study, we used a dynamic quantitative T-1 mapping strategy to more objectively compare intra-tumoral retention of the SBK2-Tris-(Gd-DOTA)(3) agent over time in comparison to non-targeted control agents. Our results demonstrate that the targeted SBK2-Tris-(Gd-DOTA)(3) agent, a scrambled-Tris-(Gd-DOTA)(3) control agent, and the non-specific clinical contrast agent Optimark all enhanced flank tumors of human glioma cells with similar maximal changes on T-1 mapping. However, the retention of the agents differs. The non-specific agents show significant recovery within 20 min by an increase in T-1 while the specific agent SBK2-Tris-(Gd-DOTA)(3) is retained in the tumors and shows little recovery over 60 min. The retention effect is demonstrated by percent change in T-1 values and slope calculations as well as by calculations of gadolinium concentration in tumor compared to muscle. Quantitative T-1 mapping demonstrates the superior binding and retention in tumors of the SBK2-Tris-(Gd-DOTA)(3) agent over time compared to the non-specific contrast agent currently in clinical use.