In-vivo Simultaneous DCE-MRI/O-15-water-PET

644 Objectives Kinetic transport constant, Ktrans, measured by dynamic contrast enhanced MRI (DCE-MRI), is a function of both blood flow (F) and product of vascular permeability and surface area (PS). O-15-water PET is the gold standard for measuring F in vivo. Therefore, we propose simultaneous DCE-MRI/O-15-water-PET to measure PS of Gd-DTPA contrast agent, which can be used to assess tumor angiogenesis directly. Methods A rabbit with 5 weeks old VX2 flank tumor was scanned on a Siemens Biograph PET-MR (mMR). Baseline T1W with 30-degree flip angle 3D gradient echo sequence and T1 mapping with variable flip angles were first obtained. Immediately after the administration of Gd-DTPA (0.2mmol/kg) and O-15-water (three 5-mCi injections separated by 15 minutes), dynamic T1-weighted MR and dynamic list-mode O-15-PET were acquired simultaneously. The concentration of Gd-DTPA as function of time was determined by using both the baseline and post-contrast T1 values. A blood pool region within the left ventricular cavity was used to produce image-derived input functions for both MR and PET. Ktrans and F were obtained using one-compartment kinetic modeling of DCE-MRI and O-15-water PET, respectively. Gd-DTPA extraction factor (E) and its PS maps were then computed from Ktrans and F using E= Ktrans /F and Ktrans = F * (1-exp(-PS/F)), respectively. Results Both Ktrans and F maps show non-homogeneous distributions across the tumor. PS distribution within the tumor is significantly different from either the Ktrans or F maps. Conclusions The results demonstrate the feasibility of deriving PS map of Gd-DTPA using simultaneous DCE-MRI/O-15-water-PET. Our method has the potential to become a new in-vivo technique for quantitatively assessment of tumor vasculature and drug pharmacokinetics. Research Support This work was supported in part by NIH (Grants No: R01-CA165221 and R01-HL118261).