2D and 3D radial multi-gradient-echo DCE MRI in murine tumor models with dynamic R*2-corrected R1 mapping

Dynamic contrast-enhanced MRI is extensively studied to define and evaluate biomarkers for early assessment of vasculature-targeting therapies. In this study, two-dimensional and three-dimensional radial multi-gradient-echo techniques for dynamic R*(2)-corrected R(1) mapping based on the spoiled gradient recalled signal equation were implemented and validated at 4.7 T. The techniques were evaluated on phantoms and on a respiratory motion animated tumor model. R(1) measurements were validated with respect to a standard inversion-recovery spin-echo sequence in a four-compartment phantom covering a range of relaxation rates typically found in tumor tissue. In the range of [0.4, 3] sec(-1), R(1) differences were less than 10% for both two-dimensional and three-dimensional experiments. A dynamic contrast-enhanced MRI pilot study was performed on a colorectal tumor model subcutaneously implanted in mice at the abdominal level. Low motion sensitivity of radial acquisition allowed image recording without respiratory triggering. Three-dimensional K(trans) maps and significantly different mean K(trans) values were obtained for two contrast agents with different molecular weights. The radial multi-gradient-echo approach should be most useful for preclinical experimental conditions where the tissue of interest experiences physiologic motion, like spontaneous extracerebral tumors developed by transgenic mice, and where dynamic contrast-enhanced MRI is performed with high-relaxivity contrast agents.