Quantitative MRI Tumor Imaging in Mice

MRIs were performed at 7 Tesla, as previously described^{20 (link)}, on 6 mice (3 at one week post tumor implant and 3 at two weeks post-implant) to validate tumor presence at one day prior to radiotracer injections. Briefly, under isoflurane anesthesia an anatomical T2-weighted RARE was used to localize the tumors with the following parameters: Repetition time (TR)/Echo time (TE) = 3000/30 ms, FOV of 20 mm, acquisition matrix = 256 × 256, 25 slices with a slice thickness of 0.5 mm, 2 averages, and a RARE factor = 8. For quantitative Dynamic Contrast Enhanced (DCE) MRI, first a T1 map was determined with a variable TR sequence using the following parameters: TR = 400, 842, 1,410, 2,208, 3,554 and 10,000 ms, TE = 7 ms, 9 contiguous 0.5 mm-axial slices centered on the tumor location, RARE factor = 2, NA = 2, 20 × 20 mm FOV and a matrix size of 128 × 128. DCE-MRI was then performed with a series of 100 dynamic RARE images with a temporal resolution of 12.8 s per frame with a TR/TE = 200/5 ms and the same geometry as above. After approximately 128 s (10 baseline images), a bolus of gadobutrol (Gadovist 1.0, Bayer, Wayne, New Jersey, 0.1 mmol/kg, 10 s duration) was manually injected via a tail-vein catheter placed during animal preparation. Pharmacokinetics of the gadobutrol bolus uptake in the tumor was analyzed using the Hoffmann model^{20 (link)} using DEC@urLAB^{21 (link)}.