All animal experiments were performed under a protocol approved by both the Johns Hopkins University Animal Care and Use Committee and the Animal Care and Use Committee of the National Human Genome Research Institute (NHGRI), National Institutes of Health (NIH). Each mouse was placed on a mouse tail illuminator restrainer to catheterize the tail vein. In vivo experiments were performed on an 11.7-T Bruker BioSpec horizontal scanner using an eight-channel mouse body phase array coil. The mouse was then placed on a cradle for imaging and anesthetized using 0.5 to 1.5% isoflurane, with the respiration rate continuously monitored. The body temperature was maintained at 37°C using a hot water circulation bed. A three-plane localizer sequence was used for finding the spatial location of the mouse kidneys. A multislice T2W RARE sequence was used to acquire the axial slice images. Twenty-one contiguous axial slices, each with a thickness of 1.5 mm, were collected using TE/TR of 6.6 ms/4 s, RARE factor of 8, and field of view of 128 × 128. A center slice of width 1.5 mm was chosen for CEST imaging, and high-resolution T2W image was obtained using RARE for anatomical overlay with CEST processed images. The acquisition time for high-resolution T2W images was 2 min and 8 s with a matrix size of 256 × 256. For CEST data acquisition, the RARE pulse sequence was used. Saturation pulses with B1 = 4 μΤ were applied for a total duration of 3 s, which consisted of 10 rectangular block pulses 300 ms long with a 10-μs delay between the pulses. WASSR images were collected for generating B0 maps using 42 offsets from −1.5 to +1.5 ppm and B1 = 1.5 μT. For the 72-offset CEST data acquisition, the offset frequency was incremented between ±7 ppm with an interval of 0.2 ppm for 1 to 2 hours after injection. The time taken for each set of 72 offsets was 6 min and 0 s, and the other sequence parameters were as follows: TE/TR, 3.49 ms/5 s; number of averages, 1; RARE factor, 32; matrix size, 48 × 48; field of view, 28 × 20 mm2; spatial resolution, 0.58 × 0.41 mm2; and centric encoding. Three sets of 72 offsets were collected with the same experimental parameters before administration of iopamidol. Iopamidol was injected through the tail vein at a dose of 1.5 g of iodine per kilogram. For the two-frequency offset data acquisition, the offset frequency was toggled between 4.2 and 5.5 ppm repeatedly, and CEST images at these two offsets were collected for 1 to 2 hours just after administering iopamidol. The time taken for each CEST image acquisition was 5 s. Eight to 10 pre-injection sets of 4.2 and 5.5 ppm images were collected. Field of view was 30 × 20 mm2, in-plane spatial resolution was 0.62 × 0.41 mm2, and other parameters were the same as in the 72-offset protocol.

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