Fig. 6.
glycoCEST imaging of a perfused fed-mouse liver at 4.7 T and 37°C. The first image (gray scale) marks the beginning of perfusion (t = 0) with glucose-free media containing 500 pg/ml glucagon. The liver tissue is darkened because of the CEST effect from presaturation at 1.0 ppm for 1 s at 3.0 μT. Upon further perfusion with glucagon, the liver signal increased, corresponding to a decrease in CEST effect. The colorized glycoCEST images as a function of time during perfusion show the relative CEST intensity [MTRasym (1 ppm)] of liver tissue as a function of perfusion time. The color scale shows that there are regions of liver where the initial asymmetry difference between ±1 ppm is as high as 55% (orange pixels) and as low as 5% (blue pixels). With time, as glycogen disappears, the CEST images become more uniformly dark blue, corresponding to minimal glycogen. The corresponding glycogen depletion for a homogeneous region of interest is quantified in the graph (n = 4).