FDG-PET identifies areas of inflammation in a case of segmental manifestations of intestinal GVHD and allows noninvasive monitoring of treatment response. The top panels (A-F) show findings in a representative patient diagnosed with intestinal GVHD. PET images showed segmental inflammation of the right colon (SUV, 5.1) and sigmoid colon (SUV, 2.2), and normal FDG uptake in the transverse (SUV, 1.0) and left (SUV, 1.6) colon segments (A,B). Histopathology of serial biopsies of the whole colon verified GVHD in those segments matching with increased local glucose uptake (C,D,F). Histopathology of colon segments with normal PET findings showed no evidence of GVHD (E). Depicted histologies are representative of at least 3 independent mucosal samples of each colon segment. Arrows indicate examples of apoptotic mucosa cells. (G) SUVs of FDG in 30 patients with (left side) or without (right side) clinical proven intestinal GVHD showed significant differences. Analyses of different intestinal segments in patients without intestinal GVHD showed a mean SUV of less than 2. In contrast, colon segments of patients with intestinal GVHD showed significant higher SUV compared with respective segments of the small gut as well as in comparison with colon segments of patients without intestinal GVHD. Error bars indicate SEM for each segment. *Statistically significant differences for each bowel segment of patients with GVHD compared corresponding segments of patients without GVHD (P < .05).