FDG positron emission tomography (PET) imaging before and after treatment. In patients with gastrointestinal stromal tumors (GIST), tumor glucose utilization is very high and these tumors can be readily visualizd by [18F]^– fluorodeoxyglucose (FDG) PET (36, 37). A striking observation in patients with GIST who are treated with STI571 (Gleevec) was that the rapid and sustained decrease in fluorodeoxglucose (FDG) uptake determined by PET scan was seen as early as 24 hours after one dose of ST1571, and this was sustained over many months. The high FDG levels seen in the kidney, ureter, and bladder are normal in both the pre- and post-Gleevec images. Figure adapted from ref. 37, with appreciation and permission from Annick Van en Abbeele, Danaa-Farber Cancer Institute, Boston, Massachusetts, USA.