A series of PET studies using phantoms is presented to characterize the imaging and quantitative performance of the positron-emitting iodine isotope 124 I. Measurements were performed on the 2D-PET scanner GE 4096+ as well as on the Siemens PET scanner HR+ operated in both 2D and 3D modes. No specific correction was applied for the g-rays emitted together with the positrons. As compared to 18 F, in studies with 124 I there is a small loss of image resolution and contrast, and an increase in background. The quantitative results varied between different scanners and various acquisition as well as reconstruction modes, with an average relative difference of À6713% (mean7SD) in respect of the phantom radioactivity as measured with g-ray spectroscopy. We conclude that quantitation of a radiopharmaceutical labelled with 124 I is feasible and may be improved by the development of specific corrections. r

SUMMARY @A macrocyclic aminopolyether (Kryptofix 2.2.2.) supported labelling method for the preparation of n.c.a. [17-FIfluoroheptadecanoic acid is described. The equimolar complex of potassium carbonate and the aminopolyetheris used to provide nucleophilicity in a homogeneous solution of acetonitrile. Nucleophilic "F-for-Br substitution in the methylester of 17-bromoheptadecanoic acid is accomplished with radiochemical yields of 9 4 + 3%. Subsequent quantitative ester hydrolysis with KOH leads to a simple "one pot" procedure. Minimization of reagent concentrations allows a direct isolation of the product from the reaction mixture by means of reverse phase HPLC. The corrected radiochemical yield of high activity level routine production is 82 + 2% after 90 minutes of synthesis time. The specific activity is > 10,000 Ci/mmol.

For clinical application of stem cell-based therapies, noninvasive detection of applied stem cells is of high importance. We report on the feasibility of detecting implanted neural progenitor cells (NPCs) noninvasively and follow their fate and functional status by sequential multimodal molecular imaging and reporter gene technology. We investigated C17.2 cells stably expressing herpes simplex virus type 1-thymidine kinase (HSV-1-tk) and green fluorescent protein (gfp) (C17.2-tkIRESgfp = C17.2-TIG) or HSV-1-tk, gfp, and firefly luciferase (luc) (C17.2-lucIREStkgfp = C17.2-LITG) and determined the detection sensitivity of positron emission tomography (PET) and bioluminescence imaging (BLI) for these cells in culture and in vivo in subcutaneous and intracranial glioma models. In addition, PET and BLI were used to further investigate and follow the fate of implanted C17.2-LITG cells in an intracranial glioma model. We show that both imaging modalities are sensitive in detecting reporter gene expressing NPCs; however, PET, by the use of 9-[4-[(18)F]fluoro-3-hydroxymethyl)butyl]guanine ([(18)F]FHBG), detects NPCs only at sites of disrupted blood-brain barrier. Furthermore, both imaging modalities can be used to detect stem cell fate and migration and indicate excessive proliferation and aberrant migration. In conclusion, multimodal imaging can be used for longitudinal noninvasive monitoring of grafted NPCs in rodents.