Dual time point F-18-FDG PET imaging for differentiating malignant from inflammatory processes

The aim of this study was to investigate the difference in the rates of FDG uptake between malignant and inflammatory cells and processes. Methods: In vitro studies: F-18-FDG uptake by different tumor cell lines (human mesoth elioma [REN]; rat mesothelioma [II45]; mice melanoma [B18F10]; mice mesothe lioma [AB12]; human myeloma [GM1500]; and human ovarian cancer [SKOV3]) and peripheral blood mononuclear cells isolated from 8. healthy human voluntee rs was measured 20 and 60 min after FDG was added into growth medium. Anima l studies: II45 cells were implanted into the left flank of rats (n = 5) an d a focal inflammatory reaction (mechanical irritation) was generated in th e right flank. PET images at 45 and 90 min after injection of FDG were obta ined and standardized uptake values (SUVs) were determined. Patient studies : Seventy-six patients who had dual time FDG PET scans were retrospectively analyzed. All results were expressed as the percentage change in SUV of th e later time image from that of the earlier time (mean +/- SID). Results: I n vitro studies: Except for the SKOV3 cell line, which had only minimally i ncreased FDG uptake (+10% +/- 26%; P > 0.3), all other tumor cell lines tes ted showed significantly increased FDG uptake over time (GM1500, +59% +/- 1 9%; B18F10, +81% +/- 15%; AB12, 93% +/- 21%; II45, +161% +/- 21%; REN, +198 % +/- 48%; P < 0.01 for all). By contrast, FDG uptake in mononuclear cells was decreased in 7 of 8 donors. Animal studies: SUVs of tumors from 90-min images were significantly higher than those from 45-min images (+18% +/- 8% ; P < 0.01), whereas the SUVs of inflammatory lesions decreased over time ( -17% +/- 13% of the early images; P < 0.05). Clinical studies: The SUVs of delayed images from the known malignant lesions compared with those of earl ier scans increased over time (+19.18% +/- 9.58%; n = 31; P < 0.001; 95% co nfidence interval, 15.8%-22.6%). By contrast, the SUVs of benign lung nodul es decreased slightly over time (-6.3% +/- 8.1%; n = 12; P < 0.05; 95% conf idence interval, -10.9% to -1.7%). The SUV of inflammatory lesions caused b y radiation therapy (+1.16% +/- 7.23%; n = 8; P > 0.05; 95% confidence inte rval, -3.9%-6.2%) and the lesions of painful lower limb prostheses (+4.03% +/- 11.32%; n = 25; P > 0.05; 95% confidence interval, -0.4%-8.5%) remained stable over time. Conclusion: These preliminary data show that dual time i maging appears to be useful in distinguishing malignant from benign lesions . Further research is necessary to confirm these results.