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Dual-Time-Point ¹⁸F-FDG PET for the Evaluation of Gallbladder Carcinoma

¹ Department of Radiology, Faculty of Medicine, Kagawa University, Kagawa, Japan; and ² First Department of Surgery, Faculty of Medicine, Kagawa University, Kagawa, Japan

Correspondence: For correspondence or reprints contact: Yoshihiro Nishiyama, MD, Department of Radiology, Faculty of Medicine, Kagawa University, 1750-1 Ikenobe, Miki-cho, Kita-gun, Kagawa 761-0793, Japan. E-mail: nisiyosi{at}kms.ac.jp

Conventional imaging techniques such as ultrasonography, CT, and MRI are able to detect gallbladder abnormalities but are not always able to differentiate a malignancy from other disease processes such as cholecystitis. The purpose of the present study was to evaluate the efficacy of dual-time-point ¹⁸F-FDG PET for differentiating malignant from benign gallbladder disease. Methods: The study evaluated 32 patients who were suspected of having gallbladder tumors. ¹⁸F-FDG PET (whole body) was performed at 62 ± 8 min (early) after ¹⁸F-FDG injection and was repeated 146 ± 14 min (delayed) after injection only in the abdominal region. We evaluated the ¹⁸F-FDG uptake both visually and semiquantitatively. Semiquantitative analysis using the standardized uptake value (SUV) was performed for both early and delayed images (SUV_early and SUV_delayed, respectively). The retention index (RI) was calculated according to the equation (SUV_delayed – SUV_early) x 100/SUV_early. The tumor-to-liver ratio was also calculated. Results: The final diagnosis was gallbladder carcinoma in 23 patients and benign disease in 9 patients. For visual analysis of gallbladder carcinoma, delayed ¹⁸F-FDG PET images improved the specificity of diagnosis in 2 patients. When an SUV_early of 4.5, SUV_delayed of 2.9, and RI of –8 were chosen as arbitrary cutoffs for differentiating between malignant and benign conditions, sensitivity increased from 82.6% to 95.7% and 100% for delayed imaging and combined early and delayed imaging (i.e., RI), respectively. With the same criteria, specificity decreased from 55.6% to 44.4% for delayed imaging and combined early and delayed imaging, respectively. The specificity of ¹⁸F-FDG PET improved to 80% in the group with a normal level of C-reactive protein (CRP) and decreased to 0% in the group with an elevated CRP level. For gallbladder carcinoma, both SUV and tumor-to-liver ratios derived from delayed images were significantly higher than the ratios derived from early images (P < 0.0001). Conclusion: Delayed ¹⁸F-FDG PET is more helpful than early ¹⁸F-FDG PET for evaluating malignant lesions because of increased lesion uptake and increased lesion-to-background contrast. However, the diagnostic performance of ¹⁸F-FDG PET depends on CRP levels.

Key Words: delayed PET • ¹⁸F-FDG PET • gallbladder tumor

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