Background:
Positron emission tomography (pet) using (18)f-fluoro-2-deoxy-d-glucose (fdg) has been used for the evaluation of various tumors, but accumulation in inflammatory lesions makes it a controversial modality. the aim of this study was to investigate the usefulness of delayed scanning in differentiation between malignant and benign lesions in the pancreas.
Methods:
Forty-seven patients with suspected pancreatic carcinoma were studied by fdg-pet. all patients received approximately 370 megabequerels of fdg after a transmission scan, and an emission scan was performed 1 hour and 2 hours later for all patients. a subset of 19 patients was also scanned at 3 hours postinjection. the standardized uptake value (suv) was determined, and the retention index was calculated by dividing the increase in the suv between 1 hour and 2 hours postinjection by the suv at 1 hour postinjection.
Results:
Of 27 malignant lesions, the suvs of 22 lesions increased at 2 hours postinjection, whereas the fdg uptake in 17 of 20 benign lesions decreased. the suvs at 3 hours postinjection were higher than those at 2 hours postinjection in 9 of 14 malignant lesions and in 2 of 5 benign lesions. malignant lesions showed a higher retention index than benign lesions (mean +/- standard deviation: 12. 36 +/- 13.37 and -7.05 +/- 17.28, respectively; p < 0.0001). applying an suv of 2.5 at 1 hour postinjection with the cut-off value for the differentiation between malignant and benign lesions caused one false negative result and seven false positive results, with a diagnostic accuracy of 83.0% (39 of 47 patients). however, combining the retention index with the suv obtained at 2 hours postinjection provided a higher diagnostic accuracy (91.5%; 43 or 47 patients) than the suv alone. the false negative rate remained constant when the retention index was taken into account. images at 3 hours postinjection usually were unhelpful in differentiating further between malignant lesions and benign lesions.
Conclusions:
The current data suggest that delayed fdg-pet scanning at 2 hours postinjection may contribute to differentiation between malignant and benign lesions in the pancreas.