Comparison of the effect of positive and negative oral contrast agents on delineation and 18F-FDG uptake of gastrointestinal tract

Objective: To compare the different effects of 1% diatrizoate meglumine, 2.5% mannitol and water as oral contrasts in PET/CT scan in gastrointestinal tract delineation and 18F-fluorodeoxyglucose (FDG) uptake. Methods: Sixty-one patients referred for PET/CT scan without gastrointestinal diseases were divided into three groups randomly (random number method). One liter of 1% diatrizoate meglumine, 2.5% mannitol, or water was orally taken by groups 1 (25 cases), 2 (20 cases) and 3 (16 cases), respectively before scan. The scan was performed with GE Discovery LS PET/CT scanner in two-dimensional (2D) mode 50 min after 18F-FDG (5.55 MBq/kg) injection. Patients with abdominal lesions were excluded from this study. The degree of gastrointestinal filling and 18F-FDG uptake was evaluated by 3 nuclear medicine physicians using visual analysis according to a 4-grade classification method: none, mild, moderate, and high. Statistically analysis was performed by Kruskal-Wallis, Mann-Whitney and paired t tests. Results: Both the differences of serum glucose and insulin levels were not significant before and after contrast taken in group 2. Group 2 had better gastrointestinal filling than that of group 1 and also better than group 3 except in rectum. The stomach, jejunum, ascending, and transverse colon were better filled in group 1 than in group 3. The degree of 18F-FDG uptake of group 3 was significantly higher than that of group 2 in stomach, jejunum and ileum (z= -3.192, -3.290, -3.290, all P<0.05), and was also significantly higher than that of group 1 (z =-3.603, P<0.05) in jejunum. The degree of 18F-FDG uptake of group 3 was significantly lower than that of group 1 in ascending colon (z =-2.706, P<0.05) and was significantly lower than that of group 1 and 2 in transverse and descending colon (z=-3.503, -2.403, - 4.225, -4. 027, all P<0.05), and was also significantly lower than that of group 2 in rectum (z =-4.128, P<0.01). The maximum CT values in stomach, jejunum, ileum and ascending colon in group 1 were (132±23), (191±31), (313±47) and (374±53) HU, respectively, whose difference was significant (t =-7.088 - -1.781, all P<0.01). Conclusion: Oral iso-osmotic mannitol intake has better gastrointestinal filling and less physiological 18F-FDG uptake compared to diatrizoate meglumine and water. (authors)