In the current study, we investigated the value of 18 F-FDG uptake measured by SUV on screening PET/CT images for the prediction of H. pylori infection and chronic atrophic gastritis determined by gastrointestinal fiberscopy. The major findings in this study were [1] The SUV of 18 F-FDG uptake in the stomach was significantly elevated in patients with H. pylori infection and in those with chronic atrophic gastritis [2]; 18 F-FDG uptake of the fornix in the stomach was significantly higher than those in corpus and antrum regardless of H. pylori infection and chronic atrophic gastritis [3]; mean SUVmean showed the highest area under ROC curves for predicting H. pylori infection (0.807) and chronic atrophic gastritis (0.784), and is useful for identifying patients who require gastrointestinal fiberscopy. Normalization of stomach SUVs by liver SUV provided minimal differences in the diagnostic performance and is not considered to be necessary.
Accumulation of 18F-FDG in the stomach
Pattern of accumulation of 18F-FDG in the stomach and its associated with endoscopic findings of the gastric mucosa and H. pylori infection were previously investigated by Takahashi et al [11] by using a visual assessment of 18F-FDG PET image. They classified 18F-FDG uptake in the stomach into three groups (A: localized accumulation in the fornix, B: diffuse accumulation throughout the entire stomach, C: no accumulation). They found that H. pylori infections were more frequent in Groups A and B than in Group C, concluding that accumulation of 18F-FDG in the stomach suggests a high probability of inflammatory changes to the gastric mucosa, forming a background for the development of cancer or malignant lymphoma. In our current study, we used a more objective approach by measuring SUVs of 18F-FDG in the fornix, corpus and antrum. Consistent with previous report [8, 11], we found that 18F-FDG uptake of the fornix was significantly higher than corpus and antrum. In addition, SUV of 18F-FDG in the fornix was significantly higher than those in corpus and antrum, not only in the subjects with H. pylori infection and chronic atrophic gastritis, but also in those without H. pylori infection or chronic atrophic gastritis, suggesting that high 18F-FDG uptake in an oral side of the stomach is physiological. We also noticed that H. pylori infection and chronic atrophic gastritis are associated with elevated SUVs in all gastric regions including the fornix, corpus and antrum. This indicates that H. pylori infection causes increased 18F-FDG uptake reflecting active inflammation throughout the entire stomach.
Detection of gastric neoplasms by 18F-FDG PET/CT
For the assessment of patients with advanced gastric cancer, 18F-FDG PET/CT has been shown to be useful in detecting nodal metastasis and distant metastasis, and in predicting prognosis [16–20]. However, 18F-FDG PET/CT is not useful for screening gastric cancers [5, 11, 21, 22]. Shoda et al. studies 2861 asymptomatic subjects and found that the sensitivity of 18F-FDG PET for gastric cancer was as low as 10 % [3]. Consequently the use of gastrointestinal fiberscopy is considered more appropriate in screening gastric cancer.
Clinical implications
Our results demonstrated that semi-quantitative assessment of 18F-FDG uptake with SUV has high diagnostic accuracy in predicting H. pylori infection and chronic atrophic gastritis. As previously mentioned, H. pylori infection and subsequent chronic atrophic gastritis lead to increased risk of gastric cancer formation. Inflammatory change in the gastric mucosa caused by H. pylori forms a background for the development of gastric cancer or malignant lymphoma. In a Japanese cohort study, the population attributable fraction (PAF) of H. pylori infection for gastric cancer incidence (i.e. the fraction of gastric cancer incident cases that is attributable to H. pylori infection) was estimated to be 84 % [3]. Despite the declined prevalence of H. pylori infection for the past 30 years, gastric cancer is the second most frequent cause of cancer death in both males and females in Japan, and the most frequent cancer in males and the second most frequent cancer in females [23]. Therefore, gastrointestinal fiberscopy should be strongly recommended for subjects with increased 18F-FDG uptake in the stomach. According to the results in this study, high area under ROC of 0.807 and high sensitivity of 86.5 % can be achieved when mean SUVmean values of > 2.66 was used as a threshold.
Limitations
Several limitations must be acknowledged in this study. First, this is a single-center study with a limited number of subjects, and there is a selection bias for subjects who underwent gastrointestinal fiberscopy. Second, the degree of chronic atrophic gastritis was not evaluated in current study, because the laboratory diagnosis by gastrointestinal fiberscopy was qualitative and operator-dependent. Third, CT images were acquired during natural breath-holding while PET images were obtained during free-breathing. This may result in misregistration artifact and alteration in SUV. Forth, SUV of 18F-FDG uptake in the stomach was not compared with the gastrointestinal fiberscopy findings in detail. Further investigation by prospective multi-center study using both PET-CT and gastrointestinal fiberscopy is necessary to determine the value of 18F-FDG PET in early detection and prevention of gastric cancer.