Comparison of gastric emptying scintigraphy based on the geometric mean of the gastric proportion of the abdominal radioactivity or on the geometric mean of the intragastric radioactivity

PURPOSE: Using gastric emptying scintigraphy the gastric retention rate is commonly calculated within a gastric region of interest (intragastric method). This technique may have significant limitations when left oblique anterior views are acquired, due in part to attenuation resulting from intragastric redistribution. To minimize these drawbacks, it was proposed to express the intragastric content as a percentage of the abdominal radioactivity (abdominal method). Our goal was to compare these two methods when anterior-posterior scanning is used. METHODS: Antero-posterior scintigraphic data of 272 consecutive patients were analysed by both methods. Retention rates were obtained by both observation and calculation by power exponential fit. Gastric emptying parameters (half-emptying time of solids (T(50,S)) and liquids (T(50,L)), lag phase (T(lag)) time and real emptying time (T(RE))), and quality of fit were also computed and compared. RESULTS: For solids, the intragastric method resulted in weakly higher experimental retention rates, whereas retention rates were quite similar for liquids. Differences between experimental and calculated retention rates were smaller for abdominal method, for both liquids and solids. As a result, values for the quality of fit were higher for the abdominal method. Significant differences were observed only for calculated T(50,S) (122+/-46 min vs. 124+/-48 min, mean difference 2+/-2 min, P<0.00001) and T(RE) (163+/-64 min vs. 168+/-68 min, mean difference 4.5+/-3.8 min, P<0.05), respectively, for the abdominal and the intragastric methods. However, the Bland-Altman statistical method revealed good agreements (<5% outliers). CONCLUSION: Intragastric and abdominal methods can be used indifferently to treat antero-posterior data of gastric scintigraphy.