Gastric emptying rate assessment based on the proportion of intra-abdominal radioactivity in the stomach

Using scintigraphic techniques, the rate of gastric emptying is calculated by quantifying the absolute radioactivity within a gastric region of interest (Âintragastric method) with the time of meal completion considered 100% retention. However, this technique has significant limitations arising from subject move ment and radionuclide gamma-ray attenuation, which may ren der curve fitting difficult, particularly in patients with gastroparesis. In an attemptto minimizethese limitations,we have expressed the intragastric content as a percentage of the total abdominal radioactivity (abdominal method) and compared these two meth ods. Methods: Forty-five subjects in a sitting position consumed a meal consisting of two fried eggs labeled with 99mTc, two slices of toast and 300 mL 5% glucose water (412 kcal). Data were acquired at a rate of one frame every 5 min from the left anterior oblique view. Using the two methods, the intragastric retention ratios at 30, 60, 90,120 and 240 min and the 50% emptying time (T50) were obtained from both observation and calculation by power exponential fit. R2, representing goodness of fit of the nonlinear curve fitting, was calculated. Results: There were no differences in the calculated values of T50 between the two methods. Quantitative estimates of T50 by extrapolation of a power exponential fit were feasible in 42 of the 45 subjects when the abdominal method was used, compared with only 29 of the 45 subjects when the intragastric method was used. In the 23 subjects with delayed emptying, quantitative estimates of T50 were feasible in 20 subjects when the abdominal method was used, compared with 7 subjects when the intragastric method was used. Using the abdominal method as opposed to the intragastric method also significantly improved R2.The difference between observed values and estimated values of T50 and Âintragastric retention ratios at 30, 90 and 120 min was smaller using the abdominal method. Conclusion: Scintigraphic mea surement of gastric emptying calculated using the proportion of the abdominal radioactivity in the stomach offers substantial advantages over conventional methods, particularly in patients with gastroparesis.