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 intere st (intragastric method) with the time of meal completion considered 100% r etention. However, this technique has significant limitations arising from subject movement and radionuclide gamma-ray attenuation, which may render c urve fitting difficult, particularly in patients with gastroparesis. In an attempt to minimize these limitations, we have expressed the intragastric c ontent as a percentage of the total abdominal radioactivity (abdominal meth od) and compared these two methods. Methods: Forty-five subjects in a sitti ng position consumed a meal consisting of two fried eggs labeled with Tc-99 m, two slices of toast and 300 mL 5% glucose water (412 kcal). Data were ac quired at a rate of one frame every 5 min from the left anterior oblique vi ew. 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 ob servation and calculation by power exponential fit. R-2, representing goodn ess of fit of the nonlinear curve fitting, was calculated. Results: There w ere 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 u sed. In the 23 subjects with delayed emptying, quantitative estimates of T5 0 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 R -2. The difference between observed values and estimated values of T50 and intragastric retention ratios at 30, 90 and 120 min was smaller using the a bdominal method. Conclusion: Scintigraphic measurement of gastric emptying calculated using the proportion of the abdominal radioactivity in the stoma ch offers substantial advantages over conventional methods, particularly in patients with gastroparesis.