Gastric emptying scintigraphy: Diagnostic value of delayed imaging and the impact on reclassification of diagnosis

INTRODUCTION: To investigate added diagnostic value of delayed imaging at 3 and 4 hours compared to 2-hour imaging as well as scanning up to 4 hours in comparison to 3, and by this means, diagnosis reclassification or changes in diagnosis across various time points.
METHODS: Seventeen patients clinically suspected of gastroparesis underwent a gastric emptying scintigraphy after ingesting standard meal. One-minute static images in anterior and posterior projections were acquired immediately after ingestion and then, at 1-, 2-, 3- and, 4-hour time points. For image analysis, a manual region-of-interest was drawn, and then, count of stomach in each projection was used to calculate geometric mean for each time point. Decay correction was applied. At 2-, 3- and 4-hour time points, percentage of retained activity was compared to standard values and therefore, each patient was labeled as normal or delayed.
RESULTS: Value of hour 3 shows extremely strong correlation with value of hour 4 (r= 0.951, p<0.001). In hour 2, of 17 participants, 11 (64.7%) were diagnosed as normal and 6 (35.3%) as delayed. In hour 3, the diagnosis made as delayed rose to 9 (52.9%), whereas normal was 8 (47.1%). Finally, in hour 4, results were 10 (58.8%) as delayed and 7 (41.2%) as normal. All subjects who were labeled as delayed in hour 3, remained with the same diagnosis and 1 out of 8 subjects categorized as normal in hour 3, changed to delayed. For testing agreement, coefficient of kappa was computed between each pair. Agreement between diagnosis in hour 2 with hours 3 or 4 was not strong (kappa<0.6 for both pairs). But a strong agreement was found between diagnosis in hours 3 and 4 (kappa=0.881).
DISCUSSION AND CONCLUSION: Extending acquisition from 3 hours to 4 hours adds little to the final diagnosis and may not be noticeably meaningful, especially in the clinical setting.