Optimal timing of imaging in gastric emptying scintigraphy for the detection of delayed emptying.

OBJECTIVE: The purpose of this study was to evaluate a standard 4-h imaging protocol for gastric emptying scintigraphy (GES) in detecting delayed gastric emptying (GE). SUBJECTS AND METHODS: Gamma camera imaging was performed in the anterior and posterior views at 0, 0.5, 1, 1.5, 2, 2.5 and 4-h as per established Miami method (MIA) and National Standard Protocol (NSP), in accordance with the consensus guidelines of the ANMS/SNM [SNMMI] Societies. Patients (N=1002) received a standardized solid meal radiolabeled with 1mCi of technetium-99 (99mTc) sulfur colloid. Quantitative analysis was performed using geometric mean calculation of decay-corrected counts at each imaging time point, expressed as percent emptying or retention. RESULTS: In our patient cohort, 21% had delayed GE at 4h, whereas 79% had normal emptying with less than 10% retention at 4h. There was a 25% increase in delayed GE studies at 4h versus 2h. From those patients who had delayed GE at 2h, 30% normalized at 4h, while 10% of patients with normal GE at 2h became delayed at 4h thus indicating that more studies changed from abnormal to normal than from normal to abnormal at 4h. Greater than 90% GE was found in 9% of patients at 2 h and 25% of patients at 2.5h and this persisted at 4h. The study at 2h as compared with 4h, had 56% sensitivity, 95% specificity, 70% PPV and 91% NPV. CONCLUSION: The 4-h imaging was very important in detecting cases that were delayed at 2h but normalized at 4h, and also cases with normal GE at 2h that became abnormal at 4h. These findings support the ANMS/SNM [SNMMI] recommendations. Gastric emptying value ≥90% at 2.5h can be used as threshold in predicting normal GE and the study could be terminated without additional imaging.