Gastric emptying scintigraphy of antro-pyloro-duodenal coordination (APDC): A dose validation study

366 Objectives: Dynamic antral contraction scintigraphy (DACS) which utilizes rapid frame acquisition of gastric emptying scintigraphy(GES) images has previously been utilized to assess the frequency and amplitude of antral contractions. DACS is used to provide additional information on patients with upper GI dyspepsia when symptoms are not explained by conventional static GES alone. A lack of antro-pyloro-duodenal coordination (APDC) is thought to be an important pathophysiologic disorder contributing to patient symptoms. Expanding DACS to include analysis of APDC may increase the diagnostic value of GES. The aim of this study was to investigate the technical feasibility of measuring APDC with DACS during GES. This is technically challenging since after trituration, solid particles of only 1-2 mm size pass the pylorus limiting the radiotracer signal in the duodenum compared to the signal available in the antrum. In this study, we investigated the dose of radiotracer and optimum image orientation to detect adequate signal in the duodenum. We also established initial normal values for APDC contractions. Methods: Normal volunteers (9 females, 11 males; average age 36.0±15.6 years) underwent GESusing the standardized SNMMI recommended 4 hr egg-white meal. DACS was performed as previously described (Knight 1997). The dose of Tc-99m sulfur colloid(SC) for GES was given in increasing doses of: 74 MBq(2 mCi )(n=6), 185 MBq(5 mCi )(n=7), and 370 MBq(10 mCi)(n=7). DACS was performed for 10 min at 0, 30, 60 min post meal ingestion in both an anterior and right anterior oblique(RAO) projection to determine optimal display of the duodenal sweep. The best projection and lowest dose of Tc-99m SC needed to measure APDC were assessed visually and by using signal to noise ratio (SNR) analysis. APDC and SNR were quantified utilizing duodenal peak activity from an ROI placed over the first portion of the duodenum where a transmitted duodenal bolus from the atrum was recorded for duodenal peaks with activity > 3SD above the mean duodenal counts. Results: Total gastric retention averaged 44.4±8.0% at 2 hrs and 7.5±8.1% at 4 hrs (mean±SD). Duodenal peaks were consistently better visualized in the RAO projection than the anterior projection and by using 185 MBq(5 mCi) and 370 MBq(10 mCi) compared to 74 MBq(2 mCi) in the images at 30 and 60 minutes post meal ingestion. APDC activity showed infrequent and irregular bolus transfers from the antrum to the duodenum. DACS showed an expected antral frequency of approximately 3 cpm. Antral activity at 30 min averaged 2.86 ±0.76 peaks/min and duodenal activity averaged 0.24±0.15 peaks/min. At 60 min, the antrum activity averaged 3.11±0.32 peaks/min and duodenum activity averaged 0.29±0.22 peaks/min. The ratio of duodenal peaks detected to antral peaks was 0.24/2.86=0.083 at 30 min and 0.29/3.11=0.090 at 60 min. Increasing SNR was observed with increasing doses of Tc-99m SC. SNR averaged 70.1±33.1 in the 74MBq images, 87.2±36.9 in the 185MBq images(p=0.02), and 93.0±38.0 in the 370MBq images(p=0.03). Conclusions: APDC can be measured during GES using DACS but requires at least a 185 MBq(5 mCi) dose of Tc-99m SC to radiolabel the test meal for adequate signal detection in the duodenum. APDC is better imaged in the RAO than the anterior projection. APDC over the first 60 min post meal ingestion is infrequent with only up to 9% of the antral contractions propagating into the duodenum in normals. This methodology appears promising to assess APDC in patients with unexplained symptoms of upper gastrointestinal dysmotility. $$graphic_9B9F6977-F690-4893-BA00-61BED17343E7$$