Evolution of the Gold Standard: Gastric Emptying scintigraphy beyond total gastric emptying.

Introduction: Patients referred for Gastric Emptying (GE) studies may have one or more of the numerous upper gastrointestinal symptoms ranging from nausea, vomiting, bloating, early satiety and distention to vague abdominal discomfort. GE scintigraphy is considered gold standard and indicated for evaluating patients with suspected gastroparesis or dyspepsia and presence of anatomic cause has been ruled out. GE study is also useful in severe GE reflux, and diffuse gastrointestinal motility disorders. This exhibit focuses on deeper understanding of GE and smptoms of dyspepsia pertaining to GE scintigraphy, and the methods that can be applied for comprehensive evaluation of gastric motility rather than overall GE alone.

Methods: Interpretation of GE scintigraphy is often limited to measurement and reporting of delayed or rapid GE. However, recent literature shows that presence of symptoms may not correlate well with such measurement of total GE. Noting the early distribution of the radiolabelled solid meal is important. GE for solid have an early lag (trituration) phase, which may be prolonged in some diseases notably in diabetic gastroparesis, while it is shortened after antrectomy, pyloroplasty, and intake of prokinetic drugs. Lag phase is followed by phase when GE occurs at a characteristic rate. Fundus and antrum play separate and important roles in GE, and understanding their role is important to understand symptomatology. Impairment of fundal accommodation is associated with early satiety, while fundal retention accounts for feeling of fullness. Antral contraction and pyloric relaxation determine the rate of GE. Visceral hypersensitivity to gastric distention leads to belching, postprandial pain, and weight loss.

Results: Calculating the total GE alone can be insufficient, and measurement of regional GE from fundus and antrum (bicompartmental analysis) by intragastric distribution of radiolabelled meal should be preferred, especially if total GE is normal. SPECT gastric accommodation studies utilize the physiological uptake of 99mTc-pertechnetate after intravenous administration and three-dimensional volumetric images of the gastric outer wall is obtained. This is a non-invasive method of assessing gastric volume, and simultaneous assessment of gastric volumetric analysis with radiolabelled meal emptying is also possible, in addition to accurate assessment of accommodation response. Identifying abnormal intragastric patterns of distribution can correlate with symptoms of dyspepsia. Scintigraphic study of antral contractions can measure frequency and amplitude of antral contractions, and hence deepen the insight in normal and abnormal GE. To minimize errors in interpretation and increase the reproducibility of results of GE scintigraphy, several factors play important roles viz, using standardized radiolabelled meals, establishing normal values of gastric emptying for meals, body position, time of the day when GE study is performed. The consensus recommendations by the Society of Nuclear Medicine and Molecular Imaging and the American Neurogastroenterology and Motility Society thoroughly addresses several essential criteria to standardize the method and interpretation of GE scintigraphy.

Conclusions: Symptoms of dyspepsia may not correlate well with overall gastric emptying time. It is important to note the regional distribution of the administered meal within the stomach. Bicompartmental analysis is helpful to understand the cause of symptoms, especially when overall gastric emptying is normal. Setting and following standardized criteria to perform and interpret GE scintigraphy is vital.