Gastric Emptying

Abstract

See CME exam on page 810. See CME exam on page 810. The gastric emptying of chyme is arguably the most important function of the stomach, just as the ejection of blood is the most important function of the heart. There is a rich history involving the assessment of gastric emptying, including the direct observation of gastric contents across a fistula,1Beaumont W. Experiments and observations on the gastric juice and the physiology of digestion. FF Allen, Plattsburgh1833Google Scholar use of intubation and aspiration methods, electrical impedance tomography, telemetric pH measuring devices, drug absorption assays, and stable isotope breath tests. However, imaging techniques have been most widely applied to measure gastric emptying because of the capacity to directly measure what is happening to the meal in the stomach in a noninvasive manner. One of the oldest methods, originally pioneered by Walter B. Cannon in the late nineteenth century in animal studies, involved administration of radiopaque contrast agent and use of fluoroscopy to assess gastric function after a meal. This is not a practical approach because of the substantial radiation exposure and the nonphysiological nature of the inert contrast meal.2Cannon W.B. The movements of the stomach studied by Rontgen rays.Am J Physiol. 1898; 1: 359-382Google Scholar Serial abdominal x-rays of barium pellets incorporated into a solid meal have also been used to determine gastric emptying, but the size and nature of the pellets indicate that the emptying occurs with the return of the interdigestive migrating motor complex rather than with the emptying of digestible food.3Feldman M. Smith H.J. Simon T.R. Gastric emptying of solid radiopaque markers: studies in healthy subjects and diabetic patients.Gastroenterology. 1984; 87: 895-902PubMed Google Scholar In contemporary times, gastric emptying scintigraphy (GES) has emerged as the most widely used test for the assessment of gastric emptying. New applications of magnetic resonance imaging (MRI) and ultrasonography (US) are also in development for measurement of gastric emptying. In this paper we will review the background, methodology, strengths, and limitations of gastric emptying scintigraphy, MRI, and US. First described in 1966,4Griffith G.H. Owen G.M. Kirkman S. et al.Measurement of rate of gastric emptying using chromium-51.Lancet. 1966; 1: 1244-1245Abstract PubMed Google Scholar GES is widely regarded as the gold standard test to determine stomach emptying.5Camilleri M. Hasler W.L. Parkman H.P. et al.Measurement of gastrointestinal motility in the GI laboratory.Gastroenterology. 1998; 115: 747-762Abstract Full Text Full Text PDF PubMed Scopus (278) Google Scholar, 6Akkermans L.M.A. Isselt J.W.V. Gastric motility and emptying studies with radionuclides in research and clinical settings.Dig Dis Sci. 1994; 39: 95S-96SCrossref PubMed Scopus (37) Google Scholar Early studies utilized dual-isotope labeling of solid and liquid phases of the meal. However, liquid emptying is physiologically different from stomach emptying of solids, because liquids require no trituration. Because liquid emptying does not become abnormal until gastroparesis is very severe, the emptying of liquids is not commonly tested in clinical practice.7Loo F.D. Palmer D.W. Soergel K.H. et al.Gastric emptying in patients with diabetes mellitus.Gastroenterology. 1984; 86: 485-494PubMed Scopus (224) Google Scholar If a single radiotracer is used to label the meal to measure stomach and small bowel transit, a second radiotracer has been used to assess colonic transit.8Camilleri M. Zinsmeister A.R. Towards a relatively inexpensive, noninvasive, accurate test for colonic motility disorders.Gastroenterology. 1992; 103: 36-42Abstract PubMed Google Scholar To obtain maximum information on gastric emptying from a single radiotracer, the optimal test meal labels the solid phase, and the composition must be standardized with regard to volume, density, and caloric and nutrient content. The method used for image acquisition also must be standardized. For example, changing body position from sitting or standing to supine can significantly slow gastric emptying by more than 50% at 1 hour.9Moore J.G. Datz F.L. Christian P.E. et al.Effect of body posture on radionuclide measurements of gastric emptying.Dig Dis Sci. 1988; 33: 1592-1595Crossref PubMed Scopus (79) Google Scholar It is important to ensure that the radiolabel remains bound to the solid food while in the stomach and does not dissociate from the solids to empty with the faster liquid phase, which consists of gastric secretions and any ingested liquid component of the test meal. Simply mixing the radiotracer with a food does not result in binding of the tracer to the component that one wishes to measure. The validation of a radiolabeled test meal requires simulation of binding under typical gastric conditions with the meal minced and suspended in 0.1 M hydrochloric acid containing pepsin agitated for at least 3 hours at 37° Celsius. After separation by filtration, scintigraphic activity of both phases is measured to ensure that the radiolabel remains >98% bound to the solid phase. The first meal to demonstrate true association of the radiolabel with food under simulated conditions of the gastric environment was the in vivo-labeled chicken liver preparation, which involved injecting a live chicken with 99mTc-sulfur colloid (99mTc-SC) for binding of 99mTc intracellularly to Kupffer cells, sacrificing the animal, removing the liver, dicing it into cubes, and cooking. More convenient meals, prepared by mixing 99mTc-SC with whole eggs (where it binds to protein) followed by cooking which fixes the label to the egg white, have been validated.10Keshavarzian A. Clinical applications of gastrointestinal nuclear medicine.in: Henkin R.E. Nuclear medicine. Mosby, Philadelphia2006: 893-905Google Scholar The current consensus meal for comparability across centers or in multicenter studies was established by Tougas et al and is prepared by mixing Egg Beaters® (ConAgra Foods Inc, Omaha, NE pasteurized egg white) with 99mTc-SC. The stability of radiolabel binding of this meal was validated in vitro under gastric conditions, and also compared in human subjects with the in vivo-labeled chicken liver meal.11Tougas G. Eaker E.Y. Abell T.L. et al.Assessment of gastric emptying using a low fat meal: establishment of international control values.Am J Gastroenterol. 2000; 95: 1456-1462Crossref PubMed Google Scholar The typical indications for performing GES or any other measure of gastric emptying are: (1) unexplained nausea, vomiting, and dyspeptic symptoms; (2) assessment of gastric motility prior to fundoplication for gastroesophageal reflux disease; (3) assessment of gastric motility prior to small bowel transplantation or colectomy for colonic inertia; and (4) to screen for gastroparesis in diabetic patients who are being considered for treatment with medications that may further retard gastric emptying (eg, pramlintide [Amylin, Amylin Pharmaceuticals, Inc, San Diego, CA] and exenatide [Byetta, Amylin Pharmaceuticals, Inc]). The principles of the consensus method are: discontinuation of all motility altering medications for 48 hours prior to the test; ensuring blood glucose control of <275 mg/dL on the day of the test; a 255 kcal low fat test meal composed of Egg Beaters® (120 g) labeled with 0.5 mCi 99mTc-SC radioisotope (cooked either in a nonstick frying pan or microwaved), 2 slices of bread, strawberry jam (30 g), and water (120 mL). The subject ingests the Egg Beaters® sandwich meal within 10 minutes. Technical factors may complicate interpretation of results of the gastric emptying test: use of a nonstandard test meal, lack of well-validated normal ranges, and imaging over 90 or 120 minutes with mathematical extrapolation of the T1/2. Scanning of the gastric area with an external gamma camera is performed immediately after meal ingestion (t- = 0), and at 1, 2 and 4 hours (Figure 1), and anterior and posterior images are obtained in standing position. In between imaging sessions, subjects are permitted to sit and to walk to and from the imaging room and bathroom, avoiding strenuous activity. Anterior and posterior images can be obtained simultaneously with a dual-head camera or sequentially with a single-headed camera to correct for tissue attenuation, as counts can increase or decrease according to the distance of gastric contents from the detector. Quantification of gastric emptying is performed by drawing regions of interest (ROI) on the anterior and posterior digital images of the entire stomach for all acquisition times (Figure 1), with attention to avoid small bowel loops in proximity to the stomach. This is typically not a problem with GES of solids, but it can be a real challenge when GES of radiolabeled liquids is evaluated. The counts measured from the stomach at each time point are directly proportional to the amount of the meal remaining in the stomach, and they are corrected for depth or distance between the camera and the intragastric radioactivity, as the plane of the stomach differs for the proximal and distal regions, and it may also differ with degree of obesity [(anterior counts × posterior counts)1/2]. Similarly, corrections are needed for 99mTc decay, using standard tables. The final results are expressed as percent remaining in the stomach at each time point, normalized to 100% for time t = 0 (first image set immediately after meal ingestion). The normal values are: at 1 hour (37%–90%), 2 hours (30%–60%), and 4 hours (0%–10%). The major limitations to widespread use of GES was lack of standardization of meal composition, patient positioning, timing of image acquisition, and lack of appropriate normal values with some meals. A consensus statement, published from the American Neurogastroenterology and Motility Society and the Society of Nuclear Medicine, described in detail a standardized protocol for Egg Beaters® meal11Tougas G. Eaker E.Y. Abell T.L. et al.Assessment of gastric emptying using a low fat meal: establishment of international control values.Am J Gastroenterol. 2000; 95: 1456-1462Crossref PubMed Google Scholar labeling and image acquisition intended for uniform adoption.12Abell T.L. Camilleri M. Donohoe K. et al.Consensus recommendations for gastric emptying scintigraphy: a joint report of the American Neurogastroenterology and Motility Society and the Society of Nuclear Medicine.Am J Gastroenterol. 2008; 103: 753-763Crossref PubMed Scopus (427) Google Scholar Because there is significant intraindividual variation in gastric emptying rates (up to 15%, even in healthy individuals13Degan L.P. Phillips S.F. Variability of gastrointestinal transit in healthy women and men.Gut. 1996; 39: 299-305Crossref PubMed Scopus (252) Google Scholar), and the relationship of gastric emptying rates with symptoms remains controversial,14Talley N.F. Locke G.R. Lahr B.D. et al.Functional dyspepsia, delayed gastric emptying, and impaired quality of life.Gut. 2006; 55: 933-939Crossref PubMed Scopus (215) Google Scholar results of GES should be interpreted judiciously in clinical practice. Thus, it is not clear that patient's symptoms are actually caused by the impaired gastric emptying. In laboratory-based studies that induced dyspepsia by altering of gastric emptying, and in patients with dyspepsia, the rate of gastric emptying accounted for <50% of the variance in symptoms.15Delgado-Aros S. Camilleri M. Castillo E.J. et al.Effect of gastric volume or emptying on meal-related symptoms after liquid nutrients in obesity: a pharmacologic study.Clin Gastroenterol Hepatol. 2005; 3: 997-1006Abstract Full Text Full Text PDF PubMed Scopus (56) Google Scholar, 16Delgado-Aros S. Camilleri M. Cremonini F. et al.Contributions of gastric volumes and gastric emptying to meal size and post-meal symptoms in functional dyspepsia.Gastroenterology. 2004; 127: 1685-1694Abstract Full Text Full Text PDF PubMed Scopus (197) Google Scholar Similarly, the degree of delay on the scintigraphy study should not be used alone to grade the severity of gastroparesis. Severity of gastroparesis is better assessed by clinical parameters including frequency of vomiting, hydration, ability to tolerate oral feeding, and nutritional status, as well as gastric residual at 4 hours.17Camilleri M. Clinical practice Diabetic gastroparesis.N Engl J Med. 2007; 356: 820-829Crossref PubMed Scopus (249) Google Scholar Radiation exposure is an important consideration; radiation dose absorbed for the total body in healthy subjects from exposure to 0.5mCi 99mTc-SC in eggs is 10 mrad.18Siegel J.A. Wu R.K. Knight L.C. et al.Radiation dose estimates for oral agents used in upper gastrointestinal disease.J Nucl Med. 1983; 24: 835-837PubMed Google Scholar This compares to approximately 12 mrad radiation exposure from a chest x-ray and yearly exposure to 300 mrad from background radiation.19Kelsey C.A. Mettler Jr, F.A. Sullivan L.M. Radiation dose and image quality of double-loaded cassettes.Med Physics. 1996; 23: 239-240Crossref PubMed Scopus (2) Google Scholar Due to radiation exposure and absence of normal values, GES is not recommended in pregnant women and, when performed in children, there should be due consideration of the benefit to risk ratio. Magnetic resonance imaging (MRI) for measurement of gastrointestinal functions was first described by Stehling et al in 1989.20Stehling M.K. Evans D.F. Lamont G. et al.Gastrointestinal tract: dynamic MR studies with echo-planar imaging.Radiology. 1989; 171: 41-46PubMed Google Scholar Schwizer et al investigated emptying of a liquid enteral nutrient test meal labeled with gadolinium tetra-azacyclododecane tetra-acetic acid (Gd-DOTA) as an MRI marker. They obtained good contrast between stomach content and surrounding tissue and validated this method by comparison with scintigraphy in 5 healthy subjects and 5 patients with delayed gastric emptying.21Schwizer W. Fraser R. Maecke H. et al.Gd-DOTA as a gastrointestinal contrast agent for gastric emptying measurements with MRI.Magnet Resonance Med. 1994; 31: 388-393Crossref PubMed Scopus (56) Google Scholar The method has also been used to study effect of prokinetic medication on gastric contractility and emptying.22Kunz P. Crelier G.R. Schwizer W. et al.Gastric emptying and motility: assessment with MR imaging--preliminary observations.Radiology. 1998; 207: 33-40Crossref PubMed Scopus (70) Google Scholar, 23Borovicka J. Lehmann R. Kunz P. et al.Evaluation of gastric emptying and motility in diabetic gastroparesis with magnetic resonance imaging: effects of cisapride.Am J Gastroenterol. 1999; 94: 2866-2873Crossref PubMed Scopus (41) Google Scholar, 24Lauenstein T.C. Vogt F.M. Herborn C.U. et al.Time-resolved three-dimensional MR imaging of gastric emptying modified by IV administration of erythromycin.Am J Roentgenol. 2003; 180: 1305-1310Crossref PubMed Scopus (21) Google Scholar However, the stability of gadolinium tetra-azacyclododecane tetra-acetic acid labeling to the liquid phase of the meal has not been completely validated. Because clinically relevant information is usually based on gastric emptying of a solid meal,25Kunz P. Feinle C. Schwizer W. et al.Assessment of gastric motor function during the emptying of solid and liquid meals in humans by MRI.J Magnet Resonance Imag. 1999; 9: 75-80Crossref PubMed Scopus (59) Google Scholar an MRI method was developed using a 523 kcal pancake meal composed of egg, potato, bacon, butter, and water. This solid meal gave sufficient contrast without addition of a contrast agent, and subjects were examined in supine position over 120 minutes with separate scans performed every 15 minutes to determine gastric volume, secretion, and motility. Gastric emptying and secretion are measured by defined areas of interest on each slice and then by determining the total volume of gastric contents by addition of the individual slice volumes.26Schwizer W. Fraser R. Borovicka J. et al.Measurement of gastric emptying and gastric motility by magnetic resonance imaging (MRI).Dig Dis Sci. 1994; 39: 101S-103SCrossref PubMed Scopus (56) Google Scholar Net gastric meal volumes, corrected for gastric secretion, are then fitted to a power exponential to obtain T1/2. The gastric emptying rates of equivalent macronutrient content, homogenized liquids, and solids, measured by MRI were similar in healthy subjects. This contrasts with findings on scintigraphy, which show solid emptying slower than homogenized liquids, as emptying of solids is associated with a well defined lag period to allow for trituration, which is not required by nutrient liquids. In subsequent MRI studies of test meals of different composition, nutrient content was a more important factor in delaying gastric emptying than meal viscosity27Faas H. Steingoetter A. Feinle C. et al.Effects of meal consistency and ingested fluid volume on the intragastric distribution of a drug model in humans--a magnetic resonance imaging study.Aliment Pharmacol Ther. 2002; 16: 217-224Crossref PubMed Scopus (6) Google Scholar and, in a separate study, body position did not affect gastric emptying rates for nonnutritive liquids.28Steingoetter A. Fox M. Treier R. et al.Effects of posture on the physiology of gastric emptying: a magnetic resonance imaging study.J Gastroenterol. 2006; 41: 1155-1164Google Scholar This is consistent with the extremely rapid, exponential emptying of noncaloric liquids. With sufficient contrast between the gastric wall and intraluminal content obtained with MRI and use of coronal scans to estimate diameters of proximal and distal stomach, the motor function of the stomach can be measured, providing visual and quantitative assessment of gastric emptying and motility including the frequency, amplitude, speed, and direction of propagated antral contractions.29Bilecen D. Scheffler K. Seifritz E. et al.Hydro-MRI for the visualization of gastric wall motility using RARE magnetic resonance imaging sequences.Abdom Imaging. 2000; 25: 30-34Crossref PubMed Scopus (29) Google Scholar A small study of 10 patients and 10 controls suggests that a gastric motility index (amplitude of antral contractions multiplied by the frequency) measured by MRI can distinguish normal patients from those with gastroparesis.30Ajaj W. Goehde S.C. Papanikolaou N. et al.Real time high resolution magnetic resonance imaging for the assessment of gastric motility disorders.Gut. 2004; 53: 1256-1261Crossref PubMed Scopus (92) Google Scholar One drawback of gastric emptying assessment by MRI is that it does not provide a direct assessment of the meal emptying from the stomach, because the volume of gastric contents measured has to be corrected for the gastric secretions which dilute the meal. Therefore, an estimate must be made of the amount of the gastric secretion based upon the relative signal intensity obtained by ex vivo imaging of the test meal at various dilutions by the addition of 0.01 M hydrochloric acid to the container.24Lauenstein T.C. Vogt F.M. Herborn C.U. et al.Time-resolved three-dimensional MR imaging of gastric emptying modified by IV administration of erythromycin.Am J Roentgenol. 2003; 180: 1305-1310Crossref PubMed Scopus (21) Google Scholar MRI has not been validated to the same degree as scintigraphy; there are few studies in disease states or in response to different perturbations other than the effects of different nutrients or drugs. MRI is also comparatively expensive (equipment, imaging time, and expertise). Current protocols require frequent imaging sequences, and subject cooperation is also necessary, such as holding breath in expiration to reduce motion artifacts during scans. Unlike GES, MRI can simultaneously assess other extragastric organs, excluding anatomical, inflammatory, or neoplastic processes in the upper abdomen, and it can evaluate relevant secretory and motility functions of the stomach, gallbladder,31Marciani L. Bush D. Wright P. et al.Monitoring of gallbladder and gastric coordination by EPI.J Magnet Resonance Imag. 2005; 21: 82-85Crossref PubMed Scopus (18) Google Scholar pancreas,32Bali M.A. Sztantics A. Metens T. et al.Quantification of pancreatic exocrine function with secretin-enhanced magnetic resonance cholangiopancreatography: normal values and short-term effects of pancreatic duct drainage procedures in chronic pancreatitis Initial results.Eur Radiol. 2005; 15: 2110-2121Crossref PubMed Scopus (72) Google Scholar and intestines.33Schwizer W. Steingoetter A. Fox M. Magnetic resonance imaging for the assessment of gastrointestinal function.Scand J Gastroenterol. 2006; 41: 1245-1260Crossref PubMed Scopus (80) Google Scholar It may also become possible to simultaneously study gut functions during brain assessment by functional MRI for a comprehensive “one-stop” assessment.34Mertz H. Morgan V. Tanner G. et al.Regional cerebral activation in irritable bowel syndrome and control subjects with painful and nonpainful rectal distension.Gastroenterology. 2000; 118: 842-848Abstract Full Text Full Text PDF PubMed Scopus (509) Google Scholar Further refinements and validation are needed before MRI is ready for application in clinical practice or research; however, the ability to resolve wall motion and assess extragastric organs and absence of radiation are additional attributes of the MRI test. Functional ultrasonography is a relatively inexpensive, safe, noninvasive method to gastric function. Gastric emptying of liquids using 2-dimensional (2D) ultrasonography was first described in the early 1980s.35Bateman D.N. Whittingham T.A. Measurement of gastric emptying by real-time ultrasound.Gut. 1982; 23: 524-527Crossref PubMed Scopus (155) Google Scholar 2D ultrasonography indirectly determines gastric emptying by the changes in the antral area over time. This has been validated by comparison with GES in healthy subjects,36Holt S. Cervantes J. Wilkinson A.A. et al.Measurement of gastric emptying rate in humans by real-time ultrasound.Gastroenterology. 1986; 90: 918-923Abstract PubMed Google Scholar, 37Marzio L. Giacobbe A. Conoscitore P. et al.Evaluation of the use of ultrasonography in the study of liquid gastric emptying.Am J Gastroenterol. 1989; 84: 496-500PubMed Google Scholar patients with type 1 diabetes mellitus,38Darwiche G. Almer L.O. Bjorgell O. et al.Measurement of gastric emptying by standardized real-time ultrasonography in healthy subjects and diabetic patients.J Ultrasound Med. 1999; 18: 673-682PubMed Google Scholar and functional dyspepsia.39Aoki S. Haruma K. Kusunoki H. et al.Evaluation of gastric emptying measured with the 13C-octanoic acid breath test in patients with functional dyspepsia: comparison with ultrasonography.Scand J Gastroenterol. 2002; 37: 662-666Crossref PubMed Scopus (36) Google Scholar Duplex Doppler techniques have been applied to study transpyloric flow of liquid meals,40King P.M. Adam R.D. Pryde A. et al.Relationships of human antroduodenal motility and transpyloric fluid movement: non-invasive observations with real-time ultrasound.Gut. 1984; 25: 1384-1391Crossref PubMed Scopus (114) Google Scholar, 41Hausken T. Odegaard S. Matre K. et al.Antroduodenal motility and movements of luminal contents studied by duplex sonography.Gastroenterology. 1992; 102: 1583-1590Abstract PubMed Google Scholar with episodes of gastric emptying defined with a mean velocity of >10 cm/sec, lasting for >1 sec.42Gilja O.H. Hatbleck J.G. Odegaard S. et al.Advanced imaging and visualization in gastrointestinal disorders.World J Gastroenterol. 2007; 13: 1408-1421PubMed Google Scholar Using this method, timing of postprandial dyspeptic symptoms and transpyloric passage of gastric contents can be studied with great temporal and spatial resolution,43Hausken T. Gilja O.H. Undeland K.A. et al.Timing of postprandial dyspeptic symptoms and transpyloric passage of gastric contents.Scand J Gastroenterol. 1998; 33: 822-827Crossref PubMed Scopus (49) Google Scholar including assessment of the effect of pharmacological intervention.44Hausken T. Gilja O.H. Odegaard S. et al.Flow across the human pylorus soon after ingestion of food, studied with duplex sonography Effect of glyceryl trinitrate.Scand J Gastroenterol. 1998; 33: 484-490Crossref PubMed Scopus (39) Google Scholar Hausken et al developed a noninvasive method to evaluate transpyloric flow and duodenogastric reflux stroke volumes using a 3-dimensional (3D) guided digital color Doppler imaging model.45Hausken T. Li X.N. Goldman B. et al.Quantification of gastric emptying and duodenogastric reflux stroke volumes using three-dimensional guided digital color Doppler imaging.Eur J Ultrasound. 2001; 13: 205-213Crossref PubMed Scopus (27) Google Scholar This offers greater accuracy and less variability than 2D ultrasonography. Healthy subjects were studied during ingestion of a liquid meal and 10 minutes postprandially. The 3D position and orientation data were acquired using a magnetic sensing system. There were high intra- and inter-individual variations of the stroke volumes of transpyloric flow episodes during the initial gastric emptying. The duodenogastric reflux episodes lasted on average 2.4 sec with an average volume of 8.3 mL. 3D ultrasonography has been validated against scintigraphy in a small number of healthy volunteers.46Gentilcore D. Hausken T. Horowitz M. et al.Measurements of gastric emptying of low- and high-nutrient liquids using 3D ultrasonography and scintigraphy in healthy subjects.Neurogastroenterol Motil. 2006; 18: 1062-1068Crossref PubMed Scopus (74) Google Scholar 3D ultrasonography allows measurement of proximal stomach accommodation after a meal in adults47van Lelyveld N. Schipper M. Samsom M. Lack of relationship between chronic upper abdominal symptoms and gastric function in functional dyspepsia.Dig Dis Sci. 2008; 53: 1223-1230Crossref PubMed Scopus (24) Google Scholar and adolescents,48Manini M.L. Burton D.D. Meixner D.D. et al.Feasibility and application of 3-dimensional ultrasound for measurement of gastric volumes in healthy adults and adolescents.J Pediatr Gastroenterol Nutr. 2009; 48: 287-293Crossref PubMed Scopus (25) Google Scholar and this is impaired in dyspepsia.47van Lelyveld N. Schipper M. Samsom M. Lack of relationship between chronic upper abdominal symptoms and gastric function in functional dyspepsia.Dig Dis Sci. 2008; 53: 1223-1230Crossref PubMed Scopus (24) Google Scholar The advantages of US techniques are widely available equipment, modest running costs, and no radiation exposure. Ultrasonography shows reasonably good interobserver agreement in the evaluation of the gastric emptying of a liquid meal.49Irvine E.J. Tougas G. Lappalainen R. et al.Reliability and interobserver variability of ultrasonographic measurement of gastric emptying rate.Dig Dis Sci. 1993; 38: 803-810Crossref PubMed Scopus (75) Google Scholar Limitations of ultrasonography are that it is best suited for assessing gastric emptying of liquids, which is of limited clinical utility. With 3D ultrasonography, very few studies have utilized a solid meal and simultaneous scintigraphy.50Benini L. Sembenini C. Heading R.C. et al.Simultaneous measurement of gastric emptying of solid meal by ultrasound and by scintigraphy.Am J Gastroenterol. 1999; 94: 2861-2865Crossref PubMed Scopus (72) Google Scholar, 51Darwiche G. Bjorgell O. Thorsson O. et al.Correlation between simultaneous scintigraphic and ultrasonographic measurements of gastric emptying in patients with type I diabetes mellitus.J Ultrasound Med. 2003; 22: 459-466PubMed Google Scholar Disadvantages are the need for a skilled operator, and suboptimal imaging in people who are not lean, and when there is air in the stomach. Ultrasonography is generally impractical for prolonged observations. MRI has the advantage of providing comprehensive information, but it has significant costs and requires further validation. Functional ultrasonography is being developed to expand current capabilities and 3D US could conceivably become the most cost-effective gastric emptying and accommodation test. However, validation is needed. Thus, GES, improved by recent consensus procedural recommendations, remains the current gold standard.