What is a gastric emptying study

A gastric emptying study is a nuclear imaging study done to evaluate the ability of the stomach to empty. Gastric emptying study is typically obtained to assess for delayed gastric emptying or gastroparesis in patients with post-prandial symptoms of nausea, vomiting, abdominal pain, and/or early satiety. Delayed gastric emptying or gastroparesis may result from a number of conditions, most commonly from diabetes mellitus. Gastroparesis may result in nausea, vomiting, bloating, sensation of early fullness during eating, or abdominal pain. Gastric emptying study is performed by administration of a meal that contains small amounts of a substance usually technetium sulfur. Images are taken of the stomach over time. Normally, within a set time, a certain amount of gastric contents exits the stomach and empties into the small intestine. This test demonstrates the amount of contents remaining in the stomach, and if the amount is below the established cut-off values, delayed stomach emptying is diagnosed.

Gastric emptying study can also provide important information in patients with esophageal reflux unresponsive to therapy or in diabetics with poor glycemic control to confirm or exclude delayed gastric emptying as a contributing factor in a patient’s poor response to therapy ¹. Additionally, gastric emptying study is beneficial in the evaluation of patients with colonic inertia being considered for colectomy since individuals with concurrent delayed gastric emptying have a much lower response rate to surgery than those with normal gastric emptying ².

Other tests used to measure gastric emptying include breath testing and wireless pH capsules ³. Breath testing is performed using a standardized meal including Spirulina labeled with Carbon-13. The meal passes through the stomach, into the duodenum where it is absorbed, metabolized in the liver and exhaled by the lungs where it is measured. As transit of the meal through the stomach is the rate-limiting step in the process, the test serves as an indirect measurement of gastric emptying, assuming normal bowel, liver, and pulmonary function. The wireless pH capsule test is performed by administering a capsule in conjunction with a nutrient bar. The capsule is monitored by a belt worn by the patient and transit from the stomach to small bowel is detected by a sudden increase in pH, denoting transition from the acidic stomach to the alkaline duodenum.

Given its noninvasive nature and physiologic methodology compared to these other tests, gastric emptying scan has become the prevailing means by which to measure gastric emptying ³. More recently, gastric emptying study has been used to evaluate for rapid gastric emptying, which can be seen early in the course of diabetes as well as with cyclic vomiting syndrome, a disorder manifested by recurrent episodes of nausea, vomiting, and lethargy ⁴.

A nuclear medicine technologist performs gastric emptying study exams under the supervision of a nuclear medicine physician or nuclear radiologist.

Gastric emptying scan

The components of a meal (size, digestibility, calories and nutrient content) all affect the rate of gastric emptying. Solids and fats empty more slowly, whereas liquids, proteins, and carbohydrates empty more rapidly ⁵. Until recently, no standard existed for the meal used in gastric emptying study. Different methodologies were used at different imaging clinics (orange juice, cereal with milk, oatmeal, scrambled eggs, chicken liver), and as a result, they often had different normal values. This was of concern to clinicians because study results from separate imaging facilities made interpretation and comparison of results problematic. As a result, in 2007 an expert panel of gastroenterologists and nuclear medicine physicians met to decide on consensus standards for gastric emptying scintigraphy. These recommendations were published in 2008.

The standardized meal described in the gastric emptying study guideline is a solid meal consisting of 0.5 to 1.0 mCi of 99mTc-sulfur colloid scrambled with 120 grams of liquid egg whites (Egg Beaters or generic), 2 slices of white toast, 30 grams of strawberry jelly, and 120 mL of water ⁶. It is recommended that this exact meal be utilized for all adult solid gastric emptying studies. The departure of the test meal from this standard precludes accurate comparison to validated normal values and thus, may factitiously alter the diagnosis of normal versus abnormal gastric emptying.

To date, the consensus guidelines only address gastric emptying in regards to a solid meal. However, liquids and solids empty differently from the stomach. Solids generally show early fundal localization (via accommodation) while liquids distribute quickly throughout the stomach. Also, given that liquids do not undergo trituration (an antral function), they empty predominantly via the control of the fundal pressure gradient. This difference may result in some patients with isolated mild-to-moderate fundal dysfunction not being accurately identified on the standard solid gastric emptying study. To overcome this potential inadequacy of gastric emptying study, additional research has been done regarding the use of a liquid meal. One of the most widely accepted standards was developed by Ziessman and colleagues at Johns Hopkins, using a non-nutrient meal comprised simply of 300 mL water labeled with 0.2 mCi of Tc-99m sulfur colloid or Indium-111 DTPA (Indium-111 diethylenetriamine pentaacetic acid) ⁷.

Gastric emptying study contraindications

Gastric emptying study contraindications include:

• Allergies to the recommended meal
• Hyperglycemia in diabetics, blood glucose greater than 250 to 275 mg/dL (13.9 to 15.3 mmol/L) ⁸

Gastric emptying study preparation

Proper patient preparation is critical to performing an accurate and reliable gastric emptying study:

• Prokinetic agents such as metoclopramide, erythromycin, tegaserod, and domperidone should be discontinued for 2 days before the study unless the test is performed to assess the efficacy of these medications.
• Medications that delay gastric emptying should also be discontinued for 2 days before the exam. These include opiates (e.g., morphine, codeine, and oxycodone) and antispasmodic agents such as atropine, dicyclomine, loperamide, and promethazine.
• Patients should not eat or drink for a minimum of 4 hours before the study. It is typical for the patient to take nothing by mouth starting at midnight and then undergo the exam in the morning.
• Insulin-dependent diabetic patients should bring their insulin and glucose monitors with them. Their blood sugar should ideally less than 200 mg/dL.
• Diabetic patients should monitor their glucose level and adjust their morning dose of insulin as needed for the prescribed meal.
  Additionally, it may be best to schedule exams for premenopausal women on days 1 to 10 of their menstrual cycle, to avoid the effects of hormonal changes on gastric emptying that has been shown in some, but not all studies ⁸.

Gastric emptying study procedure

To prepare the solid meal, the liquid egg whites are poured into a bowl, mixed with 0.5 to 1 mCi 99Tc sulfur colloid and cooked in a nonstick frying pan or microwave (note, simply adding the sulfur colloid after cooking the egg whites will result in poor labeling and lead to spurious measurements). The egg and radiopharmaceutical mixture should be stirred once or twice during cooking and cooked until it reaches the consistency of an omelet. The bread is toasted, jelly is spread on the toast, and a sandwich is made of the jellied bread and cooked egg mixture ⁹. The meal should be consumed within 10 minutes, and imaging commences.

In addition to standardizing the meal, the consensus guidelines released in 2008 standardized the imaging and interpretation, endorsing a protocol developed in 2000 by Tougas and colleagues ¹⁰. This simplified methodology for solid gastric emptying study requires 1-minute images be acquired at only 4 time points: immediately after meal ingestion and at 1, 2, and 4 hours with an optional fifth time point at 30-minutes which can be helpful in the assessment of rapid gastric emptying.

The images are ideally acquired simultaneously in the anterior and posterior projections using a dual-head gamma camera with field-of-view encompassing the entire stomach as well as the distal esophagus and proximal small bowel. If a dual-head gamma camera is not available, sequential anterior and then posterior images from a single-head gamma camera is an acceptable technique. The counts in the stomach are then measured by drawing a region-of-interest (ROI) around the stomach. Using the first time point (T=0) as the baseline (which includes all activity, to include any which has already traversed the stomach), the amount of activity retained in the stomach at each subsequent time point can be calculated using the geometric mean with decay correction and compared to validated normal values.

Gastric emptying study results

The published normal values are ¹¹:

• Thirty minutes: Greater than or equal to 70% meal retention
• One hour: 30% to 90% meal retention
• Two hours: Less than or equal to 60% meal retention
• Four hours: Less than or equal to 10% meal retention

If utilizing a liquid meal, the radiopharmaceutical is simply mixed with the 300 mL of water. The exam is then performed with the patient positioned semi-upright (45-degree angle) and imaging performed with a single-head gamma camera in the left anterior oblique projection (along the long axis of the stomach). Imaging starts immediately after the ingestion of the radiolabeled water with images acquired as 1-min frames continuously for 30 minutes. Like with solid gastric emptying, an region-of-interest (ROI) is drawn over the stomach to measure gastric retention. Unlike with solid gastric emptying, no geometric mean is calculated given the single-head camera technique and the rapid nature of liquid only emptying necessitates a time-activity-curve (TAC) be generated using each time point to calculate the time to reach 50% emptying (T-1/2). Using this protocol, a T-1/2 of fewer than 22 minutes is considered normal (mean plus 3 standard deviations) ⁷.

Gastric emptying study abnormal results

• Delayed gastric emptying (gastroparesis): A retained meal value greater than 60% at 2 hours or 10% at 4 hours
• Rapid gastric emptying: A retained meal value less than 70% at 30 minutes or less than 30% at 1 hour suggests rapid gastric emptying ¹²

Factors that may affect the performance and negatively influence the clinical validity of a gastric emptying study are:

• Incomplete meal consumption
• Slow meal consumption (taking longer than 10 minutes)
• Vomiting a portion of the meal
• Poor glycemic control

If these problems occur, they should be included in the exam report as well as a comment as to their potential impact on the accuracy of the results.

Gastroparesis and rapid gastric emptying are conditions of abnormal gastric motility in the absence of obstructive pathology.

Gastroparesis was classically thought to be the complication of previous stomach surgery or the result of long-standing diabetes ¹³. More recently, it has been found to most likely be idiopathic (32% of cases) with diabetes the second most common cause (29%) and surgery third (13%). Interestingly, women are afflicted 4-to-1 in comparison to men ¹⁴. Given its most common presenting symptoms (nausea, pain, bloating) overlap with a multitude of other diseases, exact prevalence of delayed gastric emptying (delayed gastric emptying) is unknown, though it is estimated in the US that two-thirds of the country’s 23 million people with diabetes suffer from gastroparesis while gastric dysmotility is present in 40% of adults with dyspepsia ¹⁵.

Similar to delayed gastric emptying, rapid gastric empty is identified more commonly than previously suspected. It has been found in nearly 60% of patients with cyclic vomiting syndrome who undergo gastric emptying study as well as a large proportion of individuals with autonomic dysfunction ¹⁶.

Given this high prevalence of disease and its substantial impact on public health, it is critical that those afflicted be appropriately diagnosed to guide proper treatment and effective management. Key to this is the use of properly performed gastric emptying scintigraphy following standardized consensus guidelines. Research has shown that by using these parameters appropriately, the diagnostic yield of the gastric emptying study can be improved significantly. Imaging of solid gastric emptying out to 4 hours, as recommended, increases sensitivity by a third over historical protocols that limited imaging to 2 or fewer hours. Adding a liquid gastric emptying study study in patients with a normal solid gastric emptying can further increase detection of gastroparesis by another third ¹⁷. By identifying more patients with abnormal gastric emptying, it will lead to more accurate diagnoses, which in turn will hopefully result in further development of therapies and improved care.

Gastric emptying study side effects

Gastric emptying study uses small amounts of radioactive materials called Technetium-99m sulfur colloid that are swallowed. The radioactive Technetium-99m radiotracer travels through the area being examined and gives off energy in the form of gamma rays which are detected by a special camera and a computer to create images of the inside of your body. Tell your doctor if there’s a possibility you are pregnant or if you are breastfeeding and discuss any recent illnesses, medical conditions, allergies and medications you’re taking.

Gastric emptying study risks:

• Because the doses of radiotracer administered are small, diagnostic nuclear medicine procedures result in relatively low radiation exposure to the patient, acceptable for diagnostic exams. Thus, the radiation risk is very low compared with the potential benefits.
• Nuclear medicine diagnostic procedures have been used for more than five decades, and there are no known long-term adverse effects from such low-dose exposure.
• The risks of the treatment are always weighed against the potential benefits for nuclear medicine therapeutic procedures. You will be informed of all significant risks prior to the treatment and have an opportunity to ask questions.
• Allergic reactions to Technetium-99m sulfur may occur but are extremely rare and are usually mild. Nevertheless, you should inform the nuclear medicine personnel of any allergies you may have or other problems that may have occurred during a previous nuclear medicine exam.
• Women should always inform their physician or radiology technologist if there is any possibility that they are pregnant or if they are breastfeeding.
• Some of the Technetium-99m sulfur radiotracer that are used for the study can pass into the mother’s milk and subsequently the child will consume them. To avoid this possibility, it is important that a nursing mother inform her physician and the nuclear medicine technologist about this before the examination begins.

References

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