Gastric Emptying Scan
The gastric emptying scan measures the rate at which a labelled meal leaves the stomach. It is the reference test for gastroparesis and rapid emptying. The patient eats a meal labelled with technetium-99m, and a gamma camera records the activity in the stomach over time.
The solid meal is the usual test. The label is technetium-99m sulphur colloid cooked into egg white (18 to 40 MBq), eaten with toast, jam and water. A uniform meal is needed, because emptying depends on the meal's composition, fat and calories.
Liquid emptying is measured with technetium-99m DTPA in water, and in infants with milk.
Images are taken immediately after the meal, and at 1, 2 and 4 hours. The camera is placed anteriorly and posteriorly, and the geometric mean of the counts corrects for depth. The effective dose is about 0.3 to 0.5 mSv.
Functional dyspepsia and gastroparesis symptoms affect 10 to 20% of the population, but gastroparesis is confirmed in a small fraction. Diabetes causes about a third of cases, and idiopathic and post-surgical causes make up most of the rest.
Scintigraphy is the only test that measures emptying of a physiological meal in a way that is validated, and a 4-hour study is much more accurate than a 2-hour study.
Indications.
- Chronic nausea, vomiting, early satiety, bloating, and upper abdominal pain with suspected gastroparesis.
- Diabetes with poor glucose control or unexplained vomiting.
- Post-surgical symptoms (after fundoplication, vagotomy, gastric resection or bariatric surgery) and suspected dumping syndrome.
- Suspected rapid emptying, with diarrhoea, postprandial hypoglycaemia and flushing.
- Assessment of drugs affecting motility (response to prokinetics).
- Pre-operative evaluation before fundoplication or bariatric surgery, and before gastric electrical stimulation.
- Connective tissue disease (scleroderma), neurological disease (Parkinson disease) and amyloidosis with suspected dysmotility.
- Recurrent vomiting of infancy and feeding intolerance in infants (liquid study).
- Unexplained weight loss or nutritional failure.
Contraindications and precautions.
- Pregnancy: avoid unless essential. Breast feeding: usually no interruption needed, or a brief one.
- Fasting for 6 to 8 hours (overnight). Smoking is avoided on the morning of the test.
- Drugs that change motility are stopped for 48 to 72 hours when it is safe: prokinetics (metoclopramide, domperidone, erythromycin), opioids, anticholinergics, antidepressants with anticholinergic effect, and GLP-1 receptor agonists as the local rule requires. Proton pump inhibitors and antiemetics can usually continue.
- Glucose control: the blood glucose is checked on arrival. A glucose over about 15 mmol/L (270 mg/dL) delays emptying, so the test is postponed. Insulin is given as usual in diabetes.
- Egg allergy: use another meal or the liquid test.
- Ability to complete the meal in 10 minutes. A partial meal makes the study unreliable.
- Women: timing in the menstrual cycle has a small effect on emptying.
Preparation and technique.
The patient arrives fasting, with medicines adjusted. The labelled egg white meal (120 g) is eaten within 10 minutes, with two slices of toast, jam and 120 mL water. The time taken and the amount eaten are recorded.
Images are taken in anterior and posterior views for 1 minute each, immediately and at 1, 2 and 4 hours. The patient is upright or sitting between images, and does not eat or drink other than water.
The images are decay corrected and the geometric mean is used for the stomach region.
For liquid emptying, the patient drinks the labelled water and images are taken continuously for 30 to 60 minutes, with the half emptying time calculated. For infants, the study uses milk feeds and is limited to 60 to 90 minutes.
