Gastrointestinal symptoms can be diffuse, nonspecific, and difficult to pinpoint due to the length and motile mature of the gastrointestinal tract and correlation between the different regions. Nuclear medicine provides a relatively physiological approach to image all or part of the gastrointestinal tract during consumption of a meal and its progress through the esophagus, stomach, small-bowel, colon, and excretion. Usually, the investigation is truncated to the part of the GI tract most affected, with gastric emptying being the most frequently performed investigation. However, it is worth remembering that regional motility is dependent on both input and output, so some representation of this should be included in the imaging study. There is close relationship with radiological and endoscopic techniques. Whereas nuclear medicine does not provide the anatomical detail of the other methods, it provides a complementary overview and slow dynamic imaging methods that are not really practical with X-ray, compute tomography (CT) or even magnetic resonance (MR).

Abnormal gastric emptying may be a consequence of various diseases, leading to either too slow or too fast emptying rate. Symptoms and signs indicating gastric emptying problems are difficult to interpret, and the problem is frequently psychologic. Therefore, objective method for assessment of gastric emptying is a necessity. With a radiolabeled meal and dynamic scintigraphy, it is easy to assess gastric emptying.

The emptying rate is highly dependent on the meal. Therefore, standardized meals must be used, and reference intervals for these meals must be established (1). Moreover, there is a relatively broad biologic variation in gastric emptying rate, which leads to wide reference intervals also when standardized meals are used (2). For a person with an emptying rate close to the center of the normal reference interval for a specific meal, a relatively large deviation from the normal rate is necessary to avoid a false-negative result.

Nuclear medicine test methods with solid food are considered the gold standard for measuring gastrointestinal emptying, but emptying studies with liquids are also of interest, especially in small children and patients fed through various types of tubes. The examination can be modified into a double isotope method with a mixture of differentially labeled solid food and liquid, for example, ¹¹¹In-DTPA in water that is drunk with the solid test meal labeled with ^99mTc-DTPA. The usefulness of this, however, seems limited.

Delayed emptying is seen with mechanical hindrances in the pylorus (cancer or ulcer with stenosis), diabetes mellitus with autonomic neuropathy, hypothyroidism, after a vagotomy, in collagen diseases, amyloidosis, uremia, anorexia, and depression, as well as idiopathic. Aberrant rapid emptying may be seen after gastric surgery, in patients with Zollinger-Ellison syndrome, carcinoid syndrome, duodenal ulcers, hyperthyroidism, and diabetes in the early phase.

Radioactivity, most often a ^99mTc-labeled radiopharmaceutical, is added to a standardized meal (3). The radiopharmaceutical added must be of a kind that is not absorbed from the gastrointestinal tract, and it must follow the test meal within the gastrointestinal tract. Examples are ^99mTc-labeled sulfur colloid or DTPA. After intake of the test meal, the gastric emptying rate is measured by dynamic scintigraphy from time of intake and for the next 60 or 90 min, and sometimes for a longer period if the emptying is slow.

Following up previously detected motility disorders Contraindication, special precautions, side effects

The patients are instructed to fast without food and drinks for at least 4 h, preferably 8-h fast overnight. To be scheduled for investigation, the next morning is most convenient in combination with an overnight fast.

Diabetics should postpone their morning insulin until after the test meal. Early morning doses of drugs that affect the stomach’s emptying should, if possible, be brought along and taken immediately after the investigation. Opiates, calcium blockers, anticholinergics, antidepressants, levodopa, histamine H2-antagonists, proton pump inhibitors, and antacids with aluminum tend to slow down the emptying rate. Erythromycin, metoclopramide, and cisapride increase the emptying rate.

Body mass index (BMI), age, and a history of smoking are of marginal significance to gastric emptying. However, emptying will depend on the volume of the meal and its composition, if the meal is solid or a liquid, and whether the person is standing, sitting or lying down. Hence, one must therefore strive for identical testing conditions, including standardization of the composition of test meals. A variety of standard meals are used. Eggs and bread are frequently used. With egg meals, only the egg white may be used. The yolk has a high content of fat and calories, and both these factors may reduce the emptying rate. Egg white from two eggs scrambled in the microwave oven and put between two halves of a slice of white bread is used by these authors for adult patients. The ^99mTc-sulfur colloid is added to the egg white before the heating procedure.

Individual adaptation of meal volumes or composition in relation to allergies or other illnesses, or administration routes, should be evaluated by a physician for best possible administration. Children, dependent on age, drink 150 mL of cow’s milk or other liquid nutrition, or solid food as for adults, in reduced amount. For tubefed patients, the tube position in the stomach must be verified. The intake phase should be finished within maximum 10 min.

Camera recording should start immediately after the meal has been finished. Dynamic registration is performed over the abdominal area:

For very restless children, one can take static images at regular intervals (approximately every 10 min). If the only camera available has one detector, the left anterior oblique (LAO) projection is preferable to anterior (ANT) projection. It may be appropriate to follow up with more images throughout the day. Static images should be taken in 256 × 256 format every 10 min or so.

It is important with some anatomical landmarks on these scintigrams with very little anatomy except for the gastrointestinal tract, for example by marking right shoulder.

After ingestion, solid food will remain for some time in the stomach. In this lag period or plateau phase, peristalsis prepares the food for emptying to the duodenum. Then an exponential fall in radioactive gastric content following a solid meal is observed. Men, and women after menopause, have a somewhat faster gastric emptying than premenopausal women. But this gender difference is small, and separate reference ranges are not necessary. The difference in emptying between the different patients groups is frequently due to a different length of the initial plateau phase.

Compared with solid food, the liquid test meals are poorer at discriminating between normal and pathological emptying. Different liquids may also differ in their emptying rate. The emptying immediately after intake, with no plateau phase, and there is no significant difference between genders. In adults, the normal half-life is 10 to 60 min. In children, there seems to be a particularly large difference in emptying patterns depending on the volume of milk ingested and methodology in general. Breast milk and water are emptied exponentially, as with liquid test meals in adults, while test meals of cow’s milk or infant formula often have long plateaus. Rectilinear fall with an immediate start can also be seen. Generally applicable reference values for children are lacking.

If gastrointestinal emptying examinations are carried out consistently, the emptying parameters will be reasonably well reproduced with a variation coefficient of about 15%. Patient movement bringing the stomach completely or partly outside the region of interest (ROI) is a source of error, which can be corrected and can easily be observed if the scintigrams are displayed dynamically in connection with processing. The overlap between gastric ROI and small intestine activity is another source of error.

As many practices are performing 4-h gastric emptying studies, it is useful to remember the upper limit of normal at two standard deviations above the mean forgastric retention as: (1 h: 90%; 2 h: 60%; 3 h: 30%; 4 h: 10%)

The two main problems with gastrointestinal reflux are esophagitis and pulmonary aspiration. Like in gastrointestinal emptying, dynamic scintigraphy is also well suited for monitoring if an ingested meal takes a retrograde course from the stomach into the esophagus, and further into the lungs.

Pulmonary aspiration might happen in situations with reduced consciousness after trauma or anesthesia or due to a reduced gag reflex. However, the cases suitable for scintigraphic investigation are those with a confirmed gastroesophageal reflux, and suspected to have a lung problem caused by aspiration of acidic ventricular content. Most patients with this problem are children (4).

Various investigations outside the nuclear medicine field are applied on patients suspected of having a gastric reflux problem. An X-ray examination using contrast of the upper gastrointestinal tract can detect underlying abnormalities in the esophagus, stomach, and duodenum, as well as demonstrating esophageal motility. A Meckel’s scintigraphy can detect Barrett’s esophagus with ectopic epithelium. Endoscopy and an esophagus biopsy can be used to detect esophagitis. The gold standard for reflux detection is 24 h of pH measurement in the esophagus. A fall in acidity below pH 4 for more than 4% in a 24-h period is considered pathological.

Scintigraphic examinations of gastroesophageal reflux are not invasive and produce a very low radiation dose. Sensitivity to detection of reflux is highest with patients in supine position, and equivalent to the sensitivity of pH measurement in the esophagus. The method’s main limitation is that the examination period is necessarily short. It is not possible to monitor the patient throughout the whole day and night. Nevertheless, scintigraphy is probably the most effective method available for detecting pulmonary aspiration (5).

Small and large bowel investigations are performed as a modified continuation of gastric emptying studies(6). Intestinal transit studies have been around for a while but frequently done in a multitude of different ways. To promote more standardized practice, a joint guideline was issued by the society of nuclear medicine and molecular imaging (SNMMI) and European Association of Nuclear Medicine (EANM) in 2013 (7).

The salivary glands consist of three pairs of exocrine glands. The largest are the parotid glands located immediately posterior to the mandibular ramus with a duct that extends forward and opens into the mouth in the mid buccal region. The second largest are the submandibular glands that are placed medially to the posterior lower edge of the mandibular. The ducts from these glands extend anteriorly to exit through sublingual caruncles either side of the frenulum. Finally, the sublingual glands are located anteriorly submucosally in the floor of the mouth and also drain either side of the frenulum.

Salivary gland scintigraphy was established as a method in the 1970s. There are a number of different protocols described
in the literature. Most are aimed at semi-quantitation of function to evaluate the degree of xerostomia (dryness of the mouth) (8).

A dynamic scan following intravenous injection of ^99mTc pertechnetate allows uptake of tracer into the salivary glands to be followed. Uptake is assumed to be proportional to glandular function. To assess excretion, lemon juice is given toward the end of the registration to stimulate salivary glands to empty. This also allows the drainage conditions to be evaluated.

Gamma Camera with Low Energy, High-Resolution Collimator (LEHR)

Meckel’s diverticulum is a congenital diverticulum in the ileum, with an incidence of 2%. Most people go through life without any problems related to it, not even knowing that they were born with this anatomic variation, and only 25% to 40% of them will experience symptoms from this diverticulum localized 50 to 100 cm from the ileocecal valve. As 25% of the diverticula contain heterotopic gastric mucosa, this congenital defect may be the origin of a gastrointestinal bleed. This is most common in childhood, and most frequently before the age of 5 years. Less frequently, a Meckel’s diverticulum may also lead to complications like diverticulitis, obstruction, or perforation. These complications are more common in adult patients. It is very seldom that patients presenting with Meckel-related complications are over the age of 40.