Recommended meal
(a) 118 mL (4 oz.) of liquid egg whites (e.g., eggbeaters [ConAgra Foods, Inc.] or an equivalent generic liquid egg white)
(b) Two slices of toasted white bread
(c) 30 g of jam or jelly
(d) 120 mL of water
Meal preparation
(a) Mix 18.5–37 MBq (0.5–1 mCi) of 99mTc-sulfur colloid into the liquid egg whites
(b) Cook the eggs in a microwave or on a hot nonstick skillet (as described by Ziessman et al. (2007))
(c) Stir the eggs once or twice during cooking and cook until firm—to the consistency of an omelet
(d) Toast the bread and spread the jelly on the toasted bread
Image Acquisition
There is no single universally accepted protocol for this study. Most protocols however share the same basic principles. After feeding, the child is positioned supine on the γ-camera couch. Young infants should be burped when possible prior to imaging. Restraints may be used to secure young children to the imaging bed and prevent motion. Dynamic images are acquired from the posterior view, with the stomach and chest in the field of view, at a frame rate variable between 10 and 30 s/frame for 60 min [22]. Images are obtained in the anterior and posterior projections with the child supine on the gamma camera couch using a dual head camera. Continuous data recording is preferable over recording data only at discrete time intervals, as it gives information on the lag phase and may be helpful in identifying patterns of rapid gastric emptying; moreover, with the liquid phase, during the dynamic acquisition episodes of gastroesophageal reflux can be detected. Any event during the acquisition (motion, coughing, vomiting, reflux) is recorded at the time it occurs. The dynamic images are recorded on a 128 × 128 matrix and may be followed by anterior and posterior static views of the chest, with the stomach out of the field of view, with the purpose to assess for possible aspiration. These images are recorded on a 256 × 256 matrix over 3–5 min. Further delayed images at 2 and, if required, 3 h are obtained, using the same acquisition parameters as the dynamic acquisition, so that the delayed images can be compared to the dynamic series.
With a solid-phase gastric emptying study , a dynamic acquisition in the first hour is not strictly necessary, although it is helpful to assess the lag phase in the initial part of the study. It can also inform on the distribution of the radiolabeled feed within the proximal and distal portions of the stomach, and on possible to- and fro motion between the fundus and the antrum during the dynamic sequence, which may be due to dysmotility. The solid-phase gastric emptying study has to be continued with delayed imaging acquisition at least at 2 and 3 and possibly 4 h.
Image Processing
An ROI is placed around the stomach, as seen in the immediate post-feed image. A time-activity curve, corrected for decay, is generated from the stomach ROI. Motion correction should be applied when required. Care should be taken not to include bowel activity in the gastric ROI. Gastric emptying can be expressed as a percentage of the initial activity remaining at a specific time point (residual) or as the activity emptied by the stomach at these times. The pattern of the emptying curve is important, including the presence and the duration of the lag phase (seen in solid gastric emptying), which can provide evidence on abnormalities in gastric motility. Milk usually empties in an exponential or bi-exponential manner [19].
Analysis
The normal range of a gastric emptying study in the pediatric population has not been defined in detail. In particular, it is unclear whether the normal range is different in different age groups. This is due to the difficulty in performing gastric emptying studies in normal volunteers of pediatric age.
There is a consensus based on practice, but not scientifically validated, that a milk study is still normal if at 2 h the remaining activity in the stomach is 40 % or less of the initial gastric content. A solid-phase gastric emptying study in the adult practice, with the standard meal described in the guidelines based on radiolabeled egg white, is normal if at 4 h there is <10 % of the initial gastric content still present in the stomach [3, 4]. A detailed normal range for a specific meal and age group has not been defined in pediatrics. Also, it is not clear whether in grown up children and in adolescents a solid test feed is sufficient to estimate gastric emptying or whether both a solid and a liquid test feed are required. Preliminary evidence in the adult practice seems to suggest that both test feeds are required for a comprehensive assessment of gastric emptying [28]. Two examples of gastric emptying study are shown in Figs. 14.1 and 14.2.
Fig. 14.1
(a, b) Gastric emptying study in a 2-year-old child with jejunal atresia and GERD . The dynamic acquisition over 1 h (a) shows little distribution of the milk-based radiolabeled test feed in the fundus of the stomach, with predominant distribution in the body of the stomach. The overall timing of gastric emptying is within normal limits. The delayed images at 2 h show further gastric emptying, with only approximately 25 % of the initial gastric content remaining in the stomach, as it can be seen from the time-activity curve (b). This study suggests impaired ability of the fundus of the stomach to relax after ingestion of the feed, which fits the clinical context
Fig. 14.2
(a, b) One-month-old baby with global developmental delay . The baby had a Nissen’s fundoplication and was gastrostomy fed. The gastric emptying study shows a very rapid gastric emptying (a). The time-activity curve confirms that there is no significant activity remaining in the stomach by 35 min (b). This case is an example of dumping syndrome following Nissen’s fundoplication
Issues Requiring Further Evaluation
These are multiple. First of all, agreement has to be reached on an alternative meal to radiolabeled egg white for children intolerant of or unable to eat eggs. These alternative meals have to be validated; a normal range for different age groups has to be defined. The duration of the solid and liquid phases has to be clarified. Is it necessary to acquire images at 4 h in children? The effect of factors such as the volume (is the scan non-diagnostic below a certain volume of feed ingested?) and the composition of the test feed in carbohydrates, protein, and fat also have to be established. A “normal” range in postsurgical children (e.g., following Nissen’s fundoplication ) or in children fed via a gastrostomy tube has to be defined. It would be also interesting to see if gastric emptying scintigraphy can demonstrate the coordination of the different portions of the stomach (fundus and antrum, with relaxation of the pylorus) and provide some insights on gastric dysmotility, as hypothesized [24].
Small Bowel and Colonic Transit Studies
During the clinical evaluation of gastrointestinal symptoms suspected to be caused by a motility disorder, it may be difficult for clinicians to determine whether the symptoms are caused by upper or lower gastrointestinal tract dysfunction . In clinical practice, it is therefore helpful to evaluate motility throughout the entire gastrointestinal tract. At present, whole-gut transit scintigraphy (combined gastric emptying, small bowel transit, and colonic transit) is a relatively easy study to perform and, in some centers, is a frequently used and validated method to assess motility throughout the gut. Treatment selection may be guided by the finding of upper, lower, or combined gastrointestinal transit abnormalities. In addition, in patients with chronic constipation who are being considered for colectomy, an assessment of upper gastrointestinal motility is important since upper gastrointestinal dysmotility may reduce the clinical response to surgery.
Two techniques are used to evaluate motility through the GI tract, both of which involve irradiation of the subjects: transit of radio-opaque (plastic) markers viewed by X-ray and transit of radioisotope viewed by γ-camera (scintigraphy). Together, with the assessment of rectal evacuation dynamics and rectal sensation, the radioisotope studies of colonic transit represent the cornerstone investigations in patients with chronic constipation . These investigations have led to constipation being conceptualized into three broad and overlapping categories: normal transit constipation, slow transit constipation, and evacuation disorders. Transit studies per se address the question of whether the patient has a normal or delayed colonic transit.
Common Clinical Indications
These include evaluation of g astrointestinal (GI) and colonic transit abnormalities as a cause of symptoms in patients with known or suspected gastroparesis, dyspepsia, irritable bowel syndrome, chronic constipation, chronic diarrhea, chronic intestinal pseudo-obstruction and scleroderma.
Patient Preparation
Medications that affect GI motility are withdrawn at least 2 days prior to the test, unless the purpose of the test is to assess the efficacy of these medications. These include opiate analgesics and anticholinergic medications (which slow gastrointestinal transit) and prokinetics (domperidone, erythromycin, metoclopramide), which accelerate transit. For colonic transit studies, a bowel washout is performed prior to the test, to remove possible impacted feces. A radiological contrast study of the upper GI tract in order to exclude malrotation and clarify the anatomy of the bowel is essential in the interpretation of the GI transit scintigraphy, and this should be available prior to the acquisition of the radionuclide study.
Radiopharmaceuticals
The two main radiopharmaceuticals utilized in gastrointestinal transit studies are Tc-99m-colloid, to label the solid test feed for the evaluation of gastric emptying, and In-111-DTPA water to assess intestinal transit. A contemporaneous estimate of gastric emptying allows a more accurate determination of pure intestinal transit, especially if gastric emptying is slow and the clinical question concerns the evaluation of small bowel transit; this is why evaluation of gastric emptying is strongly advised in intestinal transit scintigraphy. A dual-isotope acquisition (Tc-99m-nanocolloid and In-111-DTPA water) can be performed.
Acquisition
The recently published guidelines on small bowel and colonic transit [5] suggest three options:
A whole-gut transit study , which includes administration of a Tc-99m-colloid-labeled solid test feed together with In-111-DTPA water, to evaluate gastric emptying, small bowel transit, and colonic transit. Imaging is performed at hourly interval on the first day and then on days 2, 3, and 4 (and possibly 5, if needed).
A small bowel transit study , with In-111-DTPA-labeled water for the small bowel follow-through and a Tc-99m-colloid-radiolabeled solid-phase test feed to evaluate gastric emptying at the same time (the solid-phase meal can be given with no radiolabeling, to create mass effect in the GI tract). Imaging is acquired at hourly interval up to 6–7 h on the first day, and then at 24 h to outline the large bowel, thus helping in the identification of the cecum and ileocecal valve.
A colonic transit study with In-111-DTPA water: imaging is acquired at hourly intervals on the first day and then on days 2, 3, 4 (and possibly 5, if needed).
Markers placed on the patient’s anterior superior iliac spine facilitate identification of the small bowel. Imaging is performed with the patient in an upright position using a large γ-camera equipped with a medium-energy collimator. During the dual-isotope acquisition, images are dynamically acquired for 1 h immediately after ingestion of the meal, with a static image at 2 h to measure gastric emptying of solid and liquids. Afterwards, images are usually taken at 4, 6, 24, 48, 72, and possibly 96 h. Images at 24 and 48 h may give a sufficient summary of colonic transit with acceptable specificity and high sensitivity for detecting motility disorders, although in constipated patients it is very helpful to acquire images at 72 h and, if activity is still seen in the colon, at 96 h [34]. Anterior and posterior images are obtained for an acquisition time up to 400 s on a 256 × 256 matrix. In the initial gastric emptying phase, the pulse height analyzer of the γ-camera is centered on 140 keV with a window of ±20 % to detect counts from Tc-99m and on two peaks (173 and 247 keV) ±20 % to detect counts from In-111. Subsequent images are acquired using the In-111 energy peak only.
Analysis
The commonest scintigraphic method for assessing small bowel transit is to measure oro-cecal transit time , defined as the time taken for 10 % of small bowel radioactivity to accumulate into the cecum [35, 36]. This is a very laborious method since it requires multiple images taken every 10 min until 10 % of the activity reaches the colon. A valid surrogate for the 10 % activity is the percentage of the administered activity reaching the terminal ileum at 6 h after meal ingestion.
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