SNMMI and EANM Practice Guideline for Meckel Diverticulum Scintigraphy 2.0

A. Patient preparation

Preexamination fasting of 3–4 h may reduce the size of the gastric silhouette and improve sensitivity for the detection of ectopic gastric mucosa (1). However, fasting is not required for the examination and may not always be possible. The use of all drugs or procedures that may irritate the gastrointestinal tract should be stopped for 2–3 d before the study if possible.

It is important to determine whether the patient has undergone recent in vivo RBC labeling in which all circulating RBCs were treated with stannous ion via intravenous administration of a cold pyrophosphate kit. If so, the Meckel scan may be compromised, since intravenous ^99mTc-pertechnetate will label RBCs rather than concentrate in ectopic gastric mucosa. This may occur for days after the administration of stannous pyrophosphate and is not a problem with in vitro labeling. Recent administration of perchlorate may reduce the sensitivity of the test by decreasing uptake of ^99mTc-pertechnetate in normal and ectopic gastric mucosa.

Pretreatment options to improve the sensitivity of the study include the following:

1. Histamine H₂ blockers

Histamine H₂ blockers (cimetidine, ranitidine, famotidine) inhibit acid secretion by the parietal cells, thus limiting release of ^99mTc-pertechnetate by the mucosal cells (11–13) and improving the sensitivity of the Meckel scan (3,4). (Dose recommendations are provided in Appendix A.)

2. Proton pump inhibitors

Proton pump inhibitors are used in the pediatric population to control acid secretion, and they may be more practical than H₂-antagonists even for short-term use (14).

3. Glucagon

Glucagon relaxes the smooth muscles of the gastrointestinal tract, slightly suppressing peristalsis and transit of any secreted ^99mTc-pertechnetate through the small bowel. This movement of tracer may decrease the sensitivity of the study and the localization of ectopic gastric mucosa (4–6,9,15).

Glucagon should not be administered to diabetic patients. (Dose recommendations are provided in Appendix A.)

Pharmacologic pretreatment is not considered necessary for a high-quality Meckel scan. Any medication administered to children should be scaled according to weight and route of administration (Appendix A).

B. Information pertinent to performing the procedure

Are there signs of active bleeding? (If so, a gastrointestinal bleeding scan may be more helpful than a Meckel scan.) Is there a history of past bleeding episodes? What are the results of prior studies to localize the bleeding site? Has in vivo RBC labeling recently been done? Previous in vivo–labeled RBC scintigraphy with ^99mTc-pertechnetate and stannous pyrophosphate may give an indeterminate result.

C. Precautions

The vital signs of children suspected of having acute gastrointestinal bleeding should be constantly monitored on their arrival at the nuclear medicine clinic. The patient should have a large-bore intravenous catheter in place (if necessary), so that hypotension can be rapidly treated.

D. Radiopharmaceuticals

See also the SNMMI Guideline for the Use of Radiopharmaceuticals.

^99mTc-pertechnetate is eluted from a molybdenum–technetium parent–daughter generator with physiologic saline and injected intravenously. The administered activity should be calculated according to the recommendation of the 2012 North American consensus guidelines for pediatric radiopharmaceutical administered doses (16), the new EANM pediatric dosage card (17), and European Union directive 97/43/EURATOM: The European Directive on Health Protection of Individuals against the Dangers of Ionising Radiation in Relation to Medical Exposures (18).

Administered doses should be in the context of good practice of nuclear medicine and local regulations. The recommended administered activity for children from the 2010 North American consensus guidelines (16) is 1.85 MBq/kg (0.05 mCi/kg), with a minimum of 9.25 MBq (0.25 mCi). The EANM pediatric dose card (2007 version) (17) may also be used. A harmonization of the North American and European pediatric dosages is under way and will be published in 2014 (19). The usual administered activity for adults in the United States is 296–444 MBq (8–12 mCi) intravenously.

E. Image acquisition

1. Equipment

Images are acquired on a large-field-of-view camera, using a low-energy, high-resolution parallel collimator. The photopeak has a 20% window centered on 140 keV. The computer is used in planar mode, with a 128 × 128 matrix, 1- or 2-byte mode, and a zoom appropriate for patient size. SPECT is performed using 3° per step, 30 s per frame, a 360° rotation, a 64 × 64 or 128 × 128 matrix, and a zoom appropriate for patient size.

2. Acquisition protocol

The patient is positioned supine, and the imaging field is the abdomen and pelvis (to include stomach and bladder). In infants and small children (up to 2 y of age), the thorax should be included in the field of view, to assess for possible bronchopulmonary foregut malformation with ectopic mucosa.

Anterior abdominal dynamic flow images (1–5 s/frame for up to 1 min) are obtained to identify any focus of vascular blood pool that may be confused with ectopic gastric mucosa.

Anterior abdominal dynamic images are obtained at a frame rate of 1 image every 30–60 s for at least 30 min. Imaging up to 60 min may be performed and is especially advisable when early images are negative despite a high clinical suspicion. Imaging beyond 60 min may compromise study interpretation due to passage of activity from the stomach to the intestine.

Additional static images (anterior, anterior oblique, lateral, and posterior projection views) are recommended at the end of the dynamic acquisition. Lateral views may be useful to localize renal pelvic activity. Postvoiding images may be helpful to detect activity in a Meckel diverticulum obscured by the urinary bladder.

3. Other considerations

SPECT imaging may improve the detection of a small diverticulum, or a diverticulum obscured by the urinary bladder, when the clinical suspicion for a Meckel diverticulum is high and the planar images have negative or equivocal findings.

SPECT imaging coregistered with a simultaneously acquired low-dose CT scan on a hybrid system may be helpful for localization of a Meckel diverticulum (20–22). For SPECT, see the SNMMI Guideline for General Imaging.

SPECT/CT fusion adds a small amount of additional radiation exposure. The CT dose should be tailored to patient size and age (23). See the SNMMI Guideline for SPECT/CT.

F. Interventions

A urinary catheter to drain the bladder of activity can be helpful if the Meckel diverticulum is adjacent to the bladder and if the patient is unable to voluntarily void. Alternatively, decubitus or upright views may be helpful by causing the Meckel diverticulum to fall away from the bladder.

Furosemide (1 mg/kg intravenously) can be administered in some settings to eliminate radiopharmaceutical pooling in a dilated ureter; this may be helpful when there are time constraints for delayed imaging.

G. Processing

For SPECT, see the SNMMI Guideline for General Imaging. The field of view should be maximized for the patient’s size.

H. Interpretation criteria

Normal structures seen on the flow phase after injection of ^99mTc-pertechnetate include the heart, lungs (not typically included in the field of view), major arteries and veins, and vascular organs such as the spleen, liver, and kidneys. Stomach activity appears early on dynamic scintigraphy and is most prominent after 10–15 min. Radiopharmaceutical activity is often present in the kidneys, ureters, and bladder.

Ectopic gastric mucosa is visible as a focal, localized area of uptake that appears at the same time as the activity in the normal gastric mucosa. As the stomach activity accumulates, so does diverticular activity. The intensity of the tracer accumulation may be less in the diverticulum than within the stomach, depending on the amount of mucosa present within the diverticulum and its secretory activity. Meckel diverticula are typically located in the right lower quadrant but may also be found elsewhere in the abdomen. They may change position during the study, especially after the body position has been changed. False-positive studies can occur if excreted tracer activity in the proximal small bowel, kidneys, ureter, or bladder is mistaken for ectopic gastric mucosa. Activity in the urinary tract usually appears after activity is seen in the normal gastric mucosa. A small Meckel diverticulum may appear somewhat later than the stomach.

A lateral view at the end of the study usually allows activity in the kidney and ureters, which is in the posterior part of the abdomen, to be differentiated from activity in the diverticulum, which is usually anterior (24).

^99mTc-pertechnetate that is secreted by the gastric mucosa will gradually accumulate in the small bowel. This activity can be distinguished from a Meckel diverticulum by its delayed appearance and by its appearance as an area of mildly, ill-defined increased activity.

Viewing the dynamic image as a cine loop on a computer display that also permits adjustment of image contrast is recommended to help distinguish small-bowel or urinary tract activity from ectopic gastric mucosa.

I. Pitfalls

False-positive radiopharmaceutical activity suggestive of Meckel diverticula can result from the following conditions: duplication cyst with ectopic gastric mucosa, bowel inflammation (25), intussusception or small-bowel obstruction (26), peptic ulcer (27), and vascular lesions with increased blood pool (e.g., hemangioma or arteriovenous malformation) (27).

False-negative findings usually result from anatomic or physiologic causes (see “Sources of Errors”). Other pathologic conditions that may result in a false-negative scan include gastrointestinal bleeding unrelated to ectopic gastric mucosa (e.g., pancreatic mucosa) (28). A negative Meckel scan in a patient with significant recent gastrointestinal bleeding where no other etiology for bleeding is discovered over several weeks' time may warrant a repeated study—optimally using pretreatment with an H₂ blocker or proton pump inhibitor.

J. Reporting

Aside from patient demographics, the report should include the following information: the indication for the study; the type of procedure; the radiopharmaceutical, dose, and route of administration (intravenous); the duration of the acquisition (e.g., 30 min vs. 1 h); the frame rate (e.g., 60 s/frame); the number of projections acquired (e.g., anterior, laterals); the field of view (e.g., stomach to the bladder); the type of display (e.g., static vs. cine); the findings; any study limitations or confounding factors; and the interpretation (e.g., positive, negative, or indeterminate).

The reported findings should include the time of appearance of the gastric mucosa, the time of appearance of ectopic activity (e.g., early vs. late, correspondence with gastric activity), the location of ectopic activity, and the characteristics of ectopic activity, such as size and shape (e.g., focal, round, oblong, or diffuse) and movement (if any).

K. Quality control

Quality controls for the γ camera, computer system, and image display are as enumerated by the SNMMI Guideline for General Imaging.

L. Sources of errors

1. Procedures that may cause interference

A false-negative result may occur if the patient underwent prior barium fluoroscopy examination (25) or prior administration of perchlorate (29), and a false-positive result may occur if there was a prior cleansing enema or laxatives causing bowel irritation (30).

2. Anatomic or physiologic causes of errors

A false-positive result may occur if there is focal pooling of tracer in the urinary tract (hydronephrosis, extrarenal pelvis, ectopic kidney, hydroureter, vesicourethral reflux, bladder diverticulum) or if there is a uterine blush (30). A false-negative result may occur if the image is obscured by brisk gastrointestinal bleeding during circulation of the tracer or by the urinary bladder or dilated ureter (25), if a focus of ectopic mucosa is small (<1.8 cm ²) (31), and if there is movement of the diverticulum (25).

M. Issues requiring further clarification

The role of pharmacologic interventions requires further clarification. Studies are needed to determine whether any of the specific H₂ blockers, any of the proton pump inhibitors, or any dose alterations of these agents have an advantage over the others for pharmacologic augmentation.

The role of SPECT and SPECT/CT to improve the accuracy of Meckel diverticulum scintigraphy also requires further clarification.

A. Radiation dosimetry in fetus/embryo: ^99mTc-pertechnetate

Dose estimates to the fetus are provided by Russell et al. (32). Information about possible placental crossover of this compound was available and was used in estimating fetal doses. Table 3 provides radiation dosimetry data in the fetus.

B. The breast-feeding patient

International Commission on Radiological Protection (ICRP) publication 106, Appendix D (33), recommends interruption of breast feeding for 12 h after administration of ^99mTc-pertechnetate.

A. Cimetidine

1. Oral administration

Neonates: 10–20 mg/kg/d by mouth; infants and older children: 20 mg/kg/d × 2 d by mouth; adults: 300 mg 4 times per day × 2 d by mouth.

2. Intravenous administration

Three hundred milligrams in 100 mL of 5% dextrose intravenously over 20 min, with imaging starting 1 h later.

B. Ranitidine

1. Oral administration

Children: 2 mg/kg by mouth; adults:150 mg/kg by mouth.

2. Intravenous administration

Infants, children, and adults: 1 mg/kg intravenously (maximum, 50 mg) over 20 min, with imaging starting 1 h later.

C. Famotidine

1. Oral administration

Children: 0.5 mg/kg/d by mouth; adults: 20 mg by mouth.

2. Intravenous administration

Children: 0.5 mg/kg/d intravenously; adults: 20 mg intravenously

or

0.25 mg/kg intravenously 1 h before the scanning procedure.

D. Glucagon

Intravenous administration: 50 μg/kg intravenously, to a maximum of 1 mg, diluted to a volume of 10 mL with sterile water, infused slowly over 2 min immediately before injection of the ^99mTc-pertechnetate. Flush intravenously with sterile water immediately before and after the infusion of glucagon. Do not give glucagon to a diabetic patient. It is important to reconstitute the glucagon with sterile water, not normal saline. The patient should be observed carefully for signs of nausea or vomiting. (The primary reason for administering glucagon before the radiotracer is to reduce the likelihood of vomiting and possible aspiration during the study.)