Gastrointestinal Bleeding Scintigraphy

Michael A. McDonald, MD, PhD; Harvey A. Ziessman, MD

Disclosures

Appl Radiol. 2016;45(5):19-22. 

In This Article

Methodology and Image Interpretation

A typical RBC scintigraphy protocol for lower GIB involves imaging with a large-field-of-view gamma camera and high resolution, parallel-hole collimator.[11] After intravenous injection of 20 mCi of Tc99m labeled RBCs, flow images are acquired for 60 seconds at a rate of 1-second per frame followed by dynamic imaging for up to 90 minutes at a rate of 1-minute per frame. A further 30 minutes of imaging at 1-minute per frame can be obtained up to 24 hours after radiotracer administration. Inefficient labeling can be evaluated by acquiring static images of the anterior neck for identification of free unlabeled Tc-99m pertechnetate in the thyroid and salivary glands. Static images of the lateral pelvis can be obtained to help differentiate Tc-99m RBCs in the bladder from that in the rectum.

Criteria for interpretation of a positive RBC scintigraphy scan include demonstration both of extravasation of radiotracer from the vascular compartment and movement of radiotracer in an anterograde and/or retrograde fashion in the bowel lumen.[6] Extravasated blood exerts a cathartic effect stimulating Tc99m labeled RBC transit in the bowel. Dynamic imaging minimizes timing errors encountered with static images which may show blood in the gut that has already traveled distal to the actual site of bleeding.[10]

An elongated peripherally localized pattern of radiotracer progression is seen in large bowel GIB (Figure 1). In cinematic display mode, small bowel GIB is distinguishable by demonstration of relatively rapid radiotracer transit through more centrally located curvilinear segments (Figure 2).

Figure 1.

Technetium99m red blood cell scan demonstrating a gastrointestinal bleed in the colon originating near the splenic flexure. Angiography subsequently showed a focus of arterial contrast extravasation at the level of the mid-descending colon, likely of diverticular origin.

Figure 2.

Technetium99m red blood cell scan demonstrating active bleeding. The serpiginous pattern of transit is very suggestive of blood transiting the small bowel. The exact site of bleeding was uncertain, but thought to be proximal. Exploratory laparotomy demonstrated a bleeding ulcer in the second portion of the duodenum.

False-positive results can be the result of aneurysms, varices, inflammation or tumors and usually are seen as static areas of extravascular radiotracer accumulation on RBC scintigraphy. Penile activity can be mistaken for rectal bleeding, avoided by obtaining lateral pelvic views and positional manipulations. Poor labeling can lead to false positive studies due to free pertechnetate being secreted within gastric mucosa and duodenum and excreted into the urinary collecting system.[12] Gallbladder visualization may be due to hematobilia or alternatively transfusion-related labeling of the porphyrin group of degraded hemoglobin, with subsequent liver and biliary excretion, particularly in patients with severe renal impairment.[10]

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