G.I. Bleeding scintigraphy has been used for over 20 years for localizing sites of gastrointestinal bleeding (small or large bowel). The most relevant features of G.I. Bleeding Scintigraphy are: high sensitivity, non invasiveness, absence of contraindications. Requirements for an effective use of G.I. Bleeding scintigraphy are: availability of a 24H/7 days open Nuclear Medicine dept., ready answer to clinical questions, and therefore inclusion of G.I. Bleeding Scintigraphy into the emergency N.M. procedures (Pulmonary Embolization, Brain death, AMI rule out, Scrotal torsion, etc..)
G.I. Bleeding Scintigraphy: technical aspects Two different (and opposite) methods and radiopharmaceuticals may be used: * 99m Tc-labeled sulfur colloid (SC) * 99m Tc-labeled red blood cells (RBC) A further method can be used to localize ectopic gastric mucosa, such as in Meckel’s diverticulum.
99m Tc-SC showes a rapid intravascular clearace (half time of 2-3 min), since colloids are trapped in the reticuloendothelial system (liver, spleen, bone marrow), so that extravasation into the Gut remains visible as a hot spot in the otherwise “cold” abdomen. To be an effective diagnostic tool, it requires the presence of active bleeding at the time of tracer administration (not useful in intermittent bleeding). It takes a short time to be accomplished, it is sensitive, but with limited ability to precisely identify the site of bleeding (if a simple gamma-camera is used instead of a more sophisticated SPECT/CT system). G.I. bleeding may be difficult to identify in the upper abdomen, due to the shadowing effect of “hot” liver and spleen. G.I. Bleeding scintigraphy with 99m Tc-SC
99m Tc-SC: bleeding at the hepatic flexure
G.I. Bleeding scintigraphy with 99m Tc-RBC 99m Tc-RBC have a stable persistence within the blood pool, allowing the possibility of imaging over a prolonged period. Since gastointestinal bleeding is typically intermittent and episodic, this feature is attractive, by increasing the yield of positive studies, in presence of intermittent bleeding. A frequent evaluation is required: typically a half hour dynamic scan followed by 6 and 24 hours static images, if the early phase is negative. Theoretically the underlying background due to circulating RBC may result in an increase of the threshold for the amount of bleeding for detectability. The positivity only in delayed images is only confirmatory of intermittent bleeding, not useful in identifying the bleeding site.
99m Tc-RBC: bleeding in the cecum A: dynamic study B: 5 min C: 10 min
Sensitivity for gastrointestinal bleeding detection MethodBleeding rate Angiography0.5-1 ml/min 99m Tc-SC ml/min 99m Tc-RBC 0.1 ml/min (rate dependent time until positive)
Potential causes of Angiographic failure to detect gastrointestinal bleeding, for which radionuclide scan may be helpful Hemorrhage less than 0.5 ml/min Venous bleeding Technical failure Resolution of bleeding Temporary cessation of bleeding Hypotension Intermittent source
99m Tc-RBC: bleeding in the small bowel in patient with cirrhosis. It is possible to appreciate the typical progression of activity in the bowel over time, due to peristaltic movements
99m Tc-RBC: criteria to identify the site of bleeding Central abdomen location: small bowel Peripheral abdomen location: large bowel Since extravasated blood into the bowel usually progresses forward (but sometimes also backwards), it is important to identify the earliest site of bleeding more than the most proximal site of blood in the bowel, by using the dynamic sequence of images.
99m Tc-RBC: bleeding in the hepatic flexure It is possible to appreciate forward and backwards progression of radioactive blood in the bowel
99m Tc-RBC in G.I. bleeding with rapid forward transit Early images (10-30 sec) Late images (24-25 min)
99m Tc-RBC in G.I. bleeding with backwards transit Early images (1-3 min) Late images (45-48 min)
99m Tc-RBC in G.I. intermittent bleeding Early images (1-5 min) Late images (45-50 min)
99m Tc-RBC in G.I. minimal bleeding sec min min min
Accuracy of G.I. Bleeding scintigraphy with 99m Tc-RBC (pooled data from the literature in more than 1500 cases) Rate of positive studies: 52% (range 22%-96%) Correct identification of bleeding site: 81% (range 20%- 96%) Whilst the rate of positive studies is linked to the rate of actual bleeding during the study time, the correct identification of the bleeding site is linked to correct methodology (i.e. the correct sequence of images).
Identification of G.I. Bleeding from Meckel’s diverticulum When G.I. bleeding is suspected to originate from a Meckel’s diverticulum (ectopic gastric mucosa), it is preferable to use, as radiopharmaceutical, 99m Tc- pertechnetate, with the patient pretreated with cimetidine or pentagastrine. With this method the Meckel’s diverticulum can also be identified in the absence of active bleeding at the time of the study
Scintigraphic study performed with 99m Tc-pertechnetate, premedication with cimetidine