Radionuclide imaging of the GIT

Scintigraphic investigation of gastrointestinal bleeding.

Meckel,s diverticulum.

Radionuclide imaging of inflammatory bowel disease.

Somatostatin receptor scintigraphy.

Scintigraphic investigation of gastrointestinal bleeding.

80% of patients of GI bleeding has source in esophagus, stomach or duodenum.

Endoscopy has a high success rate in showing the cause of upper GI bleeding.

20% has source in small bowel or colon is more difficult to establish.

Indications

1.Patients with recurrent episodes of bleeding.

2.Endoscopy is negative or inconclusive.

3.Patients in whom surgical risks are high.

4.Patient with bleeding of severity to produce malena.

Techniques Two approaches have been developed.

1.Radiolabelled colloid.

2.Radiolabelled red cells.

Radiolabelled colloid Colloid particles in size range from30-

1000nm labeled with technetium.

In patients who are actively bleeding at the time of injection ,leakage of tracer into the lumen of gut will produce a focusof activity.

Subsequent images are obtained at intervals upto 45 minutes.

Extravasated blood from small bowel shows a central area which moves relatively quickly around the centre of abdomen.

Colonic activity moves fairly slowly around the periphery of the abdomen in a clock wise direction.

Radiolabelled red cells

The stability of the tracer with in the vascular compartment allows sequential imaging for upto 24 hours. Which gives the opportunity of detecting bleeding which is episodic or continuing at a slower rate.

A bolus injection of upto 400 mBq of Tc99-RBCs and followed by abdominal images obtained at 5 min intervals for about 1 hr.

Imaging can be continued at increasing intervals upto 24 hrs.

Meckel,s diverticulum It is a remnant of embryonic

omphalomesenteric duct persists into adult life in about 2% of population.

Few of them produce clinical problems like

1. peptic ulceration causing abdominal pain or occult bleeding.

2. Scarring following chronic inflammation leads to small bowel obstruction.

Scintigraphic technique. Intravenously injected pertechnetate

cleared from circulation by thyroid, salivary gland , choroid plexus of brain and by stomach from gastric mucosa which then moves along the lumen.

The procedure visualizes gastric mucosa in the stomach and also in ectopic sites including barrett,s esophagus and duplication cysts as well as meckel,sdiverticulum.

Preparation. Adults should starve overnight to reduce

gastric secretions.

Infants and children should with hold one feed.

H2 blockade is prescribed.

After 200-400 mBq of sodium pertechnetate.

Images of abdomen and pelvis are obtained with patient supine.

Images are obtained at 5 min intervals upto 45 min.

Interpretation.

Abdominal lesions with an increased blood pool or extracellular fluid component for e.g. aneurysms, tumours,inflammatorymasses show maximum activity on early images.

Gastric mucosa activity increases in intensity over 20-30 min.

Meckel,s diverticulum appears as a focal area of uptake which is remote from but synchronous with the normal gastric mucosa.

Radionuclide imaging of inflammatory bowel disease.

Autologous white cells are labeled either with technetium 99 or with indium 111 and injected into the patient.

Images obtained over the next few hours demonstrate the localization of white cells and in particular will show abnormal foci of infection or inflammation.

Bowel activity at 1 hr is taken as evidence of inflammatory bowel disease.

Applications 1.Detecting inflammatory bowel disease.

In the early stages of disease WBC scintigraphy may be the only positive test with normal barium or colonoscopy.

2. Assessing the extent and location of abnormal bowel.

3.Follow up.

4.Assessing the complications.

Somatostatin receptor scintigraphy

Octreotide is a synthetic analogue with 8 amino acids which binds to somatostatinmembrane receptors which occurs in cells of neuroendocrine origin.

Octreotide is labelled with indium 111-DTPA and is used to localize tumors of endocrine origin both primary and secondary.

Major applications for SRS are in the localization of pancreatic islet cell tumors and their metastases and in the investigation of GIT carcinoids, and related tumors and their metastases.

Technique Treatment with un labeled octreotide

reduce tracer uptake by tumor so it is desirable to stop such treatment 2 to 3 days before the test.

110MBq of indium 111chelated with DTPA bound to 10-20microgram of carrier octreotide is given intravenously. Whole body images are taken at 4 and 24 hr.

Interpretation In normal subject 90% of injected activity

is excreted in urine by 24 hr.

A high level uptake is typical in spleen and rather low grade activity in liver.

A small proportion is excreted via biliarytract.

Results SRS is highly accurate in detecting

primary bowel carcinoids and their metsin mesenteric lymph nodes.

Useful in patient presenting with liver mets when the primary site is not known.

Staging of carcinoid tumors particularly detecting extrahepatic and extra abdominal disease.

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