This document discusses several radiopharmaceutical techniques for imaging the gastrointestinal tract, including detecting gastrointestinal bleeding, Meckel's diverticulum, inflammatory bowel disease, and neuroendocrine tumors. Scintigraphy using radiolabeled red blood cells or colloids can help locate the source of gastrointestinal bleeding when endoscopy is inconclusive. Meckel's diverticulum can be identified by detecting ectopic gastric mucosa using technetium pertechnetate imaging. White blood cell scintigraphy with indium or technetium can demonstrate inflammatory bowel disease. Somatostatin receptor scintigraphy using indium-labeled octreotide is useful for detecting and staging neuroendocrine tumors such as carcinoid tumors.

1. Radionuclide imaging
of the GIT

2.  Scintigraphic investigation of
gastrointestinal bleeding.
 Meckel,s diverticulum.
 Radionuclide imaging of inflammatory
bowel disease.
 Somatostatin receptor scintigraphy.

3. 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.

4. 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.

5. Techniques
 Two approaches have been developed.
1.Radiolabelled colloid.
2.Radiolabelled red cells.

6. 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 focus
of activity.
 Subsequent images are obtained at
intervals upto 45 minutes.

7.  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.

8. 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.

9.  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.

13. 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.

14. 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.

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

16. Preparation.
 Adults should starve overnight to reduce
gastric secretions.
 Infants and children should with hold one
feed.
 H2 blockade is prescribed.

17.  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.

18.  Abdominal lesions with an increased blood
pool or extracellular fluid component for
e.g. aneurysms, tumours,inflammatory
masses show maximum activity on early
images.
 Gastric mucosa activity increases in
intensity over 20-30 min.
Interpretation.

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

22. 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.

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

24. 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.

25. Somatostatin receptor
scintigraphy
 Octreotide is a synthetic analogue with 8
amino acids which binds to somatostatin
membrane 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.

26.  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.

27. 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.

28. 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 biliary
tract.

29. Results
 SRS is highly accurate in detecting
primary bowel carcinoids and their mets
in 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.

34. Thanks