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Nuclear Medicine Imaging
and Function Studies
of the Gastrointestinal System

Gastrointestinal Bleeding Detection and Localization


Review of Pathology Principle
Indications Procedure
Interpretation Artifacts
Other Modalities Case Studies
References Quiz

Review of Pathology

Bleeding in the gastrointestinal (GI) system can be conveniently divided into two general categories:

The prognosis for a patient presenting with acute bleeding depends upon a number of factors including the:

  • rate of blood loss
  • total volume of blood lost
  • patient's age
  • presence of related disease in the patient
  • effectiveness of treatment of the bleeding.

Because gastrointestinal bleeding can be life-threatening, timely identification and localization of the bleeding site is an important aspect of the management of acute GI bleeding.

Gastrointestinal bleeding is often intermittent or slow. Nuclear medicine imaging (especially using Tc-99m red blood cells) is very effective and is up to ten times more sensitive than radiographic angiography for the detection of lower GI bleeds. The sensitivity and specificity are not as good for upper GI bleeds.


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Principle

Gastrointestinal bleeding studies are based on detection of the extravasation of an injected radiopharmaceutical into the lumen of the GI tract at a bleeding site. Since blood is an irritant within the GI tract, it is rapidly moved distally (usually - but movement can be bidirectional) along the tract and away from the bleeding site by peristaltic activity. The movement also results in dispersal of the activity making it less evident on images. For these reasons, continuous imaging / data collection is recommended during performance of a GI bleeding study.

Two radiopharmaceuticals have been used successfully for detecting GI bleeds:

  • Tc-99m sulfur colloid
  • Tc-99m red blood cells

Each has its own inherent advantages and disadvantages.

Protocols for each of the radiopharmaceuticals are presented separately.


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Indications

Gastrointestinal bleeding studies are indicated in patients with known or suspected GI bleeding to detect the presence of bleeding and to localize the site of bleeding.

It may also assist in identifying patients requiring angiography.


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Procedure using Tc-99m sulfur colloid

Patient Preparation

No specific patient preparation is required.

Explain the test procedure to the patient and obtain relevant patient history.

Pharmacological Interventions

No specific pharmacological interventional techniques are commonly used with this study.

Radiopharmaceutical(s)

  • Tc-99m sulfur colloid
  • Tc-99m tin colloid

About 300 to 600 MBq of Tc-99m labelled colloid is injected as a bolus. Significantly higher doses are used compared to liver / spleen imaging due to the expectation that only small amounts of the radiopharmaceutical will be extravasated.

Equipment

A LFOV gamma camera with a low-energy all purpose or high resolution parallel hole collimator interfaced to a nuclear medicine computer is preferred. The camera's analyzer is set at 140 keV with a 15 to 20% window. The computer acquisition uses a 128 x 128 matrix.

Image / Data Acquisition Parameters

The patient should be placed supine with the field of view adjusted to include only the lower portion of the liver and spleen and the entire abdomen and pelvic region. If images are to be recorded on film, the intensity should be set high in order to optimize visualization of the potentially small amounts of extravasated radiopharmaceutical.

An anterior flow is obtained for 2 to 3 min at a rate of 2 to 5 sec/frame. This is followed by 1 min acquisitions per image for 20 to 30 min. Delayed images obtained at about 45 to 60 min may allow better visualization of colloid extravasated at the hepatic or splenic flexures. Continuous imaging improves the sensitivity of the procedure.

More than one dose (up to ~3) may be administered if bleeding is not detected with the previous dose but is strongly suspected.

The protocol posted by The Crump Institute for Molecular Imaging at UCLA provides a clinical example of a GI Bleeding protocol using Tc-99m labelled colloid.

Data Analysis

Images are viewed in cine mode. Images may be combined together for production of hard copy images.


Procedure using Tc-99m Red Blood Cells

Patient Preparation

No specific patient preparation is required.

Explain the test procedure to the patient and obtain relevant patient history. An informed concent form should be completed.

Pharmacological Interventions

No specific pharmacological interventional techniques are commonly used with this study.

Radiopharmaceutical(s)

  • Tc-99m Red Blood Cells

In vitro labelling of the red blood cells is preferred to obtain a high labelling yield (>~97%). The higher amounts of free pertechnetate resulting from in vivo labelling (~75 to 85% labelling) and less so from in vivtro labelling (~90 to 95% labelling) can produce false positive results due to free pertechnetate secreted into the lumen of the GI tract by the gastric mucosa. The activity will eventually arrive in the bowel and may present interpretation difficulties. For a movie presentation on invivtro labelling, click here. Note: The file is 2.551 Megabytes in size and takes some time to download.

About 700 to 1000 MBq of Tc-99m labelled red blood cells is injected. Pediatric doses are adjusted appropriately.

Equipment

A LFOV gamma camera with a low-energy, high resolution parallel hole collimator interfaced to a nuclear medicine computer is preferred. The camera's analyzer is set at 140 keV with a 15 to 20% window. The computer acquisition uses a 128 x 128 x byte (or word) mode matrix (64 x 64 x byte mode if storage space is limited).

Image / Data Acquisition Parameters

The patient should be placed supine with the field of view and adjusted to include only the lower portion of the liver and spleen and the entire abdomen and pelvic region.

An anterior flow is obtained at a rate of 2 to 5 sec/frame for 1 to 2 min. This is followed by 10 to 60 second acquisitions per image for 60 to 90 min (i.e. cinescintigraphy). If computer acquired cinescintigraphy is not possible, acquire 750k to 1000k count static images every 2 to 5 minutes for 60 to 90 minutes. Shorter imaging intervals increase the likelihood of identifying the origin of a bleed.

If bleeding is not detected, delayed images may be obtained at appropriate intervals between 2 to 6 hours and 18 to 24 hours. The more frequently images are taken, the higher the probability of detecting an intermittent bleed.

The protocols posted by The Society of Nuclear Medicine (in Adobe *.pdf format) and The Crump Institute for Biological Imaging at UCLA provide clinical examples of GI Bleeding protocols using Tc-99m labelled red blood cells.

Data Analysis

Images are viewed in cine mode. Images may be combined together for production of hard copy images.


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Interpretation of a Tc-99m Sulfur Colloid Study

Because of its rapid clearance from the circulatory system, the Tc-99m sulfur colloid method requires that the bleeding site be actively hemorrhaging during the study. This being the case, the bleeding site will be observed as a focal accumulation of the radiopharmaceutical that increases in intensity with time and moves distally (usually, although retrograde movement is possible) through the intestine during the study. Structures normally visible include the liver, spleen and bone marrow of the vertebrae and pelvic girdle.

Failure to observe a bleeding site may only indicate that the patient was not actively bleeding during the study. This is the primary disadvantage of the sulfur colloid method (as it is with radiographic angiography). If bleeding is strongly suspected, a second injection may be indicated.

This method is very sensitive due to the very low background and bleeding rates in the order of 0.05 to 0.10 mL/min may be detected.

False positive interpretations may result from:

  • transplanted kidneys which will take up colloid during rejection
  • splenic tissue such as ectopic or accessory spleens
  • modified, asymmetric marrow uptake caused by myelofibrosis, tumor (primary or metastatic) or avascular necrosis
  • male genitalia
  • arterial grafts

False negative interpretations may result from:

  • patient not actively bleeding at time of injection

Interpretation of a Tc-99m Red Blood Cell Study

Because they remain within the circulatory system, the Tc-99m red blood cell method does not require that the bleeding site be actively hemorrhaging at the time of injection. The flow study normally demonstrates the major vessels and organs of the abdomen including the aorta, inferior vena cava, iliac vessels, liver, spleen and kidneys. Genitals may also be visualized, especially the uterus.

A positive bleeding site appears as an abnormal accumulation of activity that persists or increases with time and conforms to the shape of the bowel. The activity moves distally (usually) through the intestine during the study.

Although not as sensitive (~0.10 to 0.50 mL/min) as the sulfur colloid method due to the higher vascular background, a major advantage of the red cell method is its ability to detect intermittent bleeding. If bleeding is not detected within the first 60 to 90 minutes of the study, the patient can be periodically returned to the Nuclear Medicine department for additional imaging. The probability of identifying the location of the bleeding site is proportional to the frequency of imaging.

False positive interpretations may result from:

  • free Tc-99m pertechnetate secreted by the gastric mucosa
  • renal tissue such as pelvic or ectopic kidneys
  • renal pelvic retention of activity
  • hepatic hemangioma
  • varices and aneurysms of abdominal veins and arteries.

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Common Technical Difficulties and Artifacts

The primary technical concern when using the red blood cell method is ensuring that an adequate cell labelling efficiency has been achieved. Several medications and therapeutic medications can interfere with the efficiency of cell labelling. Using an in vitro labelling procedure is the best way to ensure a high quality yield is achieved.

Artifacts leading to false positive interpretations have been discussed above.


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Other Modalities for Determining the Same or Similar Information

Radiographic Angiography

Endoscopy

An endoscope may be inserted into both the upper and lower gastrointestinal tract in an attempt to visually locate and examine bleeding sites.


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Case Studies

Case #1 is located at the Mallinckrodt Institute of Radiology at Washington University Medical Center. A 53-year-old presents with dizziness and maroon stools. Anterior images at 5 minute intervals using Tc-99m RBCs are provided. Note the option to view the study in cine format. Try it.

Case #2 is located at the Mallinckrodt Institute of Radiology at Washington University Medical Center. The patient presented with a history of blood per rectum with the latest episode appearing to have stopped the day following admission. Anterior images at 2 minute intervals using Tc-99m RBCs are provided.

Case #3 is hosted by The Joint Program in Nuclear Medicine (JPNM) based at the Harvard Medical School. A 62-year-old man with known hypertension suffers a pulmonary embolism post surgery for tumor resection. He is placed on anticoagulant therapy after which he demonstrates hematochezia x 2.

Case #4 is hosted by The Crump Institute for Biological Imaging at UCLA. A 71-year-old woman presents with diverticular bleeding.

Case #5 is hosted by The Crump Institute for Biological Imaging at UCLA. A 30 year old with hematemesis and hematochezia is evaluated for possible lower GI bleeding.

Case #6 is hosted by The Crump Institute for Biological Imaging at UCLA. A 63 year old female with history of G.I. Bleeding requiring 1 unit packed RBC's every week for approx. 6 months. The patient also had a negative exploratory laparotomy approximately 1 week ago and now presents with black-tarry stools.

Case #7 is from the Virtual Hospital at the University of Iowa. The document is actually a complete lesson on GI bleeding and is very good. Some links on this page were not functioning properly at the time this document was posted.


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Specific References

Pathology

Texts

Damjanov I. Pathology for the Health - Related Professions. Philadelphia: W.B. Saunders Company, 1996: 257.

Kumar V, Cotran RS, Robbins SL. Basic Pathology. 5th ed. Philadelphia: W.B. Saunders Company, 1992: 473.

McCance KL, Huether SE. Pathophysiology. 2nd ed. St. Louis: Mosby - Year Book, 1994: 1324 - 1326.

Price SA, Wilson LM. Pathophysiology: Clinical Concepts of Disease Processes. 4th ed. St. Louis: Mosby - Year Book, 1992: 356.

Procedure

Texts

Datz FL. Handbook of Nuclear Medicine. 2nd ed. St. Louis: Mosby - Year Book, 1993: 133.

Bernier DR, Christian PE, Langan JK. Nuclear Medicine: Technology and Techniques. 3rd ed. St. Louis: Mosby - Year Book, 1994: 329 - 331.

Early PJ, Sodee DB. Principles and Practice of Nuclear Medicine. 2nd ed. St. Louis: Mosby - Year Book, 1995: 516 - 520.

Henkin

Thrall JH, Ziessman HA. Nuclear Medicine: The Requisites. St. Louis: Mosby - Year Book, 1995: 241 - 248.

Wagner H

Journals

Videos

Internet URL's

GI Bleeding Scintigraphy in Nuclear Medicine Review Manual by Dr. Scott C. Williams


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Quiz


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©1998 - 2005 Lyle J. Goodin, BSc, MRT(N), ACNM
Originally developed August 16, 1998; Last revised September 23, 2005
Comments, suggestions or questions??? Please address them to Lyle Goodin at:

email lgoodin@michener.ca or lgoodin@sympatico.ca