Bleeding in the
gastrointestinal (GI) system can be conveniently divided into two
general categories:
- upper GI bleeding occurs
proximal to the Ligament of Trietz and includes bleeding in the
esophagus, stomach or duodenum. Common causes include:
- lower GI bleeding occurs
distal to the Ligament of Trietz and includes bleeding in the
jejunum, ileum,
colon
or rectum. Common causes include:
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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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 in an irritant within the GI tract, it is rapidly moved
distally (usually - 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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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.
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Patient
Preparation
No specific patient
preparation is required.
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, 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 64
x 64 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.
The protocol posted by
The
Crump Institute for Biological Imaging at UCLA provides a
clinical example of a GI Bleeding protocol using Tc-99m labelled
colloid.
Procedure using
Tc-99m Red Blood Cells
Patient
Preparation
No specific patient
preparation is required.
Pharmacological
Interventions
No specific pharmacological
interventional techniques are commonly used with this study.
Radiopharmaceutical(s)
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 the free pertechnetate being 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.
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 not available).
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.
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),
The
University Hospital in London, ON and
The
Crump Institute for Biological Imaging at UCLA provide clinical
examples of GI Bleeding protocols using Tc-99m labelled red blood
cells.
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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
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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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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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
#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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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
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