Nuclear Medicine Resources Manual

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background activity, dominant renal excretion of the radiopharmaceutical and

low liver uptake.

(f) Biliary leaks

A biliary leak is present when tracer is found in a location other than the

liver, gall bladder, bile ducts, bowel or urine. This may be seen more easily

using a cinematic display and when the patient is imaged in the decubitus

position.

(g) Biliary atresia

Biliary atresia can be excluded by demonstrating the transit of

radiotracer into the bowel. Failure of the tracer to reach the intestinal tract can

be caused by hepatocellular disease or immature intrahepatic transport

mechanisms and is not necessarily related to biliary atresia or CBD

obstruction. However, no evidence of hepatobiliary excretion in a jaundiced

neonate having received phenobarbital is probably due to biliary atresia.

Urinary excretion of the tracer (especially into a diaper) may be confused with

bowel activity and is a potential source of erroneous interpretation.

(h) Duodenogastric bile reflux

During a hepatobiliary scan, activity may reflux from the duodenum into

the stomach. This abnormal bile reflux is highly correlated with bile gastritis, a

cause of epigastric discomfort.

(i) Post-cholecystectomy sphincter of Oddi dysfunction:

Following pretreatment with sincalide, a combination of visual and

quantitative indices (the ‘scintigraphic score’) may be used when this condition

is suspected.

5.6.2.9. Reporting

In addition to patient demographics, the report should include the

following information:

(a) The indication for the study (e.g. suspected acute cholecystitis, suspected

common bile duct obstruction or suspected bile leak).

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(b) Procedure:

— Radiopharmaceutical and dose administered;

—Other medications given and their dosage (e.g. pretreatment with

cholecystokinin or morphine, or post-treatment with cholecystokinin);

—Duration of imaging, special or delayed views obtained.

of the gall bladder, small bowel, any unusual activity (e.g. a bile leak or

enterogastric reflux) and any quantitative data generated (e.g. GBEF).

(d) Study limitations and patient reactions to drugs administered.

(e) Comparative and/or correlative imaging data.

(f) Impression: This should be concise, as precise as possible, address the

clinical question, provide a differential diagnosis and make recommenda

tions if appropriate.

(g) Any urgent or unexpected findings should be directly communicated to

the referring physician and documented.

5.6.2.10. Sources of error

(a) The causes of a false positive study (gall bladder non-visualization in the

absence of acute cholecystitis) include:

— Insufficient fasting (<2–4 hours);

—Prolonged fasting (>24–48 hours), especially total parenteral nutrition

(despite sincalide pretreatment and morphine augmentation);

—Severe hepatocellular disease;

—High grade CBD obstruction;

—Severe intercurrent illness (despite sincalide and morphine);

—Pancreatitis (rare);

—Rapid biliary-to-bowel transit (insufficient tracer activity remaining in

the liver for delayed imaging);

—Severe chronic cholecystitis;

—Previous cholecystectomy.

(b) False negative studies (gall bladder visualization in the presence of acute

cholecystitis) are rare; their causes include:

—A bowel loop simulating the gall bladder (drinking water may help

clarify the anatomy).

—Acute acalculous cholecystitis.

—The presence of the ‘dilated cystic duct’ sign simulating the gall

bladder. If this sign is present, morphine should not be given.

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—A leak of bile due to gall bladder perforation.

—Congenital anomalies simulating the gall bladder.

—Activity in the kidneys simulating the gall bladder or small bowel (this

may be clarified by a lateral image).

BIBLIOGRAPHY TO SECTION 5.6.2

BALON, H.R., et al., Procedure guideline for hepatobiliary scintigraphy, Society of

Nuclear Medicine, J. Nucl. Med. 38 (1997) 1654–1657.

KRISHNAMURTY, S., KRISHNAMURTY, K., “Quantitative assessment of hepato-

biliary diseases with Tc-99m-IDA scintigraphy”, Nuclear Medicine Annual

(FREEMAN, L.M., WEISSMANN, H.S., Eds), Raven Press, New York (1988).

ROYAL, H.D., et al., Procedure guideline for hepatic and splenic imaging, J. Nucl. Med.

39 (1998) 1114–1116.

5.6.3. Gastrointestinal bleeding

5.6.3.1. Principle

Gastrointestinal bleeding scintigraphy is performed using

99m

Tc labelled

RBCs in patients suspected of having active gastrointestinal bleeding. Sites of

active bleeding are identified by the accumulation and movement of labelled

RBCs within the bowel lumen. Since activity within the lumen of the bowel can

move antegrade and retrograde, frequent images will increase the accuracy of

localization of the bleeding site. Technetium-99m SC can be used but it has a

short residence time within the intravascular space, which limits sensitivity. The

agent is cleared from the blood by the reticuloendothelial system with a half-

time as short as 2–3 min, while radiolabelled RBCs remain for hours.

5.6.3.2. Clinical indications

Gastrointestinal bleeding can be either upper, originating above the

ligament of Treitz, or lower, distal to the ligament of Treitz. Frequent causes of

upper gastrointestinal bleeding include esophageal varices, gastric and

duodenal ulcers, gastritis, esophagitis, Mallory–Weiss tears or neoplasms.

Causes of lower gastrointestinal haemorrhage include angiodysplasia, diver

ticula, neoplasms and inflammation, and, in children and young adults,

Meckel’s diverticulum. Endoscopy and angiography provide accurate locali

zation of bleeding sites and potential therapeutic control. Scintigraphy with

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283

labelled RBCs is complementary to endoscopy and angiography because it

permits continuous monitoring over a period of hours. This is a major

advantage since most gastrointestinal bleeds are intermittent and therefore are

frequently missed by other methods.

The clinical picture for active gastrointestinal haemorrhage is often

unreliable and misleading. There is frequently a marked temporal lag between

the onset of bleeding and clinical presentation. While it may be clinically

apparent that the patient has bled from the presence of melena or a haemor

rhage, the blood may pool in the colon for hours before being evacuated. A

drop in the haematocrit and elevated serum blood urea nitrogen (BUN) also

lack the temporal resolution needed to indicate active bleeding. Orthostatic

hypotension and tachycardia occur more acutely but are insensitive and non-

specific signs.

In cases where there is occult bleeding detected only by positive stool tests,

gastrointestinal bleeding scintigraphy is unlikely to be useful, although the method

can detect bleeding rates as low as 0.1–0.35 mL/min. The guaiac test detects bleeds

at rates well below the necessary threshold to be seen by scintigraphy.

The goals of gastrointestinal bleeding scintigraphy are to locate the

bleeding site and to determine which patients require aggressive treatment as

opposed to those who can be medically managed. In some patients, the

bleeding site is identified with sufficient confidence for specific surgical inter

vention (e.g. right hemicolectomy in the case of the ascending colon). If

bleeding is detected, the site is usually localized well enough to direct the next

diagnostic test (e.g. endoscopy or arteriography).

5.6.3.3. Radiopharmaceuticals

The in vitro method for labelling RBCs is preferred due to its higher

labelling efficiency. The in vivo/in vitro method can be used, while the in vivo

method is not recommended because of potential high free pertechnetate

activity giving confusing results. Adult doses should be in the range of 370–

1110

MBq (10–30 mCi) according to the patient’s weight.

5.6.3.4. Equipment

A large FOV gamma camera is required and a low energy, all purpose,

parallel hole collimator is preferred. When the study has to be performed at the

bedside with a small detector, a diverging collimator is useful in order to

include the maximum abdominal area.

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5.6.3.5. Patient preparation

Patients suspected of acute gastrointestinal bleeding should have blood

pressure and heart rate measured upon their arrival in the nuclear medicine

department to confirm that they are haemodynamically stable. Vital signs

should be monitored periodically while the patient is being imaged. The patient

should have an intravenous catheter in place so that hypotension can be rapidly

treated with replacement of fluids or blood.

The removal of blood for radiolabelling and re-injection poses the risk of

misadministration to the wrong patient. The handling and administration of

blood products must be subject to special safeguards and procedures, in order

to prevent errors or contamination accidents.

5.6.3.6. Procedure

The procedure for gastrointestinal bleeding scintigraphy is as follows:

(a) A dynamic acquisition is important in order to accurately localize the

bleeding site:

—Photopeak, typically a 20% window at 140 keV;

—Computer, 128 × 128 matrix.

(b) Patient position: supine.

(d) Acquisition protocol:

(1) Abdominal flow study: anterior flow images (1–5 s/frame for 60 s).

(2) Dynamic abdominal imaging:

—Dynamic images are acquired at a frame rate of 10–60 s/frame

over a 60–90 min period. Acquiring these images in multiple sets

of 10–15 min each may facilitate review by the physician as the

study is in progress.

—In case a computer is not available, sequential analog images of

000 000 counts each should be obtained every 5 min for 60–

min; localization might be aided by acquiring images at shorter

intervals.

—Delayed imaging: for

99m

Tc-RBCs, if no bleeding site is identified

on the initial 60–90 min dynamic images, delayed images may be

acquired at 2–6 hours and/or at 18–24 hours after the injection of

the radiopharmaceutical. Delayed images are useful in showing

subsequent bleeding and categorizing severity, but may result in

incorrect localization of the bleeding site.

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(3) Additional views: owing to overlying bladder activity, activity in the

rectum can be obscured. Lateral views may be needed to detect

rectal bleeding. Anterior oblique and posterior views are frequently

helpful in deciding if activity is located anteriorly or posteriorly.

(4) ROI counts over extravasated blood in the bowel may be used to

estimate blood loss when normalized to counts obtained from a

blood sample drawn simultaneously from the patient and corrected

for attenuation. The precision and accuracy of estimates should be

determined for each institution.

(5) The following procedures may be useful to provide more exact local-

ization of a bleeding site:

—Review of prior barium studies;

—Oral

99m

Tc-SC to outline the upper gastrointestinal and small

bowel anatomy;

—Technetium-99m SC enema to outline the colon.

5.6.3.7. Interventions

Pharmacological intervention is controversial and is not widely used.

Glucagon studies have been suggested as an adjunct to gastrointestinal

bleeding studies. Glucagon decreases intestinal peristalsis and increases

vasodilatation, although it is not widely used.

Heparin also has been suggested as an adjunct to gastrointestinal

bleeding studies in selected patients with recurrent significant bleeding and

negative standard diagnostic tests. Six thousand units of heparin are adminis

tered intravenously as a loading dose, followed by 1000 units every hour. The

patient’s baseline coagulation status should be evaluated before giving heparin.

Surgical coverage should be immediately available as a precautionary measure

and close monitoring of the patient is necessary with protamine sulphate on

hand to reverse the effects of heparin.

5.6.3.8. Processing

Subtraction and/or contrast enhancement should be used, with no other

routine processing parameters to be observed.

5.6.3.9. Subtraction cinematography

The first frame or normalized summed set of data can be subtracted from

the latter images to improve contrast. When using this technique, the patient

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must remain still during the examination or appropriate motion correction

software should be used.

5.6.3.10. Interpretation

In addition to patient demographics, the report should include the

following information:

(a) Reasons why the study was indicated.

(b) Procedure:

(1) Radiopharmaceuticals:

—Dose;

—Radiolabelling method for RBCs (e.g. in vivo);

—Method of administration (intravenous).

(2) Acquisition:

—Duration of acquisition (e.g. 1 hour);

—Frame rate (e.g. 10 s/frame);

—Projections acquired (e.g. anterior or laterals).

(3) Display (e.g. static versus cine).

(4) Findings:

—Onset;

—Location;

—Characteristics:

● Size and shape (e.g. focal or diffuse);

● Pattern of movement (e.g. moving or stationary, serpentine small

bowel pattern or colonic pattern, antegrade or retrograde);

● Severity (e.g. waxing or waning intensity, qualitative intensity

compared with the liver, and qualitative volume (large or

small)).

(d) Interpretation (e.g. positive, negative or indeterminate) and location of

bleeding site.

(e) Sources of error:

(1) A delay in implementing the procedure should be avoided because

bleeding may have stopped.

(2) Subtle areas of bleeding may go undetected or the location of the

bleeding may be inaccurately identified if images are not displayed

in cine-mode. Use of windowing levels and different colour tables on

a computer display further facilitate the detection of subtle abnor

malities.

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287

(3) It is important to continue to acquire images after abnormal activity

has been detected. Accurate localization of the bleeding site is

dependent upon identification of the focus of initial blood collection,

and upon the movement of the blood away from the bleeding site.

(4) The entire abdomen must be examined before concluding that no

bleeding has been detected. A lateral, posterior and/or subpubic

view is best to help in identifying activity in the rectum that would

otherwise not be detected due to overlying bladder activity or soft

tissue attenuation.

(5) Inexperienced readers may mistake mesenteric varices or penile

blood pools for areas of bleeding. A full urinary bladder may

obscure sigmoidal or rectal bleeding. Radioactive urine in the renal

pelvis of a transplanted kidney, in either the right or left lower

quadrant of the abdomen, may mimic colonic activity.

(6) Gastric mucosal and renal activity are seen when free

99m

Tc-pertech-

netate is present. This potential source of error can be avoided by

using the in vitro RBC labelling method and performing a quality

control for free pertechnetate, and by recognizing that intraluminal

blood moves in a distinct pattern. Images of the thyroid and salivary

glands can confirm the presence of free

99m

Tc-pertechnetate as the

source of an artefact.

BIBLIOGRAPHY TO SECTION 5.6.3

FORD, P.V., et al., Procedure guideline for gastrointestinal bleeding and Meckel’s

diverticulum scintigraphy, J. Nucl. Med. 40 (1999) 1226–1232.

5.6.4. Meckel’s diverticulum scintigraphy

5.6.4.1. Principle

A Meckel diverticulum is a vestigial remnant of the omphalomesenteric

duct located in the ileum, about 50–80 cm from the ileocecal valve. About half

of Meckel diverticuli contain gastric mucosa. Bleeding may result from ileal

mucosal ulceration from acid secretion. Technetium-99m pertechnetate avidly

accumulates in gastric mucosa and is the study of choice for identifying ectopic

gastric mucosa in a Meckel diverticulum.

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5.6.4.2. Clinical indications

The indication for the study is to localize ectopic gastric mucosa in a

Meckel diverticulum as the source of unexplained gastrointestinal bleeding.

Bleeding Meckel diverticula usually occur in young children. A Meckel

scintigram should be used when the patient is not actively bleeding; even in

young children, active bleeding is best studied by radiolabelled RBC

scintigraphy.

5.6.4.3. Radiopharmaceuticals

Inject 370–450 MBq (10–15 mCi) of

99m

Tc-pertechnetate intravenously,

adjusting the dose according to age, but not less than 100 MBq (3 mCi).

5.6.4.4. Equipment

A large FOV gamma camera is required and a low energy, all-purpose,

parallel hole collimator is preferred.

5.6.4.5. Patient preparation

Pretreatment with histamine H

blockers is reported to enhance the

sensitivity and specificity of the Meckel scan. Histamine H

blockers

(cimetidine and ranitidine) block secretion from the cells and increase gastric

mucosa uptake, preventing release and accumulation of the tracer in the

intestinal lumen, which constitutes a common cause of false positive studies.

An oral dose of 300 mg cimetidine should be administered four times a day for

two days in adults, and doses of 20 mg/(kg

· day) for two days in children or

20 mg/(kg · day) in neonates, prior to starting the procedure. Intravenous

cimetidine should be administered at a rate of 300 mg in 100 mL of saline

dextrose over 20 min, with imaging starting 1 hour later. Ranitidine dosage is

mg/kg for infants, children and adults up to a maximum of 50 mg, infused

intravenously over 20 min with imaging starting 1 hour later, immediately after

injection of

99m

Tc-pertechnetate.

It should be determined whether the patient has received recent in vivo

RBC labelling, where all circulating RBCs were exposed to stannous ions via

intravenous administration of a ‘cold’ pyrophosphate kit. If so, the Meckel scan

may be compromised, since

99m

Tc-pertechnetate will label RBCs rather than

concentrate in the ectopic gastric mucosa. This may occur for days after the

administration of a stannous pyrophosphate but is usually not a problem with

in vitro labelling. Patients may also be placed in the left lateral decubitus

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289

position to decrease small bowel activity arising from the stomach. Nasogastric

tube suction has also been used for this purpose.

5.6.4.6. Procedure

The procedure for Meckel’s diverticulum scintigraphy is as follows:

(a) Photopeak: typically a 20% window at 140 keV;

Computer: 128 ¥ 128 matrix.

(b) Patient position: supine (the left lateral decubitus position is optional).

(d) Acquisition protocol:

—Optional acquisition of anterior abdominal flow images (1–5 s/frame

for 60 s).

—Anterior abdominal images at one image every 30–60 s for at least

min (60 min is sometimes recommended).

Additional static images in the anterior oblique, lateral and posterior

views are recommended at the end of the dynamic acquisition. Stopping the

acquisition to obtain these images when abnormal activity is first seen can be

helpful in distinguishing activity in a Meckel diverticulum from that in the

kidney, ureter or bladder. Post-void images can also be helpful in detecting

activity in a Meckel diverticulum obscured by the urinary bladder. A urinary

catheter can be helpful if the Meckel diverticulum is adjacent to the bladder.

Alternatively, the decubitus or upright views may at times cause the diver

ticulum to separate from the bladder.

5.6.4.7. Interpretation

Activity in the ectopic gastric mucosa should appear simultaneously with

normal gastric mucosa. A Meckel diverticulum may appear anywhere within

the abdomen, although it is more often located in the right lower quadrant.

Frequently confused with a Meckel’s diverticulum is activity in the kidneys,

ureter or bladder. Activity in the urinary tract usually appears after that in the

normal gastric mucosa. A small Meckel diverticulum may appear at a later time

than that for the stomach. Pertechnetate that is secreted by the gastric mucosa

will gradually accumulate in the small bowel. This activity can be distinguished

from that in a Meckel diverticulum by its delay and by its appearance as an area

of mildly ill-defined increased activity. It is also helpful to view the dynamic

study in cine-mode with an upper threshold adjustment for enhancement of

low activity areas.