07 September 2016

Lecture #9: THE GASTROINTESTINAL SYSTEM



HEPATOBILIARY SYSTEM

Clinical indication

1.      Functional assessment of the hepatobiliary sytem

2.      Integrity of the hepatobiliary tree

a.      Evaluation of suspected acute cholecystitis
b.      Evaluation of suspected chronic biliary tract disorders
c.       Evaluation of common bile duct obstruction
d.     Detection of bile leak
e.      Evaluation of congenital abnormalities of the biliary tree

Patient preparation

1.      Patient should fast 2–4 hours before tracer administration

2.      Narcotics, sedatives or other drugs that relax the sphincter of Oddi, the muscle between the common bile duct and the duodenum, should be continued for 6–12 hours prior to hepatobiliary imaging.

Acquisition parameters

1.      Images are acquired at 1 min / frame for 1 hour

2.      After 1 hour, obliques and lateral projections should be obtained to delineate bowel activity or other structures such as kidneys.

Interventional procedure

1.      Sincalide pretreatment

a.      Sincalide is a synthetic form of cholecystokinin (CCK) given in a dose of 0.01–0.02 µg/kg infused over 3 minutes, 30–60 minutes prior to tracer injection.

b.      Used for patients who have fasted for prolonged periods (>24 hours)

c.       Used for patients who are on hyperalimentation (the gallbladder is full at the beginning of imaging)

2.      Morphine sulfate

a.      Morphine causes contraction of the sphincter of Oddi which in turn increases the pressure in the bile ducts.

The increased pressure forces tracer through the cystic duct, if it patent, into the gallbladder.

b.      Non–visualization of the gallbladder following administration of morphine increases the likelihood that the patient has acute cholecystitis.

c.       By using morphine, the length of the study is shortened and the specificity of the findings is increased.

3.      Phenobarbital

a.      In jaundiced infants, in whom biliary atresia is suspected, pretreatment with Phenobarbital, 5 mg/kg/day is usually given orally in two divided doses daily for a minimum of 3–5 days prior to the hepatobiliary imaging study.

b.      Mebrofenin is preferred for biliary atresia

Image findings

1.      Normal findings

a.      Visualization of the tracer within the hepatic ducts and gallbladder occurs by 15–30 minutes. The gallbladder is well visualized by 45–60 minutes and tracer activity appears in the small intestine by 30 minutes after injection.

2.      Acute cholecystitis

a.      Persistent gallbladder non–visualization post–morphine or on the 3–4 hours delayed image.

b.      Pericholecystic hepatic band of increased activity (the rim sign) is often associated with severe phlegmonous / gangrenous acute cholecystitis, a surgical emergency is needed.

3.      Chronic cholecystitis

a.      Reduced gallbladder ejection fraction is responsible to sincalide.

4.      Common bile duct (CBD) obstruction

a.      Partial common bile duct obstruction is there is delayed biliary to bowel transit beyond 60 minutes

b.      High grade CBD obstruction should be suspected when neither the intrahepatic biliary tree, gallbladder on the small bowel are seen within 18 –24 hours post injection

5.      Biliary leak

a.      When tracer is found in localization other than liver, gallbladder, bile duct, bowel or urine.

6.      Biliary atresia

a.      Demonstration of the tracer in the bowel.

Sources of error

1.      False positive error:

a.      Insufficient fasting (<2 – 4 hours)
b.      Prolonged fasting (>24 – 48 hours)
c.       Severe hepatocellular disease
d.     High grade common bile duct obstruction
e.      Severe intercurrent illness
f.        Pancreatitis
g.      Rapid biliary–to–bowel transit
h.      Severe chronic cholecystitis
i.        Previous cholecystectomy

2.      False negative error:

a.      Bowel loop simulating gallbladder
b.      Acute calculous cholecystitis
c.       Presence of “dilated cystic duct” sign simulating GB
d.     Bile leak due to GB perforation
e.      Congenital anomalies simulating gallbladder

Radiopharmaceuticals used:

1. Disofenin (DISIDA–2,6 diisopropylacetanilido iminoacetic acid)

2.     Mebrofenin (BRIDA–bromo–2,4,6–trimethylacetanildo iminoacetic acid)

3.      The usual dose is 1.5 to 5.0 mCi for adults or higher in case of hyperbilirubinemia

LIVER AND SPLEEN IMAGING

Clinical indication

1.      Liver and Spleen Imaging

a.      For suspected focal nodular hyperplasia of the liver

b.      Assess the function of the reticuloendothelial system in patient with suspected liver disease.

2.      Liver Blood Pool Imaging

a.      Highly specific for cavernous hemangiomas of the liver of up to >2 – 3 cm.

3.      Hepatic Perfusion Imaging

a.      Useful in demonstrating hepatic artery catheters used to infuse chemotherapeutic agents.

4.      Splenic Imaging

a.      In children, to rule out congenital asplenia or polyspenia

b.      In adults, whose thrombocytopenia has been previously treated with splenectomy

c.       For characterizing an incidentally noted mass as functionally noted mass as functional splenic tissue.

Radiopharmaceuticals used

1.      Liver and Spleen imaging – 5–10 mCi sulfur colloid

2.      Liver Blood Pool Imaging – 20–25 mCi Tc99m RBC

3.    Hepatic Artery Perfusion Imaging – 1–3 mCi Tc99m MAA

4.    Splenic Imaging – 1–3 mCi Tc99m heat damaged RBC’s

Image acquisition

1.      Liver and Spleen Imaging

a.      Imaging is done after 10–15 minutes post–injection at 500k to 1M counts

b.      Obtain anterior and posterior images with oblique and laterals

c.       Breath holding views may sometimes help clarify ambiguous findings by eliminating image degradation by respiratory motion

d.     Lead markers should be placed as imprints to measure the liver

2.      Hepatic Blood Pool Imaging

a.      Images at 1 seconds/ frame for 60 seconds should be obtained on the site of the lesion previously located by MRI or CT.

b.      Blood pool images and anterior, posterior, oblique and laterals should be acquired 1–2 million counts

c.       45–180 minutes post–injection delayed images should be acquired

d.     SPECT should be done if 0.5 cm lesion is suspected

3.      Hepatic Perfusion Imaging

a.      Tc99m MAA should be infused very slowly at a measure rate through the catheter.

b.      Imaging is done immediately at 500k – 1million counts

c.   Imaging of the lung is required to identify intrahepatic arteriovenous fistulas

4.      Splenic Imaging

a.      Imaging is done 30–120 minutes after injection of the tracer.

b.      If ectopic splenic tissue is a concern, the entire abdomen should be imaged

c.       If the patient has had prior trauma that may have resulted in a diaphragmatic rupture, the chest should also be imaged.

C–14 UREA BREATH TEST

Clinical indication

1.      Detection of the presence of Helicobacter pylori in the stomach

Patient preparation

1.      Patient should be fasting for 6 hours before the test

2.      No medication from the following before the test

a.      Antibiotics                                               –          30 days
b.      Sucrasulfate and omeprazole              –          7 days
c.       Histamine H2 receptor antagonist      –          24 hours
(ramitidine, nizatidine, antacids)

Radiopharmaceutical used

1.      C–14 urea

a.      A pure beta–emitter with a physical half–life of 5730 years

b.      It has a maximum energy of 160 keV

c.       Because of the beta emissions, it has to be counted in a liquid scintillation counter

d.     Can be purchased in a lyophilized form

e.      Dosage is 0.001 – 0.01 mCi orally

Procedure of the test

1.      The lyophilized C–14 urea is reconstituted with sterile water to the desired activity concentration. It has to be refrigerated to prevent thermodecomposition or bacterial contamination.

2.      A breath collection vial composed of exact concentration of hyamine in methanol is used as CO2–trapping solution. A pH indicator should be added prior to sampling.

3.      Breath sample collection

a.      Patient should be asked to brush their teeth or remove dentures to prevent contamination of normal flora.

b.      The patient is asked to take a deep breath and hold it for approximately 10 seconds and then exhale it through a straw until pH indicator changes color.

c.       The patient may also be asked to exhale through a mylar balloon and later expelled in a trapping solution. (Alternate collection technique)

d.     The patient then receives an oral dose of C–14 urea (20–30 ml). The patient has to clean his / her teeth and gums to prevent contamination.

e.      Breath samples are then collected into separate vials at 5–10 minute intervals for 20–30 minutes.

f.        10 ml of scintillation fluid is added to each vial immediately after breath collection.

4.      Breath sample counting

a.      All timed breath samples, background, sample, standard and C–14 quenched standards are counted for 5 – 10 minutes in a liquid scintillation counter.

5.      Calculation

% dose exhaled        =          A x B x 100                
                                                (C x D) x (E x F)
Where:

                        A         =          dpm of sample
                        B          =          patient weight in kg
                        C         =          dpm of standard
                        D         =          1/fraction of dose in standard
                        E          =          volume (ml) of trapping solution
                        F          =          concentration of trapping solution (mmol/ml)

MECKEL’S DIVERTICULUM

1.      A Meckel’s Diverticulum is an outpouching of the intestine, usually located in the distal ileum. It is a remnant of an embryonic duct at the point where the yolk sac is attached to the intestine of the fetus. It is formed when the duct fails to close completely during fetal development.

2.      The diverticulum may contain gastric mucosa. Just as the gastric mucosa lining of the stomach secretes hydrochloric acid and pepsin so does the ectopic gastric mucosa of the diverticulum.

3.      Gastrointestinal bleeding can result when the secretions of the gastric mucosa cause ulceration of the adjacent normal intestine. Patient may experience lower abdominal pain as well as GI bleeding.

Radiopharmaceutical used

1.      Tc99m pertechnetate, 5 mCi

Clinical procedure

1.      The patient should be fasting for 6 hours and should not have receive any laxatives or diagnostic test that might irritate the intestinal tract for at least 3 days prior to imaging.

2.      Pentagastrin stimulates gastric secretions, thereby increasing pertechnetate secretion in the stomach and diverticulum. It is administered subcutaneously 15 minutes before the tracer.

3.      Cimetidine may be administered as it helps retain pertechnetate in the gastric mucosa. The patient receives cimetidine orally every 6 hours for 24 hours before imaging.

Imaging

1.      Imaging should be acquired 5–10 minute intervals for 1 hour with the camera centered between the xyphoid and symphysis pubis.

Image findings

1.      Meckel’s diverticulum containing functioning gastric mucosa should be visualized by 10–15 minutes after injection, at the same time tracer activity appears in the stomach. It is usually seen in the right lower quadrant but can appear anywhere in the abdomen

GASTROINTESTINAL BLEEDING LOCALIZATION

Radiopharmaceutical used

1.      Tc99m–sulfur colloid – is best used in cases of active bleeding, since it leaves the blood pool rapidly and maybe cleared before the next bleeding episode, but bleeding in the upper quadrant may be obscured by sulfur colloid.

2.      Tc99m–labeled red blood cell, 25 mCi – better choice when the bleeding is intermittent since the tracer remains in the blood pool for a long period and allows delayed imaging.

Clinical procedure

1.      Rapid sequential images are acquired as the tracer is administered. Following the dynamic study, short static images are obtained at interval, up to 1 hour following injection.

2.      If Tc99m red blood cells were used, delayed imaging may be obtained at intervals but will be normally taken up by liver, spleen, abdominal vessels, kidneys, bladder, genitals and stomach.

3.      If Tc99m sulfur colloid were used, area of active bleeding is demonstrated within the first 5 minutes of imaging and may become more intense as background activity decreases.

GASTROESOPHAGEAL REFLUX

Background

1.      In adults, recurring or continual reflux of gastric or duodenal contents into the esophagus can lead to esophagitis and dysphagia

2.      In infants, chronic reflux may cause failure to thrive and aspiration pneumonia

Clinical procedure

1.      For adults, 300 µCi Tc99m sulfur colloid is mixed with 150 ml orange juice and 150 ml 0.1 N dilute hydrochloric acid and administered orally.

2.      For infants, the tracer is mixed with infant formula and administered through a nasogastric tube or orally through a baby bottle.

3.      Imaging begins after tracer administration with stomach, esophagus and lungs included in the field of view.

4.      Serial images are obtained as varying amounts of pressure are applied to the abdomen using abdominal binder.

5.      Delayed images of the lung field up to 24 hours after tracer administration are useful for detecting intermittent reflux, which leads to aspiration of the tracer into the lung.

Image findings

1.      Esophageal reflux is confirmed by presence of activity in the esophagus or in the lungs.

GASTRIC EMPTYING

Background

Abnormal gastric emptying rates can be caused by disease or surgical procedures. Patients experience nausea, vomiting, weight loss or abdominal fullness or distention.

Radiopharmaceuticals used:

1.      Tc99m sulfur colloid, 1 mCi
2.      Indium–111 DTPA

Clinical procedure:

1.      8 hours fasting before the procedure
2.      Meal consists of solid and liquid with radiopharmaceutical should be consumed within 5 minutes.
3.      Imaging is acquired at 15 minutes intervals for 2 hours.





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