Digestive System消化系统

Digestive System,Main Contents,Part 1. Liver ImagingPart 2. Liver Blood Pool ScintigraphyPart 3. Hepatobiliary ScintigraphyPart 4. Gastrointestinal ScintigraphyPart 5. Heterotopic Gastric MucosaPart 6. Gastrointestinal Motility,Part 1.Liver Imaging,1.1 Radiopharmaceuticals,99mTc-sulfur colloidThe distribution of the reticuloendothelial system is visualized following intravenous administration of radiolabeled colloids. Particles of SC range in size from 100 nm to approximately 1 m. In the average patient, 80%-90% of injected SC is phagocytized by the RE cells of the liver (Kupffer cells), 5%-10% by the spleen, and the remainder by the bone marrow.,A quantity of 110 - 185 MBq (3-5 mCi) of 99mTc-sulfur colloid (SC) is injected intravenously for imaging of the liver; when imaging of the marrow is intended, the amount used is typically raised to 370 MBq (10 mCi) to compensate for its low marrow uptake.As a rule, smaller particles are preferentially taken up by marrow while larger particles are phagocytized by the spleen.,1.2 Technique,Imaging of the liver commences approximately 10-15 min following SC injection. Planar views of the liver are taken in multiple obliquities (anterior, posterior, right lateral, right anterior oblique, right posterior oblique). An image which includes a lead marker of standardized size placed on the costal margin is usually obtained. The left anterior oblique view is helpful in separating the left lobe of the liver from the spleen, left posterior oblique and left lateral views are often added for imaging of the spleen.,On a large field of view camera, the anterior image is usually acquired for approximately 500,000 to 1 million counts, other views are acquired for the same amount of time to facilitate comparison. SPECT imaging is especially helpful in resolving three-dimensional distributions of activity and in enabling comparison with findings on anatomic modalities, such as CT and MRI.,Normal finding,1.3 Clinical Applications,Colloid studies of the liver are currently performed to assess diffuse hepatic disease and less frequency to evaluate focal processes within the liver. Colloid splenic imaging is primarily performed to identify functional splenic tissue. These applications are discussed below.,1.3.1 Diffuse parenchymal disease of the liver,For evaluation of diffuse parenchymal liver disease, criteria of interpretation include hepatic size, splenic size, and the relative distribution of colloid between various sites within the RES.,1.3.2 Focal lesions within the liver,Colloid scintigraphy played a unique role in identifying space-occupying lesions of the liver; Most true space-occupying processes within the liver, such as metastases and abscesses(脓肿), are devoid of Kupffer cells, with resultant defects noted on SC imaging.Primary masses originating within the liver, including HCC, focal nodular hyperplasia (FNH) and hepatic adenoma, are all devoid of uptake on SC studies.,Radioactive defect in space-occupying lesions of the liver.,Part 2.Liver Blood Pool Scintigraphy,2.1 Radiopharmaceuticals,For identification of hemangioma, 750 MBq (20 mCi) of 99mTc-RBCs is used, optimally labeled by the in-vitro method. Methods of RBC labeling are common to other scintigraphic applications, such as GI bleeding studies, et al.,2.2 Technique,Generally, imaging consists of three phases: arterial perfusion (flow), immediate blood pool, and delayed blood pool. (1) Arterial perfusion imaging, typically obtained at 1 frame per second during injection of the labeled RBCs, reveals useful information about regional supply of hepatic arterial blood flow and should be performed in the view potentially suited to portray the lesion while avoiding overlap with normal vascular structures.,Normal arterial perfusion imaging,(2) Immediate blood pool images are then acquired for 1 to 2 million counts each, in this optimal projection as well as in standard anterior, posterior and right lateral views. (3) Delayed blood pool images, designed to portray the maximal wash-in of RBCs into the hemangioma, are acquired approximately 2-3 h following injection in similar projections to the immediate blood pool images. SPECT will often be necessary to visualize small lesions, especially when deep within the liver parenchyma or not detected on planar views, and is useful for comparison to other cross-sectional imaging modalities.,Liver-pool imaging,Liver-colloid imaging,2.3 Clinical Applications,Classic findings in hemangioma are absent visualization during arterial perfusion imaging, while on blood pool imaging the lesion becomes more intense than surrounding normal liver, a phenomenon termed the perfusion-blood pool mismatch. Activity greater than adjacent liver is observed on the 2-3 h delayed image but may even be noted on the immediate blood pool images.Overall imaging accuracy for detecting hemangiomas is reported to be 90%, especially if SPECT is used for smaller lesions.,Liver hemangioma planar imaging,Part 3.Hepatobiliary Scintigraphy,3.1 Radiopharmaceutical,Analogues of technetium-99m labeled iminodiacetic acid (99mTc-IDA) first became available for clinical use in the 1970s and remain the most widely used radiopharmaceuticals for hepatobiliary imaging.,After intravenous injection, these organic anions are taken up by hepatocytes in a manner similar to bilirubin. They are secreted into bile without conjugation.99mTc-IDA uniformly mixes with bile, thereby becoming a marker of bile flow to the gallbladder and bowel. No significant intestinal reabsorption or enterohepatic cycling occurs. Ideal agent exhibit high extraction efficiency by liver, rapid transit, and high concentration in bile.,3.2 Principles and Methods,3.2.1 Principles 99mTc-IDA are actively taken up and transported intracellularly by hepatocytes organic anion-transporting polypeptide (similar to nonconjugated bilirubin). They are later excreted into canaliculi unchanged via the apical ATP-dependent export pump.,3.2 Principles and Methods,3.2.2 Methods A typical adult dose is 200 MBq (5 mCi) of the compounds injected as an intravenous bolus. The patient should be fasting for a minimum of 2 hours, preferably 4 hours or overnight, otherwise the gall bladder may not fill.The framing rate for the scintiangiography phase is one frame per second for a total of 60 s, while the subsequent images are acquired at one frame per 15 s for 1 h.,Blood flow phaseLiver phaseBile excretion phaseIntestine excretion phase,Normal hepatobiliary dynamic scintigraphy,3.3 Clinical Applications,(1) Acute cholecystitis(2) Biliary atresia(3) Biliary obstruction(4) Post traumatic or post surgical bile leak,3.3.1 Acute cholecystitis,It is usually readily available in the emergency room setting, can assess multiple abdominal organs and yields results quickly. In the presence of acute inflammation it can show thickening of the gallbladder wall, pericholecystic fluid, and elicit localized tenderness. Gallbladder wall thickening and fluid are infrequent findings and are also nonspecific, being found with ascites and other edematous states.,HBS can demonstrate an obstructed cystic duct, a typical finding in acute cholecystitis (ACC), by the lack of activity in the GB. The initial useful criterion for a positive test was non-visualization of radioactivity in the GB within 4 h of imaging. It was soon recognized that most false positive results were secondary to chronic cholecystitis.,Acute cholecystitis,3.3.2 Biliary atresia,It is especially important in differentiating biliary atresia from the neonatal hepatitis syndrome.For an optimal diagnostic result, these patients must be pretreated with a minimum of 3 (preferably 5-7) days of phenobarbital, given orally in two divided doses, over a minimum of 3-5 days, in an attempt to induce hepatic enzymes and maximize excretion of radiopharmaceutical. The dosage is typically 5 mg/ (kgd) in divided doses. Oral feeding is withheld for several hours before and up to 4 h after the tracer injection to prevent dilution of biliary activity in the bowel.,For infants and children, 2-7 MBq/kg (0.05-0.2 mCi/kg) of radiopharmaceutical is typically administered with a minimum of 15 - 20 MBq (0.4-0.5 mCi). Imaging begins immediately postinjection and extends intermittently through several hours. If no bowel activity is observed, patients return for delayed imaging through 24 h. Any activity noted within the bowel or GB indicates patency of the CBD and excludes the diagnosis of biliary atresia. When no bowel excretion is visualized, findings are ambiguous, as lack of excretion may be due to either severe neonatal hepatitis or biliary atresia. In this instance, liver biopsy will be necessary to establish the diagnosis.,Congenitalbiliaryatresia,Neonatal hepatitis,3.3.3 Biliary obstruction,Bile duct dilatation is the hallmark of obstruction on anatomic imaging studies.Scintigraphy shows abnormal retention of radiotracer in the biliary tree, or if intra biliary pressure exceeds secretion pressure of the liven will show hepatic uptake with prolonged retention.Caution should be taken in diagnosing partial obstruction on the basis of scintigraphically apparent biliary duct dilation, as an increasing concentration of radiotracer even in a normal size duct creates a “blooming” artifact.,CBD obstruction,Incomplete biliary obstruction,3.3.4 Post traumatic or post surgical bile leak,Delayed Scintigraphy is essential in this instance.Extraluminal surgical drains should not be damped if the objective is to detect a bile leak but biliary drains should be clamped. Multiple views or SPECT can allow better localization and correlation with anatomic imaging. Scintigraphy is particularly helpful following laparoscopic cholecystectomy because of the acute nature of the complications. Obstruction from retained calculi or a misplace clip, or bile leaks from injury to the CBD or loss of cystic duct closure, are readily detected.,Diagnosis of post surgical bile leak.,Part 4.Gastrointestinal Scintigraphy,Bleeding from the gastrointestinal tract can be life threatening and prompt localization of the bleeding site allows for appropriate and effective therapy.Contrast angiography is the gold standard for gastrointestinal bleeding localization. However, it is invasive and there must be active hemorrhage at the time of contrast injection to localize a bleeding site.The radionuclide gastrointestinal bleeding study is more sensitive than contrast angiography. Scintigraphy can detect bleeding at approximately 0.1 ml/min, compared to 1 cc/min with contrast angiography.,The radionuclide test has two purposes. First, it gives assurance that the patient is indeed actively bleeding. Second, it can localize the approximate site of hemor rhage, giving the angiographer information on the likely vascular origin of the bleed, e. g. celiac, superior or inferior mese nteric artery. This saves time and contrast media during angiography and increases the likelihood of a diagnostic study.,4.1 Principles and Methods,4.1.1 Principles(1) Tc-99m sulfur colloid was the first radiopharmaceutical used for gastrointestinal bleeding studies. After intravenous injection, Tc-99m SC extravasates into the bowel lumen at the site of active hemorrhage. The disadvantage of this method is that the patient must be actively bleeding at the time of injection.,4.1 Principles and Methods,4.1.1 Principles(2) Tc-99m labeled red blood cells (Tc-99m RBCs) have become the standard radiopharmaceutical for gastrointestinal bleeding studies because the of intermittent bleeding is addressed. Although the target-to-background is less than with Tc-99m SC, the use of Tc-99m RBCs allows for a considerably longer imaging time, potentially up to 24 h.,4.1 Principles and Methods,4.1.2 MethodsMost centers use a labeled red blood cell technique for visualizing GI bleeds. It is critical that minimal free 99mTc-pertechnetate be present in the preparation since pertechnetate, which accumulates in the gastric wall and is secreted into the lumen, can cause a false positive examination. To minimize the amount of free pertechnetate, the in vitro labeling technique is preferred.,4.1 Principles and Methods,4.1.2 MethodsDynamic imaging is performed for at least one hour or until a site of active GI bleeding is clearly identified. Many centers employ further delayed imaging if no active GI bleeding is encountered.,4.2 Clinical Applications,Gastrointestinal Bleeding Specific criteria are mandatory for accurate diagnosis of the bleeding site. These include: (1) activity is seen in the abdomen where none was initially; (2) activity increases over time; and (3) the activity moves in a pattern that conforms anatomically to small or large intestines.,Gastrointestinal Bleeding,Part 5.Heterotopic Gastric Mucosa,Although the term ectopic gastric mucosa is commonly used, this refers to an organ that has migrated, e. g. ectopic kidney, while heterotopic refers to a tissue out of its site of origin, e. g. gastrointestinal duplications, Barretts esophagus, post-operative retained gastric antrum, and Meckels diverticulum. Meckels diverticulum is the most common clinical presentation of heterotopic (ectopic) gastric mucosa.,Tc-99m pertechnetate (99mTcO4-) is taken up by the mucosa of the gastric fundus, although gastric parietal cells were initially suspected to be responsible for uptake. However, Tc-99m uptake occurs in gastric tissue with no parietal cells, and autoradiographic studies have localized the Tc-99m uptake to the mucin than the parietal cell.,5.1 Radiopharmaceutical,Barium contrast studies should not be performed for several days prior to the study. Patients are advised to have nothing by mouth for 4-6 h prior to the study to minimize stomach size. The imaging field of view should be from the xiphoid to symphysis pubis. Tc-99m pertechnetate, 30-100 Ci/kg, is injected intravenously. Flow images, 1-3 s/frame, are acquired for 1 min, followed by 1-min frames for 60 min.,5.2 Technique,Normal abdomen imaging by 99mTcO4-,5.3 Clinical Applications,5.3.1 Meckels diverticulumMeckels diverticulum is the commonest congenital anomaly of the GI tract and occurs in 1%-3% of the population. men : women=3 : 2. Diverticula are variable in position: on gamma camera pictures, they most commonly appear in the lower abdomen; anatomically, they are usually in the ileum within 1 m of the ileocecal valve.,Meckels diverticulum is found on the antimesenteric side of the small intestine, usually 80-90 cm from the ileocecal valve. The diverticulum is caused by failed closure of the embryonic omphalomesenteric duct, which connects the yolk sac to the primitive foregut through the umbilical cord. Heterotopic gastric mucosa is present in 10%-30% of patients with Meckels diverticulum, in 60% of symptomatic patients, and in 98% of those with gastrointestinal bleeding.,Most symptomatic patients are children, often under 2 years of age. However, it can present in older children and adults. The gastric mucosal secretions cause peptic ulceration of the diverticulum or adjacent ileum, resulting pain, bleeding, and/or perforation. The diagnosis is often missed on small bowel radiography because of a narrow ostium that fills poorly and empties rapidly. Surgery is definitive and resection therapeutic. The Tc-99m pertechnetate scan (Meckels scan) is the most reliable preoperative diagnostic method.,Meckels diverticulum appears as focal areas of uptake, usually in the right lower quadrant. Diverticular uptake usually occurs simultaneously with gastric uptake. Upright or oblique images can be helpful in differentiating a Meckels diverticulum from urinary activity, the most common cause for a false positive study. False negative studies may occur because of small size (2 cm2), rapid mucosal washout, or impaired blood supply, e. g. intussusception or volvulus.,Meckels diverticulum,5.3 Clinical Applications,5.3.2 Intestinal duplication30% to 50% of gastrointestinal duplications contain gastric mucosa. The duplications are cystic or tubular congenital abnormalities with mucosa, smooth muscle, and alimentary epithelium attached to any part of the gastrointestinal trace, often in the ileum. 20% occur in the mediastinum. Tc-99m pertechnetate scans have been used to diagnose a retained gastric antrum after Billroth II gastrojejunostomy or a Barretts esophagus. This purpose is rarely requested in current practice.,The child withintestinalduplication,Part 6.Gastrointestinal Motility,Gastrointestinal Motility,Esophageal motilityGastroesophageal refluxGastric emptyingIntestinal motility,6.1 Esophageal motility,6.1.1 TechniqueThe details of the imaging study vary from department to department. Technetium colloid has been most commonly used as a non-absorbable marker, although other alternatives are equally appropriate, such as 99mTc-DTPA. It is usually given in liquid form (with water) or semi-solid form.,6.1 Esophageal motility,6.1.2 Normal images It is conventional to divide the esophagus into upper, middle, and lower portions. Up to 10% of the bolus may remain normally in the lower esophagus. The remainder of the bolus of colloid should traverse the esophagus in under 15 s. Normal transit