Barium sulfate suspensions are the preferred material for most examinations.
Water-soluble contrast agents, which contain organically bound iodine, are primarily to demonstrate perforation of a hollow viscus.
UPPER GASTROINTESTINAL TRACT
pharynx, esophagus, stomach, and duodenum.
Filming of the pharynx is usually done with the patient in the frontal and lateral positions.
In the frontal view, the paired valleculae and piriform sinuses are separated.
The lateral view of the pharynx ---base of the tongue, hyoid bone, and epiglottis anteriorly, and the posterior pharyngeal wall and cervical spine posteriorly.
The esophagus, stomach, and duodenum are usually examined together as part of the upper gastrointestinal series.
Observation of esophageal motility
single-contrast upper gastrointestinal series
double-contrast upper gastrointestinal series -- involves the use of a high-density barium suspension plus gas-producing crystals
Prone frontal radiograph of stomach and duodenum from a single-contrast upper gastrointestinal examination. The duodenal bulb (D) is attached to the gastric antrum by the pyloric channel.
Supine frontal film of the stomach and duodenum from a double-contrast upper gastrointestinal examination in which a high-density barium suspension and gas crystals (CO 2 ) are used.
Barium studies of the upper gastrointestinal tract evaluate gastric function poorly.
Radionuclide gastric emptying studies are more effective for this purpose.
The duodenum assumes a C-shape configuration within the upper abdomen.
consists of the jejunum and ileum.
The following three methods can be used to examine the small intestine:
(1) peroral small bowel series,
(2) enteroclysis, and
(3) various retrograde techniques.
(1) peroral small bowel series,
most commonly used and is often done immediately following an upper gastrointestinal series.
The patient ingests 16 to 24 ounces of barium suspension and serial films of the abdomen are obtained in a timely order.
In addition, smaller films with pressure on the abdomen (i.e., compression) are used to separate and visualize all of the loops of the small bowel; the entire small bowel, including the terminal ileum, is filmed in this fashion.
Large film of the abdomen from a peroral small-bowel examination with the entire small intestine opacified with barium suspension.
Compression film of the small bowel from a peroral examination with separation and clear visualization of the small bowel loops.
Enteroclysis is an intubated examination of the small intestine.
The small intestine is intubated by a nasal or oral route with a small-bore enteric tube, which is directed with fluoroscopic guidance into the distal duodenum or proximal jejunum.
Single contrast technique.
Double contrast technique.
Compared to the peroral small-bowel examination, the enteroclysis techniques permits more exact visualization of small-bowel loops.
Large film of the abdomen from an enteroclysis examination of the small intestine. The small bowel is intubated with the tip of the tube ( arrow ) in the jejunum. Compared to the peroral examination, the small-bowel loops are distended more fully, causing the mucosal folds to assume a transverse orientation.
Compression film of the small-bowel loops in the pelvis with the patient in a prone position. Although the loops are overlapped, the "see-through" effect using a dilute barium suspension permits their clear visualization.
As with the upper gastrointestinal examinations, the colon can be evaluated by the following techniques:
(1) single-contrast barium enema or
(2) double-contrast barium enema.
Both examinations require insertion of a rectal tip for installation of the examining materials.
The large intestine consists of the rectum, sigmoid colon, descending colon, splenic flexure, transverse colon, hepatic flexure, ascending colon, and cecum.
The mucosal surface has a smooth appearance and the colonic contour is indented by the haustra, which are less numerous in the descending portion of the colon.
Double-contrast view of the right side of the colon showing the cecum (C), ileocecal junction (J), refluxed terminal ileum (I), and the appendix ( arrow ). The multiple haustrations of the colon are seen well and are produced by the teniae coli
Upper gastrointestinal endoscopy visualizes the mucosal surfaces of the esophagus, stomach, and duodenum.
Endoscopy does not assess functional abnormalities of these organs.
The major advantage of endoscopy compared to barium examination of the upper gastrointestinal tract is a better demonstration of milder inflammatory processes, such as small peptic ulcers and erosions.
Endoscopy of the mesenteric portions of the small intestine is called Enteroscopy .
diffuse small-bowel disease, especially if biopsy is needed
those with unexplained gastrointestinal bleeding.
Colonoscopy is both a diagnostic and therapeutic modality.
Inflammatory and neoplastic diseases of the colon.
Biopsies can be obtained when needed.
colonic polyps can be removed through the colonoscope.
A major role of CT scanning, especially in the esophagus and colon, is staging malignancy of these organs.
Recurrent masses appearing after surgery may also be biopsied percutaneously.
An ultrasound can be used to assess for inflammatory disorders, such as acute appendicitis.
MAGNETIC RESONANCE IMAGING
MR imaging of the GIT is being used
to evaluate and stage malignancies, especially of the esophagus and rectum
to assess inflammatory and obstructive bowel disease.
Upper gastrointestinal tract and small bowel
require minimal preparation when compared to the colon.
For an upper gastrointestinal or small-bowel examination, the patient should have nothing orally after midnight or the next morning preceding the radiographic study.
Fluid and food in the stomach and small intestine degrade the examination by interfering with good mucosal visualization and causing artifacts that may mimic disease.
oral fluids, and several cathartics the day preceding the barium enema examination.
The standard preparation includes
(1) a 24-hour clear liquid diet,
(2) oral hydration,
(3) a saline cathartic (e.g., magnesium citrate) in the afternoon,
(4) an irritant cathartic (e.g., castor oil) in the early evening, and
(5) a tap-water cleansing enema the morning of the radiographic examination 30 to 60 minutes before the barium enema is performed.
Magnesium containing cathartics is avoided in patients with renal failure.
Specific Contrast Examinations
Selection of an appropriate technique will depend on the clinical indications for the examination, the efficacy of the various techniques, and the age and physical condition of the patient being examined.
UPPER GASTROINTESTINAL TRACT
dysphagia, odynophagia, suspicion of esophageal varices, dyspepsia, upper gastrointestinal bleeding, and evaluation of obstruction.
The diseases that are detected most effectively include malignancies, peptic stricture, esophageal mucosal ring, moderate to severe reflux.
gastrointestinal bleeding that is not localized to the other organs of the gastrointestinal tract
diarrhea or more specifically steatorrhea
inflammatory bowel disease
small-bowel bleeding causes: Meckel's diverticulum, Crohn's disease, ischemic enteritis, and primary and secondary neoplasms.
Small-bowel obstruction is usually due to adhesions, external hernias, or intrinsic or extrinsic neoplasms.
The enteroclysis examination is often preferred for evaluating small-bowel obstruction or potential focal lesions of the small intestine, such as Meckel's diverticulum.
suspicion of inflammatory bowel disease,
question of neoplastic disease, and
evaluation of colonic obstruction.
Common causes of Colonic bleeding are diverticulosis, idiopathic colitis, larger colonic polyps and carcinoma, and ischemic colitis.
Common causes of colonic obstruction include diverticulitis, colonic malignancy, volvulus of the large bowel, and extrinsic disorders, especially pelvic malignancy invading the rectosigmoid region of the colon.
The diseases that are detected most effectively include diverticular disease and its complications, more severe forms of idiopathic and ischemic colitis, larger colonic polyps (i.e., greater than 1 cm in size), and colonic carcinoma.
LIVER, BILIARY TRACT, AND PANCREAS
The diagnosis of diseases of the liver, biliary tract, and pancreas optimally depends on using both clinical and radiographic data.
Contrast studies such as endoscopic retrograde cholangiopancreatography (ERCP) and percutaneous transhepatic cholangiography (PTC) are often helpful in analyzing diseases of the liver, biliary tree, and pancreas.
Digital cross-sectional imaging, nuclear medicine (NM) and an important form of NM called positron emission tomography (PET), and angiography .
Cross-sectional techniques consist of ultrasound (US), computed tomography (CT), and magnetic resonance (MR) imaging.
TECHNIQUES AND NORMAL ANATOMY
With USG, normal organs are displayed as structures of different echogenicity.
Vascular flow can be visualized by US with Doppler imaging, which consists of three types:
color, spectral, or power Doppler imaging.
In color Doppler imaging, Color shade and color intensity reflect blood flow direction and velocity, respectively.
Spectral Doppler imaging is portrayed as a sine-wave form in which peaks represent increasing velocity and valleys represent decreasing velocity of flow.
This is often combined with color Doppler imaging and together is called duplex imaging .
Nuclear medicine techniques utilize the administration of radioactively labeled substances chemically bonded to physiologic agents.
A more recent application of NM is PET, in which positrons emitted, often from radioactive sugar-containing compounds, are detected and imaged.
The term for different shades within a nuclear medicine image is activity .
The term for different shades within a CT image is attenuation or density .
CT showing normal liver (L), pancreas ( arrowheads ), and biliary tree, in both the liver and pancreas ( arrows ).
The term for different shades within an angiographic image is density .
Magnetic Resonance Imaging
MR imaging has superb contrast resolution.
Generalized parenchymal lesion detection and characterization, together with MR angiography, or MRA, have been improved greatly with the use of MR imaging-specific intravenous contrast agents, especially gadolinium, Gd.
The term for different shades within an MR image is signal intensity .
Flow is identified by signal intensity changes in the blood vessels.
Dynamic gadolinium-enhanced T 1 -weighted gradient echo image of the upper abdomen, taken at the level of the midliver, demonstrating homogeneous liver, with interspersed intrahepatic vessels, and spleen.
Dynamic gadolinium-enhanced T 1 -weighted gradient echo image of the upper abdomen, taken at the level of the pancreas and kidneys, demonstrating the homogeneous pancreatic body and tail with pancreatic duct ( arrow ), and the corticomedullary differentiation in the kidneys.
Diseases of the liver, biliary system, and pancreas can be conveniently divided into the following categories to help illustrate the optimal sequences of imaging techniques: diffuse hepatocellular disease, focal hepatic diseases, abdominal trauma, inflammatory disease of the biliary tract, and pancreatic inflammation or neoplasm.
Diffuse Hepatocellular Disease
CT is the first study used to survey the liver because it is moderately sensitive to liver lesions and is also helpful for evaluating surrounding organs.
MR imaging may be the most sensitive modality for detecting and characterizing diffuse diseases of the liver, including cirrhosis and hemochromatosis, especially when combined with contrast agents.
Focal Hepatic Diseases
USG is often used first, because it is inexpensive, widely available, and moderately sensitive to localized lesions in the absence of preexisting diffuse diseases, such as cirrhosis.
CT is a pivotal examination, often employed after US. It is used as a survey of the entire body, is easy to compare in serial studies, and is sensitive to disease.
Contrast-enhanced MDCT scanners can be used to perform CT angiography, or CTA, which is a noninvasive means of producing images depicting vessels much like conventional angiography.
NM techniques can be used to analyze a focal lesion within the liver for possible cavernous hemangioma.
MR imaging is used frequently to characterize focal lesions within the liver, especially those discovered during survey techniques like US or CT.
NM and MR imaging are considered the optimal means for evaluating the liver for cavernous hemangioma, and both are highly accurate (approximately 95%) in evaluating the liver for cavernous hemangioma.
CT is the only commonly accepted means for analyzing abdominal trauma, particularly of the liver.
CT is reasonably accurate in the detection of trauma-related abnormalities of the liver, biliary system, and pancreas.
US may be useful if CT is not available or to quickly identify intraperitoneal hemorrhage in patients who are in the emergency department and are going directly to the operating room.
Angiography may be useful to embolize persistently bleeding arteries in the liver or spleen when surgery is not possible.
Pancreatic Inflammation or Neoplasm
Ultrasound is often the initial means to study pancreatic inflammation or neoplasm.
If a lesion has already been detected by US and additional confirmation is required, CT is the method of choice.
Recent advances in MR imaging, especially MRCP, aids in pancreatic and biliary duct evaluation.
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