Special Procedures

chapter 18 Special Procedures



CHAPTER OUTLINE


Indications

Contrast Media

Patient Preparation

Contrast Studies of the Gastrointestinal Tract

Contrast Studies of the Urinary System

Additional Techniques: A Brief Overview


GLOSSARY


Angiocardiography: An intravenous radiographic contrast study evaluating the vascular system and chambers of the heart.


Angiography: An intravenous radiographic contrast study evaluating the vascular system.


Antegrade urethrogram: A method of urethrography in which the contrast medium is voided from the urinary bladder.


Arthrography: A radiographic contrast technique evaluating the articular cartilage, joint space, and joint capsule.


Barium sulfate: A common positive-contrast medium that is available in various forms and is often used as a suspension in gastrointestinal evaluations.


Cholecystography: An oral or intravenous radiographic contrast study evaluating the bile ducts and gallbladder.


Contrast medium: A substance that is either radiolucent or radiopaque and can be administered to increase radiographic contrast within an organ or system.


Cystography: Radiographic contrast studies evaluating the urinary bladder.


Double contrast: A radiographic contrast technique that uses a combination of positive- and negative-contrast media simultaneously.


Double-contrast cystogram: A radiographic study of the urinary bladder involving distending the bladder with a gas and then adding a small amount of positive iodinated contrast medium.


Esophagography: A radiographic contrast study performed to evaluate esophageal function and morphology.


Excretory urography: An intravenous radiographic contrast study of the kidneys and ureters.


Fistula: An abnormal tubelike passage within body tissue.


Fistulography: A positive or negative radiographic contrast study used to determine the depth and origin of a fistulous tract.


Gastrography: A radiographic contrast study performed to evaluate the size, shape, position, and morphology of the stomach.


Intravenous pyelogram (IVP): A radiographic contrast study of the kidney structure and collection system.


Intravenous urogram (IVU): A radiographic contrast study of the kidney structure and collection system.


Lower gastrointestinal (LGI) study: Commonly referred to as a barium enema; a radiographic contrast study evaluating the rectum, colon, and cecum.


Lymphography: A radiographic contrast study evaluating lymphatic vessels and lymph nodes.


Myelography: A radiographic contrast study evaluating the subarachnoid space surrounding the spinal cord.


Negative-contrast agents: Gases that are more radiolucent to x-rays than are soft tissues and have a black appearance on a radiograph.


Nephrogram: A phase of an excretory urogram characterized by the diffuse opacification of the renal parenchyma.


Parasympatholytic agents: Drugs that eliminate the influence of the parasympathetic nervous system.


Pneumocystogram: A negative-contrast radiographic technique evaluating the urinary bladder.


Pneumoperitoneography: A negative-contrast radiographic study consisting of the introduction of a gas into the peritoneal cavity.


Positive-contrast agents: Substances containing elements of high atomic number that are more radiopaque to x-rays than are tissue and bone and have a white appearance on a radiograph.


Positive-contrast cystogram: A radiographic study of the bladder involving distention of the bladder with positive iodinated contrast medium.


Pyelogram: A phase of an excretory urogram characterized by the opacification of the renal collection system.


Retrograde urethrogram: A method of urethrography by which the contrast medium is infused via a catheter placed at the distal end of the urethra.


Sialography: A radiographic contrast study evaluating the salivary glands and ducts.


Triiodinated compounds: A common component of iodinated positive-contrast media that contains three atoms of iodine per molecule.


Upper gastrointestinal (UGI) study: A radiographic contrast study evaluating the stomach and small intestines.


Urethrography: A radiographic contrast study evaluating the urethra.


Vaginography: A radiographic contrast study evaluating the female reproductive organs.



INDICATIONS


Special radiographic procedures are used to supplement or confirm information garnered from routine survey radiographs. Under normal circumstances, soft tissue structures or organs are difficult or impossible to identify on plain films due to lack of contrast. A contrast medium is a substance that is either radiolucent or radiopaque and can be administered to an animal to increase radiographic contrast within an organ or system. With the use of a contrast medium, soft tissue structures can be visualized, and the structure under investigation can be evaluated for size, shape, and position. In addition, defects in the mucosal surface of an organ or its luminal contents can be identified. In some instances it is possible to evaluate organ function or to assess the physiologic condition. Although contrast studies can be extremely helpful for a complete diagnosis, at no time should a special procedure replace routine survey radiography.



CONTRAST MEDIA


The two basic categories of contrast media are positive and negative. Positive-contrast agents, such as barium or iodine compounds, contain high atomic number elements. These agents absorb more x-rays than do soft tissues or bones. Positive-contrast media are radiopaque to x-rays and appear white on a radiograph. These compounds can be used to fill or outline a hollow organ (e.g., urinary bladder, alimentary tract), or they can be injected into a blood vessel (sterile, water-based compounds only) for immediate visualization of the vascular supply or for subsequent excretion evaluation. Negative-contrast agents consist of gases (e.g., oxygen, carbon dioxide) that have a low specific gravity. Substances with a low specific gravity are more radiolucent to x-rays than are soft tissues and have a black appearance on a radiograph.


Many different compounds are used as radiographic contrast media. In addition, various manufacturers market identical contrast agents under different names and concentrations. Although it is virtually impossible to become familiar with all of the contrast agents available, it is possible to place them into one of three general categories: (1) positive-contrast iodinated preparations, (2) positive-contrast barium sulfate preparations, and (3) negative-contrast gases. Each category has basic characteristics used to classify contrast agents. These characteristics allow a better understanding of each individual medium.


The majority of agents currently available are intended for human use; however, some products are specifically approved by the U.S. Food and Drug Administration for animals. Contrast agent choice should be made on the basis of the type of study to be performed, the condition of the patient, the possible side effects, and the judgment of the veterinarian that it is the best available product for use.



Iodine Preparations


Iodine compounds are divided into two subcategories: water-soluble agents and viscous/oily agents.



Water-soluble agents.


Water-soluble iodine preparations make up the largest group of contrast agents. Most water-soluble iodine preparations are opaque to x-rays, pharmacologically inert, low in viscosity for rapid intravenous injection, low in toxicity, rapidly excreted by the kidneys, and chemically stable so that no iodine is released in the body.


The choice of radiographic contrast agent is a matter of personal preference. The triiodinated compounds are widely accepted because they are well tolerated by the body and provide excellent contrast. Triiodinated compounds contain three atoms of iodine per molecule. They are supplied as sodium or meglumine salts of iothalamic diatrizoic or metrizoic acids or as a mixture of these two salts.


In general sodium salts are less viscous. The meglumine salts reduce toxicity, minimize high sodium concentrations, and lessen tissue irritability. These contrast agents are usually injected into a vascular system for immediate visualization of the system or for subsequent demonstration of the excretory system. In addition, water-soluble agents can be infused into the bladder via a urinary catheter to show the urinary mucosa and bladder shape and size.


Possible toxicity is a concern with any pharmaceutical. The ionic (salt) preparations all have a local irritant effect and should be administered intravascularly or infused into an organ. Because of this property, iodine agents are contraindicated for myelography and arthrography. An intravenous injection of an iodinated contrast agent can cause side effects such as mild discomfort and nausea in an animal patient. Although they are extremely rare, more severe reactions such as cardiac arrest, hypovolemia, and anaphylaxis have been cited in a few clinical cases. In general, sodium salts are more toxic than meglumine salts but are included in the compound to reduce viscosity for easier administration.


Low-osmolar contrast media such as metrizamide, iopamidol, and iohexol are nonionic and reduce adverse side effects resulting from hyperosmolarity. Although expensive, these contrast agents are suitable for both intravascular and myelographic studies.


Water-soluble contrast agents are sometimes indicated for gastrointestinal use in patients with a suspected perforation. If this type of contrast agent were to enter the alimentary tract through a perforation, it would be rapidly absorbed because of its solubility. These agents are not used routinely, however, because of their fast transit time and hypertonicity. The iodine agents lose their contrast because they rapidly absorb fluid in the alimentary tract and become progressively dilute. With these agents, mucosal detail is poor. In some cases, the contrast agent is absorbed into the vascular system and excreted through the urinary system, which causes a confusing radiologic pattern.



Oily/viscous agents.


Oily/viscous agents have little application in veterinary radiography. Their use is limited to lymphography.


Oily contrast media consist of iodized oils. The oil contains a suspension of propyliodone in either water or arachidic oils. Because of their viscous nature and insolubility in water, they are not resorbed in the body and produce fat embolism. The iodized oils cannot be administered intravascularly. In addition, the agent does not mix with cerebrospinal fluid during myelography. The oils tend to coagulate within the spinal canal and fail to outline lesions clearly. Current practice does not include oily media for myelography. If the agent is not removed, the absorption rate within the spinal canal is extremely slow. The absorption rate is estimated at approximately 1 mL/year.



Barium Preparations


Barium sulfate is a positive-contrast suspension and is the medium of choice for radiographic studies of the gastrointestinal tract. Because it is completely insoluble, it is not diluted by alimentary secretions and is not absorbed through the intestines. Barium is available in various forms (e.g., liquid, paste, and powder for reconstitution with water).


The primary disadvantage of barium sulfate is that if it should pass through a perforation in the alimentary tract into the thorax or abdomen, it would not be absorbed or eliminated. The barium can remain in the body indefinitely and could potentially produce a granulomatous reaction. In cases in which a perforation is suspected, it is advisable to use a water-soluble contrast medium. However, if the water-soluble study is negative, a barium study should follow to avoid missing a perforation.


Morbidity and mortality are no worse than those with a leakage of gastrointestinal contents, if the barium is surgically flushed out of the abdominal cavity within 6 to 8 hours. Barium that is inadvertently aspirated into the trachea is usually cleared by coughing. If the medium reaches the small bronchi and alveoli, it is unlikely to be removed.



Negative-Contrast Agents: Gases


Gases used for negative-contrast radiographic studies include air, oxygen, nitrogen, nitrous oxide, and carbon dioxide. Of all the gases available, air, oxygen, and carbon dioxide are most frequently used. Carbon dioxide has an advantage over room air because it is better absorbed into the body when administered into a hollow organ; room air can cause air emboli.


Gases are inexpensive, relatively safe, and easy to administer. Negative-contrast media enhance the contrast between the various soft tissues but produce less mucosal detail than positive-contrast media. Some special procedures call for the use of both negative- and positive-contrast media, or double contrast. A double-contrast study gives optimum mucosal detail and avoids masking small anomalies by large volumes of positive-contrast media.



PATIENT PREPARATION


Proper patient preparation is vital to a diagnostic radiographic study. Before the study, the patient’s gastrointestinal tract should be emptied by withholding food for 12 to 24 hours and, if necessary, administering a cleansing enema. The presence of any gastrointestinal contents can detract from a quality study and may obstruct the view of certain areas of interest as a result of superimposition. Keep in mind that cathartics and enemas often produce gastrointestinal gas. To reduce the amount of gas present in the gastrointestinal tract during a study, the cathartic should be administered 4 to 12 hours before the radiographic procedure, and a radiographic study should not be administered within 1 hour of enema administration.


Evacuation of the gastrointestinal tract should be as atraumatic as possible, especially when working with an acutely ill patient. When an enema is contraindicated because of the poor condition of the patient, it is usually sufficient to fast the animal. However, if fasting would compromise the patient’s health further, mild, nongranular nourishment such as baby food or other commercially available foods (e.g., Hill’s a/d, Clinicare) can be given.


Many special radiographic procedures require sedation or anesthesia. Use caution so that the procedure is not compromised by the anesthetic. For example, general anesthesia is contraindicated for a gastrointestinal study due to subsequent slowed motility. If sedation is necessary, it should be limited to the use of a phenothiazine tranquilizer such as acepromazine maleate. Phenothiazine tranquilizers have only minimal effects on gastrointestinal motility or transit time. The use of parasympatholytic agents such as atropine should also be avoided for certain studies because of their anticholinergic effect.



CONTRAST STUDIES OF THE GASTROINTESTINAL TRACT


A patient presenting with diarrhea or vomiting is not uncommon in veterinary medicine. If medical management has failed, and survey radiographs are inconclusive, a contrast study may be indicated.


Radiographic studies of the gastrointestinal tract consist of the introduction of contrast media either by oral administration or via an orogastric tube. Radiographs are then taken at intervals to evaluate changes in morphology, the rate of gastric emptying, and small bowel transit time. The studies described here do not include the use of fluoroscopy because the majority of veterinary practices do not have this type of equipment.



Esophagography


Esophagography is performed to evaluate esophageal function and morphology. An esophagogram is indicated for patients with a history of regurgitation of undigested food, acute gagging, or dysphagia. This study consists of administering a positive-contrast medium orally and exposing a number of radiographs during and after the patient swallows the contrast agent. Liquid barium sulfate is usually the contrast medium of choice. Barium sulfate is also available in a thick paste form, which is more difficult to swallow but provides good mucosal coating of the esophagus. Barium can be mixed with canned or hard food, or both, to evaluate the function of the esophagus or for a partial obstruction that may be missed during a plain liquid barium swallow.



Precautions.


When introducing an oral contrast medium, proper care must be taken to minimize the possibility of the patient aspirating the agent into the lungs. If a perforation or rupture is suspected, an iodinated contrast medium should be used rather than a barium compound. Beware of iodinated contrast agents if aspiration is likely. The hypertonicity of these agents, if the ionic variety is used, can cause massive fluid shifts into the lung. The iodinated contrast medium is readily absorbed by the body if it enters the thoracic cavity, whereas barium is not absorbed and can remain in the body indefinitely. A foreign substance such as barium can stimulate granuloma formation within the thoracic cavity.



Upper Gastrointestinal Study


An upper gastrointestinal (UGI) study is performed to evaluate the stomach and small intestines. A UGI series may be indicated for patients that have recurrent unresponsive vomiting, abnormal bowel movements, suspected foreign body or obstruction, chronic weight loss, or persistent abdominal pain.


The contrast medium is administered orally (per os or via stomach tube), and radiographs are taken during the passage of the agent. The UGI series is performed in a systematic manner so that the maximum amount of information can be obtained. Both positive- and negative-contrast media can be used if the stomach is the target. However, most studies are performed with a positive-contrast medium such as barium sulfate.



Precautions.


If the patient is suspected of having a gastrointestinal perforation, barium sulfate is contraindicated. If barium were to enter the abdominal cavity, it would not be absorbed and could induce granuloma formation. In the instance of a perforation, an oral iodinated contrast medium should be used. Unfortunately, iodinated contrast media do not produce as much radiographic contrast. Iodine compounds tend to become diluted as they pass through the bowel because they draw extracellular fluid from the digestive tract. In addition, because of their osmotic activity, they are not recommended for dehydrated patients.




TECHNIQUE OUTLINE


Contrast Media:


70% to 100% barium sulfate (liquid and paste) or iodinated oral contrast agent


Equipment/Supplies:


Optional canned/hard pet food


Patient Preparation:


None necessary


Procedure—Esophagography


I. Expose survey radiographs.

II. Place patient in lateral recumbency on x-ray table.

III. Slowly infuse liquid contrast medium into patient’s cheek.

IV. Expose several radiographs of the thorax to monitor the passage of contrast medium. The field of view should include the entire esophagus from the pharyngeal region to the stomach. (NOTE: The first radiograph should be exposed within seconds of swallowing.)

V. Repeat steps III and IV with the patient in dorsal recumbency.

VI. Place the patient in lateral recumbency once again.

VII. Slowly administer barium paste, and expose the radiograph during the swallow (Fig. 18-1).

VIII. If abnormalities still are not detected, mix the liquid contrast medium with canned or hard pet food, or both, and administer per os.

IX. Radiographs are repeated; right and left lateral views may be indicated. Ventrodorsal views are contraindicated for patients with a dilated esophagus full of contrast medium. Placing the patient on its back may result in aspiration.

image

Figure 18-1 Radiograph of a lateral view of an esophagram immediately after administration of liquid barium.




TECHNIQUE OUTLINE


Contrast Media:


30% to 60% liquid barium sulfate or iodinated oral contrast agent


Equipment/Supplies:


60-mL catheter-tip syringes


Orogastric tube


Patient Preparation:


Fast for 12 to 24 hours


Enema if necessary 2 to 4 hours before study


Sedate if necessary


Procedure—UGI Study


I. Expose survey radiographs.

II. Administer barium to distend the stomach with contrast medium.
A. Route: Per os by placing the positive-contrast medium into the oral cavity and allowing the patient to swallow or via orogastric tube. To ensure correct placement of the orogastric tube, infuse a small amount of water. If the tube is incorrectly placed and is located in the trachea, the patient should cough, signaling incorrect placement.

B. Dose: 4 to 8 mL/kg body weight.

III. Expose dorsoventral, ventrodorsal, right lateral, and left lateral radiographs immediately after contrast administration (Figs. 18-2 and 18-3).

IV. Expose right lateral, ventrodorsal, or dorsoventral radiographs at intervals until contrast agent reaches the large bowel (suggested times: 15, 30, 60, and 90 minutes) (Figs. 18-4 and 18-5).

image

Figure 18-2 Lateral view of an upper gastrointestinal study exposed 5 minutes after the administration of barium.


image

Figure 18-3

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May 27, 2016 | Posted by in ANIMAL RADIOLOGY | Comments Off on Special Procedures

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