Radiographic Contrast Studies Of The Gastrointestinal Tract

The rapid digestive tract transit time of birds and the anatomy of their digestive tract make it possible to study the majority of the digestive tract using a single radiographic protocol. The digestive tract from the esophagus to the large intestine can be radiographically evaluated by administering contrast medium orally. The term "UGI" (upper gastrointestinal) tract contrast study is a misnomer in birds because the colon, and occasionally the cloaca, is also evaluated on these studies. Evaluation of the cloaca is best performed with retrograde studies, wherein the contrast medium is administered directly into the cloaca.

Ideally, the ingluvies (crop) and proventriculus should be empty before beginning a digestive tract contrast medium study, although the effects of food deprivation must be considered. A fasting period before administration of the contrast medium is recommended, and the duration of the fasting period depends on the metabolic requirements of the bird and its overall health. Smaller birds do not tolerate food restriction as well as larger birds because of their higher metabolic rate. Recommendations for food restriction are provided in the discussion on patient preparation. The presence of food in the ingluvies (crop) decreases the volume of contrast medium that can be safely administered. Ingesta in the gastrointestinal tract also degrades the detail of the interface between contrast medium and the digestive tract mucosa by absorbing the contrast medium and impeding full contact of the contrast medium with the digestive tract mucosa. Ingesta may also delay passage

Macaws Appearance And Anatomy

Figure 1-6 Positioning technique for the mediolateral radiographic study of the avian thoracic extremity (wing) with the patient in dorsal recumbency. Positioning of the body for the mediolateral radiographic study of the wing is similar to that described for the ventrodorsal coelomic study, except the body is positioned to the side of the cassette so that the entire wing of interest will be included on the radiographic image. The wing is fully extended laterally from the pectoral girdle and taped directly to the radiographic cassette. Immobilization of the wing is best achieved by crossing the tape in the region of the carpus. Additional tape can be applied to the proximal and distal aspects of the wing if necessary. The x-ray beam ( + ) is centered in the mid-diaphyseal region of the radius and ulna. The x-ray beam field (dotted lines) encompasses the entire wing, including the scapulo-humeral joint. Metallic "R" and "L" markers are placed on the radiographic cassette indicating the laterality of the patient.

Figure 1-6 Positioning technique for the mediolateral radiographic study of the avian thoracic extremity (wing) with the patient in dorsal recumbency. Positioning of the body for the mediolateral radiographic study of the wing is similar to that described for the ventrodorsal coelomic study, except the body is positioned to the side of the cassette so that the entire wing of interest will be included on the radiographic image. The wing is fully extended laterally from the pectoral girdle and taped directly to the radiographic cassette. Immobilization of the wing is best achieved by crossing the tape in the region of the carpus. Additional tape can be applied to the proximal and distal aspects of the wing if necessary. The x-ray beam ( + ) is centered in the mid-diaphyseal region of the radius and ulna. The x-ray beam field (dotted lines) encompasses the entire wing, including the scapulo-humeral joint. Metallic "R" and "L" markers are placed on the radiographic cassette indicating the laterality of the patient.

of the contrast medium through the digestive tract. Hyperali-mentation preparations are particularly unpredictable in the way they mix with contrast media. Pelleted foods also affect the appearance of the intestinal mucosal contrast medium interface. Birds eating pelleted diets often have an indistinct intestinal contrast medium mucosal interface on radiographs. The cause of this is unknown. It is recommended that birds weighing more than 300 grams not be fed pelleted diets within 4 hours of digestive tract contrast studies if their health status allows such a fasting period. This general recommendation is based on clinical experience, and currently no scientific studies have been performed to validate this theory.

Survey ventrodorsal and right laterolateral radiographs are made immediately before digestive tract contrast studies are initiated. The caudal cervical area and the entire coelom are included on the images. These survey radiographs provide information regarding the distention and location of the digestive tract and are essential for confirming that the radio-

graphic exposure factors are optimized. Radiographs made on previous days are not sufficient to serve as survey radiographs because they may not reflect the current status of the digestive tract. As a general rule, positive contrast medium studies utilize slightly higher kVp settings (2-4 kVp) than those kVp settings used for survey radiographs. This compensates for the increased opacity of the contrast medium.

The contrast medium used for the digestive tract studies in this text was barium sulfate 30% weight to volume (w/v). The contrast medium can be warmed to a temperature slightly greater than room temperature by immersing the syringe containing the contrast medium in warm water. Just prior to contrast medium administration, the liquid in the syringe should be mixed and tested to check the temperature. Warming the contrast medium decreases abnormal peristalsis and hypothermia caused by chilled contrast medium. The dose of contrast medium/gram body weight varies among species of birds. A very broad recommendation would be

Figure 1-7 Positioning technique for the caudocranial radiographic study of the avian thoracic extremity (wing). The anesthetized bird is held in an inverted position with the head directed toward the floor and long axis of the bird's body perpendicular to the surface of the x-ray table. The wing to be imaged is fully extended, and the cranial (leading) edge of the wing is placed on the film cassette. The bird is angled so that the x-ray beam is aligned in a true caudocranial direction through the wing. The x-ray beam ( + ) is centered in the middle of the wing, which is usually the mid-diaphyseal region of the radius and ulna. The x-ray beam field (dotted lines) encompasses the entire wing, including the scapulo-humeral joint. Care should be exercised so that the technician's hands are outside of primary x-ray beam. The appropriate metallic "R" or "L" marker is placed on the radiographic cassette indicating whether the radiographic image is of the right or left wing, respectively.

25 to 50 ml/kg body weight. An alternative method of dose calculation is to estimate the volume of food that could be safely administered to the patient via crop gavage and administer 50% to 75% of this amount of contrast medium. Species variation in crop and proventricular volume and the presence of generalized disease or digestive tract pathology, including suspected obstruction, necessitate reducing the amount of contrast medium administered. The survey radiographs made just prior to the administration of contrast medium provide information regarding the digestive tract volume and mitigating circumstances that could affect the volume of contrast medium administered. Hygroscopic water-soluble contrast media (e.g., diatrizoate meglumine and diatrizoate sodium, Gastrografin®, Bracco Pharmaceuticals, Princeton, N.J.) used in mammals are not recommended for radiographic studies of the digestive tract of birds because they can precipitate severe metabolic and fluid imbalances. In addition, the mucosal detail using hygroscopic water-soluble contrast media is less than with barium sulfate. The double contrast studies utilize a combination of positive contrast medium and air. These studies are intended to speed the progression of the contrast medium through the digestive tract. Double contrast studies may also produce superior proventricular mucosal detail. It is important for the clinician to be aware of the potential for regurgitation of the contrast material that may occur as a result of the increased volume of room air in the gastrointestinal tract.

For the radiographic studies in this text, the contrast medium was administered via a rigid or soft gavage tube passed into the crop. Before administering the contrast medium, the position of the gavage tube was verified by palpation to ensure that the tube was not intratracheal. The right cervical area can be palpated as the tube is passed. If the tube is within the trachea, the gavage tube will not be palpable as a separate entity from the trachea. While the contrast material is being administered, the bird's oral cavity should be visually monitored constantly to ensure that fluid is not accumulating in the oropharynx.

For the digestive tract contrast studies published in this text, birds were anesthetized to facilitate administration of the contrast medium, optimize patient positioning, and reduce handling. These concepts also apply to clinical patients; however, the overall health of the patients should be evaluated to determine if anesthesia is safe. In general, it is recommended that birds be anesthetized for the survey radiographs, then administered the contrast medium while still under anesthesia and subsequent images acquired before the patient is allowed to recover from anesthesia. In our practice we typically acquire the survey, 0.25 and 0.5 hour radiographic images under anesthesia if the patient's health allows. Tracheal intubation to maintain anesthesia should be utilized to minimize aspiration of contrast material while the series of radiographic images are acquired for the study. Anesthesia of smaller patients (e.g., lovebirds, cockatiels) can be maintained utilizing an anesthetic cone. Patients of this size are typically not intubated because of the risk of tracheal mucosal irritation, and subsequent formation of a transluminal membrane which outweighs the risk of contrast medium aspiration. For both the intubated and the nonintubated birds, the cranial portion of the bird's body can be elevated by securing the bird to the acrylic positioning device and elevating the cranial end of the board by sliding an object such as a sandbag under it. Elevation of the cranial portion of the bird's body can minimize retrograde flow of the contrast medium into the oral cavity. Minimizing retrograde flow of contrast medium into the oral cavity can also be

Avian Gastrointestinal Anatomy

Figure 1-8 Positioning technique for the mediolateral radiographic study of the avian pelvic limb. The bird is positioned in lateral recumbency on the positioning device so that the limb of interest is dependent and fully extended. Radiolucent tape is applied to the distal tarsometatarsus and digits of the leg of interest. The contralateral limb is pulled caudally and dorsally to minimize superimposition. In order to apply enough traction to the contralateral limb, gauze bandage is wrapped around the distal tarsometatarsus and secured with tape. The x-ray beam is centered (+] on the mid-diaphyseal region of the tibiotarsal bone, and the x-ray beam field (dotted lines) includes the entire limb of interest (including the coxofemoral joint). The appropriate metallic "R" or "L" marker is placed on the radiographic cassette indicating whether the radiographic image is of the right or left leg, respectively.

achieved by placing loose elastic bandage material around the bird's neck to partially occlude the cervical esophagus, but care should be exercised to ensure that the bandage does not compress the trachea. During the entire procedure and immediately before extubation, the oral cavity should be monitored for the presence of regurgitated contrast medium. The impact of anesthetic protocols on gastrointestinal transit time has not been scientifically studied in avian patients; however, given their rapid digestive tract transit time, the impacts appear to be minimal in healthy avian patients. It is important to note that in some birds, hypersensitivity to the gas anesthetic may induce vomiting and the bird may vomit upon recovery from the anesthetic event.

Contrast medium regurgitation and subsequent tracheal aspiration can occur when performing digestive tract contrast studies and is most common when larger volumes of contrast medium are administered. The authors find regurgitation to be less frequent in anesthetized birds than non-anesthetized birds. If contrast medium regurgitation does occur and the bird is anesthetized, attempts to remove the contrast medium from the oropharynx should be immediately initiated to minimize tracheal aspiration and reflux of

Crop Radiography Birds

Figure 1-9 Positioning technique for the craniocaudal radiographic study of the avian pelvic limb. The bird is positioned in dorsal recumbency on the positioning device. Gauze bandage is wrapped around the distal tarsometatarsus and traction applied to fully extend the pelvic limb. The toes are individually secured using radiolucent tape. The x-ray beam is centered ( + ) on the mid-diaphyseal region of the tibiotarsal bone, and the x-ray beam field (dotted lines) includes the entire limb of interest (including the coxofemoral joint). The appropriate metallic "R" or "L" marker is placed on the radiographic cassette indicating whether the radiographic image is of the right or left leg, respectively.

Figure 1-9 Positioning technique for the craniocaudal radiographic study of the avian pelvic limb. The bird is positioned in dorsal recumbency on the positioning device. Gauze bandage is wrapped around the distal tarsometatarsus and traction applied to fully extend the pelvic limb. The toes are individually secured using radiolucent tape. The x-ray beam is centered ( + ) on the mid-diaphyseal region of the tibiotarsal bone, and the x-ray beam field (dotted lines) includes the entire limb of interest (including the coxofemoral joint). The appropriate metallic "R" or "L" marker is placed on the radiographic cassette indicating whether the radiographic image is of the right or left leg, respectively.

contrast medium through the choanal slit into the nasal cavity. Cotton-tipped applicators can be used to remove the contrast medium from the mouth. Contrast medium aspirated into the trachea can be identified on radiographs. In addition to seeing contrast material in the trachea, it may also be visualized in the major bronchi and air sacs, most commonly the left caudal thoracic air sac. Small volumes of aspirated contrast medium are usually well tolerated; however, larger volumes may result in bronchial obstruction. Contrast medium in the pulmonary parenchyma is rarely identified and seen only in cases in which the bird has aspirated a large volume of material. If the contrast medium is aspirated into the lungs, it is usually associated with severe respiratory distress.

Digestive tract transit time is generally more rapid in birds than mammals, especially in the smaller birds and the frugivo-rous species. In order to perform a complete digestive tract study, each segment of the digestive tract (i.e., cervical esophagus, crop, thoracic esophagus, proventriculus, ventriculus, small intestines, large intestines, and occasionally the cloaca when it is distended with contrast medium) should be documented. Documentation of proventricular emptying is also helpful.

Timing of the radiographic exposures for digestive tract radiographic studies is based on many factors, but all studies should include laterolateral and ventrodorsal projections made immediately after the administration of the contrast medium, especially if the esophagus, crop, and proventriculus are of primary interest. In some species (i.e., ducks and geese), the gastrointestinal transit times are extremely rapid and the contrast medium may have already entered the small intestines on the first set of radiographs. In such a case, additional radiographs are then made at 15- to 30-minute intervals and then hourly. Because of the variation in digestive tract transit times of different species of birds, the contrast material, and the effects of systemic disease, it is very difficult to propose rigid guidelines for timing the exposures. The timing is usually determined by evaluating the progress of the contrast medium on the initial set of radiographs. If contrast medium has entered the intestines on the immediate postcontrast administration radiographs, the next series of radiographs are taken in 15 minutes. If only a small volume of contrast medium has exited the crop, the next series of radiographs are taken 30 to 60 minutes postcontrast medium administration. Ventrodorsal and laterolateral radiographs are then made every 30 minutes until contrast medium has entered the colon.

Double contrast digestive tract studies usually have shorter transit times and produce superior mucosal detail than is seen on the positive contrast study. Because the crop and proven-triculus are more fully distended on double contrast proce

Radiography Bird Leg

Figure 1-10 Positioning technique for the mediolateral radiographic study of the avian distal pelvic extremity (foot). The bird is placed in lateral recumbency with the leg of interest in the dependent position. The distal portion of the leg is taped at the distal aspect of the tarsometa-tarsus. The digits of the foot are also secured with individual pieces of radiolucent tape. Radi-opaque numeral markers can be placed adjacent to the digits to assist in their identification on the radiograph. Radiolucent tape is preferred over gauze because it allows more precise positioning of the digits. The nondependent foot is extended caudally to separate the feet and minimize superimposition. The kVP is slightly reduced (i.e., 2-4 kVP) from the technique used for the laterolateral radiographic examination of the coelom, to prevent overexposure of the digits. The x-ray beam is centered (+) on the condyles of the tarsometatarsal bone, and the x-ray beam field (dotted lines) includes all of the phalanges. The appropriate metallic "R" or "L" marker is placed on the radiographic cassette indicating whether the radiographic image is of the right or left foot, respectively.

Figure 1-10 Positioning technique for the mediolateral radiographic study of the avian distal pelvic extremity (foot). The bird is placed in lateral recumbency with the leg of interest in the dependent position. The distal portion of the leg is taped at the distal aspect of the tarsometa-tarsus. The digits of the foot are also secured with individual pieces of radiolucent tape. Radi-opaque numeral markers can be placed adjacent to the digits to assist in their identification on the radiograph. Radiolucent tape is preferred over gauze because it allows more precise positioning of the digits. The nondependent foot is extended caudally to separate the feet and minimize superimposition. The kVP is slightly reduced (i.e., 2-4 kVP) from the technique used for the laterolateral radiographic examination of the coelom, to prevent overexposure of the digits. The x-ray beam is centered (+) on the condyles of the tarsometatarsal bone, and the x-ray beam field (dotted lines) includes all of the phalanges. The appropriate metallic "R" or "L" marker is placed on the radiographic cassette indicating whether the radiographic image is of the right or left foot, respectively.

dures, the double contrast procedures may be better suited for evaluation of mural thickness and mucosal patterns of these organs than the single contrast studies. Double contrast procedures usually require anesthesia because the gas infused into the crop will be regurgitated in most awake birds. If air is immediately expelled, it is acceptable to administer additional volumes of air to distend the crop. Because of the smaller amount of contrast medium used and the faster time in which the contrast medium evacuates the crop, the potential for contrast medium aspiration into the respiratory tract may be less than in the positive contrast studies.

Optimal evaluation of hollow organs requires that they be fully distended at the time of image capture. Orally administered contrast medium does not predictably result in cloacal distention. Therefore retrograde administration of contrast medium (i.e., via the vent) is required. Before administration of the contrast medium, the cloaca can be gently flushed with isotonic saline. Positive and double contrast procedures can be performed. The double contrast cloacagram usually follows the positive contrast cloacagram and requires removal of the positive contrast medium before administration of room air or carbon dioxide. Carbon dioxide is favored over room air to minimize the potential for intravascular air embolization. Removal of positive contrast medium pooled in the cloaca should be performed before the negative contrast (i.e., room air or carbon dioxide) is introduced. This facilitates visualization of the cloacal mucosal surface. Theoretically, it is possible to reflux fecal matter into the ureters when performing retrograde cloacograms, but this phenomenon has not been recognized in our studies.

Because radiographic images are two-dimensional representations of three-dimensional objects, additional studies

pelvic extremity (foot). The bird is placed in dorsal recumbency, and the distal portion of the leg is secured with radiolucent tape. The digits of the foot are fully extended and separated using individual pieces of radiolucent tape. The kVP is reduced slightly (i.e., 2-4 kVP) from the technique used for the ventrodorsal radiographic examination of the coelom to prevent overexposure of the digits. The x-ray beam is centered (+) on the condyles of the tarsometatarsal bone, and the x-ray beam field (dotted lines) includes all of the phalanges. The appropriate metallic "R" or "L" marker is placed on the radiographic cassette indicating whether the radiographic image is of the right or left foot, respectively.

may be required to fully assess the motility of the digestive tract. Flouroscopy can be used to evaluate proventricular and ventricular motility, but this requires specialized equipment.

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