Abstract

Raptor and companion bird radiology presents several unique challenges when compared to mammalian counterparts. This masterclass is designed to give the practitioner the basic tools needed to properly acquire diagnostic radiographs and to interpret these images. We will discuss proper restraint options, positioning, and image acquisition techniques. Following this, we will review several examples of normal and abnormal radiographic anatomy.

Restraint

Restraint of birds for radiographic examination is commonly achieved through sedation or anesthesia.¹ Conscious restraint is not ideal in most cases and increases the risk of injury for the bird and decreases the ability to position most birds correctly for radiographs. This author prefers gas anesthesia with isoflurane due to its rapid onset and recovery. Sedation, with compounds such as midazolam, has been well tolerated by most birds. If the condition is painful, often sedation alone is not enough to allow for adequate relaxation for positioning.

Positioning

Positioning is key to diagnostic radiographs. There are a few items that can make positioning easier. Foam wedges or pads can be very useful to elevate heads or hips to get proper alignment for lateral views. Foam can also be useful in separating legs in a lateral view. White tape or masking tape can be used to secure limbs in position with minimal damage to feathers.² Bird Boards have also been used to aid in positioning.³ These devices are made of acrylic and are more appropriate for larger birds. Most of these devices have straps or ties to secure wings and legs and an acrylic plate to secure the head in place. This author prefers the use of foam and tape.

A properly positioned ventrodorsal view of the coelom should, if possible, include the thoracic inlet cranially and legs caudally. The patient’s dorsum should be laid flat on the table with the keel pointed straight toward the ceiling. This should result in the keel being superimposed directly over the thoracic vertebrae in the resulting imaging.¹ Both legs should be extended equally to prevent rotation of the body. Wings should also be extended equally to prevent rotation of the body. When using tape to restrain, wing tape should touch the wing over the distal radius/ulna. Leg tape should contact the leg over the distal tarsometatarsus. The keel should be aligned with the “+” created with the light of the beam, and the beam should be centered over the caudal portion of the keel. The entire coelomic cavity should fit within a single image in all but the largest bird. Labeling with a metal R or L is, of course, part of standard procedure.

When positioning for a lateral view of the coelomic cavity, both wings should be fully extended dorsally. It is important to not superimpose the wings directly on top of each other. The down wing is commonly placed more cranial to allow easy identification on the resulting image. Tape can again be placed over the distal radius/ulna. In large birds, a foam pad or wedge between the wings can prevent over-extending wings. Legs should be extended ventrocaudally. Again, avoid superimposing legs by moving the down leg more cranially. Tape can again be placed around the distal tarsometatarsus. In most birds, the hips are narrower than the shoulders. This will cause most birds to rotate their hips toward the down side, twisting the coelom. Placing a small foam wedge under the hips will help prevent this rotation and make a well-aligned image. To confirm correct positioning, the heads of the humerus should be superimposed as well as the head of the femur on the final image.

Lateral images of the wings are designed to have the beam base from the ventral aspect of the wing through the dorsal aspect. To position this view, place the patient on the table in dorsal recumbency. Extend the wing that you wish to view until it reaches the natural end of its range of motion. In this position, it is best to use tape passing over the metacarpus to make sure both the elbow and carpus are fully extended. In larger birds, tape can be added over the mid radius and ulna to spread the pressure of the tape out. Center the x-ray tube over the mid radius and ulna if you can fit the entire wing in the field. In larger birds, it may take two or three images to get the entire wing radiographed.

The caudal-cranial view of the wing is another often-used position. This positioning starts with the patient in dorsal recumbency on the table. Feet should be toward the restrainer, and the head should point away from the restrainer. While keeping the patient’s head flat on the table, the restrainer grasps the legs and tail in a glove hand and raises them toward the ceiling. Be aware this technique has an increased risk of regurgitation. The other hand holds the primary feathers of the wing and extends the wing out from the body. The beam should pass from the caudal aspect of the wing through the cranial aspect. Be sure to avoid getting fingers in the view. The beam can be centered over the proximal radius and ulna. In large birds, multiple views may be required to get the entire wing imaged. If the image is properly positioned, the radius and ulna will be superimposed in the resulting image.

Lateral images of the legs can be accomplished by placing the patient in the same position as the lateral whole-body images. In the case of the legs, the down leg should be moved cranially (example, the right lateral view of the legs should have the right leg moved cranially). The toes should be spread out and taped in position to prevent superimposition. The beam should be centered over the proximal tibiotarsus, and the entire leg from the femur to the toes should be included in the image if possible. Large birds or long-legged birds may require multiple images.

A ventrodorsal view of the pelvis is achieved by placing the patient in dorsal recumbency. The legs are fully extended and tapped in place, similar to the positioning for the VD images of the whole body. Toes should be spread out and tapped in place to prevent superimposition. The beam should be centered over the proximal tibiotarsus, and the entire leg from the femur to the toes should be included. In larger birds or long-legged birds, multiple images may be required.

The H view is a recent addition to the toolkit of avian practitioners. It is used to examine the coracoid, clavicle, and scapula without these bones being superimposed upon one another. This image is acquired by placing the patient in the same position that would be used for a standard whole-body ventrodorsal view. It is important that the patient’s head and feet are aligned with the length of the table. This technique requires a machine that will allow for the head of the x-ray machine to rotate to 30–45°. The exact angle depends on the species of bird being examined. This practitioner routinely starts at 30° for most patients and increases the angle if there is still superimposition of the bones of interest. Rotate the head of the machine to the desired angle and then move the machine caudally in relation to the patient. The beam should be aimed at the shoulders of the patient passing through it in a caudal-ventral/cranial-dorsal angle. As this beam is at an angle to the patient, traditional measurement for the determination of technique can be difficult. Technique set based on VD measurements of the patient tend to result in overexposed images. This practitioner uses a VD measurement and decreases the technique by 1 cm in most cases.

Technique

Radiographic technique can be highly individual for each machine. It is recommended to develop your own technique chart for avian radiographs. In most avian⁴ patients, a low milliamperage-sec (mAs) and kilovoltage peak (kVp) are used. A suggested technique chart is provided below.

Suggested technique chart

It is important to consider conventional film vs. digital systems when determining technique. Generally, digital systems require slightly higher mAs and kVp than conventional film systems (around 10 to 15%). All digital systems are not created equal. Digital systems use an algorithm to create the image after it is acquired on the cassette or plate. The algorithms vary based on what you set the computer to (for example, a thorax algorithm reads the plate differently than an abdominal algorithm). To be clear, the algorithm is a processing function of the computer; it is not the mAs or kVp that you set your radiograph machine to. These algorithms can vary between manufacturers. Some systems have exotic/avian algorithms. For those without, use a setting for a small mammal (such as a cat) extremity. Consult your manufacturer if you are having trouble with your image quality.

Image Interpretation

Image interpretation should be done in a systematic manner. This author prefers to first evaluate position and technique to confirm they are adequate. Next, examination of the skeletal structures, noting any abnormalities. Following that, this author then examines soft tissue structures. There can be a significant amount of variation in size and position of organs between different species of birds. A reference text or reference films are important tools to have on hand. Several examples of raptor and psittacine anatomy will be covered in this masterclass.

References

1.  Naldo J, Saggese M. Avian Medicine. St. Louis, MO: Elsevier; 2016.

2.  Krautwald-Junghanns M, Pees M. Handbook of Avian Medicine. St. Louis, MO: Elsevier; 2009.

3.  Krautwald-Junghanns M. Essentials of Avian Medicine and Surgery. Ames, IA: Blackwell; 1997.

4.  Silverman S, Tell L. Radiology of Birds. St. Louis, MO: Elsevier; 2010.