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May/June 2014 Today's Veterinary Practice 53 ImagIng EssEnTIals Peer reviewed tvpjournal.com T he anatomy of the skull, temporomandibular joints (TMJ), and region of the tympanic bullae in the dog and cat is complex because of superimposition of cavities, sinuses, mandible, maxilla, dental arcades, and neurocalvarium. Radiography of specific areas requires close attention to the details of normal anatomy that will aid in proper positioning for each image, based on the type of study being done. Improperly positioned radiographs can lead to anatomic distortion of the skull anatomy, resulting in potential false positive diagnoses. RADIOGRAPHIC EXPOSURE Exposures should be made using: • High mAs: Lowest mA that, if there is an option, allows use of a small focal spot in order to improve geometric sharpness and, thus, ability to see fine osseous detail. • Grids: Use if areas thicker than 10 cm are being imaged; otherwise, tabletop technique is recommended. Routine PRojections: skull, tMj, & tyMPanic Bullae LATERAL PROJECTION (Figure 1, page 54) Positioning 1. For the right lateral projection, place the patient in right lateral recumbency, with the nose and skull in an ex- tended position. 2. In dolichocephalic and mesaticephalic dog breeds, place a small rectangular sponge under the tip of the nose to keep it parallel with the table. For brachycephalic dog breeds and cats, use a 45-degree oblique sponge (wide end away from the head). 3. Place the cervical spine, thoracic limbs, and thorax in a lateral straight position relative to the skull. 4. Pull the thoracic limbs caudally. To ensure the patient is straight in a lateral position: • Place your hand along the ventral mandibles, positioning your hand perpendicular to the table and the mandibles. • Feel for the external occipital protuberance along the caudodorsal margin of the skull (not as prominent in brachycephalic breeds). • Compare the relative level with the middorsal aspect of the nasal cavity; this imaginary line should be parallel to the table. THE NEED FOR ANESTHESIA although some basic skull views may be obtained with heavy sedation, general anesthesia is required to obtain diagnostic skull radiographs for several reasons: • During each imaging series of the skull, one of the projections requires the mouth of the dog or cat to be open when an exposure is made. • The oblique and skyline projections require exact positioning that is not possible in an awake dog or cat, even if heavily sedated. Imaging Essentials provides comprehensive information on small animal radiography techniques. The following anatomic areas have been addressed in previous columns; these articles are available at tvpjournal.com (search "Imaging Essentials"). RadiogRaphy of the Small animal Skull: TEMPOROMANDIbULAR JOINTS & TYMPANIC bULLAE Mary Wilson, RT(R), CT, MR, CV; Danielle Mauragis, CVT; and Clifford R. Berry, DVM, Diplomate ACVR University of Florida • Thorax • Elbow and antebrachium • abdomen • Carpus and manus • Pelvis • Tarsus and pes • stifle joint and crus • Cervical, thoracic, and lumbar spine • scapula, shoulder, and humerus • nasofacial and frontal sinuses 2014-0506_IE_Skull2.indd 53 5/23/2014 12:59:37 PM