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| ImagIng EssEnTIals Today's Veterinary Practice May/June 2014 56 tvpjournal.com LATERAL 30-DEGREE ObLIQUE PROJECTION (Figure 4) Positioning For a complete study, both right lateral and left lateral oblique projections are needed. 1. Place the patient in lateral recumbency, with the nose and skull in an extended position. 2. Ensure the mouth remains open, which can be ac- complished with a syringe case, and secure the en- dotracheal tube to the mandible. 3. Place a 30-degree wedge sponge under the maxilla to ventrally oblique the skull. When the initial projection is finished, take the op- posite oblique projection by: 1. Rolling the patient over, with the original nonre- cumbent side now on the table. 2. Placing a wedge sponge under the maxilla to ven- trally rotate the head by 30 degrees. Collimation 1. Position the central beam just ventral to the nonre- cumbent external auditory canal (that closest to the tube head). 2. Adjust collimation to include only the tympanic Figure 4. Dog positioned in left lateral recumbency for a 30-degree oblique radiograph of the nonrecumbent, right tympanic bulla and TMJ (A) and corresponding radiograph (B). Note: A roll of tape or a syringe case can be used to keep the mouth open. A b bulla and TMJ from the level of the third maxillary premolar to C1/C2. 3. If the patient is in right lateral recumbency, for ex- ample, the left TMJ, tympanic bulla, and ear will move ventrally when positioned correctly. 4. Place the radiopaque markers outside soft tissue structures: For the right lateral projection, place the right marker ventral to the oblique, recumbent bulla and the left marker just dorsal to the skull. For the left lateral projection, the opposite is true, with the left marker placed ventral to the oblique, recumbent bulla. Ensuring Image Quality The lateral oblique projection should extend from mid mandible to C1. One of the TMJs and tympanic bulla should appear ventral but without superimposition of the cranium. Care should be taken to avoid over rotating the patient, causing foreshortening of the vertical mandibular ramus and tympanic bulla. LATERAL 25- TO 30-DEGREE ROSTROCAUDAL ObLIQUE PROJECTION (Figure 5, page 57) Positioning For a complete study, both right lateral and left lateral oblique projections are needed. 1. Place the patient in lateral recumbency, with the cranium and nasal passages in true lateral position. 2. Place a triangular- or wedge-shaped radiolucent sponge under the rostral aspect of the nose and mandible, which lifts the nasal planum, nasal cav- ity, and mandible 25- to 30-degrees away from the table. 3. Ensure the mouth remains open, which can be ac- complished by placing a syringe case between the upper and lower canines. When the initial projection is finished, take the op- posite oblique projection by rolling the patient over, with the original, nonrecumbent side now on the table. It is important to note that, in left lateral recum- bency, the: • Right TMJ and tympanic bulla are caudal and, therefore, best visualized by this projection • Left TMJ and tympanic bulla appear superimposed over the caudoventral aspect of the skull. The opposite is true for right lateral recumbency. Collimation 1. Direct the central beam just rostral to the TMJ (that closest to the tube head). 2. Adjust collimation to include only the tympanic bulla and TMJ. 3. Mark the recumbent side, which will appear more rostral on the radiograph. Ensuring Image Quality The rostrocaudal oblique projection should extend 2014-0506_IE_Skull2.indd 56 5/23/2014 12:59:39 PM