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| ImagIng EssEnTIals Today's Veterinary Practice May/June 2014 54 tvpjournal.com detail and to reduce geometric magnification. The radiograph should be reviewed to ensure that the right and left sides of the skull are symmetrical for evaluation. Positioning To obtain the VD projection: 1. Place the patient in dorsal recumbency. 2. Extend the skull, with the external occipital protuberance rest- ing on a thin sponge. 3. Ensure the ventral aspect of the mandibles and the hard pal- ate, which cannot be visualized because the animal's mouth is closed, are parallel to the table. 4. Use a V-trough to help maintain the patient in a straight posi- tion. To obtain the DV projection: 1. Place the patient in ventral or sternal recumbency. 2. Extend the skull, with the mandibular rami placed on the table/ cassette/detector. 3. To ensure stabilization, place a thin radiolucent sponge be- tween the patient's ventral skull and the table/cassette/detec- Collimation 1. Set the central beam to the mid cranium, with the collimator opened to just include the crani- um and nasal cavity (cross hairs just caudal and ventral to the eyes). 2. Place an external radiopaque marker ventral to the caudal mandible on the table or radiograph- ic cassette. 3. If the area of interest is lateralized to one side, place the side of interest closest to the detector, in which case, the marker indicates which recum- bency the patient has been placed. 4. If the area of interest is at the level of the max- illa or mandible, the upper and lower jaw can be separated (opened) by placing a syringe case between the mandibular and maxillary canines. Ensuring Image Quality The lateral projection of the skull should extend from the rostral end of the nose (nasal planum) through the first cervical vertebra (C1). The wings of the atlas and C1 should be even and superim- posed, and all aspects of the skull should be super- imposed, such as the zygomatic arches, mandibles, and tympanic bullae. Superimposition is more difficult in brachy- cephalic breeds because their skulls are much wider—geometric distortion from the divergent na- ture of the x-ray beam may make superimposition of all structures impossible. VENTRODORSAL/DORSOVENTRAL PROJECTION (Figure 2) Ventrodorsal (VD) or dorsoventral (DV) position- ing is dependent on the breed of dog or cat; while deep-chested dogs are better imaged in VD position, brachycephalic and small breed dogs and cats may be better imaged in a DV position. The area of interest should be as close to the film/cassette/detector as possible for the best overall Figure 1. Dog positioned for a right lateral radiograph of the caudal skull centered over the TMJ and tympanic bullae (A) and corresponding radiograph (B). Collimated radiographs can be obtained if the area of interest only includes the TMJ and tympanic bullae (C and D). A syringe case can be used to open the mouth for the lateral or the oblique projections to ensure separation of the maxillary and mandibular dental arcades. A b C D Figure 2. Dog positioned for VD radiograph of the caudal skull centered over the TMJ and tympanic bullae (A) and corresponding radiograph (B). A b 2014-0506_IE_Skull2.indd 54 5/23/2014 12:59:38 PM