Alpacas commonly develop dental abnormalities, such as tooth root abscesses, mandibular osteomyelitis, malocclusion, fractured teeth, uneven teeth, overgrown teeth, worn teeth, and persistent deciduous teeth.1 Traditionally, radiography has been used to identify which teeth are involved and determine the extent of osteomyelitis, sequestra, and draining tracts in alpacas with dental disorders.1–3
For alpacas, acquisition of optimal radiographs of the skull requires sedation and a minimum of 4 views.1,3 Standard radiographic views of the skull include lateral, dorsoventral, left-to-right lateroventral-laterodorsal oblique, and left-to-right laterodorsal-lateroventral oblique views, and an additional intraoral view of the mandible may be necessary for some patients.1,3 Small dental x-ray sensors are routinely used for intraoral imaging in small animals, but to our knowledge, use of those systems for intraoral imaging in alpacas has not been described. The acquisition of diagnostic radiographs of the skull of alpacas can be laborious because rotation of the animal from sternal to lateral recumbency and insertion of a mouth gag for oblique and intraoral images is generally required.1,3 In a study3 involving cadaveric skulls of alpacas and llamas, CT was superior to radiography because of its increased contrast resolution, lack of superimposition of soft tissue and osseous structures, and the ability to reconstruct multiplanar and 3-D volume rendering images. From a clinical perspective, imaging the skulls of alpacas with CT rather than radiography allows the animals to be positioned in a natural body position (sternal vs dorsal recumbency), reduces the need for repositioning, and potentially decreases procedure time.
Both single and multislice CT scanners are now readily available to veterinarians.4 A CT scan can be acquired in either sequential (axial) or helical (spiral) mode. In dogs, the optimal 4-slice CT protocol for evaluation of dentition is sequential with a 1-mm slice thickness.4 Helical image quality is reported to be equivalent to sequential image quality when CT scanners with > 16 slices are used.4–6 Determination of the optimal CT slice thickness for evaluation of dentition in alpacas is important owing to the frequency of dental disorders in this species. The optimized CT protocol should prioritize visualization of the tooth roots and surrounding alveolar bone because those are the structures that are most frequently affected by dental disease.
Literature regarding the positioning of alpacas for CT scans of the skull is scarce. The literature that is available describes imaging results for detached cadaveric heads3 or is in the form of clinical reports7,8 of individual animals, in which the CT examination was performed under inhalant anesthesia. In another study,9 the skulls of llamas that were anesthetized with inhalant anesthesia and positioned in dorsal recumbency were scanned with a single-slice CT scanner at a slice thickness of 5 mm. The llamas of that study9 were supported by the normal CT couch and easily positioned within the gantry.
Historically, alpacas are anesthetized with inhalant agents for major surgical procedures or when restraint or immobilization is required for a prolonged period. Compared with other species, the trachea of camelids is small relative to the overall body size, which in conjunction with a deep oral cavity, makes oral intubation difficult.10 Camelids, including alpacas, tend to be calm and quiet when recovering from injectable anesthesia and generally do not attempt to stand until they are awake and fully functional.10 Ketamine is the most common injectable anesthetic used in camelids and is often administered in combination with an α2-adrenergic receptor agonist (eg, xylazine) and opioid (eg, butorphanol). Alpacas can be effectively restrained with injectable anesthetics for short periods (< 30 minutes) with variable levels of systemic analgesia.10
Owing to the rapid speed with which images can be acquired with 64-slice CT scanners and the minimal discomfort for alpacas when restrained in natural sternal recumbency, we believe that injectable anesthetic protocols should be sufficient to provide the depth of anesthesia and analgesia necessary for CT examination of the skull. The development of a positioning protocol for the acquisition of diagnostic CT scans of the skull of alpacas under injectable anesthesia should decrease both handling and anesthesia times and may be more cost effective for clients because injectable anesthesia is generally less expensive than inhalant anesthesia.
The purpose of the study reported here was to determine an optimal protocol for the acquisition of CT images of the dentition of alpacas with the animals anesthetized with injectable anesthetics and positioned in sternal recumbency. Six CT protocols were compared. We hypothesized that optimal CT images would be obtained by use of a 64-slice CT scanner in helical mode with a slice thickness of 1.25 mm.
Supported by the Purdue University Veterinary Clinical Science Graduate Student Competitive Research Fund. The funding source did not have any involvement in the study design, data analysis and interpretation, or writing and publication of the manuscript.
The authors declare that there were no conflicts of interest.
Lightspeed 64-slice CT Scanner, GE Healthcare Inc, Princeton, NJ.
OsiriX imaging software, version 5.4, OsiriX Foundation, Geneva, Switzerland.
2. Niehaus AJ, Anderson DE. Tooth root abscesses in llamas and alpacas: 123 cases (1994–2005). J Am Vet Med Assoc 2007;231:284–289.
3. Rostami A, Geissbühler U, Schellenberger F, et al. Computed tomographic and radiographic examination of dental structures in South American camelid specimen of different ages. BMC Vet Res 2014;10:4.
4. Esmans MC, Soukup JW, Schwarz T. Optimized canine dental computed tomographic protocol in medium-sized mesaticephalic dogs. Vet Radiol Ultrasound 2014;55:506–510.
5. Abdeen N, Chakraborty S, Nguyen T, et al. Comparison of image quality and lens dose in helical and sequentially acquired head CT. Clin Radiol 2010;65:868–873.
6. Davis AJ, Ozsvath J, Vega E, et al. Continuous versus sequential acquisition head computed tomography: a phantom and clinical image quality comparative study. J Comput Assist Tomogr 2015;39:876–881.
7. Hardefeldt LA, Rylander H, Iskandar BJ, et al. Diagnosis and surgical treatment of an intracranial cyst in an alpaca cria. J Am Vet Med Assoc 2012;240:1501–1506.
8. Britt LG, Middleton JR, Warhover TT, et al. Acanthomatous ameloblastoma of the maxilla of an adult aplaca. Vet Radiol Ultrasound 2005;46:65–68.
9. Hathcock JT, Pugh DG, Cartee RE, et al. Computed tomography of the llama head: technique and normal anatomy. Vet Radiol Ultrasound 1995;36:290–296.
11. Jones JC, Wilson ME, Bartels JE. A review of high resolution computed tomography and a proposed technique for regional examination of the canine lumbosacral spine. Vet Radiol Ultrasound 1994;35:339–346.
12. Zarelli M, Schwarz T, Puggioni A, et al. An optimized protocol for multislice computed tomography of the canine brain. Vet Radiol Ultrasound 2014;55:387–392.
13. Dowsett D, Kenny PA, Johnston RE. Computed tomography. In: The physics of diagnostic imaging. 2nd ed. Boca Raton, Fla: CRC Press, 2006;381–435.
14. Porat-Mosenco Y, Schwarz T, Kass PH. Thick-section reformatting of thinly collimated computed tomography for reduction of skull-base-related artifacts in dogs and horses. Vet Radiol Ultrasound 2004;45:131–135.
15. Silver MD, Taguchi K, Hein IA, et al. Windmill artifact in multislice helical CT. In: Medical imaging. Bellingham, Wash: International Society for Optics and Photonics, 2003:1918–1927.
16. Oliveira CR, Ranallo FN, Pijanowski GJ, et al. The Vetmousetrap: a device for computed tomographic imaging of the thorax of awake cats. Vet Radiol Ultrasound 2011;52:41–52.
Subjective scoring system used by 3 board-certified veterinary radiologists to independently evaluate tooth root visibility, tooth root sharpness, and image noise artifact on CT images of the dentition for 3 healthy adult male alpacas obtained by each of 6 protocols during a study to determine the optimized CT protocol for assessment of dentition in alpacas.
|Score||Tooth root visibility||Tooth root sharpness||Image noise artifact|
All images were acquired with a 64-slice CT scanner in the sequential mode at a slice thickness of 1.25 (S1.25 protocol), 2.5 (S2.5 protocol), and 5 (S5 protocol) mm and in the helical mode at a slice thickness of 1.25 (H1.25 protocol), 2.5 (H2.5 protocol), and 5 (H5 protocol) mm.