Introduction

• Computed tomography (CT) is a non-invasive imaging modality that can be used to evaluate the anatomy, function and pathology of many tissues.
• Tomographic scanners rotate to divide the object and organize it into spatially consecutive, parallel image sections.
• Most images are acquired in a transverse plane.
• Multiplanar images and 3D renderings can be mathematically reconstructed.
• X-ray attenuation is measured by detectors which are aligned behind the patient, opposite to the x-ray source.
• The CT computer collects x-ray attenuation data and generates a matrix of values, Hounsfield units (HU), depicted in various shades of gray:
  • There are 4096 gray tones which represent different density levels in HUs.
  • Water is equal to 0 and dry air is equal to 1000 HU.
  • The monitor can display a maximum of 256 gray tones though the human eye is able to only discriminate about 20.
  • Manipulation of the gray scale can be performed to enhance the appearance of different tissues.
  • The density levels of almost all soft-tissue organs lie between 10 and 90 HUs.
  • The density level of bone is around 300 HUs.
  • The density level of lung is around 600 HUs.
  • The window level should be set as close to the mean density level of the tissue to be examined.
  • The window width influences the contrast of the image.
  • The narrower the window, the greater the contrast since the 20 observable gray tones cover a smaller range of densities.

Uses

• Computed tomography is a very useful technique to investigate not only dental diseases in rabbits, but also pathological and non-pathological abnormalities of the skull , bones and chest , as well as detection of tumors.

Advantages

• The major advantage of CT over conventional radiographs is the improved contrast and spatial resolution. 
• Unlike conventional x-rays, CT scanning provides very detailed images of many types of tissue as well as the lungs, bones and blood vessels.
• Structure and function may be evaluated concurrently in some cases. 
• CT examination is generally painless, fast and simple.
• CT is less sensitive to the high respiratory rate of rabbits than magnetic resonance imaging (MRI) Magnetic resonance imaging.
• CT can be performed if the rabbit is presented with a metal medical device, unlike MRI.
• Pre and postprocessing CT data manipulation is possible, allowing tissues of varying density to be better evaluated. 
• Multiplanar image reconstruction and 3D renderings can be configured. 
• Initial cost and maintenance of equipment is not prohibitive as compared to MRI. 
• Imaging times are significantly reduced as compared to MRI. 
• Refurbished CT equipment can be purchased at affordable prices. 
• CT is superior to all other imaging modalities when examining bone.

Disadvantages

• Rarely available.
• Expensive.
• Not suitable for detecting abnormalities of soft tissue.
• General anesthesia is required Anesthesia: overview.
• There is always a slight chance of excessive exposure of the animal to radiation.
• The risk of allergic reaction to contrast materials has been reported in the literature in people but not in rabbits. However, it is a side effect that needs to be taken in consideration during the procedure. 
• The area of interest must be well defined prior to imaging to avoid patient repositioning and excessive anesthesia times. 
• Study interpretation may be lengthy due to the large number of images acquired with most CT examinations. 
• Ionizing radiation is utilized.

Requirements

Preparation

Procedure

Aftercare

Outcomes

Further Reading

Publications

Refereed papers

• Recent references from PubMed and VetMedResource.
• Kwan V, Quesenberry K & Le Roux A B (2020) Mensuration of the rabbit pituitary gland from computed tomography. Vet Radiol Ultrasound 61 (3), 322-328 PubMed.
• Kyllar M, Putnová B, Jekl V et al (2018) Diagnostic imaging modalities and surgical anatomy of the temporomandibular joint in rabbits. Lab Anim 52 (1), 38-50 PubMed.
• Müllhaupt D, Wenger S, Kircher P et al (2017) Computed tomography of the thorax in rabbits: a prospective study in ten clinically healthy New Zealand White rabbits. Acta Vet Scand 59 (1), 72 PubMed.
• Ajlan A M, Al-Khatib T, Al-Sheikah M et al (2015) Helical computed tomography scanning of the larynx and upper trachea in rabbits. Acta Vet Scand 57, 67 PubMed.
• Van Caelenberg AI, De Rycke L M, Hermans K et al (2010) Computed tomography and cross-sectional anatomy of the head in healthy rabbits. Am J Vet Res 71 (3), 293-303 PubMed.
• Capello V & Cauduro A (2008) Clinical technique: application of computed tomography for diagnosis of dental disease in the rabbit, guinea pig and chinchilla. J Exotic Pet Med 17 (2), 93-101 ScienceDirect.
• Bouchgua M, Alexander K, Carmel E et al (2006) Bone mineral density assessed by computed tomography in an in vivo rabbit model of osteoarthritis. Osteoarthritis & Cartilage 15 (Suppl C), C173-174 CORE.
• Souza M J, Greenacre C B, Avenell J S et al (2006) Diagnosing a tooth root abscess in a guinea pig (Cavia porcellus)​ using microcomputed tomography imaging. J Exotic Pet Med 15 (4), 274-277 ResearchGate.

Other sources of information

• Girling S (2002) Mammalian Imaging and Anatomy. In: BSAVA Manual of Exotic Pets. Eds: Meredith A & Redrobe S. 4th edn. pp 1-12.
• RadiologyInfo - a public information website developed and funded by the American College of Radiology (ACR) and the Radiological Society of North America (RSNA). Website: www.radiologyinfo.org.