Frequently Asked Questions - CT


What is Computed Tomography (CT)?

CT is a tomographic imaging technique that uses x-ray beam to create high-resolution, thin-section anatomical images. During CT, the animal is placed on a table which moves through the circular opening of the CT scanner (the gantry). X-rays are generated by a high-power x-ray tube in the gantry; after the x-rays travel through the patient, their attenuation is measured by detectors located on the opposite side of the gantry. Attenuation values are translated into CT numbers (or Hounsfield units, HU) and converted to shades of gray that are displayed as an image. The sensitivity of CT to subtle difference in x-ray attenuation is 10 times higher than conventional radiography: this means that CT identifies bone lysis and production earlier that radiography. In addition, CT allows evaluation of osseous, pulmonary and soft tissue structures with a single scan, by manipulating the image display. Further, cross sectional images greatly facilitate evaluation of area of complex anatomy, such as joints, the thorax and the skull.

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What are possible applications for CT in Veterinary Medicine?

Musculoskeletal disorders

CT is the best imaging modality to evaluate osseous structures; it is commonly used to evaluate complex fractures, for surgical planning in cases of angular limb deformity, and for evaluation of elbow dysplasia.

Thoracic disorders

CT is the best imaging modality to evaluate the lungs: it is superior to radiography in its ability to identify pulmonary nodules. In addition, CT is commonly used to evaluate pulmonary, mediastinal and chest wall masses and to determine their extent for surgical planning; CT angiography is the gold standard to evaluate for pulmonary thromboembolism (PTE).

Abdominal disorders

Evaluation of the extent, origin and margins of intra-abdominal masses can be performed quickly and easily with CT. CT is also the best imaging modality to determine the morphology of vascular anomalies such as portosystemic shunts, and of ectopic ureters.

Nasal/paranasal sinus, orbital and ear disorders

CT is extremely useful in the evaluation of nasal disease, orbital disease and ear disease, and can identify very subtle bone lysis or proliferation. Administration of iodinated contrast allows evaluation of the neighboring brain parenchyma; however, MRI remains the modality of choice for brain evaluation.

Spine

CT can be used to evaluate the spine especially when an aggressive osseous process is suspected. CT can also be used to evaluate dogs with suspected disc herniation: however, CT will only identify mineralized disc material. Therefore MRI remains the modality of choice in non-chondrodystrophic and large breed dogs, which are more likely to have non-mineralized discs.

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Veterinarian: How do I refer a patient?

Please refer to the CT Request Form for detailed information regarding the referral process.

If you have any questions regarding a potential referral case, please call us under (865) 974-5601.

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Pet owner: How do I set up an appointment for my pet?

Once you have a referral from a veterinarian you or your veterinarian you can call us and set up an appointment phone (865) 974-5601.

Your veterinarian will need to fax the referral documents at the latest one day before your appointment. This way we can make sure we have all the information necessary to perform the examination.

Please refer to Client Instructions for further information.

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How does the CT examination process work?

Please refer to client instructions.

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Are there any risks associated with the CT examination?

CT is considered a very safe imaging modality.

The examination is performed under general anesthesia or heavy sedation. This is necessary to keep the animal from moving and minimize examination time. There is a certain risk associated with anesthesia, which is not different when performing a CT examination from other instances where anesthesia is required.

While CT uses ionizing radiation, the dose received by the patient is low, typically less than that of a human receiving a similar procedure. CT should be avoided in breeding animals in the first trimester of pregnancy.

Iodinated contrast media is routinely used in CT to enhance the evaluation of soft tissue structures. Iodinated contrast media are excreted by the kidneys and used routinely for angiographic studies and radiographic contrast studies. The intravenous injection of iodinated contrast medium is considered relatively safe: idiosyncratic reactions are rarely reported in people, and are extremely rare in animals. The most common complication in animals is contrast induced renal failure; this is also rare, and is typically reversible with diuresis. Animal with underlying renal failure and dehydrated animals have a higher risk: veterinarians referring an animal with underlying renal disease should contact us at (865) 974-5601.

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