Veterinary Computer Tomography

Computer Tomography

for veterinarians

Computer Tomography in Veterinary

Computed tomography (CT) is now a widely used method of radiological examination of humans and is becoming increasingly popular in veterinary medicine. A CT scanner consists of an X-ray machine, a radiation detector, and a computer that analyzes the absorption of radiation and converts the results into images with different gray scales. During the scan of a patient we obtain mainly images of layers arranged transversely to the long axis of the body, but it is possible to obtain images of sagittal, frontal layers and even three-dimensional images. Most of the CT examination will provide further information when used in combination with intravenous iodinated contrast. CT studies are best utilized with bone or lung pathology or to determine the extent of growth of a soft tissue mass. Studies include but are not limited to the evaluation of disease involving the nasal passages or tympanic bullae, evaluation for metastasis or lung diseases, body wall masses, head, or spinal trauma, retrobulbar and pituitary masses.

There is no doubt that CT is superior to radiography in the evaluation of many diseases, but radiography remains the primary diagnostic technique because it is widely available and inexpensive. In addition, it allows you to examine the area before deciding if, and which, more expensive further investigations should be undertaken. The disadvantages of CT are definitely the cost of buying the equipment and the very large amount of data for high-resolution scans, which lengthens the image processing (a powerful processor is needed). The patient's exposure to X-rays is 400 times higher than in classical radiography. Working with computed tomography requires a highly skilled and experienced team of people. Sedation or general anesthesia of the patient is usually required. We must keep in mind the possibility of adverse reactions after contrast administration. These can be mild (apathy, vomiting, diarrhea, urticaria) or severe (blood pressure drop, pulmonary edema, apnea, shock, arrhythmias, cardiac arrest).

 

Advantages of tomography and its comparison with other radiographic examinations

The advantage of a CT scan is that the entire procedure can range from less than a minute to 20 minutes, depending on the procedure being performed, the size of the patient and the technology available. Unlike ultrasound, Computed tomography allows assessment of the entire thorax with cross-sectional images. Ultrasonography only provides a limited field of view and assessment of the entire thorax is difficult or impossible. In addition, CT allows assessment of air-filled lung, which is not possible with ultrasonography (due to the almost complete reflection of sound at the soft tissue–air interface). This examination provides cross-sectional images with greater contrast than radiographs and has a much higher sensitivity for lung nodules and other pathology. CT is of particular value for assessment of pleural space disease, surgical planning for thoracic masses, assessment of vascular malformations, staging of neoplasia and investigation of respiratory disease where radiographs have been inconclusive. Due to motion artefacts, computed tomography offers little or no advantage over radiography for the investigation of cardiac disease unless high end machines are available. Radiology often underestimates the complexity and number of fractures, particularly in the carpus and tarsus where computed tomography is considerably more accurate in assessing the fracture configuration. CT is indicated for the majority of spinal disorders and have largely replaced radiography for the diagnosis of spinal diseases in veterinary medicine. It can be combined with myelography to provide information about spinal cord pathology such as oedema, atrophy,  mass lesions, malacia (spinal cord necrosis), gliosis (scarring of the spinal cord) and information about peripheral nerves.

The quality of CT images depends on the parameters of the radiation source, number of measurements, quality of detectors, image reconstruction method, image grid size and occurrence of artifacts. Artifacts may be created by the movement of the examined object or echo of objects (e.g. when metal elements are present, streaks in the image are created). The veterinarian must adequately prepare the patient for the examination by performing a clinical examination, appropriate tests (e.g., morphology and blood biochemistry), and general stabilization of the patient. Owners should provide appropriate documentation (medical history, previous examinations, allergy information) and must sign a written consent for anesthesia and contrast agent use. Depending on the examination, an appropriate length of patient starvation or enema is recommended. It is the radiologist's responsibility to adjust the radiation dose to the patient's body diameter and use appropriate shielding outside the scanning area. With proper procedures and an educated team, a CT scan is a safe examination that provides us with the information we need to save the health and lives of our patients.