Computed tomography (CT) over the last 15 years has become quite readily available in veterinary practice. CT, like radiography, uses x-ray beams to form images of the vertebral column. Tomography refers to the imaging of part of the body in sections or slices. CT images are usually collected in slices, recent ultra rapid imaging spiral and helical scanner.
CT is very useful for imaging of the vertebral column and skull, providing excellent spatial resolution. Imaging is most often done in 3mm slices, but can be refined to 1mm slices or less over specific lesions. Imaging diseases resulting in changes to the bone are particularly useful and include skull or vertebral fractures, vertebral instability, mineralized intervertebral disc extrusions (as seen in many small dogs), bone tumors, bone infections including diskospondylitis or otitis media/interna and also hemorrhage.
Imaging of the brain and spinal cord with just CT is of limited usefulness. This is because soft tissues are less clearly defined using the attenuation of x-rays. Large masses in the brain resulting in anatomical distortion, collection of fluid in large cysts or hydrocephalus and hemorrhage are indications for using CT. However small masses, small-moderate sized ischemic strokes, or inflammatory disorders are better imaged with MRI. In addition the CT artifacts (beam-hardening) seen due to the very dense bone in the low skull (petrous temoral bone of the caudal fossa) make imaging of the brain stem and cerebellum challenging.
Intravenous (iodinated) contrast agents can be administered to assist in the detection and extent of soft tissue involvement or diseases, particularly tumors, infectious or inflammatory diseases. Possible complications of intravenous agents include allergic reactions and anaphylactic shock. These complications are rare and generally manageable in the hospital setting, but could result in death.
CT does require anesthesia of the patient, but does not require specialized monitoring equipment. CT can be rapidly performed within a few minutes. Technicians must NOT remain in the same room as the patient and window or remote anesthesia monitoring devices should be employed.