What is a CT (or “CAT”) scan and how does it differ from radiographs?
A CT (or computed tomography) scan is similar to radiographs, although produces a 3-D (instead of 2-D) image for evaluation of a patient. During the scan, cross-sectional images (using x-rays) of an organ/area are acquired, creating slices of the patient (similar to a loaf of bread being sliced into small pieces). This type of imaging allows the clinician to evaluate the size, shape, and spatial relationship of soft tissue and bony structures within a specific area, which produces much finer detail compared to radiographs. In many situations contrast agent is administered intravenously, which can illuminate certain lesions (such as liver/splenic nodules, lymph nodes, masses, etc.) that may appear normal on a regular scan without contrast.
How are CT scans used for cancer patients?
CT scans are often used for cancer patients to gain more information about primary tumors and to evaluate the patient for internal metastatic disease that cannot be detected on routine radiographs or ultrasound (see below for information about ultrasound). In some cases tumors have a “tip-of-the-iceberg” appearance, where they feel small from the outside, but have a large base that infiltrates into underlying important structures. As a result, a CT scan (with contrast) can help the clinician decide if surgical removal is feasible, and if so, what risks are involved with the procedure. Scanning of the regional lymph nodes, lungs, and abdomen can often show changes consistent with tumor spread, and may prompt your veterinarian to recommend further diagnostics (such as fine needle aspiration with cytology) to confirm metastatic disease.
CT scans are also commonly used for radiation therapy planning purposes. Certain patients with cancer may require radiation therapy as a form of treatment either in the setting of gross or microscopic disease. Once the CT images are required they can be inserted into a special computer program that is ultimately connected to the radiation therapy unit. This allows the radiation oncologist to provide accurate dosing and distribution of radiation to the site being treated, in order to give the highest dose the affected area while minimizing damage to normal surrounding tissues.
Is a CT scan safe?
While CT scans generally require the patient to be placed under general anesthesia for a brief period of time, the procedure is still very safe with minimal risk to the patient. Since the images are acquired slice by slice as the patient passes through a donut-like machine, it is important that the patient is as still as possible. As a result, general anesthesia (or less commonly heavy sedation) is required to ensure that the images are captured without movement to minimize artifact. The procedure is non-painful and minimally invasive. The procedure takes roughly 30-90 minutes (depending on the size of the area being evaluated), and the patient is closely monitored by a doctor and/or anesthesia technician the entire time.