What is CT?
A CT scan, also known as computed tomography scan or a computerised axial tomography (CAT) scan, is a computerised x-ray imaging procedure that generates cross-sectional images, or “slices” of the body. Once a number of successive slices are collected by the machine’s computer, they can be digitally “stacked” together to form a three-dimensional image of the patient. This allows for easier identification of body structures and for accurate surgical planning.
Unlike x-ray, a CT scan can differentiate between different types of soft tissue and thus can be used in the investigation of a wide range of non-orthopaedic diseases. CT scans are also particularly useful in oncology cases, both in delineating the extent of a primary tumour and in assessing for metastatic disease. With the administration of an intravenous contrast agent, a ‘contrast’ CT can detect subtle regions of pathology within a wide range of body tissues.
How does it work?
A CT scanner uses a motorised x-ray source that shoots x-rays as it rotates around the body. Special detectors are located directly opposite the x-ray source and each time the x-ray source completes one full rotation, a computer then produces a 2D image or a ‘slice’ of the patient. In a 16-slice scanner there are 16 detectors and thus each revolution acquires 16 slices simultaneously.
When a full slice is completed, the image is stored, the motorised bed moved forward incrementally and then the process is repeated to produce another image slice. This process continues until the desired number of slices is collected. A full body CT can be acquired in less than one minute in most patients.
Image slices can be displayed individually, which allows the region of interest to be viewed without with any superimposition of other structures. This is invaluable in orthopaedics and at HSR we routinely use CT scanning in the assessment of elbow dysplasia, specifically with regard to the diagnosis fragmentation of the coronoid process (FCP). CT is also the gold standard for the diagnosis of humeral intercondylar fissures, a problem commonly seen in Spaniels and Labradors.
Individual images can also be ‘stacked’ together by the computer to generate a 3D image of the patient. These reconstructed 3D images can then be rotated and be viewed from any angle. They, in turn, can be used to make custom implants and cutting guides using sophisticated computer software and 3D printing technology.
Which cases is CT most effective in?
- For assessment of complex anatomic areas such as the skull or spine
- Planning of complex fracture repair
- For soft tissue and oncological cases
- Investigation of diseases of the thorax and abdomen, as the rapid acquisition of the images negates the movement artefact that would occur during an MRI scan.
Our CT scanner
Our Canon Medical Aquilion Lightning 16 is a 16-slice CT scanner, customised for use in small animals, with a high-resolution detector incorporating the smallest elements of any CT scanner, giving slices of 0.5mm. The scanner is particularly high speed, providing fast examination times and reducing the amount of anaesthesia required.