MRI or CT Imaging?

With recent advancements in technology CT and MRI imaging are becoming more readily available to a wider number of veterinary practices so which imaging technique should the vet recommend for the patient, CT or MRI.

Both imaging techniques have advantages and disadvantages, some of which include time, cost, availability and personnel preference. In deciding which technique suits your patient needs it is important to consider the anatomical region of the body under investigation. CT - Computed tomography is an X-Ray based technique which uses a high powered X-Ray tubes which an X-Ray beam passes through the body to create an image. The CT imaging technique uses ionising radiation, and requires extensive radiation protection measures. The images produced are in the transverse plane but with multi detectors, the resolution of the image can be reconstructed in additional planes giving a 3D representation.

CT is useful in cases which involve the general skeleton, fracture repair, angular limb deformities, in the thorax region such as pulmonary parenchyma and has superior metastatic screening when compared to X-Rays. It is the most common technique used at the moment for the diagnosis of elbow disease, abdominal evaluation and is excellent for determining osseous diseases. In the future though you may see a switch in the favour of MRI imaging techniques for diagnosis in these areas of the body.

The MRI - Magnetic resonance imaging on the other hand is a safe non evasive radiation free technique that uses magnetic fields and radiofrequency pulses to create an image of the anatomy under examination by creating a map of hydrogen's atoms in the field of view (FOV).

The equipment and maintenance is much more expensive for an MRI scanner compared to that of the CT scanner. Unlike the CT though, the images produced can be acquired in any plane (sagittal, dorsal, tranverse or oblique). The 3D image can be further enhanced by the use of a contrast medium generally Gadolinium, which is a rare earth element making it easier to distinguish anatomy from pathology. MRI is a slower technique than CT imaging as it can take up to 45 minutes to scan an animal, however it will take 45 minutes to reconstruct the image produced by the CT scanner anyway.

MRI is extensively used in cases dealing with spine and brain images where the CT may over look significant lesions. MRI is without question the imaging modality of choice for neurology. MRI is a better imaging technique in the assessment of nasal cavities and frontal sinuses and detection of the presence of fluid or mass legions within the ears and external ear canals.
MRI has greater potential for evaluation of joint or muscular injuries in the pelvic, elbow and shoulder regions also increasingly used in abdominal region and whole body screening. Spectacular images can be produced of any soft tissue structure using MRI and this can be particularly useful when dealing with cancer cases.