Frequently Asked Questions - MRI
What is Magnetic Resonance Imaging (MRI)?
MRI is an imaging method based principally upon sensitivity to the presence and properties of water (more precise: mobile hydrogen protons). “Water” is present in abundance in the body, making MRI a useful tool in assessing physiologic and pathologic processes.
In MR terminology “water” describes both “free water” (liquids like urine, CSF, cystic fluids) and “bound water” (intra- and extracellular fluid in tissues). Pathologic processes change the water content and properties in tissues. Examples include cysts or abscesses (i.e. cavities containing free water), edema (i.e. increase in water content of tissue), inflammation and neoplasia (i.e. presence of cells that normally would not be present).
MRI is very sensitive in picking up these abnormalities in water distribution and composition.
Images are created by subjecting the patients to a magnetic field and monitoring the behavior of tissues in this environment. MRI does not involve radiation, and is therefore considered a very safe imaging modality.
What are possible applications for MRI in Veterinary Medicine?
Neural tissue disorders - brain, spinal cord, peripheral nerves
MRI is the best modality to evaluate the nervous system. It is non-invasive and has the best contrast resolution of all imaging modalities.
Musculoskeletal disorders - MRI can be used not only to examine bony structures, it is superior to all other imaging modalities when evaluating muscles, tendons and ligaments.
Soft tissue tumors, abscesses, draining tracts - MRI is excellent in evaluating extent and margins of soft tissue lesions. In case of chronic wounds and draining tracts, it will help identifying foreign bodies within the wound. It will allow evaluation of bone involvement, assessment of resectability of a lesion and diagnosis of regional lymph node enlargement.
Nasal/paranasal sinus, orbital and ear disorders - MRI is very useful when evaluating patients with signs of nasal disease, disorders of the orbit and disorders of the ear. It is the modality of choice when extension of the disease process into the brain is suspected.
Thoracic and abdominal disorders - MRI complements other imaging modalities when evaluating patients with thoracic and abdominal disorders. Screening for enlarged lymph nodes, evaluation of thoracic or abdominal wall mass lesions and diagnosis of abdominal organ parenchymal lesions are only few examples of indications for thoracic or abdominal MRI examinations.
Are there any risks associated with the MRI examination?
MRI is considered an extremely safe imaging modality.
The examination is performed under general anesthesia. This is necessary to keep the animal from moving and minimize examination time. There is a certain risk associated with anesthesia, which is not different when performing an MRI examination from other instances where anesthesia is required.
Due to the strong magnetic field in the room, the presence of metal in the room or within the patient can potentially cause a problem. In humans, complications have been reported in patients with metallic structures in the brain (surgical aneurysm clips, metallic shrapnel fragments) or in the eye (metallic shavings in the eyes of welders). Examples for metallic structures potentially present in animals include identification microchips, metallic sutures, orthopedic implants and gunshot/birdshot pellets. To the best of our knowledge, not a single hazardous complication due to the presence of metal in a Veterinary patient has been reported. For safety reasons, we suggest to wait 3 months between implantation of a microchip or an orthopedic device and an MRI examination. If metal is present in a patient close to the area of interest, artifacts might interfere with image interpretation. In very rare instances, a study might be non-diagnostic due to a metallic foreign body in the patient.
In rare cases, a serious complication (Systemic Nephrogenic Fibrosis; SNF) has been seen in human patients after administration of MRI contrast material. This has not been reported in animals.