Magnetic Resonance Imaging (MRI) in Cats

Where an MRI Performed in Cats?

Though the availability of MRI for pets is increasing, there are still only a few institutions or hospitals in the United States that offer MRI services to cats. Large institutions that offer the service may have long waiting periods, up to a couple of weeks.

The primary reason that MRI is limited for pets is expense. With equipment prices reaching $1,000,000 and more, it is unlikely your local practitioner owns one. In addition, the cost of running the unit is prohibitive to most professionals with the exceptions of well-funded private institutions or subsidized universities. In fact, many veterinary hospitals offering the service have arranged access to the units at nearby human hospitals instead of having the unit on their premises. It’s possible that your pet may have an MRI at the same hospital that treats you.

What Is Involved in an MRI?

Depending on the seriousness of the disease, your cat may or may not be hospitalized several days before the scan. The day of the scan your cat will not be allowed to eat; although water will be available. A catheter will be placed to give medications and anesthesia. Once the cat is under anesthesia, he will be transported to the MRI unit. A scan of the brain takes approximately two hours to generate. Though the scanning times are getting shorter with newer units, MRI is a modality in which imaging of the area of interest takes a long time. MRI uses magnetic fields and radio waves to form an image. The technology is therefore considered less invasive than radiographs, which uses potentially harmful X-rays to make images of the body. Since there is no ionizing radiation involved with MRI, no harmful effects to the body have been noted with its use to this date. The risk of doing the exam actually comes from the need for general anesthesia, which is considered very low, and not from the use of the magnetic field or the radio waves generated by the unit.

Prior to the scan, it is very important that you inform the specialists if your cat has any metal implants. This includes pins, wires and screws that may have been used in the past to repair a fracture. Microchips, old bullets and metallic clamps used during surgeries such as spays are also important to know. Preliminary X-rays will often reveal these metallic items even if you are unaware of their presence. Metal will degrade the quality of the MRI images. It can also distort and obscure an important area.

Immediately after the examination is completed, your cat will be transferred to the recovery room. It will take him about two hours to be fully awake. Often, the imaging specialist makes the diagnosis as soon as the images appear on the screen. Common brain diseases that are diagnosed with MRI include brain tumors, brain infarcts (lack of blood to an area of the brain), brain abscesses and inflammation of the external layers of the brain (meninges). In the spine, disease such as herniated discs and tumors are commonly seen.

What Does the MRI Unit Look Like?

The MRI unit looks like a large cube with a small hole in the center. This cube houses a powerful magnet. The patient is placed completely inside the MRI unit, actually in the middle of the magnet. MRI takes advantage of the many protons found at the atomic level in the body. To understand this technology, imagine these protons as spinning tops. These protons are all spinning in a random manner within the body. When your pet is placed in the magnetic field, all the protons in his body start spinning in a synchronized fashion. This spinning creates a low energy field. When the unit’s radio waves reach the cat, the protons move to a high energy level. Simply stated, the patient is absorbing energy in the form of radio waves. When the radio waves are turned off, the protons will release the energy they have absorbed, in the form of more radio waves. The MRI unit then recovers the radio waves emitted from the body and uses them to generate a computer image.

What Can an MRI Show in Cats?

The technology of the MRI allows a veterinary radiologist to take a closer look at the inside of the patient’s head. An X-ray of the head shows only the bones of the skull. The contents of the head (that is the brain) remain hidden inside the skull. In other words, the bones of the skull cover the brain. A popular analogy to explain this concept is the “sliced bread analogy.” Without slicing the bread, you see only the oven-baked golden external surface. If we want to look at the white part of the bread we have to slice the bread and remove one of the pieces. A slice of bread is the equivalent of one MRI image. Taking this analogy further, thinner or thicker slices can be made and the bread can even be sliced in any orientation. This is a major advantage over CT.

At Tufts University School of Veterinary Medicine, MRI is now considered the standard technique to assess the brain and the spinal cord. During the last two years there has been an accelerated interest in making MRI more accessible to pet owners and the public is taking advantage of it. However, the best initial treatment for your cat is the treatment given by your family veterinarian. Despite wonderful imaging modalities such as MRI, a complete physical examinations and routine veterinary checkups is what will ensure the good health and long life of your cat.