MRI stands for magnetic resonance imaging. MRI is a relatively new imaging modality in veterinary medicine. It was initially utilized on a very limited basis in veterinary patients in the late 1980’s. Its use was predominantly at a few referral hospitals and universities. At that time is was utilized almost exclusively to visualize the head and brain. Now MRI’s are commonly available at referral centers and veterinary schools. They are utilize to image orthopedic structures, the brain, the head (sinuses, oral cavity, eyes ) the brain, spinal cord and spinal column, abdomen, and on a limited bases the thorax.
MRI allows imaging of different parts of the body through a non invasive technique. The types of images generated with an MRI can can be orientated on the long axis of the patient, these are called axial views, across the long access of the patient which are transverse views and moving from top to bottom, called coronal views.These views are provided in sequential slices that are mere millimeters thick. MRI’s afford visualization of the internal architecture of the area being studied from all these vantage points. The MRI also provides differentiation in tissue types and fluids within the area being studied.
All this information is accumulated by the MRI creating a magnetic field that changes the movement or spin of the hydrogen nucleus (proton) within the area being studied. Hydrogen is an element that is abundant within the body with each of the tissues in the body containing differing amounts of hydrogen. Normally, nuclei of elements spin or resonance. The magnet causes some of the hydrogen protons to spin in a fixed frequency. Through the influence of the magnet the change in proton frequency causes increase in energy within the proton, when the magnets influence is removed the protons return to their previous frequency (spin) and they release the absorbed energy.
This process then allows us to visualize tissues at different phases of the protons return to it’s normal, resting position. Some of the more common sequences are referred to as T1 relaxation, T2 relaxation, STIR sequence, FLAIR sequence and gradient echo sequencing.
There are many different types of MRI, mostly described by the size of their magnet. Recently low field MRI’s have been used in veterinary medicine very successfully and this has allowed machines to be more readily accessible to veterinary practices. As you might imagine, MRI’s require a great deal of expertise to interpret and are usually reviewed by a veterinary radiologist and also veterinary surgeons, neurologists and internists.
MRI’s are valuable diagnostic tools, they are not used for treatment of illnesses, but the identification of the changes that occur as a result of diseases.With the benefit of a MRI we are able to appreciate structural deformities that cannot be appreciated on plain radiographs. For example, since the brain is encased by the bones of the skull we are unable to see it on a radiograph, only the structures of the bony skull. The MRI allows us not only to appreciate the contours of the brain, but its inner architecture. The MRI also affords us a chance to see the changes within tissues, such as inflammation, fluid accumulation, altered blood flow, and tumors that would otherwise not be appreciated on a radiograph. MRI’s are often used to evaluate the brain, spinal cord, joints(such as the knees, shoulder,etc), and the abdomen. Through the use of the different sequences we discussed previously, different information can be gleaned about the systems beingg studies.
A MRI is non-invasive. However, your pet will need to be anesthetized since any movement will interfere with the quality of the study. During the MRI a contrast agent called gadolinium will be administered to learn more about the area of your pets body being studied.
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