MRI for Pets

Safari has MRI diagnostic capabilities for your pet.

coil is placed around the area of pet to be imaged

Magnetic Resonance Imaging (MRI) for pets is the Gold Standard for imaging the spine and brain. At Safari we use a human MRI system that is rented “Afterhours” for pet use. We have pet specific protocols and settings of the machine that have been developed over the past 10 years that ensures optimal images. The pet is first placed under general anesthesia and then a coil is placed around the area to be imaged, then the pet is placed inside the magnet.

What is an MRI?

The MRI uses magnets to produce diagnostic images of the internal tissues of the body. MRI uses powerful magnetic fields that force protons in the body to align with that field. Hydrogen ions are the protons in the body and are combined with oxygen as H2O forming water which is ubiquitous in body tissues. Hydrogen ions are charged like miniature magnets with positive and negative poles and when you put one magnet next to another magnet such as in the MRI field, their poles align. Radiofrequency waves are then introduced that will cause the hydrogen ions to reverse alignment with the MRI’s magnetic field for a short period of time. The radio waves are then turned off causing the hydrogen ions to bounce back into alignment with the MRI magnetic field. This realignment releases or emits new radio waves that can be detected and the speed with which this happens reveals information about the tissue which in turn is used to paint a digital picture of the body part being examined. Because the radio waves that are being detected are very low in signal strength, detecting them is difficult and therefore the whole MRI machine must be contained in a copper lined sealed box called a Faraday cage. This cage of copper prevents any outside radio waves from interfering in the signal emitted by the hydrogen ions in the tissue. Stronger magnets produce stronger tissue signal and thus result in better images.

Figure 1. The MRI uses magnets to produce diagnostic images of the internal tissues of the body. This is our Phillips 3T MRI at Safari.

New 3-Tesla MRI at Safari League City

Safari is committed to providing the most advanced care for your pets. To better serve our clients and patients we have recently upgraded from our open MRI system to a 3-Tesla (3T) MRI. A 3T MRI generates a magnetic field that is twice as strong as a normal 1.5T MRI, and 10 to 15 times as strong as open MRI scanners. MRI magnet strength is measured in Tesla units after Nicola Tesla. One Tesla is 10,000 times the power of the earth’s gravitational pull. 3-Tesla MRIs provide advantages for veterinarians not realized in MRI’s used for humans.

Figure 2. The bore of powerful “High Field” magnets is circular while “Low Field” magnets have a clamshell opening.
  • Pets must be anesthetized for an MRI! Therefore, the most important reason to use a 3-Tesla machine in veterinary practice is the reduced scan time. The 3-Tesla MRI is 4 times faster than a 1.5 Tesla machine. The “Open” MRIs are only 0.3 Tesla and scan times with these machines are 10 times longer than with a 3T machine.
  • The 3T MRIs provide higher detailed images produced by scanning in tiny slices. Slices as small as 1mm are essential in smaller pets such as dachshunds with spinal cord disease. A 1.5 Tesla usually scans a 3mm slice.
  • The higher resolution of the 3T MRI produces more detailed images, which are beneficial when diagnosing pathological conditions involving the brain, spine, and musculoskeletal system.
  • The resolution and clarity also allow radiologists to identify smaller lesions and anatomical structures that cannot be seen with less powerful machines.
  • Blood flow can be seen without contrast with a 3T magnet. These machines provide high-quality vascular imaging, decreasing the need for invasive catheter studies.
  • The higher quality scans can detect smaller abnormalities of fractures or joints.
  • They offer detailed imaging of ligaments, tendons, and cartilage to assess the stability of joints.
  • Canine cruciate rupture can now be evaluated including the degree of damage to the meniscus. 3T MRI is also one of the most sensitive methods for detecting bone and other types of infections that cause tissue changes. See Figure 3.
Knee imaging
Figure 3. Knee imaging with 0.3Tesla, 1.5 Tesla, and 3 Tesla. Showing same knee comparison. Red box shows lesion only imaged
with the 3 Tesla machine. The Open 0.3 Tesla MRI scan time is 60 minutes, and the 3 Tesla MRI is 15 minutes.
Only the 3T MRI machine shows the bone infection

In the brain there is an overall increased clarity and resolution, and blood vessels are individually imaged. See Figure 4. All of this helps veterinarians ensure a more accurate diagnosis, which leads to better outcomes for pets thanks to early diagnosis and a better understanding of which parts of the brain are affected.

MRI of the same brain
Figure 4. MRI of the same brain at the same location (red rectangle) using a 1.5T and a 3T. MRI. Notice the detail and vascular structures that can be seen with the 3T image.

Pets must be anesthetized for MRI
Figure 5. Pets must be anesthetized for MRI while humans can be told to just lie still.

Anesthesia is difficult in the MRI setting as non-magnetic anesthesia machines and non-magnetic monitoring devices must be used. In addition to being non-magnetic, the devices must not emit any interfering radio waves, or the image quality could be compromised. Human monitors of the anesthesia cannot be in the room with the pet, so all monitoring is done from the control room.

Low Field
Figure 6. The “Low Field” open MRI is shown here. The open refers to the clamshell arrangement of the machine. This is compared to the circular bore of the more powerful “High Field” machine.

The Open MRI is commonly used in veterinary medicine as they are less expensive, but their power is only 0.3T to 0.5T and they are designated as “Low Field” MRI. Their advantage is that they use a permanent magnetic field whereas the “High Field” 1.5T to 3T machines use an electromagnetic field requiring liquid nitrogen to cool the electric coil used to generate the magnetic field. Permanent magnets are not strong enough to create a “High Field” magnetic flux. These machines have a smaller magnetic field size as well as low field strength. Adequate images can be obtained but the pet usually must undergo several hours of scan time under anesthesia.