MRI Scanner Types: Permanent vs. Superconducting MRI. Closed vs. Open MRI
Most conventional high field strength MRI scanners are superconducting magnets that utilize cryogens to maintain the magnetism of the MRI.
These cryogens must be replenished and can unexpectedly discharge the cryogens into the atmosphere (AKA MRI quenching) and potentially injuring a patient. Most superconducting MRI scanners are considered a “Closed MRI“ and have an elongated tubular shaped gantry into which a movable table positions the body part to be examined into the center of the gantry. The tubular gantry resembles a coffin and leads many patients to label closed MRI scanners as the ‘Tube of Terror“.
Open MRI scanners are generally permanent magnets including a large iron core magnetized by electricity or “ramped up” with the magnetism maintained by a relatively small electric current. “Open” MRI configurations have an open side or the head is not required to be within the center of the MRI in order to examine the extremities or spine as in the Esaote G-Scan Brio MRI. Claustrophobia is almost nonexistent in Open MRI scanners like the Esaote G-scan MRI.
MRI scanners are also described by the strength of the associated magnetic field measured in Tesla. High field strength MRI scanners are 1.5-3.0 Tesla magnets. Mid-field-strength MRI scanners are generally 0.5T-1.0 Tesla. Low field strength MRI scanners have magnetic field strengths of <0.5 Tesla.
Generally high field strength MRI scanners are closed superconducting MRI scanners and are generally utilized for imaging of the brain, heart, and vascular scanning where high speed imaging and high signal to noise are required. Generally, low field strength MRI scanners are smaller and require less shielding and are utilized for in-office orthopedic and spine MRI installations and produce much less metallic artifact from metallic orthopedic and spinal surgical implants which is a distinct advance in these practices.