Magnetic resonance imaging or MRI, is an imaging modality that utilizes radiofrequency and a strong magnetic field to obtain diagnostic images. Many people may not realize that all MRI machines or scanners are not the same or manufactured by the same company. The types of MRI scanners can often be differentiated by their magnetic field strength or tesla (T), such as 1.5T. MRI scanners can also be identified by construction or orientation, such as open, closed or standing.
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High-Field MRI Scanners
High-Field MRI scanners use a magnet of at least 1.5T and up to 3.0T, in a clinical setting. These are typically identified as closed MRI scanners. Some people may also call this type a “tunnel” or “tube”. A 1.5T MRI scanner is useful because it provides great image quality, fast scan times, and the ability to evaluate how certain structures in the body function. The 3.0T MRI scanner, which is double the strength of the 1.5T MRI scanner, is great for visualizing very fine detail, such the vessels of the brain or heart. There is also an ultra-high field scanner which has a strength of 7.0T. It is not widely available and is typically used for research.
Low-Field MRI Scanners
Low-Field MRI scanners have a range of 0.23T-0.3T and are typically identified as open MRI scanners. These scanners are useful for people who are claustrophobic or unable to have a closed MRI scan due to weight restrictions or body circumference. Low-field or open MRI scanners, are typically open on the sides which allow greater visibility and comfort for the claustrophobic patient. Low-field MRI scanners have decreased image quality and require a longer scan time compared to high-field MRI scanners, but they provide an alternative for those who otherwise would not be able to have an MRI scan.
Stand-Up MRI Scanners
Stand-Up MRI scanners are useful for those who are unable to lie down or who have conditions where the body part needs to be visualized while standing, bending or sitting. This type of scanner is best used for the spine and joints, where weight-bearing is necessary. With this type of scanner, a person could also watch TV or read a book, which is not an option with open or closedl MRI scanner.
Extremity MRI Scanners
Extremity MRI scanners are limited-use scanners that specifically scan the extremities, which include elbows, hands, wrists, fingers, knees, ankles, feet and toes. These scanners provide an alternative to the full-body scanners. Unfortunately, there are not many extremity scanners available.