Magnetic resonance imaging machines, or MRI machines, are used to conduct tests that utilize a magnetic field and radio waves to produce images of internal body structures and organs, according to WebMD. Open MRI machines have a larger opening than typical machines, and are used for obese patients.
Open MRI machines may be preferred by patients who are uncomfortable in small, confined areas. However, open MRI machines are not as common as normal MRI machines, as some open machines have fewer magnets that normal MRI machines. Some open machines cannot perform certain MRI tests due to magnets not surrounding the entire body, states WebMD.