High magnetic field strengths are generally desirable in MRI because the higher the field, the higher the image resolution. Superconducting magnets produce the highest fields, yet lower cost electromagnets (as used by FONAR) and permanent magnets (the base of Esaote’s scanners) can produce enough resolution for many studies. According to Esaote’s Strategic Marketing Department, optimising all their scanners’ components allows good image quality for bone, muscles and tendons in joints at the relatively low fields they use (0.25T for their G-scan for example). They see musculoskeletal scans being increasingly performed in dedicated systems.
“We believe it is a waste of healthcare resources to use a 3T system for a routine knee examination,” they say. FONAR also cite cost-effectiveness, along with high performance and a desire to “provide a set of unique imaging applications” as main R&D drivers.
The future development – and use – of MRI scanners could, however, be thrown into jeopardy by the 2004 European Commission (EC) directive restricting occupational exposure to electromagnetic fields (Directive 2004/40/EC). This was due to come into effect in April 2008 and would, in its present form, limit the use of all MRI systems, including the open scanners. But as a result of further investigations showing workers routinely exceed the recommended limits for exposure with no evidence of side-effects and lobbying – in part by the UK’s Institute of Physics – the implementation has been stalled until April 2012.