TwinTree Insert

18-05 Regulations and Legal Aspects

t is difficult to get a proper overview of regulations concerning MRI equipment on national or international levels. For the operator or operating company of an MR apparatus is imperative to check and follow the local regulations and ensure that the equipment does fulfill the local requirements. In some countries, the re­gu­la­tions are more stringent than in others; in other countries, they are nonexistent.

Since the early 1980s, a number of national and international health and ra­di­a­tion pro­tec­tion boards established recommendations concerning magnetic resonance equip­­ment and spectroscopic units; we refer only to some of them: ⇒ BAuA 1998, ⇒ ICNIRP 1998, 2009, ⇒ FDA 1982, 1988, and ⇒ NRPB 1981, 1992.

All limits set by them were recommended levels, not mandatory ones. In the mean­time, however, some manufacturers start­ed using field strengths beyond 2.0 T, dif­fe­rent pulse sequences, and gra­dient switching procedures without any reported ill effects.

Adjustments made do not cover all possible medical applications of MR imaging, although the US-American Food and Drug Administration extended the designation of non­sig­ni­fi­cant risk to MR systems with field strengths of up to 4.0 T in 1997 and 8.0 T in 2003 (4.0 T in neonates younger than one month) [⇒ FDA 2003]. The In­ter­na­ti­o­nal Electrotechnical Commission followed suit in 2016 [⇒ IEC 2016].

At present, there is an investigational device exemption of the US Food and Drug Administration for fields up to 9.4 Tesla.

The RF energy during an MR examination must be adjusted to avoid pro­duc­ing a core temperature rise in excess of 1°C and localized heating greater than 38°C in the head (3.2 W/kg averaged over head mass), 39°C in the trunk (or 10 W/kg over any 10 grams), and 40° C in the extremities (or 10 W/kg over any 10 grams) [⇒ NEMA 2008].

spaceholder redThe legal requirements must be guaranteed by the manufacturer because the user in general is unable to check power output, gradient strength, or even field strength. This guarantee must cover authorized hardware and software updates after the initial installation. Specially designed computer programs usually su­per­vi­se the power output of MR systems and will not allow or will interrupt any imaging or spectroscopy procedure exceeding those limits considered safe.

According to the specific FDA criteria for SAR (specific absorption rate) limits [⇒ FDA 2003], the SAR must not be greater than:

spaceholder darkblue4 W/kg averaged over the whole body for any 15-minute period;

spaceholder darkblue3 W/kg averaged over the head for any 10-minute period; or

spaceholder darkblue8 W/kg in any gram of tissue in the extremities for any period of 5 minutes.

An update of the US-American FDA guidelines was published in 2021 [⇒ FDA 2003].

spaceholder redSome European countries have also issued national SAR restriction. No common de­­no­­mi­­na­­tor has been found.

In July 2016, the European Commission's Directive on electromagnetic fields (EMF) came into force. At present, this directive addresses only short-term effects, not yet possible long term effects. And, also at present, MRI equipment is excluded from the regulations of this directive [⇒ European Commission 2013, 2015].