Specific absorption rate as a poor indicator of magnetic resonance-related implant heating.

Recent publications of the magnetic resonance safety profile of neurostimulators, cardiac pacemakers, and other implanted devices imply that these devices are no longer a contraindication for magnetic resonance imaging. It is very promising that patients who have these implanted devices may in the future no longer be denied an important diagnostic modality. On the other hand, the safety recommendations given in a number of publications included the maximum permissible whole-body specific absorption rate (SAR). This is one factor indicating potential heating, but there are a number of other factors that may have an even higher impact on the potential heating of tissue in the vicinity of leads or implanted devices. Using only the whole-body SAR as a recommendation for a safety profile is potentially dangerous.

[Safety and safety limits in MRI]. / Sicherheit und Grenzwerte in der MRT.

The influence of electromagnetic fields on humans through the use of magnetic resonance tomography is an ongoing topic in the scientific literature. However, the contents of relevant standards and legal regulations governing the operation of MR equipment are less well known. We summarize the actual status and give an overview of the national and international bodies in charge of generation and publication of guidelines and regulations.

Comparison of the threshold for peripheral nerve stimulation during gradient switching in whole body MR systems.

PURPOSE: To compare thresholds for peripheral nerve stimulation from gradient switching in whole body magnetic resonance (MR) equipment of different design. MATERIALS AND METHODS: Threshold data obtained in three experiments were reformatted into a single joint data set describing thresholds for anterio-posterior (AP) gradient orientation and Echo Planar Imaging (EPI) waveforms with bipolar ramp times between 0.07 and 1.2 ms. Reformatting included the use of: a) the rate of change of the maximum field in the patient space as a measure of gradient output, b) lowest observable thresholds, c) lognormal distribution of thresholds, and d) equal standard deviation (SD) of all samples. RESULTS: The joint data fit a hyperbolic threshold function. The residues were not significantly different between experiments. CONCLUSION: Then expressed in appropriate format, the thresholds for peripheral nerve stimulation in volunteers for whole body MR equipment can be described with a hyperbolic threshold curve with rheobase 18.8 +/- 0.6 Tesla/second and chronaxie 0.36 +/- 0.02 milliseconds.