Safety in High field MRI: Practical Aspects

Aim:The aim of this paper is to contribute to formalization of some technical/practical safety aspects in terms of risk management in MR sites, that are actually not formalized by law, but are completely under the responsibility of safety manager of the MRI system. The considerations shown in the paper are the results of the, practical experience acquired in the management of the 4T MR scanner, installed at the University of Trento - Italy, and validated by the Health Minister . Materials and Methods: The technical aspects discussed in present work are: 1) electrical system for the oxygen monitoring and emergency ventilation systems, 2) ventilation air change rates. 1)The oxygen monitoring and emergency ventilation systems of MR room should have a correct and safe power supply system. This system should manage in safe mode the limit condition of malfunction of the main oxygen monitoring unit:this condition should be converted in an immediate activation of the emergency ventilation system. Due to this the main oxygen monitoring unit and the emergency ventilation system should have the same power supply of the MR scanner (uninterruptible power supply - UPS, and/or Power Engine) adding a normally open contact. With this technical solution, in normal working conditions, the emergency ventilation will be activated only if, in case of low concentration of oxygen, the main oxygen monitoring unit closes the contact of a relay. This relay will be released, in case of a limit condition of no power supply in the main oxygen monitoring unit, and the emergency ventilation will be activated. 2) The right ventilation air change rates is evaluated on the basis of specific emergency procedure for every MR site.This value warranties the possibility to operate in the worst case of a quench in the MR room. This values is obtained considering specific parameter , like the RM room volume, the quantity of liquid Helium in the magnet Dewar, and the minimum time for evacuation of the room in case of quench. Results and Discussion: On the basis of these parameters and of the consideration that the quench is a casual phenomenon which cannot be described by specific mathematical laws, but can be explained with two high occurrence probability situations, like: 1)or parabolic not all the liquid He evaporates, with the consequence that the quench is a multistage process like multi expansions 2)or the quench is a transient with exponential characteristic, where the percentage of He gas produced can be calculated it is possible to calculate the right ventilation air change rates, necessary for the management of a quench. In the worst case of quench pipe out of working, considering a minimum height in the room equal to 170 cm, the time necessary for the operator to warranty the evacuation emergency procedure of the patient from the MR room, is 35-40 seconds, if the number of ventilation air change is equal to 20. Conclusions:. Both technical solutions, which are perfectly working, show as the knowledge of technical and safety aspects in the MR site, improve the safety standards, and both are a valid instrument for the Responsible Expert in the MR risk management.