Helium-free MRI

In case of spontaneous loss of field, the temperature of the superconducting coils increases and the pressure in the cooling system increases to a medium pressure that is fully contained. This pressure is four times lower than the pressure that was used when filled during manufacturing (at room temperature). The magnet is fully designed to accommodate this and meets the ASME and PED standards related to pressurized vessels.

IEC International standard 60601-2-33 describes the particular requirements for the safety of magnetic resonance equipment for medical diagnosis. Since the BlueSeal magnet has a fractional amount of helium contained in a closed cooling system, no helium can escape during a loss of field. As a result, the following IEC requirements do not apply, which helps to simply on-site safety procedures:

• NO provisions for supply of liquid cryogen. e.g procedures to be performed after gas release or precautions against lack of oxygen.
• NO safety provisions in the event of a quench. e.g emergency plan in the event of a quench

The resulting magnet performance is amongst the best in the industry, with excellent homogeneity (≤ 0.9 ppm, at 45 cm DSV), high gradients linearity (amplitude 45 mT/m, slew rate 200 T/m/s) and a superb field-of-view of 55 cm.

In case of a patient emergency, the system will ramp-down immediately after pushing the Emergency Ramp Down Unit button (ERDU). It will take < 3 days to be back in operation. In case an object is stuck in the bore (injector, cleaning tool, etc.), it will take about 1 hour to de-energize the magnet from the service environment on the operator console and <24 hours to be back in operation⁶. In both cases, all helium moves to gas state and remains contained in the fully sealed cooling system.