MRIs must keep their helium and vacuum leaks to a minimum for patient safety and system availability. Annual maintenance costs for these systems can range from $100,000 to $150,000, and the yearly liquid helium costs between $8,000 and $12,000. Hence, it's critical to check for leaks in the magnet liquid-helium vessel and auxiliary helium gas refrigeration system.

A miniaturized series of helium-leak detectors makes for more effective leak checking around magnetic resonance imaging (MRI) facilities. The 8-kg Pico units from MKS Instruments, Wilmington, Mass. (mksinst.com) are easily carried in one hand. The small configuration is a complete system that performs comparably to larger leak detectors. The Pico series of mass spectrometers use an ion-trap principle for adequate sensitivity to quickly detect and locate small leaks (1 × 10^-7 atm cc/s minimum detectable leak rate for atmospheric helium leak detection and 1 × 10^-10 atm cc/s for vacuum leak detection). The unit typically takes less than one sec. to detect a helium leak.

The best MRI imagers use high core magnetic fields that need low-temperature superconducting magnets. These systems consist of a liquid-helium-core vessel (boiling point: -268.9°C) and a recirculating helium refrigeration system (-195.5°C). An insulating vacuum transitions the helium refrigerant to room temperature.

A “sniffer” probe on the Pico extends up to 20 feet from the instrument to detect leaks in hard-to-reach areas. A test port is also available to detect inward-leakage in vacuum insulating layers of the MRI. Developers say the detector has been tested during operation within magnetic fields greater than any stray fields that might be encountered within an MRI environment.