Cryogenics
Cryogenics
Magnetoencephalography
Magnetoencephalography
In September 2022, Absolut System supplied, delivered, installed, commissioned and trained a Helium purification and liquefaction system for the neuroimaging platform’s Magnetoencephalography (MEG) system at the Centre d’Exploration et de Recherche Médicales par Émission de Positons (CERMEP).
CERMEP’s MEG department offers the neuroscience community a non-invasive technique for functional exploration of the human brain. By definition, Magnetoencephalography (MEG) is a functional brain imaging technology that involves recording live, close to the head, the magnetic fields generated by the brain’s neurons. The cerebral magnetic field is around 1 billion times weaker than the earth’s magnetic field, so the imager is placed in an examination room (a Faraday cage-type shielded room) to avoid being subjected to potential external magnetic fields.
CERMEP’s MEG imager consists of a special cryostat, a helmet covering the subject’s head and 275 SQUIDS (Superconducting QUantum Interference Device) magnetic flux sensors, enabling measurements with excellent spatial resolution and sub-millisecond temporal resolution. To achieve sufficient measurement sensitivity, these sensors are immersed in liquid helium at 4.2K (-269°C), the temperature at which their superconducting capabilities can be expressed. The department is equipped for auditory, visual, tactile and electrical sensory stimulation.
Helium management
in closed loop
Helium management in closed loop
Helium evaporated by the MEG is collected in a low-pressure network
then compressed to 200 bars and stored in 600-liter spheres.
Helium evaporated by the MEG is collected in a low-pressure network
then compressed to 200 bars and stored in 600-liter spheres.
It is then expanded, purified, liquefied and stored in a 150-liter vacuum super-insulated tank (dewar) close to the MEG room, awaiting liquid transfer for top-up. The scrubber and liquefier installed use Pulse-Tube cryocoolers, offering high reliability, low maintenance and low vibration and noise levels. Helium liquefaction capacity was measured at 31 liters/day by Absolut System engineers, making CERMEP completely self-sufficient in helium management.
The proposed system consists of the following components:
- An automatic helium scrubber integrated between the high-pressure gas storage and the liquid helium storage dewar,
- A liquid helium storage dewar,
- A Pulse-Tube cold head for helium liquefaction, integrated on the storage dewar,
- HP/BP helium compressor,
- The various hoses for closed-cycle operation of the purifier, cold head and compressor.