Whole-head MEG systems based on the low-Tc SQUID sensors utilize liquid helium to reach the temperature around 4 K. Until recent years, a typical MEG system needed a liquid helium refill once or twice per week. However, the increasing cost and the lack or limited availability of liquid helium for regular fillings have motivated commercial MEG manufacturers to develop zero-boiloff systems that maintain the low temperature without losing helium. In this section, we present the challenges, history, and state of the art of low helium consumption systems which employ a compact helium liquefier in open-loop, closed-loop, or integrated configurations. In addition we discuss possibilities for the future in liquid helium-free systems incorporating cryocoolers.
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