Development and Performance Analysis of a Novel SQUID-Based Cryogenic Detection Line for Ultra-Low-Field MRI

Ultra-low-field (<10mT) magnetic resonance imaging (MRI) opens the possibility to perform medical imaging with enhanced T1 contrast [1], facilitating efficient diagnosis of different clinical conditions, at only a fraction of the cost and infrastructure of conventional MRI. Yet, as signal vanishes with lower applied magnetic field, the use of ultra-sensitive and ultra-low noise detectors becomes paramount to acquire medically relevant images in a reasonable timeframe. Superconducting QUantum Interference Device (SQUID), because of their wide detection bandwidth offering a flat frequency response and their exceptional noise figures, are particularly well-suited for this application. Here, we report on the design and performances of a SQUID-based 10mT MRI system built by the Chipiron team. In particular, we report on the realization of a novel cryogenic flux transformer cooled by a dry 4K cryostat showing greatly suppressed Johnson-Nyquist noise. In comparison with previous SQUID-based MRI design [2], which were based on a low-temperature superconducting coil connected to a SQUID sensor within a non-metallic liquid helium cryostat, Chipiron’s detection line offers vastly improved operational ease. More importantly, our setup, designed with market’s requirement in mind, also permits unprecedented versatility in the geometric design of the RF receive coils while achieving clinically relevant images.

[1] Bödenler M. et al., MRM., 86(4):2049–­2063 (2021)

[2] Seton et al., Cryogenics 45 (2005)