Digital SQUID Array for Portable Low-Field MRI System for Combat Diagnostics

Recent research has shown that Superconducting Quantum Interference Devices (SQUIDs) may be used to measure the very weak magnetic signal in Magnetic Resonance Imaging at ultra-low magnetic fields in the milli-tesla range or below. However, the signal-to-noise ratio (SNR) is quite low, requiring very long averaging times to obtain reasonable spatial resolution. The use of large arrays of SQUIDs would be expected to enhance the SNR, but feedback control circuitry and inter-channel crosstalk in conventional analog SQUIDs would make scaling to large arrays difficult to implement in a practical system. Hypres proposes to make use of fully integrated digital SQUID systems, based on Rapid Single Flux Quantum (RSFQ) digital logic, without external feedback loops and crosstalk issues. Furthermore, the digital outputs can be multiplexed in flexible and scalable ways, so that the number of input/output lines may be dramatically reduced. In Phase I, we propose to design, fabricate, and test a digital SQUID array with 4 sensors, and demonstrate how digital multiplexing may be achieved. In Phase II, we will extend these results to an array of at least 128 elements, and demonstrate this in a prototype MRI system.