# Ultra-sensitive SQUID instrumentation for MEG and NCI by ULF MRI

## TL;DR

This paper discusses the development of ultra-sensitive SQUID systems optimized for biomagnetic applications like MEG and ultra-low-field MRI, emphasizing noise reduction, coil design, and field tolerance.

## Contribution

It introduces a hybrid pick-up coil system and a single-channel SQUID setup with enhanced noise performance and field tolerance for diverse biomagnetic imaging applications.

## Key findings

- Hybrid coil system improves sensitivity for various noise sources.
- Single-channel SQUID achieves near-intrinsic noise levels.
- Design enables field-tolerance up to 200 mT for MRI applications.

## Abstract

The requirements for the construction of ultra-sensitive SQUID instrumentation as used in biomagnetism are presented. Typically, SQUIDs are inductively coupled to pick-up coils and for this arrangement one can improve the noise performance by increasing the sensing coil area. To achieve optimum sensitivity one has to consider the signal-to-noise ratio (SNR), which is an intricate interplay between source characteristics and noise origin. It turns out that separate pick-up coil designs are needed for various noise characteristics even for an identical source. Hence, a hybrid system with differently sized pick-up coils presents the best option for multipurpose applications. A single channel system with close to SQUID intrinsic noise level is also described. This is possible by utilizing a special dewar design and thereby enabling a further increase in SNR. Such a system might be used for current density imaging and neuronal current imaging by ultra-low-field magnetic resonance where it also must be able to be field-tolerant to up to 100-200 mT.