Research of Highly Sensitive High-Temperature Superconducting Pickup Coils for Magnetic Particle Imaging

Magnetic particle imaging (MPI) and other medical magnetic detection technologies often employ coil sensors to detect signals. Although high-temperature superconducting (HTS) pickup coils offer excellent nearzero-resistance background interference at low frequencies, enabling very high signal-to-noise ratio, the internal losses and equivalent resistance of HTS pickup coils increase significantly above 1 kHz which is necessary for MPI. This article establishes a theoretical calculation model for the losses of HTS tape materials under MPI environment (i.e., combined external driving field and induced secondary magnetic field with high frequency) as a pickup coil, including the generation mechanisms and loss calculations of superconducting loss, Eddy current loss, and hysteresis loss produced by various thin films of the superconducting tape, as well as the analysis of their correlation with coil sensitivity. Based on the model analysis and mechanical conditions of HTS tapes, a series of HTS pickup coils were fabricated and their performance was verified. The numerical and experiment results show that Eddy current loss of the HTS pickup coil is the dominant loss under various loss mechanisms in MPI conditions. HTS materials with thinner copper stabilizers can greatly reduce internal coil losses near MPI frequencies, significantly improving the sensitivity limit. Furthermore, this article also presents the development of a mechanical MPI system optimized for the HTS pickup coil and an ultrahigh sensitivity MPI imaging experiment. A small 32-mm-diameter HTS pickup coil made of copper-free HTS tape was used in the MPI system, which successfully imaged 100 μg of superparamagnetic iron oxide nanoparticles from 100 mm away.