Evaluation of a Mouse-Sized Radial Gradiometer Receive Coil for Magnetic Particle Imaging

Magnetic particle imaging (MPI) uses the nonlinear magnetization response of superparamagnetic iron-oxide nanoparticles (SPIONs) for fast, sensitive, and quantitative imaging of SPION distributions in biological systems. However, the SPIONs’ signal is overshadowed by the much larger excitation signal, necessitating the use of gradiometric receive coils, which often suffer from reduced homogeneity and adverse cross-talk with the MPI system. We develop a new high-sensitivity receive coil by extending the radial geometric design for gradiometers, where cancellation coil parts have larger diameter, thus providing stronger coupling to the excitation field. This enables us to both reduce cancellation coil windings and increase the winding density of the smaller-diameter pick-up coil part, achieving greater sensitivity and homogeneity. The developed mouse-sized receiveonly (Rx) coil is optimized for the use in Bruker’s preclinical MPI scanner and its performance is compared to the scanner’s built-in transmit-receive (TxRx) coil. Power transfer measurements and the particle signal-to-noise ratio show a sensitivity improvement of (20 – 21) dB in the range of (10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> – 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>) kHz compared to the TxRx coil. The sensitivity varies within ±9% across the field-ofview, providing higher homogeneity than standard gradiometers. With reconstructed images of SPION dilutions using perimag® particles, we show an iron limit-of-detection of 8.5 ng for the novel Rx coil, which is a ten-fold improvement compared to the original TxRx coil. The high sensitivity and homogeneity provided by the Rx coil will advance the application of MPI in preclinical research by enabling the visualization and quantification of lower iron concentrations, as well as providing higher spatial and temporal resolution.