A High-Throughput, Arbitrary-Waveform, MPI Spectrometer and Relaxometer for Comprehensive Magnetic Particle Optimization and Characterization

Abstract

Magnetic Particle Imaging (MPI) is a promising new tracer modality with zero attenuation deep in tissue, high contrast and sensitivity, and an excellent safety profile. However, the spatial resolution of MPI is limited to around 1 mm currently and urgently needs to be improved for clinical applications such as angiography and brain perfusion. Although MPI resolution is highly dependent on tracer characteristics and the drive waveforms, optimization is limited to a small subset of possible excitation strategies by current MPI hardware that only does sinusoidal drive waveforms at very few frequencies. To enable a more comprehensive and rapid optimization of drive waveforms for multiple metrics like resolution and signal strength simultaneously, we demonstrate the first untuned MPI spectrometer/relaxometer with unprecedented 400 kHz excitation bandwidth and capable of high-throughput acquisition of harmonic spectra (100 different drive-field frequencies in only 500 ms). It is also capable of arbitrary drive-field waveforms which have not been experimentally evaluated in MPI to date. Its high-throughput capability, frequency-agility and tabletop size makes this Arbitrary Waveform Relaxometer/Spectrometer (AWR) a convenient yet powerfully flexible tool for nanoparticle experts seeking to characterize magnetic particles and optimize MPI drive waveforms for in vitro biosensing and in vivo imaging with MPI.

Multifrequency magnetic particle imaging enabled by a combined passive and active drive field feed‐through compensation approach

“…The frequency dependence results from capacitive coupling between the two coils and the frequency‐dependent nonuniform current distribution along the wire in each coil. The suppression values reported by other research groups using gradiometer coils for passive decoupling are comparable …”

“…One promising approach to get access to functional parameters is particle excitation at multiple frequencies . By multifrequency excitation, the frequency dependence of the relaxation times can be obtained and employed for parameter estimation.…”

“…However, to enhance the access to the mentioned parameters, a signal chain that allows for a wide range of adjustable frequencies is required. Only magnetic particle spectrometers (MPS) that feature this kind of frequency flexibility have been developed . To the knowledge of the authors, an MPI scanner that offers a wide range of excitation frequencies and imaging capability has not been published before.…”

Combining magnetic particle imaging and magnetic fluid hyperthermia in a theranostic platform

“…Instead, a sinusoidal excitation and linear bias field are superposed to test the aggregate response of a sample in the applied magnetic field space (Tay et al 2016). This system can reconstruct 1D MPI point-spread functions (PSFs) (Croft et al 2016; Tay et al 2016). The AWR was used to test the quality of MPI at the higher frequencies used in MFH.…”

Magnetic particle imaging for radiation-free, sensitive and high-contrast vascular imaging and cell tracking

“…This technique relies on analyzing the harmonic spectra of the MPI signal (Magnetic Particle Spectroscopy - MPS) to determine if the SPIOs are still within the cell or have been released to the outside after cell death. With new particle and arbitrary excitation design 33 , it may be possible to further distinguish stem-like states versus apoptotic or non-stem states.…”