Drive-Field Frequency Dependent MPI Performance of Single-Core Magnetite Nanoparticle Tracers

Abstract

The drive-field frequency of Magnetic Particle Imaging (MPI) systems plays an important role for system design, safety requirements and tracer selection. Because the commonly utilized MPI drive-field frequency of 25 kHz might be increased in future system generations to avoid peripheral nerve stimulation, a performance evaluation of tracers at higher frequencies is desirable. We have studied single-core magnetite nanoparticles that were optimized for MPI applications, utilizing Magnetic Particle Spectrometers (MPS) with drive-field frequencies in the range from 1 kHz up to 100 kHz. The particles have core diameters of 25 nm and a hydrodynamic size of 77 nm. Measurements in the frequency range above 5 kHz were carried out with a newly designed MPS system. In addition, to exclude possible particle interaction, samples of different concentrations were characterized and compared.

Magnetic Characterization of Clustered Core Magnetic Nanoparticles for MPI

“…The transmission electron Manuscript For magnetic characterization, suspensions (i.e., liquid) as well as freeze-dried (i.e., immobilized) particle samples were prepared. The MPS was recorded at a drive field with amplitude 25 mT/μ 0 and frequency f 0 = 25 kHz with a commercial MPS system (Bruker BioSpin MRI GmbH; Germany) as well as with a multi-parameter setup the details of which are described in [5]. The latter MPS system allows measurements at excitation frequencies between 1 and 100 kHz; optionally static background fields of up to 20 mT can be applied.…”

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

“…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.…”

“…13,14,20 One promising approach to get access to functional parameters is particle excitation at multiple frequencies. 10,13,21,22 By multifrequency excitation, the frequency dependence of the relaxation times can be obtained and employed for parameter estimation. The drive field frequency dependence is mainly caused by the different relaxation mechanisms, which are N eel (internal magnetization change) and Brownian relaxation (rotation of bulk material).…”

“…Only magnetic particle spectrometers (MPS) that feature this kind of frequency flexibility have been developed. [21][22][23] 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.…”