Magnetic fluid hyperthermia (MFH) is a promising avenue for noninvasive or minimally invasive therapies including tissue ablation, hyperthermia, and drug delivery. Magnetic particle imaging (MPI) is a promising new medical imaging modality with wide-ranging applications including angiography, cell tracking, and cancer imaging. MFH and MPI are kindred technologies leveraging the same physics: Both MFH and MPI function by exciting iron oxide magnetic nanoparticles with AC magnetic fields. In this manuscript, we show that this can be leveraged for combined MPI-MFH. The gradient fields employed in MPI can benefit MFH by providing high resolution targeting anywhere in the body, and a dual system provides opportunities for real-time diagnostic imaging feedback. Here we experimentally quantify the spatial localization of MFH using MPI gradient fields with a custom MPI-MFH system, demonstrating approximately 3 mm heating resolution in phantoms. We show an ability to precisely target phantom components as desired and provide heating of approximately 150 W g-1. We also show preliminary simultaneous MPI-MFH data.
Magnetic particle imaging (MPI) has emerged as a new imaging modality that uses the nonlinear magnetization behavior
of superparamagnetic particles. Due to the need to avoid contamination of particle signals with the simultaneous excitation
signal, MPI transmit systems require different design considerations from those in MRI, where excitation and detection
are temporally decoupled. Specifically, higher order harmonic distortion in the transmit spectrum can feed through to and
contaminate the received signal spectrum. In a prototype MPI scanner, this distortion needs to be attenuated by 90 dB at all
frequencies. In this paper, we describe two methods of filtering out harmonic distortion in the transmit spectrum. The first
method uses a Butterworth topology while the second a cascaded Butterworth-elliptic topology. We show that whereas the
Butterworth filter alone achieves around 16 and 32 dB attenuation at the second and third harmonics, the cascaded filter
can achieve around 65 and 73 dB at these harmonics. Finally, we discuss how notch placement in the stopband can also be
applied to design highpass filters for MPI detection systems.
Magnetic particle imaging (MPI) is a new medical imaging modality that maps the instantaneous response of superparamagnetic
particles under an applied magnetic field. In MPI, the excitation and detection of the nanoparticles occur
simultaneously. Therefore, when a sinusoidal excitation field is applied to the system, the received signal spectrum contains
both harmonics from the particles and a direct feedthrough signal from the source at the fundamental drive frequency.
Removal of the induced feedthrough signal from the received signal requires significant filtering, which also removes part
of the signal spectrum. In this paper, we present a method to investigate the impact of temporally filtering out individual
lower order harmonics on the reconstructed x-space image. Analytic and simulation results show that the loss of particle
signal at low frequency leads to a recoverable loss of low spatial frequency information in the x-space image. Initial experiments
validate the findings and demonstrate the feasibility of the recovery of the lost signal. This builds on earlier work
that discusses the ideal one-dimensional MPI system and harmonic decomposition of the MPI signal.
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