Relaxation-based viscosity mapping for magnetic particle imaging

TL;DR

This paper introduces a viscosity mapping method for Magnetic Particle Imaging (MPI) that estimates nanoparticle relaxation times without prior nanoparticle information, validated through extensive experiments across various viscosities and frequencies.

Contribution

It presents a novel relaxation time constant estimation technique for MPI-based viscosity mapping that does not require prior nanoparticle data.

Findings

Effective viscosity mapping within biologically relevant ranges.

Validated method across multiple frequencies and field strengths.

Demonstrated potential for functional MPI applications.

Abstract

Magnetic Particle Imaging (MPI) has been shown to provide remarkable contrast for imaging applications such as angiography, stem cell tracking, and cancer imaging. Recently, there is growing interest in the functional imaging capabilities of MPI, where color MPI techniques have explored separating different nanoparticles, which could potentially be used to distinguish nanoparticles in different states or environments. Viscosity mapping is a promising functional imaging application for MPI, as increased viscosity levels in vivo have been associated with numerous diseases such as hypertension, atherosclerosis, and cancer. In this work, we propose a viscosity mapping technique for MPI through the estimation of the relaxation time constant of the nanoparticles. Importantly, the proposed time constant estimation scheme does not require any prior information regarding the nanoparticles. We validate this method with extensive experiments in an in-house magnetic particle spectroscopy (MPS) setup at four different frequencies (between 250 Hz and 10.8 kHz) and at three different field strengths (between 5 mT and 15 mT) for viscosities ranging between 0.89 mPa.s to 15.33 mPa.s. Our results demonstrate the viscosity mapping ability of MPI in the biologically relevant viscosity range.