Probing viscosity via relaxation in magnetic particle imaging

Abstract

Magnetic Particle Imaging (MPI) is a high-contrast imaging modality with applications such as angiography, stem cell tracking, and cancer imaging. In recent years, MPI was shown to be a potential functional imaging modality through \color MPI" techniques, where responses from different nanoparticles can be distinguished. These techniques can be extended to differentiate environmental conditions or states such as different viscosities. Increased viscosity in vivo was shown to be related with various diseases such as hypertension, atherosclerosis, and cancer. Through color MPI techniques, MPI shows a great promise for mapping viscosity and for helping in the diagnosis of these important diseases. This thesis demonstrates the capability of MPI to map viscosities through an estimation of relaxation time constant of nanoparticles. This capability is verified through an extensive experimental work with a magnetic particle spectrometer (MPS) setup that is custom designed. These experiments are conducted for the biologically important viscosity range between 0.89 mPa.s and 15.33 mPa.s, at four different frequencies (between 250 Hz and 10.8 kHz) and at three different field amplitudes (between 5 mT and 15 mT). The results demonstrate MPI's viscosity mapping capability in a biological range.