Exploring sensitivity and resolution for cell tracking with Magnetic Particle Imaging: the effects of cell proliferation and intracellular nanoparticle relaxation

Abstract

Magnetic particle imaging (MPI) is an emerging modality that directly detects SPIOs.our first aim is to quantify the dilution of SPIOs in breast cancer cells in vitro using MPI. MPI signal is generated from a combination of Néel (internal rotation of magnetization) and Brownian (physical rotation of nanoparticle) relaxation. Brownian relaxation of SPIO is influenced by the nanoparticle’s surroundings and we hypothesize this may have implications for detecting partially immobilized intracellular SPIOs. A second aim is to determine how MPI signal and resolution change when SPIOs are intracellular (live cells) compared to free SPIOs (lysed cells). A reduction in MPI signal was measured from SPIO-labeled 4T1 cells following proliferation in vitro. Our measurements of intracellular iron are in close agreement with a theoretical reduction of 66%( day 1) and 87% (day 2). Future work will examine this in vivo. As ferucarbotran was incorporated into MSC, a reduction in MPI sensitivity and improvement in resolution were measured for lysed cells. MPI cell tracking is in its infancy and these studies contribute important knowledge towards monitoring proliferative cells in vivo and optimizing resolution and sensitivity for cell detectio