Using MicroCT Imaging Technique to Quantify Heat Generation Distribution Induced by Magnetic Nanoparticles for Cancer Treatments

Magnetic nanoparticles have been used in clinical and animal studies to generate localized heating for tumor treatments when the particles are subject to an external alternating magnetic field. Currently, since most tissue is opaque, the detailed information of the nanoparticle spreading in the tissue after injections cannot be visualized directly and is often quantified by indirect methods, such as temperature measurements, to inversely determine the particle distribution. In this study, we use a high resolution microcomputed tomography (microCT) imaging system to investigate nanoparticle concentration distribution in a tissue-equivalent agarose gel. The local density variations induced by the nanoparticles in the vicinity of the injection site can be detected and analyzed by the microCT system. Heating experiments are performed to measure the initial temperature rise rate to determine the nanoparticle-induced volumetric heat generation rates (or specific absorption rate (SAR$W/m3$⁠)) at various gel locations. A linear relationship between the measured SARs and their corresponding microCT pixel index numbers is established. The results suggest that the microCT pixel index number can be used to represent the nanoparticle concentration in the media since the SAR is proportional to the local nanoparticle concentration. Experiments are also performed to study how the injection amount, gel concentration, and nanoparticle concentration in the nanofluid affect the nanoparticle spreading in the gel. The nanoparticle transport pattern in gels suggests that convection and diffusion are important mechanisms in particle transport in the gel. Although the particle spreading patterns in the gel may not be directly applied to real tissue, we believe that the current study lays the foundation to use microCT imaging systems to quantitatively study nanoparticle distribution in opaque tumor.