Magnetic Particle Imaging for Magnetic Hyperthermia Treatment: Visualization and Quantification of the Intratumoral Distribution and Temporal Change of Magnetic Nanoparticles <i>in Vivo</i>

Abstract

Purpose: Magnetic hyperthermia treatment (MHT) is a strategy for cancer therapy using the temperature rise of magnetic nanoparticles (MNPs) under an alternating magnetic field (AMF). Recently, a new imaging method called magnetic particle imaging (MPI) has been introduced. MPI allows imaging of the spatial distribution of MNPs. The purpose of this study was to investigate the feasibility of visualizing and quantifying the intratumoral distribution and temporal change of MNPs and predicting the therapeutic effect of MHT using MPI. Materials and Methods: Colon-26 cells (1 × 10 6 cells) were implanted into the backs of eight-week-old male BALB/c mice. When the tumor volume reached approximately 100 mm 3 , mice were divided into untreated (n = 10) and treated groups (n = 27). The tumors in the treated group were directly injected with MNPs (Resovist ®) with iron concentrations of 500 mM (A, n = 9), 400 mM (B, n = 8), and 250 mM (C, n = 10), respectively, and MHT was performed using an AMF with a frequency of 600 kHz and a peak amplitude of 3.5 kA/m. The mice in the treated group were scanned using our MPI scanner immediately before, immediately after, 7 days, and 14 days after MHT. We drew a region of interest (ROI) on the tumor in the MPI image and calculated the average, maximum, and total MPI values and the number of pixels by taking the threshold value for extracting the contour as 40% of the maximum MPI value (pixel value) within the ROI. These parameters in the untreated group were taken as zero. We also measured the relative tumor volume growth (RTVG) defined by (V−V0)/V0, where V 0 and V are the tumor volumes immediately before and after MHT, respectively. Results:

Comparative Study of Extracellular and Intracellular Magnetic Hyperthermia Treatments Using Magnetic Particle Imaging

“…were measured with a caliper every day and the tumor volume (V) was calcu- After the MPI studies, we drew a region of interest (ROI) on the tumor in the MPI image ( Figure 2) and calculated the average and maximum MPI values in the same manner as that in our previous papers [14] [15]. We also calculated the number of pixels within the ROI and then calculated the total MPI value from the product of the average MPI value and the number of pixels.…”

“…MPI is capable of imaging the spatial distribution of MNPs in positive contrast without any background and with high sensitivity and spatial resolution [11]. We recently have developed an MPI scanner based on the field-free-line encoding scheme [12] [13] and succeeded in Open Journal of Applied Sciences imaging the intratumoral distribution of MNPs and quantifying its temporal change in vivo [14] [15]. We also showed that MPI is useful for predicting the therapeutic effect of MHT [14] [15].…”

Magnetic Particle Imaging for Quantitative Evaluation of Tumor Response to Magnetic Hyperthermia Treatment Combined with Chemotherapy Using Cisplatin

“…It has been reported that the cytotoxicity of CDDP increases linearly with increasing temperature when combined with hyperthermia 25) . We previously reported that the temperature in a tumor increased after the start of MHT and reached a higher temperature with increasing concentration of MNPs 26) . Thus, it is expected that the therapeutic effect of CDDP increases with increasing concentration of MNPs in the tumor or the dose of CDDP can be reduced when combined with MHT.…”

Magnetic field dependence of heating property of resovist® for magnetic hyperthermia

“…Among the magnetic materials for biomedical applications, superparamagnetic nanoparticles have been gaining more attention due to their potential as not only therapeutic agents for magnetic hyperthermia but also as diagnostic agents for magnetic particle imaging, which has been proposed to visualize the spatial distribution of superparamagnetic nanoparticles recently . So far, a MRI contrast agent named Resovist® that is clinically approved for human use has been widely used to evaluate magnetic hyperthermia and/or magnetic particle imaging applications . To the best of our knowledge, there is little or no information on its heating property dependence on the applied magnetic field.…”