Calibration Phantom for Quantitative Tomography Analysis of Biodistribution of Magnetic Nanoparticles

Abstract

Ferrofluids are being investigated for cancer treatments such as magnetic drug targeting (MDT) and magnetic heating treatments with the aim of treating the cancer locally, since magnetic nanoparticles with attached drugs are concentrated within the target region. Thus, the side effects are considerably reduced. One of the crucial factors for the success of these therapies is the magnetic nanoparticle distribution. Microcomputed X‐ray tomography (XμCT) has been introduced as adequate technique for non‐destructive three‐dimensional analysis of biological samples enriched with magnetic nanoparticles. The biological tissue specimens, in this case tumor bearing mice after intra‐tumoral magnetic nanoparticle injection, have been analyzed by means of XμCT. Complementary measurements have been performed by magnetorelaxometry (MRX). This technique enables a sensitive quantification of magnetic nanoparticles down to few nanograms. For multi‐phase samples, such as biological tissue enriched with magnetic nanoparticles the polychromasy and beam hardening artifacts occurring in XμCT with conventional X‐ray tubes cause severe problems for quantitative density determination. This problem requires an appropriate calibration of the polychromatic tomography equipment enabling a semi‐quantitative analysis of the data. For this purpose a phantom system has been implemented. These phantoms consist of a tissue substitute containing different amounts of magnetic nanoparticles. Since the attenuation of the beam also depends on the thickness i.e. the path length of the beam transmitting the object, the reference sample has been defined to a cone shape. Thus, with one phantom the information about the magnetic nanoparticle concentration as well as the attenuation in dependence of the path length can be determined. Two phantom systems will be presented, one based on agarose‐gel and one based on soap.