Non-Invasive Registration of Magnetic Particles in a Biological Medium Using Magnetic Field Sensors

Abstract

Methods of noninvasive registration of magnetic particles and nanoparticles in a biological medium are considered. A simple analytical formula is obtained for calculating the maximum distance from the magnetic field sensor to the object under study, linking this distance with the parameters of magnetic particles and the threshold magnetic sensitivity δB of the sensor. Test magnetic measurements of aqueous suspensions containing superparamagnetic iron oxide particles with a concentration of 1-5 wt.% were carried out. The measured and estimated values of the maximum distance between the magnetized magnetic particles and the magnetic field sensor at which their registration is possible are compared. In the case when magnetic particles acquire magnetization in the Earth’s magnetic field, they are registered at a distance no greater than 23 mm from the magnetic field sensor with a strength of δB =10 nT. The estimate of this distance obtained according to the proposed formula is 8 mm. In another case, in a constant magnetic field of 70 mT, magnetic particles acquired a magnetization of 1.6-1.8 A⋅m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /kg, and the recorded and estimated distances (49 and 48 mm) practically coincide. It is shown that for some types of commercial magnetic particles having high values of magnetization (> 50 A⋅m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /kg), the specified distance can be < 200 mm, that is, they can be registered at any depth of their occurrence in the human body during the process of theranostics. At low concentrations ≤10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−5</sup> wt.% of magnetic particles, they can be controlled only by SQUID magnetometer having δB ≤10 fT.