Non-calorimetric determination of absorbed power during magnetic nanoparticle based hyperthermia

Abstract

Nanomagnetic hyperthermia (NMH) is intensively studied with the prospect of cancer therapy. A major challenge is to determine the dissipated power during in vivo conditions and conventional methods are either invasive or inaccurate. We present a non-calorimetric method which yields the heat absorbed during hyperthermia: it is based on accurately measuring the quality factor change of a resonant radio frequency circuit which is employed for the irradiation. The approach provides the absorbed power in real-time, without the need to monitor the sample temperature as a function of time. As such, it is free from the problems caused by the non-adiabatic heating conditions of the usual calorimetry. We validate the method by comparing the dissipated power with a conventional calorimetric measurement. We present the validation for two types of resonators with very different filling factors: a solenoid and a so-called birdcage coil. The latter is a volume coil, which is generally used in magnetic resonance imaging (MRI) under in vivo condition. The presented method therefore allows to effectively combine MRI and thermotherapy and is thus readily adaptable to existing imaging hardware.

Theory of superlocalized magnetic nanoparticle hyperthermia: rotating versus oscillating fields

“…For example, we propose to use well separated isotropic nanoparticles in an aerogel matrix where only the magnetic moment can rotate. There are proposals for the technical realisation of a rotating applied field, see, e.g., [34] and [67]. For example, in [34] the authors discuss possible experimental realisation of generating a rotating applied field.…”

“…Also non-calorimetric technics [68], [69] are used to measure the energy losses in various applied fields. In [67], the authors present the validation of a resonators with a so-called birdcage coil. This represents another realisation of rotating magnetic field.…”

Magnetic Fluid Hyperthermia Based on Magnetic Nanoparticles: Physical Characteristics, Historical Perspective, Clinical Trials, Technological Challenges, and Recent Advances

“…c) Size‐dependence of coercivity for magnetic particles. Reproduced with permission [91 . ] Copyright 2017, RSC Publishing Group.…”

“…[ 90 ] Nevertheless, difficulty in standardization and matching experimental set‐ups with precise thermal models results in some degree of uncertainty. [ 91 ] Magnetic methods, on the other hand, provide an accurate measurement of SAR/SLP values, however they do not function in the clinical MFH regime. For more details regarding the SAR/SLP measurement techniques, readers are recommended to study the review articles by Petri‐Fink and co‐workers [ 92 ] and Andreu and Natividad.…”

Non-exponential magnetic relaxation in magnetic nanoparticles for hyperthermia

“…Concerning the physics and material science challenges, i) the efficiency of the heat delivery, ii) its accurate control and iii) its precise characterization are the most important ones. Concerning the latter, various solutions exists which includes modeling the exciting RF magnetic field with some knowledge about the magnetic properties of the ferrite [15][16][17][18][19] , measurement of the delivered heat from calorimetry 15,17,[20][21][22] , or determining the dissipated power by monitoring the quality factor change of a resonator in which the tissue is embedded 23,24 .…”