Nanoparticle-mediated radiofrequency capacitive hyperthermia: A phantom study with magnetic resonance thermometry

Abstract

In hyperthermia, focusing heat generation on tumour tissues and precisely monitoring the temperature around the tumour region is important. To focus heat generation in radiofrequency (RF) capacitive heating, magnetic nanoparticles suspended in sodium carboxymethyl cellulose (CMC) solution were used, based on the hypothesis that the nanoparticle suspension would elevate electrical conductivity and RF current density at the nanoparticle-populated region. A tissue-mimicking phantom with compartments with and without nanoparticles was made for RF capacitive heating experiments. An FDTD model of the phantom was developed to simulate temperature increases at the phantom. To monitor temperature inside the phantom, MR thermometry was performed intermittently during RF heating inside a 3Tesla MRI magnet bore. FDTD simulation on the phantom model was performed in two steps: electromagnetic simulation to compute specific absorption rate and thermal simulation to compute temperature changes. Experimental temperature maps were similar to simulated temperature maps, demonstrating that nanoparticle-populated regions drew more heat than background regions. Nanoparticle-mediated RF heating could mitigate concerns about normal tissue death during RF capacitive hyperthermia.

Electroquasistatic Model of Capacitive Hyperthermia Affected by Heat Convection

“…Furthermore, if the dielectric properties of tissues in between the two electrodes can be modulated in a similar manner, more power may be delivered [32] 0.69 [32] (172 − j1, 552) 0 lung 264.9 [33] 0.42 [33] (264.9 − j945) 0 tumor 402 [33] 0.68 [33] (402 − j1, 530) 0 to the tumor. Potential materials to increase the electrical conductivity include nanoparticles [34] and saline water [35]. In treating liver tissue of rabbits with RF ablation [35], hypertonic saline (36% NaCl) was injected to decrease the electrical impedance η of liver tissue from 116.3 Ω to 73 Ω, where…”

“…which implies that σ is increased by about 2.5 times (at 8 MHz). Alternatively, solution containing nano-particles was used to increase the electrical conductivity of local tissues by less than 10% in capacitive hyperthermia [34]. Figure 4(a) shows the original (unmodulated) case where the adipose with ( , σ) = (13.7, 0.0245) is marked in light-blue, and the two electrodes are marked by thick curves.…”

Systematic review of pre-clinical and clinical devices for magnetic resonance-guided radiofrequency hyperthermia

“…-Capacitive: a two-channel capacitive RF heating system, consisting of four electrodes operating at 26 MHz, was evaluated on a phantom aiming to heat a deep-seated target region in which electrical conductivity was elevated by nanoparticle mediation [57,58]. When one electrode pair was activated, the other electrode pair was electrically isolated to prevent RF current leakage between the electrodes.…”

Role of Simulations in the Treatment Planning of Radiofrequency Hyperthermia Therapy in Clinics

“…Temperature increase due to SAR from RF fields has been numerically and experimentally validated with phantom models that provide good agreement and demonstrate the possibility of using simulations to ensure safety during MRI [52]. The feasibility of using nanoparticles with RF systems has been reported with phantom models to increase tissue temperature in localized and deep-seated tumor regions [49, 50, 77]. The addition of magnetic nanoparticles to regions drew more heat than that by surrounding regions in both simulations and MR thermometry [50], and a two-channel RF system exhibited superior capability in localizing heat to the nanoparticle-mediated tumor region compared with that in the normal region [77].…”