Enhanced Heat Transfer and Thermal Dose Using Magnetic Nanoparticles During HIFU Thermal Ablation—An In-Vitro Study

Abstract

Avoiding collateral damage to healthy tissues during the high intensity focused ultrasound (HIFU) ablation of malignant tumors is one of the major challenges for effective thermal therapy. Such collateral damage can originate out of the need for using higher acoustic powers to treat deep seated or highly vascularized tumors. The objective of this study is to assess the utility of using magnetic nanoparticles (mNPs) during HIFU procedures to locally enhance heating at low powers, thereby reducing the likelihood of collateral thermal damage and undesired destruction due to cavitation. Tissue phantoms with 0% (control), 1% and 3% mNPs concentrations by volume were fabricated. Each tissue phantom was embedded with four thermocouples (TCs) and sonicated using transducer acoustic powers of 5.15 W, 9.17 W, and 14.26 W. The temperature profiles during the heating and cooling periods were recorded for each embedded TC. The measured transient temperature profiles were used for thermal-dose calculations. The increase in the concentration of mNPs in the tissue phantoms, from 0% to 3%, resulted in the rise in the peak temperatures for all the TCs for each acoustic power. The thermal dose also increased with the rise in the concentration of mNPs in the tissue phantoms. For the highest applied acoustic power (14.26 W), the peak temperature at TC 1 (T1) in tissue phantoms with 1% and 3% mNPs concentrations increased (with respect to tissue phantom with 0% (control) mNPs concentration) by 1.59Â and 2.09Â, respectively. For an acoustic power of 14.26 W, the time required to achieve cellular necrosis as defined by a 240 equivalent min thermal dose was approximately 75 s in the absence of mNPs, 14 s for the 1% concentration, and 8 s for the 3% concentration. Magnetic nanoparticles have the potential to significantly reduce the time for HIFU thermal-ablation procedures. They can also decrease the likelihood of collateral damage by the propagating beam in HIFU procedures by reducing the intensity required to achieve cellular necrosis.

Nanoparticle-assisted ultrasound: A special focus on sonodynamic therapy against cancer

“…In particular, the achievement of elevated temperatures when the region of interest is deep or hypervascularized can be problematic. Actually, a solution could be to enhance the acoustic power or the exposition time, however it would increase the risk of side effects, as skin burns and nerve injury [ 47 , 48 ]. Thus, various types of micro and nano–bubbles [ 49 ], as well as other particles [ 50 ], were proposed in combination with HIFU for therapy and diagnostic imaging.…”

“…These structures are indeed able to enhance HIFU-associated mechanical effects, providing cavitation nuclei [ 48 ]. Furthermore, they increase the acoustic attenuation with a consequent temperature rise [ 51 ], reducing the ultrasound intensity and the exposure time required to obtain bioeffects [ 47 ].…”

Remotely Activated Nanoparticles for Anticancer Therapy

“…Also, magnetic NPs could be used for SDT [148,155,156]. Ebrahimi et al investigated the sonodynamic properties of iron oxide nanoparticles in a breast carcinoma cell line.…”

Comparison of Heat Transfer Enhancement Between Magnetic and Gold Nanoparticles During HIFU Sonication

“…The amount of absorbed ultrasound energy for the 0.0625% mNPs and 0.125% gNPs, derived from the initial slope of the temperature trace [13], is provided in Table 2. An initial time of 2.5 s is chosen to compute the slopes.…”

“…One strategy for reducing the adverse effects associated with high intensities and long exposure times in HIFU ablation procedures is to introduce microcapsules and nanoparticles (NPs) at the tumor site [13,14]. Sun et al [15,16] reported the effects of PLGA-coated Fe 3 O 4 microcapsules in HIFU therapy and have found enhancement in hyperthermia due to the microcapsules.…”