Simulation-based design and characterization of a microwave applicator for MR-guided hyperthermia experimental studies in small animals

Abstract

Purpose:The objective of this study was to design and characterize a 2.45 GHz microwave hyperthermia applicator for delivering hyperthermia in experimental small animals to 2 -4 mm diameter targets located 1 -3 mm from the skin surface, with minimal heating of the surrounding tissue, under 14.1 T MRI real-time monitoring and feedback control. Materials and methods:An experimentally validated 3D computational model was employed to design and characterize a non-invasive directional water-cooled microwave hyperthermia applicator. We assessed the effects of: reflector geometry, monopole shape, cooling water temperature, and flow rate on spatial-temperature profiles. The system was integrated with realtime MR thermometry and feedback control to monitor and maintain temperature elevations in the range of 4 -5 °C at 1 -3 mm from the applicator surface. The quality of heating was quantified by determining the fraction of the target volume heated to the desired temperature, and the extent of heating in non-targeted regions.Results: Model-predicted hyperthermic profiles were in good agreement with experimental measurements (Dice Similarity Coefficient of 0.95 -0.99). Among the four considered criteria, a reflector aperture angle of 120 °, S-shaped monopole antenna with 0.6 mm displacement, and coolant flow rate of 150 ml/min were selected as the end result of the applicator design. The temperature of circulating water and input power were identified as free variables, allowing considerable flexibility in heating target sizes within varying distances from the applicator surface. 2 -4 mm diameter targets positioned 1 -3 mm from the applicator surface were heated to hyperthermic temperatures, with target coverage ratio ranging between 76 -93 % and 11 -26 % of non-targeted tissue heated. Conclusion:We have designed an experimental platform for MR-guided hyperthermia, incorporating a microwave applicator integrated with temperature-based feedback control to heat deep-seated targets for experimental studies in small animals.

Nanomaterials responding to microwaves: an emerging field for imaging and therapy

“…85 However there are noted limitations in the MW applicators, with further work looking to model the design of more focussed applicators. 86 Multiwalled carbon nanotubes (MWNTs) have been extensively characterised for their MW absorption properties. [87][88][89][90] With this in mind, recent work 91 has sought to combine these desirable properties with composite nanomaterials (comprising lithium, zinc, cobalt and iron oxide) through integration into the matrix.…”

“… 85 However there are noted limitations in the MW applicators, with further work looking to model the design of more focussed applicators. 86 …”

Preclinical Studies in Small Animals for Advanced Drug Delivery Using Hyperthermia and Intravital Microscopy

“…The directional microwave hyperthermia applicator was previously described by Curto et al and Faridi et al [29,30]. In brief, a monopole was implemented with a coaxial cable, as illustrated in Figure 4A.…”

Experimental assessment of microwave ablation computational modeling with MR thermometry

“…Models of microwave ablation (MWA) are widely used during the design and optimization of ablation applicators, and are also frequently used to characterize applicator performance as part of regulatory submissions. [1][2][3][4] Models are also used for comparative assessment of energy delivery strategies 5 and for assessing the impact of various sources of uncertainty on ablation outcome. [6][7][8][9][10] Recently, there has been growing interest in the development of computational models for guiding planning of clinical ablation procedures, and for assessing treatment outcome.…”

“…Computational models of thermal ablation procedures aim to predict the extent of the thermal ablation zone, which is a function of the transient temperature profile within the heated tissue, for a candidate set of treatment delivery parameters. Models of microwave ablation (MWA) are widely used during the design and optimization of ablation applicators, and are also frequently used to characterize applicator performance as part of regulatory submissions 1–4 . Models are also used for comparative assessment of energy delivery strategies 5 and for assessing the impact of various sources of uncertainty on ablation outcome 6–10 .…”