This study aimed to adapt the clinically used BSD-500 microwave hyperthermia system for experiments in mice by designing and performing base validation of a dedicated small-animal applicator. The objective was to produce an accessible, easy-to-use, 3D-printable applicator and to perform electromagnetic and thermal validation prior to in vivo testing.
The applicator was developed iteratively. Design iterations combined hands-on testing with mouse cadavers and numerical modelling using the life-sciences simulation environment Sim4Life. The final concept couples a microwave antenna to the animal using an agarose coupling phantom, and the applicator was made compatible with the BSD-500 clinical device and its electromagnetically stable 4-wire sensing approach.
An agarose-based phantom was used to mediate microwave energy transfer between the antenna and the tissue surrogate. The phantom's dielectric and thermal properties were measured and reported to closely approximate muscle tissue at the operating frequency noted in the abstract (915 MHz). The abstract contained truncated values for some dielectric comparisons; specific numeric dielectric values were not reported in full in the provided source excerpt.
Temperatures in cadaver experiments were monitored with the clinical device's electromagnetically stable 4-wire sensors, which were read out independently from the BSD-500 control electronics. The independent readout achieved a 3 Hz data collection rate. The standard deviation of sensor readings compared with a reference thermometer was reported as smaller than 0.01, but the abstract did not state the measurement unit for that standard deviation.
Validation experiments used mouse cadavers with visual positioning of the applicator and tumour surrogates. According to the reported results, visual positioning alone was sufficient to ensure the tumour-surrogate region reached therapeutic temperatures using only a control sensor embedded in the agarose gel that contacted the mouse body. The abstract gives a lower bound of 40 for the therapeutic temperature range; however, the upper bound and units for that reported temperature range were truncated in the source excerpt.
Extrapolating from experimental and simulation data, the authors report the highest temperature should occur in the gel at the antenna tip, reaching approximately 43 (unit not specified in the abstract; temperature values are conventionally degrees Celsius). The therapeutic zone depth was estimated to extend between 9.3 mm and 17.6 mm (95% confidence interval), indicating a focal heating region suitable for small-animal tumours at typical subcutaneous depths.
Electromagnetic simulations in Sim4Life were used to predict heating-rate distributions. These simulations matched experimental observations and were reported to be robust to changes in material properties and geometry of the setup. In addition, perfusion-aware simulations based on the Pennes bioheat equation were performed to account for heat loss due to blood perfusion. These perfusion-inclusive simulations predicted at most a 21% reduction in tumour heating under physiological perfusion conditions, suggesting that the applicator should still achieve therapeutic temperature levels in vivo despite perfusion-related cooling.
Key findings from the combined experimental and simulation work include:
The agarose phantom provides coupling that closely approximates muscle dielectric and thermal response at the operating frequency noted (915 MHz), allowing predictable energy transfer to superficial targets.
The expected hotspot is near the antenna tip within the gel coupling medium, with an extrapolated peak temperature around 43 (unit not provided in the abstract).
The therapeutic heating zone extends roughly 9.3–17.6 mm in depth (95% CI), a depth range compatible with many small-animal tumour models.
Perfusion reduces heating but not to an extent that would preclude achieving therapeutic temperatures in vivo, with an estimated maximum reduction of 21% in tumour heating predicted by Pennes-based models.
The abstract reports several important outcomes and establishes base validation of the applicator; however, some numeric details and units were truncated or missing in the provided source excerpt. Examples include explicit dielectric values at 915 MHz, the complete therapeutic temperature range (upper bound and explicit unit), and the unit for the reported sensor standard deviation. These details were not reported in the abstract text supplied here.
The authors conclude that this work substantially narrows the gap toward a practical small-animal hyperthermia applicator and provides the base validation needed before progressing to in vivo experiments. The next logical steps, as indicated by the study's framing, are in vivo validation experiments using the applicator and further refined temperature control and dosimetry under physiological conditions.