Assessment of the performance characteristics of a prototype 12-element capacitive contact flexible microstrip applicator (CFMA-12) for superficial hyperthermia

Abstract

The electrical performance of the CFMA-12 operating at 433 MHz is assessed under laboratory conditions using a RF network analyser. From measurements of the scattering parameters of the CFMA-12 on both a multi-layered muscle- and fat/muscle-equivalent phantom, the optimal water bolus thickness, at which the transfer of the energy to the phantom configuration is maximal, is determined to be ∼1 cm. The SAR distribution of the CFMA-12 in a multi-layered muscle-equivalent phantom is characterized using Schottky diode sheets and a TVS-600 IR camera. From the SAR measurements using the Schottky diode sheets it is shown that the contribution of the E_x component to the SAR (SAR_x) is maximal 7% of the contribution of the E_ycomponent to the SAR (SAR_y) at different layers in both phantom configurations. The complete SAR distribution (SAR_tot) at different depths is measured using the power pulse technique. From these measurements, it can be seen that SAR_yat a depth of 0 cm in the muscle-equivalent phantom represents up to 80% of SAR_tot. At 1 and 2 cm depth, SAR_y is up to 95% of SAR_tot. Therefore, in homogeneous muscle-equivalent phantoms, E_y is the largest E-field component and measurement of SAR_y distribution is sufficient to characterize SAR-steering performance of the CFMA-12. SAR steering measurements at 1 cm depth in the muscle-equivalent phantom show that the SAR maximum varies by 40% (1 SD) around the average value of 38.8 W kg⁻¹ (range 10–65 W kg⁻¹) between single antenna elements. The effective fieldsize (E₅₀) varies by 14% (1 SD) around the average value of 19.1 cm².

• Microstrip applicators
• SAR characterization
• superficial hyperthermia
• antenna arrays
• quality assurance