Performance and use of current sheet antennae for RF-hyperthermia of a phantom monitored by 3 tesla MR-thermography

Abstract

Several MR-compatible current sheet antennae (CSA) of different height ( h ) (16cm ( l ) &#50 8cm ( w ) &#50 1-5cm ( h )) were built for simulated RF (96MHz) hyperthermia of a medium-sized (12 l ) tissue-equivalent phantom inside a 3 tesla whole body tomograph. Prior to use, efficiencies of the CSA were determined by network analysis and by calorimetry. Depending on the height h of the CSA and on the thickness d bolus of the water bolus used for RF-coupling of the CSA to the lossy medium, their efficiency varied between 20-70% and the CSA with h = 3cm was selected for simulated RF hyperthermia. During heating, spatial temperature distributions (20-42°C) of five slices (voxel size 2 &#50 2 &#50 10mm 3 ) were recorded intermittently within 4 s/slice by measuring the temperature dependent shift of the 1 H resonance frequency (125.32MHz). A phased array consisting of two identical CSA produced distinctly different spatial temperature distributions at 0 and 180° phase difference between both RF channels feeding the antennae. Within a one-dimensional heat diffusion model, the specific absorption rate (SAR) of the electromagnetic wave generated by a single antenna was deduced from the experimental data resulting in a penetration depth (1/e 2 ) of ~4cm.

• Hyperthermia
• Current Sheet Antennae
• Calorimetry
• Magnetic Resonance Thermography