Development of Coaxial Needle Applicator Made of Shape Memory Alloy

This paper describes a new heating method using a developed coaxial needle applicator made of a shape memory alloy(SMA)to avoid undesirable hotspots and to provide a larger heating area. The radio frequency(RF)interstitial hyperthermia treatment has a direct local heating area around the needle. However,because this heating method uses a discoid electrode on the body surface,the RF current flows between the needle applicator and the discoid electrode. The RF current that flows between the electrodes is known to damage healthy nerves and tissues. To overcome this problem,a new heating method using a coaxial needle applicator was developed. This applicator consists of an inside electrode and an outside electrode, and the discoid electrode is not needed. Moreover, to expand the heating region, an SMA was used as the material for both electrodes. In this paper, we estimated the electromagnetic field around the needle applicator by finite element method (FEM) and performed experiments with the agar phantom using the proposed coaxial needle applicator made of the SMA. First,the structure of the developed SMA coaxial needle applicator is presented. Second,the estimated results with the developed coaxial needle applicator are compared with the results of the straight needle using the discoid electrode. After comparing computer simulation results,the experimental results from both of the applicators are discussed. Furthermore as an example, simulate the treatment of brain tumors;calculated results from the 3D anatomical human head model reconstructed from 2D medical images were discussed. Finally, the experimental results from the SMA coaxial expandable needle applicator and the LeVeen needle,which is used in clinics now,are compared. From these results,it was concluded that the developed SMA coaxial needle applicator is capable of heating a larger region without damaging healthy tissues and nerves. Coaxial needle applicator made of SMA・Y.Shindo et al. ― ― 27 Received 28 March,2014,Accepted 4 June,2014. Corresponding author;Tel,+81-44-934-7355;Fax,+81-44-934-7907; e-mail,yshindo@isc.meiji.ac.jp doi:10.3191/thermalmed.30.27 ©2014 Japanese Society for Thermal Medicine