A FERRITE CORE METALLIC SHEATH THERMOSEED FOR INTERSTITIAL THERMAL THERAPIES

An alternative form of ferromagnetic seed for thermal therapy has been developed following Matsuki, Murakami, and their colleagues [1]-[4]. A nearly lossless ceramic ferrite core (FC) is surrounded by an electr ically conductive sheath, The FC has a high relative intrinsic permeab ility, typically 3000 at low magnetic field strengths, and a sharp tra nsition from the ferrimagnetic state to the nonmagnetic state. The she ath is either a metallic-tube or coating on the core, When this compos ite seed is excited with a radiofrequency magnetic field, large eddy c urrents are induced in the metallic sheath (MS) due to the concentrate d magnetic flux in the core leading to Joule heating, Advantages of th is configuration are that this ferrite core/metallic sheath (FC/MS) th ermoseed has high power absorption efficiency and a sharp transition c ompared to ferromagnetic alloy systems; means of optimizing efficiency are apparent from simple expressions; the outer sheath can be of any biocompatible metal; the production method for the ferrites leads to l arge quantities of seeds with reproducible properties, The FC/MS confi guration soh es many of the technical problems that have hindered the clinical implementation of thermally regulating ferromagnetic implants for thermal therapies.