RADIOFREQUENCY RING APPLICATOR - ENERGY-DISTRIBUTIONS MEASURED IN THECDRH PHANTOM

SAR distributions were measured in the CDRH phanton, a 1 cm fat-equiva lent shell filled with an abdomen-equivalent liquid (sigma = 0.4-1.0 S m(-1), dimensions 22 X 32 X 57 cm) to demonstrate the feasibility of the ring applicator to obtain deep heating. The ring electrodes were f ixed in a PVC tube; diameter 48 cm, ring width 20 cm and gap width bet ween both rings 31.6 cm. Radio-frequency energy was fed to the electro des at eight points. The medium between the electrodes and the phantom was deionised water. The SAR distribution in the liquid tissue volume was obtained by a scanning E-field probe measuring the E-field in all three directions. With equal amplitude and phase applied to all feedi ng points, a uniform SAR distribution was measured in the central cros s-section at 30 MHz. With RF energy supplied to only four adjacent fee ding points (others were connected to a 50 Omega load), the feasibilit y to perform amplitude steering was demonstrated; SAR values above 50% of the maximum SAR were measured in one quadrant only. SAR distributi ons obtained at 70 MHz showed an improved focusing ability; a maximum at the centre exists for an electric conductivity of the abdomen-equiv alent tissue of 0.6 and 0.4 S m(-1).