Theoretical comparison of the SAR distributions from arrays of modified current sheet applicators with that of lucite cone applicators using Gaussian beam modelling.

The technical comparison of Current Sheet Applicator (CSA) and Lucite Cone Applicator (LCA) arrays covering an area of approximately 20 x 20 cm2 is investigated based on Gaussian beam (GB) predicted SAR distributions. The comparison is made in muscle equivalent tissue at 1 cm depth (maximum SAR normalized to 100%) and over a volume of 3 cm depth under the aperture of the antennae. The planar SAR distribution is tested on field sizes (FSx: area covering x% SAR), penetration depth (PD) and homogeneity coefficient (HC = FS75/FS25). From the SAR volume, a SAR-Volume histogram (volume enclosing y% SAR/total volume) is calculated as well as the volumetric HC. First, the prototype CSA (aperture 58 x 67 mm2, FS50 = 21 cm2) is technically modified to assure clinical safety and load independence. The modified CSA, the D-CSA, has an aperture of 66 x 75 mm2 with an FS50 = 28 cm2 and a PD of 10 mm, the LCA (aperture 105 x 105 mm2) has an FS50 = 76 cm2 and PD = 12 mm. The HC equals 0.21 (D-CSA), respectively 0.22 (LCA). Secondly, a 3 x 3 D-CSA array is compared with a 2 x 2 LCA array. The FS50s equals 72% (D-CSA), respectively 75% (LCA). The SAR-volume histograms, planar and volumetric HC show no significant difference; however, the planar HCs for D-CSA and LCA increase from 0.2-0.3, indicating that incoherently powered arrays from these antennae build SAR distributions constructively.