A spherical-section ultrasound phased array applicator for deep localized hyperthermia.

Computer simulation shows that a new ultrasound phased-array with nonplanar geometry has considerable potential as an applicator for deep localized hyperthermia. The array provides precise control over the heating pattern in three dimensions. The array elements form a rectangular lattice on a section of a sphere. Therefore, the array has a natural focus at its geometric center when all its elements are driven in phase. When compared to a planar array with similar dimensions, the spherical-section array provides higher focal intensity gain which is useful for deep penetration and heat localization. Furthermore, the relative grating-lobe level (with respect to the focus) is lower for scanned foci synthesized with this array (compared to a planar array with equal center-to-center spacing and number of elements). This could be the key to the realization of phased-array applicator systems with a realistic number of elements. The spherical-section array is simulated as a spot-scanning applicator and, using the pseudo-inverse pattern synthesis method, to directly synthesize heating patterns overlaying the tumor geometry. A combination of the above two methods can be used to achieve the desired heating pattern in the rapidly varying tumor environment.