Hyperthermia: Field Conjugate Acoustic Lenses For Deep Heating

Simple focused ultrasound transducers produce foci that are too small (1-3") to heat large volumes unless scanned. Using phased arrays, it is possible to design treatment ytterns with the field conjugation method. Field conjugate foci can also be synthesized with a single transducer coupled to a complex lens. Lenses have been designed using field conjugation calculations, and fabricated on a computer controlled milling machine. The measured beam patterns from the lenses agree closely with the beam patterns predicted from theory for the equivalent phased arrays. Results are presented for a test focus of three points, and a rotating focus pattern designed to produce a flat treatment field.