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Prototype dual frequency bilaminar array transducer capable of therapeutic exposure at 500 kHz and Doppler monitoring at 2 MHz

It is known that ultrasound can enhance thrombolysis with tissue plasminogen activator (tPA). Blood flow monitoring is required for optimum control of the tPA injection and the therapeutic sonication. In order to transmit ultrasonic waves at two frequencies, one for imaging and the other for therapy, from the same aperture, we propose a probe consisting of a therapeutic array with an imaging array overlaid on it. Between these two arrays, a frequency selective isolation layer is inserted to ensure independent oscillatory motions of the two arrays. The function of this layer is to reflect the waves from the imaging array and allow the waves from the therapeutic array to pass through. A prototype sector array transducer was designed and constructed based on numerical simulation. B-mode and color flow images of human brains obtained with the prototype were comparable to those obtained with conventional structure transducers with respect to sensitivity and resolution. Schlieren images showed that the sidelobe levels of the therapeutic beam were less than -20 dB when steering angle was limited to 45 degrees in each direction.