Dual frequency array transducer for ultrasonid-enhanced transcranial thrombolysis

It is known that ultrasound can enhance thrombolysis with tissue plasminogen activator (tPA). A blood flow monitoring is required for an optimum control of the tPA injection and the therapeutic sonication. In order to transmit ultrasonic waves at two frequencies for imaging and 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 was inserted to ensure independent oscillatory motions of the two arrays. The function of this layer is expected to reflect the waves from the imaging array and allow the waves from the therapeutic array to pass through. Numerical simulation was performed using a finite element code, PZFlex. In this model, the imaging and therapeutic array used PZT ceramic with a center frequency of 2 MHz and 500 kHz, respectively. An epoxy resin isolation layer with 50 micro-meters reduced the amplitude of the unwanted response at 2 MHz by 13 dB, while it reduced the amplitude of the therapeutic waves at 500 kHz only by 2 dB.