Virtual prototyping of a catheter transducer array for internal hepatic sonoporation

Sonoporation for targeted cancer chemotherapy in the liver with an external ultrasonic source is hampered by the ribs and fat surrounding the organ. Current therapies rely on array beam forming with sequential triggering of elements to spare the ribs. However, the peak negative pressures (PNPs) achieved in hepatic tumors are rather low and there is risk associated with high power ultrasound incident on the ribs. Here, we focus on the development of a 1-3 connectivity piezocomposite linear ultrasonic array that can be incorporated in an 11 Fr catheter to perform sonoporation of the liver from within a larger blood vessel. Issues encountered in the transducer design are mostly caused by the reduced dimensions of the catheter, which are inimical to the low frequency and high power therapeutic requirements. Thus, our approach to produce a transducer design is through a series of parametric sweeps of array parameters using finite element analysis. The output parameters of interest are PNP and beam forming to steer at more than 45° from normal. Two frequencies are considered: 1.5 MHz, set by the maximum physical transducer thickness, and 3.0 MHz, corresponding to the frequency of resonance of the contrast agents to carry the drugs. Piezoelectric materials of interest are ceramic (PZT-5H) and single crystal (PMN-29%PT, 26%PIN-PMN-32%PT). The parametric sweeps indicate that fewer pillars laterally per element, higher volume fraction (>0.68) and higher pillar aspect ratio (>0.42) achieve the lowest PNP in the load.