Feasibility of miniature high-frequency piezoelectric ceramic hollow spheres for exposimetry and tissue ablation

Miniature, high frequency piezoelectric ceramic hollow spheres were evaluated for potential use as hydrophones for exposimetry of high intensity ultrasound fields and as minimally invasive tissue ablation devices. Spheres with diameters ranging from 0.7 to 1.0 mm, with resonance frequencies from 1.8 to 2.7 MHz were used as hydrophones. An almost constant sensitivity was reported for these hydrophones and an omni directional receive pattern was also demonstrated. The hollow sphere hydrophone exhibited twice the sensitivity of a needle hydrophone but with no pre-amplification stages and could withstand four times higher pressure. As a minimally invasive interstitial ablation device, the results demonstrated an increased necrosed tissue volume for increasing exposure time. For example, with a 1.0 mm diameter sphere (f = 1.87 MHz), the necrosed tissue diameter as a function of exposure times was 2.35 +/- 0.34, 3.00 +/- 0.37 and 4.61 +/- 1.13 mm for 5, 10 and 15 sec. sonications, respectively.