In Vivo Ultrasonic Microprobe for Tumor Diagnosis

The objective of this initiative is to develop the basis for a fundamentally new technology for an in situ clinical diagnosis of solid tumors with the expectation of rapid and accurate detection and diagnosis of cancer. A prototype invasive in vivo ultrasonic microprobe has been developed and evaluated. A new high-strain piezocrystal was developed to provide sufficient electromechanical efficiency for the ultrasonic microprobe. High-strain piezocrystals, (1-x)Pb(Zn_1/3Nb2/3O₃-xPbTiO₃ x=0.08~0.09, (PZN-PT) were grown by a modified flux growth method. We have also developed a fabrication process for realizing the proposed ultrasonic probe. The silicon probe is realized by using wet anisotropic etching of <100> oriented silicon substrate with thermally-grown silicon dioxide as the mask. Probe leads are subsequently patterned on top of the shank following its release. Both transmitted and pulse-echo patterns of the microprobe have been characterized. The results are consistent with the new high-strain piezocrystal geometry and its mounting geometry onto the silicon substrate.

Figure 1. Silicon microprobe.

UPDATE: 1/24/01

Recent microprobes have been constructed on the top of thick needles. The goal is to continue to decrease the size of the needle and transducer for invasive procedures. At present, focused microprobes have been constructed with central frequencies of 15-20 MHz. Figure 2 shows the beam pattern of a microprobe with a 6.7 mm focus.

Figure 2. Beam pattern of focused microprobe.

A B-mode image of a rat liver taken by the focused microprobe is shown in Figure 3.

Figure 3. Bmode of rat liver taken with microprobe.