A biopsy tool with integrated piezoceramic elements for needle tract cauterization and cauterization monitoring

This paper reports the feasibility of biopsy needle tract cauterization and cauterization monitoring using an embedded array of piezoceramic microheaters. Circular heaters of lead zirconate titanate (PZT-5A), with 200 μm diameter and 70-80 μm thickness, are fabricated using a batch mode micro ultrasonic machining process. These are then assembled into cavities in the walls of 20-gauge stainless steel needles and sealed with epoxy. Experiments are performed by inserting the proposed biopsy needle into porcine tissue samples. The needle surface exceeds the minimum target temperature rise of 33°C for either radial or thickness mode vibrations. The corresponding input power levels are 236 mW and 325 mW, respectively. The tissue cauterization extends 1-1.25 mm beyond the perimeter of the needle and is uniform in all directions. After cauterization, the fundamental anti-resonance frequency and the corresponding impedance magnitude of the PZT heater decrease by 4.1% and 42.6%, respectively, thereby providing a method to monitor the extent of tissue cauterization. A sensing interface circuit capable of measuring the resonance frequency shift of the PZT elements is built and tested using discrete integrated circuit components. The circuit detects the resonance frequency shift from 8.22 MHz to 7.96 MHz of the PZT elements when the biopsy needle is inserted into wax medium. An interface circuit for actuation of the PZT elements for tissue cauterization is also described.