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Researchers at the 2010 American Urological Association (AUA) Annual Meeting has intended to present urologists a new equipment to reposition kidney stones and stone fragmants for easier clearance.

The device is being developed by a team of urologists and ultrasound physicists at the University of Washington, Seattle, Washington.

Lower pole kidney stone and fragment clearance is particularly difficult compared with other locations due to dependent positioning and difficult access, Dr.Anup Shah, MD, University of Washington Center for Industrial and Medical Ultrasound explained. Residual stone fragments trapped in the lower pole often lead to increased morbidity and an increased rate of secondary surgery.

Researchers are developing a focused ultrasound device that can manipulate stone fragments within the kidney using a hand-held transcutaneous device. The goal is to move fragments from a dependent position in the lower pole to a more superior position within the collection system where natural flushing activity can clear residue from lithotripsy or other treatment. Porcine trials of the device were described during a podium presentation.

The newly developed probe consists of an 8-element annular array with a nominal frequency of 2.0 MHz, acoustic power output of 5 to 20 watts, and programmable focal depth of 4.5 to 8.5 cm, Dr. Shah reported. An opening in the centre of the therapeutic probe contains an HDI P4-2 imaging probe that provides 2-dimensional ultrasound imaging guidance. Diagnostic ultrasound and fluoroscopy showed that both artificial and human kidney stones placed in transparent kidney phantoms and live porcine kidneys can be reliably guided and moved under operator control.

The stones used were between 2 and 6 mm in the largest dimension, Dr. Shaw reported. These early tests showed stones moving up to 3 cm within the kidney at a velocity of about 1 cm per second. Newer iterations of the device can deliver motive energy deeper than 8.5 cm, making it possible to reposition stones in more obese patients whose kidneys are 10 cm and deeper below the skin.

"We believe that ultrasound can move stones through the kidney in a therapeutically effective manner," Dr. Shaw said. "There was no evidence, gross or microscopic, of any thermal or mechanical injury to thekidney. We are working at less than 50 watts, orders of magnitude less than the energy used in HIFU [high-intensity focused ultrasound]."

Source:AUA