Thursday, November 1, 2012
Mechanical and Civil Engineering Seminar
Focused Ultrasound to Expel Calculi from the Kidney
Michael Bailey, Assistant Professor, Department of Mechanical Engineering, University of Washington
Background: Our research group has introduced a non-invasive transcutaneous ultrasound device to move kidney stones. This technology has potential to expel small stones or residual fragments after lithotripsy or relocate an obstructing stone to a non-obstructing location.
Objective: To evaluate the efficacy and safety of ultrasonic propulsion in a live porcine model using a new 2nd-generation device.
Design, Setting and Participants: In kidneys from eight domestic swine, stones and metalized beads (2-8 mm) were implanted ureteroscopically. A reference bead was placed in the upper pole, and targeted stones and beads were placed in the middle or lower pole of the kidney.
Intervention: Ultrasonic propulsion was performed using a Philips HDI C5-2 commercial imaging transducer and a Verasonics diagnostic ultrasound platform. Stone propulsion was visualized using fluoroscopy, ultrasound, and the ureteroscope.
Outcome measurements and Statistical Analyses: Successful stone movement was defined as relocating a stone to the renal pelvis, ureteropelvic junction or proximal ureter. Efficacy and procedure time was determined. Three blinded experts evaluated for histologic injury in control, sham, and treatment arms.
Results and Limitations: Stones were successfully implanted in 12 porcine kidneys. All stones were moved. 65% (17/26) of stones/beads were moved the entire distance to the renal pelvis (3), ureteropelvic junction (2), or ureter (12). Average procedure per stone required 14.2±7.9 min and 23±16 pushes. Each push averaged 0.9 sec in duration with a maximum of 1 sec. Mean interval between pushes was 41±13 sec. No gross or histologic damage was identified from the ultrasound propulsion procedure.
Conclusions: Ultrasonic propulsion is effective with most stones being relocated to the renal pelvis, ureteropelvic junction, or ureter in a timely fashion. The procedure appears safe without evidence of injury. We are pursuing FDA approval for a human feasibility study in the United States.
Refreshments are at 10:45 a.m. in 210 Thomas.