Researchers

Adam Maxwell

Senior Fellow - Trainee

CIMU Department

APL-UW

Wayne Kreider

Senior Engineer

CIMU Department

APL-UW

Bryan Cunitz

Engineer IV

CIMU Department

APL-UW

Oleg Sapozhnikov

Senior Principal Engineer

CIMU Department

APL-UW

Vera Khokhlova

Senior Principal Engineer

CIMU Department

APL-UW

Mathew Sorensen

Assistant Professor

UW Deptartment of Urology

Jonathan Harper

Assistant Professor

UW Department of Urology

Mike Bailey

Senior Principal Engineer

CIMU Department

APL-UW

Assistant Professor, Mechanical Engineering and Adjunct Assistant Professor, Urology

Madeline Hubbard

Student Researcher

UW Department of Civil Engineering

Chris Hunter

Engineer
CIMU Department

APL-UW

Yak-Nam Wang

Senior Engineer

CIMU Department

APL-UW

Funding

National Institute of Diabetes and Digestive and Kidney Diseases

National Space Biomedical Research Institute

Collaborators

International Kidney Stone Institute

Computational Flow Physics Group

California Institute of Technology

Jonathan Freund

Professor, U. Illinois Urbana-Champaign

Burst Wave Lithotripsy

An Experimental Method to Fragment Kidney Stones

In many ways, this is a narrow bandwidth version of shock wave lithotripsy. Rather than hitting the stone with a hammer, it's a series of waves that enables the stone to be broken with more control and into uniform fragments.

So far, we found we can treat most stone types. We can treat some of them very rapidly.

We imagine there is going to be a range of sizes of stones we can break. We're trying to find the limits of what indications burst wave lithotripsy could be used for.

Effective, Noninvasive Fragmentation of Stones

The most common treatment for kidney stones is shock wave lithotripsy (SWL). SWL is a noninvasive procedure where shock waves are focused into the body and onto the stone, shattering it into small fragments that the patient will pass spontaneously. Because it is noninvasive, SWL is the treament most preferred by patients. Unfortunately, this procedure is unsuccessful about 40% of the time, and large residual stone fragments sometimes remain that require repeat treatments or alternative, more invasive methods of extraction.

Researchers at the Center for Industrial and Medical Ultrasound — CIMU — have been performing SWL research for nearly 20 years. Through simulations and experiments, our research has led us to understand more precisely the physical principles for how shock waves fracture kidney stones. Based on this work, we are now investigating an alternative noninvasive method to fragment stones by using ultrasound pulses rather than shock waves to fragment stones, called burst wave lithotripsy or BWL. Ultrasound bursts consist of consecutive acoustic cycles that can accumulate to concentrate energy within the stone, enabling comminution at relatively low peak pressures of the incident sound field. In this way, BWL can cause stresses and fractures in the stone through resonances, much in the way an opera singer can shatter a wine glass with their voice. A key characteristic of this method is that the size fragments generated when the stone disintegrates is controlled by the ultrasound frequency. In this way, the technique can be 'tuned' to create small fragments that the patients will pass naturally, and potentially improve the success rate of lithotripsy procedures.

Experiment Documentation

Real-time video of a 6 mm natural calcium oxalate monohydrate stone exposed to burst wave lithotripsy in a water bath. The ultrasound is focused onto the stone from the top. The exposure is initiated 2 seconds from the start of the video and the stone is quickly fractured into small fragments.

Real-time video of a natural struvite stone exposed to burst wave lithotripsy in a water bath. The ultrasound is focused onto the stone from the left-hand side. The entire stone is reduced to a series of fragments smaller than 3 mm in 5 seconds.

Recent Publications

Fragmentation of urinary calculi in vitro by burst wave lithotripsy

Maxwell, A.D., B.W. Cunitz, W. Kreider, O.A. Sapozhnikov, R.S. Hsi, J.D. Harper, M.R. Bailey, and M.D. Sorensen, "Fragmentation of urinary calculi in vitro by burst wave lithotripsy," J. Urol., 193, 338-344, doi:10.1016/j.juro.2014.08.009, 2015.

More Info

1 Jan 2015

Purpose
We have developed a new method of lithotripsy that uses short, broadly focused bursts of ultrasound rather than shock waves to fragment stones. This study investigated the characteristics of stone comminution by burst wave lithotripsy in vitro.

Materials and Methods
Artificial and natural stones (mean 8.2±3.0 mm, range 5–15 mm) were treated with ultrasound bursts using a focused transducer in a water bath. Stones were exposed to bursts with focal pressure amplitude 𕟮.5 MPa at 200 Hz burst repetition rate until completely fragmented. Ultrasound frequencies of 170 kHz, 285 kHz, and 800 kHz were applied using 3 different transducers. The time to achieve fragmentation for each stone type was recorded, and fragment size distribution was measured by sieving.

Results
Stones exposed to ultrasound bursts were fragmented at focal pressure amplitudes 𕟴.8 MPa at 170 kHz. Fractures appeared along the stone surface, resulting in fragments separating at the surface nearest to the transducer until the stone was disintegrated. All natural and artificial stones were fragmented at the highest focal pressure of 6.5 MPa with treatment durations between a mean of 36 seconds for uric acid to 14.7 minutes for cystine stones. At a frequency of 170 kHz, the largest artificial stone fragments were <4 mm. Exposures at 285 kHz produced only fragments <2 mm, and 800 kHz produced only fragments <1 mm.

Conclusions
Stone comminution with burst wave lithotripsy is feasible as a potential noninvasive treatment method for nephrolithiasis. Adjusting the fundamental ultrasound frequency allows control of stone fragment size.

Development and testing of an image-guided prototype system for the comminution of kidney stones using burst wave lithotripsy

Cunitz, B., A. Maxwell, W. Kreider, O. Sapozhnikov, F. Lee, J. Harper, M. Sorenson, and M. Bailey, "Development and testing of an image-guided prototype system for the comminution of kidney stones using burst wave lithotripsy," J. Acoust. Soc. Am., 136, 2193, doi:10.1121/1.4899951, 2014.

More Info

1 Oct 2014

Burst wave lithotripsy is a novel technology that uses focused, sinusoidal bursts of ultrasound to fragment kidney stones. Prior research laid the groundwork to design an extracorporeal, image-guided probe for in-vivo testing and potentially human clinical testing. Toward this end, a 12-element 330 kHz array transducer was designed and built. The probe frequency, geometry, and shape were designed to break stones up to 1 cm in diameter into fragments <2 mm. A custom amplifier capable of generating output bursts up to 3 kV was built to drive the array. To facilitate image guidance, the transducer array was designed with a central hole to accommodate co-axial attachment of an HDI P4-2 probe. Custom B-mode and Doppler imaging sequences were developed and synchronized on a Verasonics ultrasound engine to enable real-time stone targeting and cavitation detection, Preliminary data suggest that natural stones will exhibit Doppler %u201Ctwinkling%u201D artifact in the BWL focus and that the Doppler power increases as the stone begins to fragment. This feedback allows accurate stone targeting while both types of imaging sequences can also detect cavitation in bulk tissue that may lead to injury.

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