Ultrasound has been a useful tool in the detection of kidney stones. It is a low-cost solution that does not require ionizing radiation that would be harmful to vulnerable populations such as children and recurrent stone formers. However, it suffers from a broad range of sensitivity (78 to 96%) and specificity (31 to 100%) in the detection of stones.
Work at the University of Washington has been directed towards improving both the sensitivity and specificity of the stone detection by improving both B-mode ultrasound and leveraging an artifact that occurs when a kidney stone is imaged under color-flow Doppler. This is called stone-specific ultrasound imaging mode, or S-mode.
Because of the acoustic properties of the kidney stone, it is much more hyperechoic relative to surrounding kidney tissue. However, due to compression of the grayscale color map, it can be difficult to distinguish stones from the sinus fat in the kidney’s collection space. Additional imaging processing layers that are optimized for improving imaging of the soft tissues tend to blur out small stones as well. Therefore, work was done to change the B-mode imaging settings to optimize for stone contrast relative to surround tissue. Additionally, there is an acoustic shadow that tends to appear for stones larger than 4 to 5 mm, which is also useful for accurate stone sizing.
When a stone is imaged under color-flow Doppler, it is often shown as a fluctuation of the entire color map known as twinkling artifact. The cause of this artifact was investigated so that an optimal imaging sequence could leverage whatever phenomenon is at work to improve the sensitivity and specificity of the detection beyond B-mode. Following a hypothesis that there are micron-size bubbles trapped in the cracks and crevices of the stone, a test was performed that pressurized the fluid surrounding a kidney stone while it was being imaged under color-flow Doppler ultrasound. As the pressure increased, bubble activity was suppressed and the Doppler power decreased; after the pressure returned to atmosphere, the twinkling returned. Doppler transmit parameters were then optimized to enhance the stone bubble activity without exceeding the regulatory safety requirements for ultrasound. These changes were shown to improve the SNR of the stone relative to surrounding tissue.
All of these modifications have been incorporated into a clinical research system, and data is being collected to show an improvement in kidney stone detection.
This work was done by Bryan Cunitz, Julianna Simone, Barbrina Dunmire, Yasser Hader, Jonathan Harper, Matthew Sorenson, and Michael Bailey of the University of Washington for Johnson Space Center. For further information, contact the JSC Technology Transfer Office at (281) 483-3809.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
University of Washington
Campus Mail Box 355640
Seattle, WA 98105
Refer to MSC-25140-1