1. Project Aims
The twinkling artifact (TA) is a rapid color-shift that selectively highlights hard objects such as kidney stones in color-Doppler ultrasound images; however, its inconsistent appearance has limited its clinical use. Our objective is to develop an ultrasound imaging protocol to enhance kidney stone detection in space, addressing ExMC Gap 4.13. In the 3rd year renewal proposal, the aims are: AIM 1: Develop, refine, and test in space analogs improved ultrasound imaging protocols to enhance kidney stone detection. AIM 2: Determine the effect of breathing gas composition on twinkling in swine. AIM 3: Determine the role of bacteria in twinkling.
2. Key Findings
Twinkling was reduced when 9 swine were exposed to elevated carbon dioxide (CO2) levels (similar to what is found on the International Space Station (ISS)) with the degree of reduction in twinkling correlating with the concentration of CO2; twinkling increased when swine were exposed to 100% oxygen. When 4 swine were exposed to elevated CO2 levels versus normal air, there was an unrecoverable decrease in twinkling over the course of the study. Concentrations of gases in the blood and urine suggest both O2 and CO2 contribute to twinkling. Imaged 7 human subjects in the hyperbaric chamber and found a statistically significant increase in twinkling when subjects breathe 100% O2 at 1.6 ATA (the decompression stop) compared to initial twinkling levels. Growing several different species of bacteria on sterilized stones did not induce or increase twinkling; bacteria grown on agar plates also did not twinkle. Found evidence suggesting the contribution of internal micro-cracks to twinkling in addition to the surface crevice bubbles. Low frequency ultrasound was found to enhance twinkling if already present on stones, but did not cause non-twinkling stones to twinkle. Published 2 papers in peer-reviewed scientific journals; 4 additional papers are in preparation. Presented at 5 scientific conferences including an invited talk at the Acoustical Society of America Meeting in Honolulu, HI. Mentored a Pacific Science Center summer high school student and a summer undergraduate student. Organized a Wide World of Sound Booth at Engineering Discovery Days as Chair of the Outreach Committee, Cascadia Regional Chapter, Acoustical Society of America. Was interviewed for 2 National Space Biomedical Research Institute (NSBRI)/University of Washington promotional videos and a book on women in science. Accepted a tenure-track assistant professor position in the Graduate Program in Acoustics, Department of Aerospace Engineering at the Pennsylvania State University.
We have discovered that breathing CO2 significantly reduces twinkling in swine and have shown that breathing normal air (0.04% CO2) is insufficient to restore twinkling. The results also suggest that breathing elevated O2 may restore or enhance twinkling, which is supported in our human hyperbaric study. Bacteria grown on sterile stones or agar plates was found to be insufficient to induce or enhance twinkling; bacteria may need to be present in the stone formation process to contribute to twinkling. While increasing the energy delivered to the stone or lowering the transmitted frequency has been found to enhance twinkling, there remains some stones that do not twinkle. Further investigation into the stone formation process and/or the presence or absence of internal micro-cracks, which have been shown to play a role in twinkling in addition to the surface crevice bubbles, may help elucidate why some stones are resistant to twinkling so new techniques can be developed.
4. Proposed research
While this project is ended with NSBRI, we plan to finish recruiting and imaging the last subject for the human hyperbaric study and plan to submit 3 more journal publications. We are also looking to investigate in humans the effect of either an elevated CO2 or O2 environment on kidney stone twinkling.