Effect of Carbon Dioxide on the Twinkling Artifact in Ultrasound Imaging of Kidney Stones: A Pilot Study

Abstract

Bone demineralization, dehydration, and stasis put astronauts at an increased risk of forming kidney stones in space. The color-Doppler ultrasound “twinkling artifact”, which highlights kidney stones with color, can make stones readily detectable with ultrasound; however our previous results suggest twinkling is caused by microbubbles on the stone surface which could be affected by the elevated levels of carbon dioxide found on space vehicles. Four pigs were implanted with kidney stones and imaged with ultrasound while the anesthetic carrier gas oscillated between oxygen and air containing 0.8% carbon dioxide. Upon exposing pigs to 0.8% carbon dioxide, twinkling was significantly reduced after 9–25 minutes and recovered when the carrier gas returned to oxygen. These trends repeated when pigs were again exposed to 0.8% carbon dioxide followed by oxygen. The reduction of twinkling from exposure to elevated carbon dioxide may make kidney stone detection with twinkling difficult in current space vehicles.

An investigation into the clinical accuracy of twinkling artifacts in patients with urolithiasis smaller than 5 mm in comparison with computed tomography scanning

“…[ 1 ] It is used to detect calcifications in various tissues such as prostate, testicular, kidney, bladder, liver, bile duct, pancreas, breast, and ureter, as well as non-calcified bilirubin stones and irregular hard and reflexive surfaces. [ 4 7 10 ] Studies suggest that this artifact can increase the sensitivity and specificity of ultrasound in diagnosis of kidney stones. [ 11 ] It can also transform the management and treatment of kidney stones.…”

Developing Complete Ultrasonic Management of Kidney Stones for Spaceflight

“…Specific conditions that occur in space, such as changes in ambient pressure and gas composition, have been found to affect twinkling [27], [29]. On the International Space Station (ISS), astronauts are exposed to elevated levels of carbon dioxide 10–20 times the carbon dioxide concentration on Earth [30]–[32].…”

“…On the International Space Station (ISS), astronauts are exposed to elevated levels of carbon dioxide 10–20 times the carbon dioxide concentration on Earth [30]–[32]. In pigs implanted with kidney stones, twinkling was found to be significantly reduced or eliminated upon exposure to elevated levels of carbon dioxide at the upper end of what is found on the ISS [29]. If elevated inspired carbon dioxide adversely effects twinkling, it could make kidney stone detection with twinkling difficult in space, unless the ultrasound detection algorithm is refined, the ambient carbon dioxide levels are reduced, or effective countermeasures are employed to restore twinkling, such as exposure to oxygen or hypobaric pressure (shown in the lab to increase twinkling by enlarging the bubbles) [27].…”