DEVELOPING COMPLETE ULTRASONIC MANAGEMENT OF KIDNEY STONES FOR SPACEFLIGHT

Abstract

Bone demineralization, dehydration, and stasis put astronauts at an increased risk of forming kidney stones in space. The incidence of kidney stones and the potential for a mission-critical event are expected to rise as expeditions become longer and immediate transport to Earth becomes more problematic. At the University of Washington, we are developing an ultrasound-based stone management system to detect stones with S-mode^™ ultrasound imaging, break stones with burst wave lithotripsy (BWL^™), and reposition stones with ultrasonic propulsion (UP^™) on Earth and in space. This review discusses the development and current state of these technologies, as well as integration on the flexible ultrasound system sponsored by NASA and the National Space Biomedical Research Institute.

Figure 1

An example of the kidney stone twinkling artifact in a pig kidney, which shows the stone as a mosaic of colors in a greyscale ultrasound image.

Figure 2

Ultrasound images of (upper) a human kidney and (lower) stones on a tissue phantom taken with (left) conventional B-mode ultrasound and (right) with S-mode^™ ultrasound developed at the University of Washington. Left: Conventional B-mode ultrasound clearly shows kidney structures including the collecting system, calyces, and papilla of the kidney; however, the lower image shows that the kidney stone brightness is not different than the tissue phantom and small stones of 1–2 mm diameter spaced 3–4 mm apart cannot be resolved. Right: S-mode^™ ultrasound clearly shows the collecting system and calyces of the kidney, though without the same degree of soft tissue resolution as shown in the conventional B-mode ultrasound image; however, the lower image shows that stones appear significantly brighter than the soft tissue phantom and the small stones can be resolved.

Figure 3

(a) Ultrasound image of an ex vivo human kidney stone showing the difference in stone size measurements between the hyperechoic stone and the posterior acoustic shadow. This image was featured on the cover of the Journal of Urology (January 2016) and is reprinted with permission from Elsevier Publishing [24]. (b) Ultrasound images of a 4.4 mm stone in the lower pole of a human kidney. Measurement of the stone width (blue) overestimates the stone size by 3.2 mm, whereas measurement of the posterior acoustic shadow (yellow) overestimates the stone size by 1.0 mm.

Figure 4

a) Photograph of the preclinical BWL^™ system showing the driving electronics and BWL^™ transducer with a center-cutout for a commercially-available imaging transducer. b) Photographs of a calcium oxalate monohydrate kidney stone before (left) and after (right) BWL^™ therapy. Photographs courtesy of Dr. Adam Maxwell.

Figure 5

Images of a tissue phantom kidney in a torso training phantom imaged with a NASA FUS C1-5 transducer and driven by a Verasonics® ultrasound system. Left: Image of the stone at the initial position with the twinkling capability on, which shows the stone in color. Center: Image of the stone (arrow) after the first “push” attempt, showing the stone has moved approximately 2 cm to the left. Right: Image of the same kidney after the second push where the stone has moved out of the image plane and to the exit of the kidney.