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Julianna C. Simon
Postal:
Graduate Program in Acoustics Pennsylvania State University 201E Applied Science Building University Park, Pennsylvania 16802 USA
Email:
jcsimon@psu.edu
Adam D. Maxwell
Postal:
Center for Industrial and Medical Ultrasound Applied Physics Laboratory and Department of Urology University of Washington 1013 NE 40th Street Seattle, Washington 98105 USA
Email:
amax38@uw.edu
Michael R. Bailey
Postal:
Center for Industrial and Medical Ultrasound Applied Physics Laboratory; Department of Mechanical Engineering; and Department of Urology University of Washington 1013 NE 40th Street Seattle, Washington 98105 USA
Email:
mbailey@uw.edu
Some Work on the Diagnosis and Management of Kidney Stones with Ultrasound
Ultrasound is currently the only noninvasive technology able to completely diagnose and manage kidney stones.
Introduction
Kidney stones currently affect 1 in 11 Americans over their lifetime (Scales et al., 2012) and the prevalence is rising. Although often asymptomatic in the kidney, a stone can cause debilitating pain, nausea, and/or changes in urination as it ob- structs urine flow in the passage from the kidney to the bladder. The focus of treat- ment for kidney stones in the emergency room is to manage the pain, although about 20% of patients are admitted for an urgent surgical procedure to release urine backup (generally the source of the pain; Ghani et al., 2014). If stones do not pass naturally (usually occurring when the size is >5 mm), at least one sur- gery must be performed to remove the stone. Once a patient has had a kidney stone, there is a 40% chance of having another symptomatic stone within 5 years (Worcester and Coe, 2008). Emergency room visits coupled with the various man- agement options and monitoring for kidney stones puts the estimated annual cost in the United States at over $10 billion (Litwin and Saigal, 2012). The goal of this article is to report on the acoustical principles behind new techniques and tech- nologies for the diagnosis and management of kidney stones with ultrasound.
Background
Kidneys are bean-shaped organs (Figure 1) located just below the rib cage on ei- ther side of the spine. Each about the size of a fist, kidneys filter over a liter of blood per minute, extracting water and metabolic waste to form urine. In normal kid- neys, microscopic crystals form in supersaturated urine and pass harmlessly from the body; however, when these crystals adhere to structures in the kidney, stones begin to form. Stones can form not only in the urine-filled collecting space of the kidney but also in the 200- to 300-μm-diameter ducts that filter the waste from the blood in the cortex and renal pyramids. Kidney stones are very heterogeneous structures composed of inorganic crystals held together by an organic protein ma- trix, as shown in the X-ray microcomputed tomography (μCT) image of a stone in Figure 2 (Williams et al., 2010). The most common type of kidney stone is calcium oxalate, which accounts for approximately 80% of stones, at least in the United States (Worcester and Coe, 2008). Other types of stones include calcium phos- phate, uric acid, struvite, and cystine. Except for struvite stones that form from the metabolic by-product of some infectious bacteria, it is not clear what causes stones to form, although genetics, diet, and hydration all contribute.
Interest by the National Aeronautics and Space Administration
and the Department of Defense
The National Aeronautics and Space Administration (NASA) and the Department of Defense (DoD) have a unique interest in portable and noninvasive technologies for the diagnosis and management of kidney stones (Simon et al., 2016). Astro-
52 | Acoustics Today | Winter 2017 | volume 13, issue 4 ©2017 Acoustical Society of America. All rights reserved.