title: Use of the Acoustic Shadow Width to Determine Kidney Stone Size with Ultrasound.
abstract: OBJECTIVE
  Ultrasound is known to overestimate kidney stone size. We explored measuring the acoustic shadow behind kidney stones combined with different ultrasound imaging modalities to improve stone sizing accuracy.
  
  
  METHODS
  A total of 45 calcium oxalate monohydrate stones were imaged in vitro at 3 different depths with the 3 different ultrasound imaging modalities of conventional ray line, spatial compound and harmonic imaging. The width of the stone and the width of the acoustic shadow were measured by 4 operators blinded to the true size of the stone.
  
  
  RESULTS
  Average error between the measured and true stone width was 1.4 ± 0.8 mm, 1.7 ± 0.9 mm, 0.9 ± 0.8 mm for ray line, spatial compound and harmonic imaging, respectively. Average error between the shadow width and true stone width was 0.2 ± 0.7 mm, 0.4 ± 0.7 mm and 0.0 ± 0.8 mm for ray line, spatial compound and harmonic imaging, respectively. Sizing error based on the stone width worsened with greater depth (p <0.001) while the sizing error based on the shadow width was independent of depth.
  
  
  CONCLUSIONS
  Shadow width was a more accurate measure of true stone size than a direct measurement of the stone in the ultrasound image (p <0.0001). The ultrasound imaging modality also impacted the measurement accuracy. All methods performed similarly for shadow size while harmonic imaging was the most accurate stone size modality. Overall 78% of the shadow sizes were accurate to within 1 mm, which is similar to the resolution obtained with clinical computerized tomography.
authors: Center for Industrial and Medical Ultrasound, Applied Physics Laboratory, University of Washington, Seattle, Washington. Electronic address: mrbean@uw.edu.
authors: Barbrina
authors: B
authors: Dunmire
authors: Department of Urology, University of Washington School of Medicine, Seattle, Washington.
authors: Jonathan D
authors: JD
authors: Harper
authors: Center for Industrial and Medical Ultrasound, Applied Physics Laboratory, University of Washington, Seattle, Washington.
authors: Bryan W
authors: BW
authors: Cunitz
authors: Department of Urology, University of Washington School of Medicine, Seattle, Washington.
authors: Franklin C
authors: FC
authors: Lee
authors: Department of Urology, University of Washington School of Medicine, Seattle, Washington.
authors: Ryan
authors: R
authors: Hsi
authors: Department of Biostatistics, Indiana University Schools of Medicine and Public Health, Indianapolis, Indiana.
authors: Ziyue
authors: Z
authors: Liu
authors: Center for Industrial and Medical Ultrasound, Applied Physics Laboratory, University of Washington, Seattle, Washington; Department of Urology, University of Washington School of Medicine, Seattle, Washington.
authors: Michael R
authors: MR
authors: Bailey
authors: Department of Urology, University of Washington School of Medicine, Seattle, Washington; Division of Urology, Department of Veteran Affairs Medical Center, Seattle, Washington.
authors: Mathew D
authors: MD
authors: Sorensen
mesh_terms: D000162:Acoustics; D002129:Calcium Oxalate; D006801:Humans; D007669:Kidney Calculi / Q000000981:diagnostic imaging* / Q000473:pathology*; D014463:Ultrasonography
chemical_list: D002129:Calcium Oxalate
keywords: calculi; lithotripsy; nephrolithiasis; ultrasonography