title: Average sound speed estimation using speckle analysis of medical ultrasound data.
abstract: OBJECTIVE
  Most ultrasound imaging systems assume a pre-determined sound propagation speed for imaging. However, a mismatch between assumed and real sound speeds can lead to spatial shift and defocus of ultrasound image, which may limit the applicability of ultrasound imaging. The estimation of real sound speed is important for improving positioning accuracy and focus quality of ultrasound image.
  
  
  METHODS
  A novel method using speckle analysis of ultrasound image is proposed for average sound speed estimation. Firstly, dynamic receive beam forming technology is employed to form ultrasound images. These ultrasound images are formed by same pre-beam formed radio frequency data but using different assumed sound speeds. Secondly, an improved speckle analysis method is proposed to evaluate focus quality of these ultrasound images. Thirdly, an iteration strategy is employed to locate the desired sound speed that corresponds to the best focus quality image.
  
  
  RESULTS
  For quantitative evaluation, a group of ultrasound data with 20 different structure patterns is simulated. The comparison of estimated and simulated sound speeds shows speed estimation errors to be -0.7 ± 2.54 m/s and -1.30 ± 5.15 m/s for ultrasound data obtained by 128- and 64-active individual elements linear arrays, respectively. Furthermore, we validate our method via phantom experiments. The sound speed estimation error is -1.52 ± 8.81 m/s.
  
  
  CONCLUSIONS
  Quantitative evaluation proves that proposed method can estimate average sound speed accurately using single transducer with single scan.
authors.affiliation: Department of Bioengineering, The University of Tokyo, Yayoi 2-11-16, Bunkyo, Tokyo, 113-8656, Japan. quxiaolei@iml.t.u-tokyo.ac.jp
authors.forename: Xiaolei
authors.initials: X
authors.lastname: Qu
authors.forename: Takashi
authors.initials: T
authors.lastname: Azuma
authors.forename: Jack T
authors.initials: JT
authors.lastname: Liang
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Nakajima
mesh_terms: D000465:Algorithms; D007089:Image Enhancement / Q000379:methods; D012815:Signal Processing, Computer-Assisted; D013016:Sound; D014463:Ultrasonography / Q000379:methods*