title: Enhancing effect of phase coherence factor for improvement of spatial resolution in ultrasonic imaging.
abstract: OBJECTIVE
  Spatial resolution is one of the important factors that determines ultrasound image quality. In the present study, methods using the phase variance of ultrasonic echoes received by individual transducer elements have been examined for improvement of spatial resolution.
  
  
  METHODS
  An imaging method, i.e., phase coherence imaging, which uses the phase coherence factor (PCF) obtained from the phase variance of received ultrasonic echoes, was recently proposed. Spatial resolution is improved by weighting ultrasonic RF signals obtained by delay-and-sum (DAS) beam forming using PCF. In the present study, alternative PCFs, i.e., exponential PCF, harmonic PCF, and Gaussian PCF, have been proposed and examined for further improvement of spatial resolution.
  
  
  RESULTS
  Spatial resolutions realized by the proposed PCFs were evaluated by an experiment using a phantom. The full widths at half maxima of the lateral profiles of an echo from a string phantom were 2.61 mm (DAS only), 1.46 mm (conventional PCF), and 0.48-0.62 mm (proposed PCFs).
  
  
  CONCLUSIONS
  The PCFs newly proposed in the present study showed better spatial resolutions than the conventional PCF. The proposed PCFs also realized better visualization of echoes from a diffuse scattering medium than the conventional PCF.
authors.affiliation: Graduate School of Science and Engineering for Research, University of Toyama, 3190 Gofuku, Toyama, 930-8555, Japan. hasegawa@eng.u-toyama.ac.jp.
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Hasegawa
mesh_terms: D007089:Image Enhancement / Q000379:methods*; D019047:Phantoms, Imaging; D014463:Ultrasonography / Q000295:instrumentation / Q000379:methods*
keywords: Coherence factor; Phase variance; Spatial resolution; Ultrasonic image