Analysis and correction of ultrasonic wavefront distortion based on a multilayer phase-screen model.
A model is introduced that incorporates the cumulative wavefront distortion effects caused by spatial heterogeneities along the path of propagation, and a corresponding model-based wavefront distortion-correction method is presented. In the proposed model, a distributed heterogeneous medium is lumped into a series of parallel phase screens. The distortion effects can be compensated--without a priori knowledge of the distorting structure--by backpropagation of received wavefronts through hypothetical multiple phase screens located between the imaging system and targets, while each pointwise time shift is adjusted iteratively to maximize a specified image quality factor at the final layer. Theoretical analyses indicate that the mean speckle brightness decreases monotonically with the root-mean-square value of distributed phase distortions; therefore, the speckle brightness can be used as an image quality factor. Experimental one-dimensional (1-D) array data with simulated distortion effects based on a real 2-D abdominal-tissue map were used to evaluate the performance of the proposed method and existing aberration-correction techniques. The simulated characteristics of wavefront distortion and relative performance of existing correction techniques were similar to reports based on abdominal-wall data and breast data. This investigation shows that the proposed method provides better compensation for wavefront distortion.
Huang
Deng-Huei
DH
Graduate Institute of Communication Engineering, National Taiwan University, Taipei, Taiwan 106, R.O.C.
Tsao
Jenho
J
D000005:Abdomen / Q000000981:diagnostic imaging*; D000465:Algorithms; D003198:Computer Simulation; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D008954:Models, Biological; D011786:Quality Control; D012542:Scattering, Radiation; D012680:Sensitivity and Specificity; D014463:Ultrasonography / Q000379:methods*; D016217:Ultrasonography, Mammary / Q000379:methods