The Department of Medical Biophysics, University of Toronto, Sunnybrook Health Science Centre, Riechmann Research Building, 2075 Bayview Ave., Toronto, Ontario M4N-3M5, Canada
Abstract:
Two methods for correction of unknown phase aberrations induced by inhomogeneous acoustic velocities in tissues are explored for the two dimensional geometry of a sectored annular array system. The methods employed are adaptations of a cross correlation technique and a speckle brightness maximization technique. The methods correct phase distortions via the introduction of phase shifts in the timing sequence at the beamformer stage of a sectored annular array transducer. The techniques are investigated employing software models and a computer controlled automated scanning system. A 65-element sectored annular array is modelled via a rotating 5 element transducer. Tissue equivalent materials were moulded into a double layer aberrating medium to simulate phase distortions encountered in the rectus abdominis muscle in vivo. A comparison of the effectiveness of the two correction methods is presented. Contrast of an anechoic region is increased from 0.34 ± 0.08 to 0.48 ± 0.06 for the cross correlation technique, and up to 0.62 ± 0.05 for the speckle brightness maximization method. The performance of these correction techniques on target phantoms suggests that considerable improvements in image quality should be possible for clinical systems.