Browsing by Author "O'Donnell, M."
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Item Open Access Influence of missing array elements on phase aberration correction for medical ultrasound(IEEE, 1994) Karaman, M.; Köymen, Hayrettin; Atalar, Abdullah; O'Donnell, M.The influence of missing array elements on aberration correction based on time delay estimation using radio frequency signals of neighboring elements is experimentally investigated. Normalized cross correlation and sum of absolute differences are employed as the cost functions in aberration estimation. Their performance is tested through various measurements using radio frequency data acquired with a 3.3 MHz, 64-element phased array. Variation of cost functions and phase estimation error are obtained for different combinations of number of missing elements, amount of aberration, and noise level. For a particular combination of these parameters, a set of B-scan images is reconstructed and presented to examine the effects of residual phase errors on image quality.Item Open Access A phase aberration correction method for ultrasound imaging(IEEE, 1993) Karaman, M.; Atalar, Abdullah; Köymen, Hayrettin; O'Donnell, M.A computationally efficient method for phase aberration correction in ultrasound imaging is presented. The method is based on time delay estimation via minimization of the sum of absolute differences between radio frequency samples of adjacent array elements. Effects of averaging estimated aberration patterns over scan angles, and truncation to a single bit wordlength are examined. Phase distortions due to near-field inhomogeneities are simulated using silicone rubber aberrators. Performance of the method is tested using experimental data. Simulation studies addressing different factors affecting efficiency of the method, such as the number of iterations, window length, and the number of scan angles used for averaging, are presented. Images of a standard resolution phantom are reconstructed and used for qualitative testing.Item Open Access Reduction of effects of inactive array elements in phase aberration correction(IEEE, 1993) Karaman, Mustafa; Köymen, Hayrettin; Atalar, Abdullah; O'Donnell, M.Phase aberration correction based on time delay estimation via minimization of sum of absolute difference (SAD) between radio frequency (RF) signals of neighboring elements is studied in the presence of missing elements. To examine the influence of inactive elements, phase estimation error is measured for various combinations of different number of missing elements, aberration level, and SNR. The measurements are performed on an experimental RF data set. Aberration delays of missing elements are interpolated using the phase estimate between the nearest active elements. The B-scan images are reconstructed for qualitative examination.