Browsing by Subject "Ultrasonic imaging"
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Item Open Access An adaptive speckle suppression filter for medical ultrasound imaging(Institute of Electrical and Electronics Engineers, 1995-06) Karaman, M.; Kutay, M. A.; Bozdagi, G.An adaptive smoothing technique for speckle suppression in medical B-scan ultrasonic imaging is presented. The technique is based on filtering with appropriately shaped and sized local kernels. For each image pixel, a filtering kernel, which fits to the local homogeneous region containing the processed pixel, is obtained through a local statistics based region growing technique. The performance of the proposed filter has been tested on the phantom and tissue images. The results show that the filter effectively reduces the speckle while preserving the resolvable details. The simulation results are presented in a comparative way with two existing speckle suppression methods.Item Open Access Enhancement of images corrupted with signal dependent noise: Application to ultrasonic imaging(1993-11) Kutay, M. Alper; Karaman, Mustafa; Bozdağı, GözdeAn adaptive filter for smoothing images corrupted by signal dependent noise is presented. The filter is mainly developed for speckle suppression in medical B-scan ultrasonic imaging. The filter is based on mean filtering of the image using appropriately shaped and sized local kernels. Each filtering kernel, fitting to the local homogeneous region, is obtained through local statistics based region growing. Performance of the proposed scheme have been tested on a B-scan image of a standard tissue-mimicking ultrasound resolution phantom. The results indicate that the filter effectively reduces the speckle while preserving the resolvable details. The performance figures obtained through computer simulations on the phantom image are presented in a comparative way with some existing speckle iippression schemes.Item Open Access Microfabricated ultrasonic transducers: towards robust models and immersion devices(IEEE, 1996-11) Ladabaum, I.; Jin, X.; Soh, H. T.; Pierre, F.; Atalar, Abdullah; Khuri-Yakub, B. T.The successful fabrication of ultrasonic immersion transducers is reported. Transducers are observed to operate from 1 MHz to 20 MHz in water, with the frequency range limited by electronics, not the transducers. Transmission results are included which show that a single pair of transducers is able to operate in water at 4, 6, and 8 MHz with a signal to noise ratio of at least 48 dB. The same transducer pair is shown to operate in air at 6 MHz. A model is introduced which highlights the significant parameters of transducer design. The model enables the design of optimized transducers.Item Open Access Micromachinable leaky wave air transducers(IEEE, 1997-11) Değertekin, F. L.; Atalar, Abdullah; Khuri-Yakub, B. T.In this paper, ultrasonic air transducers which use the lowest order antisymmetric (A/sub 0/) mode Lamb waves in a thin plate as a means of efficient coupling of ultrasonic energy to air are discussed. For a silicon plate of 1 /spl mu/m thickness, the energy leak rates can go up to 0.6 dB per wavelength. At MHz frequencies the plate thickness should be in the range of 1-10 /spl mu/m, which requires micromachined structures to be used. The radiation pattern of the transducers can be controlled by the geometry of the transducer, which can also be used for focusing. A theoretical model to calculate the efficiency and optimized transducer dimensions is presented. This model is applied to common micromachining materials such as silicon, silicon nitride and silicon dioxide. The analysis show that, with these transducers it is possible to achieve a conversion loss with a minimum of 8.7 dB and 78% fractional bandwidth. Experimental results on transmission imaging are also presented using an implementation of the transducer operating around 580 kHz.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.Item Open Access VLSI circuits for adaptive digital beamforming in ultrasound imaging(IEEE, 1993) Karaman, M.; Atalar, Abdullah; Köymen, HayrettinFor phased-array ultrasound imaging, alternative beamforming techniques and their VLSI circuits are studied to form a fully digital receive front-end hardware. In order to increase the timing accuracy in beamforming, a computationally efficient interpolation scheme to increase the sampling rate is examined. For adaptive beamforming, a phase aberration correction method with very low computational complexity is described. Image quality performance of the method is examined by processing the non-aberrated and aberrated phased-array experimental data sets of an ultrasound resolution phantom. A digital beamforming scheme based on receive focusing at the raster focal points is examined. The sector images of the resolution phantom, reconstructed from the phased-array experimental data by beamforming at the radial and raster focal points, are presented for comparison of the image resolution performances of the two beamforming schemes. VLSI circuits and their implementations for the proposed techniques are presented.Item Open Access A VLSI receive beamformer for digital ultrasound imaging(IEEE, 1992-03) Karaman, Mustafa; Kolağasıoğlu, Ertuğrul; Atalar, AbdullahA VLSI architecture for real-time digital receive beamforming in phased array ultrasound imaging is proposed. The architecture is an inverse binary tree like structure with N stages where N is the number of array elements. The sampled signals from the phased array channels are coherently added in a pairwise manner within the stages of the architecture in a pipelined data flow scheme. The storage requirement for the synchronization of the asynchronously received samples corresponding to a focal point is significantly reduced. The architecture is modular and has a regular communication scheme which make the VLSI implementation rather easy and straightforward.