Point Targets In Images Research Articles

Phase-Shift Depth Migration for Plane-Wave Ultrasound Imaging.

Plane-wave ultrasound imaging is an important modality that enables very high frame rates, which is necessary for adequate characterization of blood flow and tissue motion properties. This work describes a novel Fourier-domain method for plane-wave ultrasound image reconstruction that can be used in situations where the speed of sound varies with depth in a layered propagation medium. Our approach is based on geophysical phase-shift migration technique that has been modified to handle plane-wave ultrasound data processing. Our simulation results show that the proposed method is capable of accurately imaging point targets in a three-layer medium, mimicking tissue-bone-tissue ultrasound propagation.

Evaluation of a frequency-domain ultrasonic imaging attenuation compensation technique.

Ultrasound attenuation is typically compensated for in clinical scanners by using time gain compensation (TGC). However, TGC operates in a frequency-independent fashion and therefore the spatial resolution of the echographic images degrades as the examination depth increases. In the current study, the capability of a multi-band attenuation compensation (MBAC) TGC technique to recover both magnitude and spatial resolution in lossy media was evaluated. Simulations were performed using a 5-MHz transducer for imaging point targets embedded in a medium with attenuation coefficient slope (ACS) of 0.5 dB/(cm.MHz). For performance assessment, the magnitude and spatial resolution of the reflected point spread functions (PSFs) were compared to the ones obtained from point targets embedded in a lossless medium. The results showed a complete recovery of the spectral content when using MBAC for all depths when compared to the lossless case. Both the magnitude and spatial resolution of the compensated PSFs were in agreement with the lossless result (i.e., less than 1 dB and 3 % difference in PSF magnitude and spatial resolution, respectively). The MBAC was then applied to in vivo liver imaging using a scanner equipped with a 5-MHz linear array. Attenuation compensation was performed using ACSs reported in the literature for skin, fat and muscle, and experimentally estimated ACS using the spectral log difference technique for the liver. The lateral and axial extent of the autocorrelation function was estimated in the liver tissue. The experimental MBAC image exhibited only 6 % and 11 % variation in speckle magnitude and lateral autocorrelation length for depths between 2.5 and 4 cm. These results suggest that MBAC technique may enhance speckle uniformity in homogeneous tissue regions.

Algorithms of background suppression in the problem of detection of point targets in images

Various approaches to estimation and suppression of a motionless background with the use of texture correlations in the problem of detection of small-size dynamic targets are considered. Algorithms of suppression of a locally flat background, background suppression by means of bilateral filtration, and an algorithm of background estimation and suppression with the use of an autocorrelation function are implemented. For anisotropic textures with boundary transitions, an algorithm of background estimation and suppression along the boundary and an algorithm of three-channel filtration are proposed and implemented. Operation of these algorithms on textures representing different classes of images is compared. It is demonstrated that the algorithm with background estimation along the boundaries yields good results for model data with a large number of linear boundaries, but its operation on mixed-type textures is less efficient than that of other available approaches. Among the considered algorithms, the approach based on three-channel filtration ensures the greatest increase in the signal/noise ratio for various textures modeling real images.