Novel beamforming techniques for robust contrast enhancement in ultrasound imaging

2014-05-19Ultrasound is one of the most widely used imaging modalities in clinics today. Despite its numerous advantages, ultrasound often suffers from poor image contrast, making visualization of anatomical structures difficult. In order to address this problem, a novel beamforming technique called Dual Apodization with Cross‐correlation (DAX), which can achieve significant improvements in ultrasound image contrast, was proposed. The novelty in DAX is that, instead of a single receive apodization utilized in conventional delay‐and‐sum (DAS) beamforming, it uses two distinct receive apodizations to generate two point spread functions having similar mainlobe signals but very different clutter patterns. The differences in the clutter patterns can then be detected by means of normalized cross‐correlation, and the coefficients can be multiplied with the standard DAS beamformed RF data to suppress contributions of clutter without any comprise in spatial resolution. Although this technique has potentials for better image quality and hence, more accurate diagnosis, the robustness of the algorithm in the presence of high levels of phase aberration and reverberation clutter needs to be improved. The contributions of this dissertation include demonstrating the limitations of DAX, proposing several new strategies to overcome such limitations, and evaluating their performance in simulation, tissue‐mimicking phantom and in‐vivo. Since DAX requires a good focusing quality for better clutter suppression, one of these new strategies is a method that combines DAX with a phase aberration correction technique which aims to restore some of the coherence lost by sound speed inhomogeneities in soft tissues. The second method proposed in this dissertation aims to improve the performance by employing an approach that combines DAX with harmonic imaging, which has been shown to produce reduced effects of phase aberration and reverberation clutter. ❧ Furthermore, a modified version of DAX called Multi‐Apodization with Cross‐correlation (MAX) as well as a new technique called Multi‐Phase Apodization with Cross‐correlation (MPAX), which utilizes multiple phase apodization pairs, are proposed and their performance is evaluated both in phantom and in‐vivo. In summary, this dissertation describes novel beamforming techniques that can achieve a large improvement in image contrast and demonstrates their feasibility and potentials if successfully implemented in commercial scanners used in clinics