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As the medical ultrasound signals are not stationary, the radiation pattern of the corresponding input data does not have a specific shape. Thus, their reconstruction using adaptive beamformer (BF) become indispensable in order to improve the quality of the image. Generalized Side Lobe Canceller (GSC) is a robust realization against clutter and interference, resulting from an elegant representation...
Non-contrast blood perfusion imaging with ultrasound is difficult due to tissue clutter caused by patient physiological and sonographer hand motion. This motion causes spectral broadening of the tissue clutter signal, which then overlaps with the perfusion signal. To address this problem, we previously introduced an adaptive frequency and amplitude demodulation scheme to reduce the bandwidth of the...
Ultrafast plane wave microvessel imaging significantly improves ultrasound Doppler sensitivity. The rich spatiotemporal plane wave data enables robust clutter filtering based on singular value decomposition (SVD). However, due to the lack of transmit focusing, plane wave microvessel imaging is very susceptible to noise. The mid-to-deep region of the microvessel image is typically saturated by noise,...
Power Doppler (PD) is the preferred technique for accessing weakly scattering blood cells with low-velocity flow. However, strong clutter decreases sensitivity of the blood signals, which degrades micro-vasculature imaging. Eigen-based filtering methods have been developed to separate the independent scattering sources using both spatial and slow-time statistics of echo data. We recently found that...
Off-axis clutter is a significant cause of image degradation in ultrasound. Adaptive weighting methods based on signal coherence, and adaptive beamforming approaches based on signal direction of arrival, have been proposed to address this problem. Clutter removal is also an important component of pre-processing prior to flow estimation, and adaptive clutter filters based on singular value decomposition...
In the last 10 years the advent of high frame rate ultrasound imaging has allowed the visualization and study of mechanical wave propagation in order to estimate the elastic properties of tissue. Theses waves are detected through the estimation of motion induced by the wave propagation. Despite efficient motion estimator such as speckle tracking or Tissue Doppler Imaging (TDI), the detection of mechanical...
Ultrafast compound Doppler imaging enables high-sensitivity microvascular imaging using the large amount of spatial and temporal samples within a short acquisition time. In addition, the longer ensemble length from the ultrafast transmit strategy facilitates efficient clutter rejection filtering. However, the ultrafast microvascular imaging using plane-wave excitation, which is widely used in linear...
Eigen-filters with attenuation response adapted to clutter statistics in color flow imaging (CFI) have shown improved flow detection sensitivity in the presence of tissue motion. However, its practical adoption for routine use in clinical scanners is hindered by the long processing time required to derive the eigen-components. In this work, we seek to overcome this issue by formulating a parallel-computing...
Signal from tissue will always be present within the lumen of vessels or in the heart. To image blood flow, this clutter needs to be suppressed sufficiently for the weaker blood signal to appear. As the magnitude and direction both of surrounding tissue and blood flow varies throughout the cardiac cycle, non-adaptive clutter filters will inevitably either yield dropouts or a significant tissue velocity...
Singular value decomposition (SVD)-based clutter filtering has demonstrated superior clutter rejection performance in the emerging field of ultrasound microvessel imaging. To alleviate the computational burden of SVD, here we present a fast and robust clutter filter using randomized SVD (rSVD) and randomized spatial downsampling (rSD). rSVD accelerates SVD by approximating and removing the first k-order...
Epi-optoacoustic (OA) imaging allows flexible clinical use, but out-of-plane and echo clutter from strong OA sources limits contrast. In localized vibration tagging (LOVIT), a focused ultrasonic pushing beam creates transient localized displacement and thus a signal phase shift. Subtraction of OA acquisitions before and at the peak displacement highlights signal from the focus and eliminates out-of-plane...
Doppler measurements in coronary arteries are difficult due to rapid motion of the myocardium and small vessel dimensions. High frame rate 3D Doppler imaging with retrospective spectral Doppler processing could potentially solve this. However, the combination of low blood flow velocities and excessive tissue motion in parts of the cardiac cycle makes clutter suppression challenging. In the present...
Recently, ultrafast ultrasound imaging has been proposed for many clinical applications. However, most operational frequencies of ultrafast ultrasound imaging are around 3.5 to 15 MHz. Currently, ultrafast 40 MHz high frequency ultrasound imaging has been developed in our Lab. High frequency ultrasound is a good choice for blood flow mapping because the backscattering signals from blood is increased...
Nonlinear shear waves have a cubic nonlinearity which generates a unique odd harmonic signature. This behavior was first observed in a homogeneous gelatin phantom with ultrafast plane wave compounding ultrasound imaging and correlation-based tracking algorithm that determines particle motion. However, in heterogeneous tissue, like brain, clutter degrades motion tracking and destroys the weak odd harmonics...
Carpal tunnel syndrome (CTS) is the most common wrist neuropathy. Ultrasound can image the tendons in real-time, enabling analysis of tendon dynamics. We earlier developed and validated a speckle tracking algorithm [1] using Normalized Cross Correlation (NCC) on a stationary region of interest (ROI) over the tendon path (Fig 1a). However, NCC is sensitive to clutter and shadows which lead to motion...
Over the past years, the design principle for clutter removal has remained basically the same. The clutter signal has been separated from the blood signal based on the difference in their spectral frequencies. This design presents a major challenge for angle independent estimators, because at high beam-to-flow angles tissue and blood frequency spectra tend to overlap. This work presents a novel filtering...
Recent studies have shown the ability of concurrent spatial-temporal processing methods such as singular value decomposition (SVD) filtering in visualization of the small vessels without using any type of contrast agents. The vessel images resulting from SVD filtering suffer from local and global residual background that limit the visibility of the entire vessel networks within a fixed dynamic range...
Ultrasound plane-wave imaging is desirable for its ability to achieve high frame rates, allowing the capture of fast dynamic events and continuous Doppler data. In most implementations, multiple low-resolution images from different plane-wave azimuthal steering angles are compounded to form a single high-resolution image, thereby reducing the effective frame rate and attenuating signals with high...
Echocardiographic image sequences are frequently corrupted by quasi-static artifacts superimposed on the moving myocardium (“clutter”). Prior work (e.g. Lediju et al., Trans. UFFC 2009) has shown that blind source separation methods can be effective in the removal of clutter. In our prior work (Sathyanarayana et al. IUS 2016), we demonstrated an accelerated method to detect the region of clutter and...
The beamformer is one of the most important components of an ultrasound imaging system. Therefore, numerous beamforming algorithms have been proposed. Two well-known methods for evaluating beamformer performance include reporting the full-width at half-maximum of the lateral beam profile and the contrast ratio observed inside an anechoic cyst relative to the background. However, these metrics are...
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