Immediate postoperative assessment of trans-arterial chemoembolization (TACE) using gold standard modalities, MRI and CT, is unreliable due to confounding interactions with lipiodol and post-embolization inflammatory changes. We previously demonstrated that recent advancements in power Doppler ultrasound processing enables changes in slow blood flow to be detected immediately following TACE. Recently, we have developed a filtering method that employs a higherorder singular value decomposition (HOSVD) applied to aperture data to mitigate thermal noise and acoustic clutter. Here, we investigate HOSVD as a tool to improve non-contrast ultrasound evaluation of TACE. Preliminary feasibility is demonstrated in a small pilot study. Treatment-induced changes in perfusion are visualized most readily using the HOSVD filter in comparison to conventional filtering methods. The HOSVD filter produced the greatest change in contrast between pre-TACE and post-TACE power Doppler images.
Ultrasonic flow imaging remains susceptible to cluttered imaging environments, which often results in degraded image quality. Coherent Flow Power Doppler (CFPD)–a beamforming technique–has demonstrated efficacy in addressing sources of diffuse clutter. CFPD depicts the normalized spatial coherence of the backscattered echo, which is described by the van Cittert-Zernike theorem. However, the use of a normalized coherence metric in CFPD uncouples the image intensity from the magnitude of the underlying blood echo. As a result, CFPD is not a robust approach to study gradation in blood echo energy, which depicts the fractional moving blood volume. We have developed a modified beamforming scheme, termed power-preserving Coherent Flow Power Doppler (ppCFPD), which employs a measure of signal covariance across the aperture, rather than normalized coherence. As shown via Field II simulations, this approach retains the clutter suppression capability of CFPD, while preserving the underlying signal energy, similar to standard power Doppler (PD). Furthermore, we describe ongoing work, in which we have proposed a thresholding scheme derived from a statistical analysis of additive noise, to further improve perception of flow. Overall, this adaptive approach shows promise as an alternative technique to depict flow gradation in cluttered imaging environments.
Interest in ultrasound perfusion imaging has grown with the development of more sensitive algorithms to detect slow blood flow. Unfortunately, there are not many phantoms that can be used to evaluate these techniques. Some have used small linear tubes, while others have adapted dialysis cartridges. Here we propose a technique using conventional gelatin cast around a sacrificial polymer network. Specifically, we form a gelatin phantom, doped with graphite scatterers to mimic the diffuse scattering in soft tissue, around a polymer resin. The resin structure can be dissolved leaving behind a network of small randomly oriented channels that are connected to a large channel which is connected to a pump to perfuse blood mimicking fluid through the phantom. The phantoms were qualitatively demonstrated to show perfusion through visual confirmation and the speckle SNR, and speed of sound were calculated.
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