Speckle noise is an integral component in medical ultrasound imaging, which have a random granular pattern formation. This noise degrades the visual quality of ultrasound images and complicates image-based interpretation and diagnosis. The removal of interference-induced noise is a primary challenge as ultrasound image studies seek to achieve higher accuracy and characterize more subtle small and low-contrast lesions. In this study, a novel method, which combines the nonlocal-means (NLM) filter with a simple unsupervised deep model named Laplacian Eigenmaps network (LENet), has been proposed for ultrasonic speckle reduction. The proposed method exploits both the global features, redundancy information and self-similarity properties of noisy images, which first extract features from the noisy image by the Laplacian Eigenmaps algorithm, and then apply it to refine the image self-similarities weight for helping the NLM filter to provide better despeckling performance. Specifically, this is a two-stage approach that the first stage is to learn filter banks from a small quantity of training samples by LENet network and the following stage is to utilize the output eigenvectors as similarity metrics of pixels within the NLM filter. The performance of our approach is compared with related state-of-the-art methods on synthetic images, simulated image and real ultrasound images. The results show that our method can provide better noise removal ability over many previously despecking filters.
Ultrasound contrast agents (UCAs) such as SonoVue or Optison have been used widely in clinic
for contrast-enhanced vascular imaging. However, microbubbles UCAs display limitations in
tumor-targeted imaging due to the large sizes, nanoscaled UCAs has consequently attracted increasing
attentions. In this work, we synthesized nanobubbles (NBs) by ultrasonic cavitation method, then a
fluorescent marker of Alexa Fluor 680 was conjugated to the shell in order to observe the localization
of NBs in tumor tissue. Measurement of fundamental characteristics showed that the NBs had
homogeneous distribution of mean diameter of 267.9 ± 19.2 nm and polydispersity index of 0.410 ±
0.056. To assess in vivo tumor-selectivity of NBs, we established the rabbits VX2 hepatocellular
carcinoma model though surgical implantation method. After the rabbits were intravenous administered
of NBs, contrast-enhanced sonograms was observed in the surrounding of VX2 tumor, which showed
there are rich capillaries in the tumor periphery. We additionally investigated the toxic of the NBs by
hematoxylin-eosin staining. The results indicated that the NBs is a biocompatible non-toxic lipid
system. Furthermore, the VX2 tumors and major organs were analyzed using ex vivo fluorescence
imaging to confirm the targeted selectivity of NBs, and the results verified that the NBs were capable
of targeting VX2 tumor. Confocal laser scanning microscopy examination showed that the NBs can
traverse the VX2 tumor capillaries and target to the hepatocellular carcinoma tumor cells. All these
results suggested that the newly prepared NBs have a potential application in molecular imaging and
tumor-targeting therapy.
Recent literatures have reported that the targeted nanoscale ultrasound contrast agents are becoming more and more important in medical application, like ultrasound imaging, detection of perfusion, drug delivery and molecular imaging and so on. In this study, we fabricated an uniform nanoscale bubbles (257 nm with the polydispersity index of 0.458) by incorporation of antibody targeted to vascular endothelial growth factor receptor 2 (VEGFR2) into the nanobubbles membrane by using avidin-biotin interaction. Some fundamental characterizations such as nanobubble suspension, surface morphology, particle size distribution and zeta potential were investigated. The concentration and time-intensity curves (TICs) were obtained with a self-made ultrasound experimental setup in vitro evaluation. In addition, in order to evaluate the contrast enhancement ability and the potential tumor-targeted ability in vivo, normal Wistar rats and nude female BALB/c mice were intravascular administration of the nanobubbles via tail vein injection, respectively. Significant contrast enhancement of ultrasound imaging within liver and tumor were visualized. These experiments demonstrated that the targeted nanobubbles is efficient in ultrasound molecular imaging by enhancement of the contrast effect and have potential capacity for targeted tumor diagnosis and therapy in the future.
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