Microvessel Imaging Research Articles

Analysis of microvasculature morphological features for prediction of metastatic lymph nodes in breast cancer patients via contrast-free ultrasound imaging

Axillary lymph nodes (ALNs) are generally among the first to be impacted by the metastatic spread of breast tumors. Consequently, evaluating their condition is of great importance as the removal of affected ALNs can potentially curtail the further spread of cancer cells to other parts of the body. Conventional ultrasound imaging suffers from low sensitivity and specificity and does not provide a comprehensive picture of the status of the node. In this work, we utilize an ultrasound microvessel imaging technique to visualize vascular structures within ALNs and, through several image processing steps, characterize the morphology of these structures. Several morphological metrics are used as biomarkers to differentiate between reactive and metastatic lymph nodes of patients with suspicious ALNs. A group of 68 patients is included in this study. Pathology examination results are used as the gold-standard reference for data labeling. A support vector machine (SVM) model is trained, and its performance is evaluated. Statistical analysis of the discriminative potential of individual biomarkers and receiver operating characteristic (ROC) curve analysis of the trained model are presented. Preliminary results suggest that a sensitivity of 0.88, specificity of 0.88, and area under the curve of 0.94 are achievable. Work supported by NIH-R01CA239548.

Resolution and contrast improved ultrafast power Doppler microvessel imaging with null subtraction imaging

In this work, we demonstrate a novel non-linear beamforming technique, called null-subtraction imaging (NSI), to improve spatial resolution and image contrast of ultrafast, power Doppler microvessel imaging without significantly increasing computational cost compared to traditional delay and sum (DAS). NSI is a non-linear beamforming technique that operates on receive data by subtracting envelopes of beamforming results from three apodization windows. An array transducer and Verasonics Vantage 256 system were used to capture 1600 frames of raw ultrasonic radio frequency (RF) channel data by scanning a rat brain using nine plane waves spanning angles between -4° and 4° at a pulse repetition frequency of 1000 Hz. A singular value decomposition filter was applied on the raw RF channel data to filter out the tissue signal. Coherent compounding was performed individually on the beamformed result for each apodization window. Next, the subtraction of the envelopes for each apodization was conducted to form the NSI image. A total of 1,600 frames of NSI images were accumulated to form the final image. The NSI based ultrafast power Doppler microvessel imaging provided a ten-fold improvement in spatial resolution and a three-fold improvement in image contrast compared with the traditional DAS-based ultrafast power Doppler microvessel imaging.

Ultrasensitive US Microvessel Imaging of Hepatic Microcirculation in the Cirrhotic Rat Liver.

Background Liver microcirculation dysfunction plays a vital role in the occurrence and development of liver diseases, and thus, there is a clinical need for in vivo, noninvasive, and quantitative evaluation of liver microcirculation. Purpose To evaluate the feasibility of ultrasensitive US microvessel imaging (UMI) in the visualization and quantification of hepatic microvessels in healthy and cirrhotic rats. Materials and Methods In vivo studies were performed to image hepatic microvasculature by means of laparotomy in Sprague-Dawley rats (five cirrhotic and five control rats). In vivo conventional power Doppler US and ex vivo micro-CT were performed for comparison. UMI-based quantifications of perfusion, tortuosity, and integrity of microvessels were compared between the control and cirrhotic groups by using the Wilcoxon test. Spearman correlations between quantification parameters and pathologic fibrosis, perfusion function, and hepatic hypoxia were evaluated. Results UMI helped detect minute vessels below the liver capsule, as compared with conventional power Doppler US and micro-CT. With use of UMI, lower perfusion indicated by vessel density (median, 22% [IQR, 20%-28%] vs 41% [IQR, 37%-46%]; P = .008) and fractional moving blood volume (FMBV) (median, 6.4% [IQR, 4.8%-8.6%] vs 13% [IQR, 12%-14%]; P = .008) and higher tortuosity indicated by the sum of angles metric (SOAM) (median, 3.0 [IQR, 2.9-3.0] vs 2.7 [IQR, 2.6-2.9]; P = .008) were demonstrated in the cirrhotic rat group compared with the control group. Vessel density (r = 0.85, P = .003), FMBV (r = 0.86, P = .002), and median SOAM (r = -0.83, P = .003) showed strong correlations with pathologically derived vessel density labeled with dextran. Vessel density (r = -0.81, P = .005) and median SOAM (r = 0.87, P = .001) also showed strong correlations with hepatic tissue hypoxia. Conclusion Contrast-free ultrasensitive US microvessel imaging provided noninvasive in vivo imaging and quantification of hepatic microvessels in cirrhotic rat liver. © RSNA, 2022 Supplemental material is available for this article. See also the editorial by Fetzer in this issue.

Contrast free super-resolution microvessel imaging based on deep learning

Super-resolution microvascular imaging (SRMI) based on ultrasound localization microscopy (ULM) breaks the diffraction limit of conventional ultrasound by exploiting intravascular microbubbles. However, microbubble injection makes ULM not entirely noninvasive and less practical. On the other hand, power Doppler (PD) is contrast-free and widely available in clinic, but PD’s spatial resolution falls short of revealing tissue microvasculature. In this study, we propose a deep learning-based, contrast-free SRMI method to improve the spatial resolution of PD. We designed a modified U-Net structure with 4 layers in depth with 64 to 512 channels. Ultrafast ultrasound data (1000 Hz frame rate) acquired from 16 mice were made into the 4080 data blocks used for training. Reconstructed ULM images using 32 s acquisition served as the labelled ground truth. Contrast-free ultrasound data using 0.4 s acquisition were used as the network input. The results have shown that the proposed DL-based method can significantly improve the spatial resolution of contrast-free power Doppler without creating fake vessels. The full width half-maximum (FWHM) of the cross-sectional profile of a microvessel was improved from 66 to 24 μm. Robust generalizability of the proposed DL method was also demonstrated on various tissues and organs that were absent in training.

Adaptive and Robust Vessel Quantification in Contrast-Free Ultrafast Ultrasound Microvessel Imaging.

The morphological features of vasculature in diseased tissue differ significantly from those in normal tissue. Therefore, vasculature quantification is crucial for disease diagnosis and staging. Ultrasound microvessel imaging (UMI) with ultrafast ultrasound acquisitions has been determined to have potential in clinical applications given its superior sensitivity in blood flow detection. However, the presence of spatial-dependent noise caused by a low imaging signal-to-noise ratio and incoherent clutter artifacts caused by moving hyperechoic scatterers degrades the performance of UMI and the reliability of vascular quantification. To tackle these issues, we proposed an improved UMI technique along with an adaptive vessel segmentation workflow for robust vessel identification and vascular feature quantification. A previously proposed sub-aperture cross-correlation technique and a normalized cross-correlation technique were applied to equalize the spatially dependent noise level and suppress the incoherent clutter artifact. A square operator and non-local means filter were then used to better separate the blood flow signal from residual background noise. On the de-noised ultrasound microvessel image, an automatic and adaptive vessel segmentation method was developed based on the different spatial patterns of blood flow signal and background noise. The proposed workflow was applied to a CIRS phantom, to a Doppler flow phantom and to an inflammatory bowel, kidney and liver, to validate its feasibility. Results revealed that automatic adaptive, and robust vessel identification performance can be achieved using the proposed method without the subjectivity caused by radiologists/operators.

High-Resolution Imaging of the Ocular Vasculature of Conjunctivitis in Mice Using Highly Bright Polymer Dots.

Ocular diseases are mainly caused by vascular aberrations in the eye, and accurate imaging and analysis of the ocular vascular structure is crucial. In this study, poly(9,9-dioctylfluorene-alt-benzothiadiazole) (PFBT) polymer dots (Pdots), with the advantages of easy synthesis, high brightness, and low toxicity, are used as nanoprobes to perform high-resolution imaging of the vasculature of the eyeball and optic nerve. Moreover, rapid imaging of the choroidal microvessels is carried out by stereoscopic fluorescence microscopy with a resolution of up to 1.6µm. The comprehensive 3D vascular information of retinal aorta and optic nerve microvessels is obtained by combining tissue clearing and multiphoton microscopy. In addition, the vascular density of Schlemm's canal and iris blood vessels is compared between the conjunctivitis mice and the normal mice. These results suggest that PFBT Pdots have great application potential in the fast and accurate imaging of ocular diseases.

Adipose Stromal Vascular Fraction Reverses Mitochondrial Hyperfission in Coronary Microvessels in Aging

IntroductionIn aging post‐menopausal women, Coronary Microvascular Disease (CMD) leads to hyperconstricted tone, reduced perfusion and chronic micro‐ischemia with angina. We previously showed an age‐related increase in coronary microvascular ROS alongside increased prooxidant gene and protein expression associated with blunted vasodilation. Adipose Stromal Vascular Fraction (SVF) is a heterogenous cell population that reduces vascular ROS to improve vasodilation. Oxidative stress with aging may be mediated by mitochondrial dysfunction, including fission/fusion imbalance. Therefore, we hypothesize aging leads to mitochondrial hyperfission and reduced fusion gene and protein expression, reversed by SVF therapy.MethodsCoronary microvessels from young (YC, 4 months), old (OC, 24 months), or old + SVF (OSVF, tail vein injection 4 weeks prior to sacrifice) from female Fischer 344 rats were assessed via RNA sequencing (n=3) and immunofluorescence imaging of fission/fusion proteins Dynamin Related Protein 1 (DRP‐1) and Mitofusin 1 & 2 (MFN1 & 2). Morphometric analysis was accomplished using ImageJ and the MiNA Image‐J tool to analyze 60x confocal images of microvessels stained with antibodies against mitochondrial TOM20. Statistics were preformed using One‐Way ANOVA with Bonferroni post hoc analysis.ResultsGene expression of DRP‐1 was significantly reduced, and MFN‐1 significantly enhanced in OSVF vs. OC (p = 0.035, 0.019). There was no significant difference in gene expression of fission or fusion mediators Fis‐1, MFN‐2 or Opa‐1. Protein expression of DRP‐1 was enhanced with aging, reduced to youthful levels by SVF (p = 0.007, 0.033) (Fig.1a). There were no differences in MFN1 or MFN2 protein expression with aging, however, protein expression of MFN‐1 was significantly increased after SVF (YC vs. OSVF p = 0.003, OC vs. OSVF p < .001). Mitochondrial aspect ratio and form factor were reduced in aging (p = 0.024, < 0.001), restored to youthful levels by SVF (p = < 0.001, < 0.001) (Fig. 1b). Mitochondrial fission factor was elevated with aging (p = < 0.001), reversed by SVF therapy (p = < 0.001) (Fig. 1c). Mitochondrial area was reduced with aging (p = 0.002). Mitochondrial branch length and numbers of branches within a network were greatest in youth, significantly attenuated with aging (p < 0.001, < 0.001), and significantly increased (albeit not to youthful levels) with SVF therapy (OC vs. OSVF: p = 0.017, 0.011, YC vs. OSVF: p = 0.004, 0.003) (Fig. 1d).ConclusionsDuring youth, mitochondrial morphology is more rod‐like and interconnected, vs. punctate and isolated in aging. Injection of SVF reversed mitochondrial circularity and partially restored mitochondrial network density in aging. These findings were complimented by enhanced expression of DRP‐1 with aging with reduced DRP‐1 and enhanced MFN‐1 expression with SVF. SVF is a plausible therapy for CMD by reversing mitochondrial dysfunction including alleviating oxidative stress, attenuating mitochondrial fission, and rejuvenating mitochondrial fusion.

Ultrasound high-definition microvasculature imaging with novel quantitative biomarkers improves breast cancer detection accuracy

ObjectivesTo overcome the limitations of power Doppler in imaging angiogenesis, we sought to develop and investigate new quantitative biomarkers of a contrast-free ultrasound microvasculature imaging technique for differentiation of benign from malignant pathologies of breast lesion.MethodsIn this prospective study, a new high-definition microvasculature imaging (HDMI) was tested on 521 patients with 527 ultrasound-identified suspicious breast masses indicated for biopsy. Four new morphological features of tumor microvessels, microvessel fractal dimension (mvFD), Murray’s deviation (MD), bifurcation angle (BA), and spatial vascularity pattern (SVP) as well as initial biomarkers were extracted and analyzed, and the results correlated with pathology. Multivariable logistic regression analysis was used to study the performance of different prediction models, initial biomarkers, new biomarkers, and combined new and initial biomarkers in differentiating benign from malignant lesions.ResultsThe new HDMI biomarkers, mvFD, BA, MD, and SVP, were statistically significantly different in malignant and benign lesions, regardless of tumor size. Sensitivity and specificity of the new biomarkers in lesions > 20 mm were 95.6% and 100%, respectively. Combining the new and initial biomarkers together showed an AUC, sensitivity, and specificity of 97% (95% CI: 95–98%), 93.8%, and 89.2%, respectively, for all lesions regardless of mass size. The classification was further improved by adding the Breast Imaging Reporting and Data System (BI-RADS) score to the prediction model, showing an AUC, sensitivity, and specificity of 97% (95% CI: 95–98%), 93.8%, and 89.2%, respectively.ConclusionThe addition of new quantitative HDMI biomarkers significantly improved the accuracy in breast lesion characterization when used as a complementary imaging tool to the conventional ultrasound.Key Points• Novel quantitative biomarkers extracted from tumor microvessel images increase the sensitivity and specificity in discriminating malignant from benign breast masses.• New HDMI biomarkers Murray’s deviation, bifurcation angles, microvessel fractal dimension, and spatial vascularity pattern outperformed the initial biomarkers.• The addition of BI-RADS scores based on US descriptors to the multivariable analysis using all biomarkers remarkably increased the sensitivity, specificity, and AUC in all size groups.

Real-time X-ray imaging of mouse cerebral microvessels in vivo using a pixel temporal averaging method.

Rodents are used extensively as animal models for the preclinical investigation of microvascular-related diseases. However, motion artifacts in currently available imaging methods preclude real-time observation of microvessels invivo. In this paper, a pixel temporal averaging (PTA) method that enables real-time imaging of microvessels in the mouse brain in vivo is described. Experiments using live mice demonstrated that PTA efficiently eliminated motion artifacts and random noise, resulting in significant improvements in contrast-to-noise ratio. The time needed for image reconstruction using PTA with a normal computer was 250 ms, highlighting the capability of the PTA method for real-time angiography. In addition, experiments with less than one-quarter of photon flux in conventional angiography verified that motion artifacts and random noise were suppressed and microvessels were successfully identified using PTA, whereas conventional temporal subtraction and averaging methods were ineffective. Experiments performed with an X-ray tube verified that the PTA method could also be successfully applied to microvessel imaging of the mouse brain using a laboratory X-ray source. In conclusion, the proposed PTA method may facilitate the real-time investigation of cerebral microvascular-related diseases using small animal models.

Quantitative Biomarkers for Cancer Detection Using Contrast-Free Ultrasound High-Definition Microvessel Imaging: Fractal Dimension, Murray's Deviation, Bifurcation Angle & Spatial Vascularity Pattern.

A growing body of evidence indicates that there is a strong correlation between microvascular morphological features and malignant tumors. Therefore, quantification of these features might allow more accurate differentiation of benign and malignant tumors. The main objective of this research project is to improve the quantification of microvascular networks depicted in contrast-free ultrasound microvessel images. To achieve this goal, a new series of quantitative microvessel morphological parameters are introduced for differentiation of breast masses using contrast-free ultrasound-based high-definition microvessel imaging (HDMI). Using HDMI, we quantified and analyzed four new parameters: 1) microvessel fractal dimension (mvFD), a marker of tumor microvascularcomplexity; 2) Murray’sdeviation(MD), the diameter mismatch, defined as the deviation from Murray’s law; 3) bifurcation angle (BA), abnormally decreased angle; and 4) spatial vascular pattern (SVP), indicating tumor vascular distribution pattern, either intratumoral or peritumoral. The new biomarkers have been tested on 60 patients with breast masses. Validation of the feature’s extraction algorithm was performed using a synthetic data set. All the proposed parameters had the power to discriminate the breast lesion malignancy (p < 0.05), displaying BA as the most sensitive test, with a sensitivity of 90.6%, and mvFD as the most specifictest, with a specificityof 92%. The results of all four new biomarkers showed an AUC = 0.889, sensitivity of 80% and specificity of 91.4% In conclusion, the added value of the proposed quantitative morphological parameters, as new biomarkers of angiogenesis within breast masses, paves the way for more accurate breast cancer detection with higher specificity.

Study on the Application of Super-Resolution Ultrasound for Cerebral Vessel Imaging in Rhesus Monkeys.

Background: Ultrasound is ideal for displaying intracranial great vessels but not intracranial microvessels and terminal vessels. Even with contrast agents, the imaging effect is still unsatisfactory. In recent years, significant theoretical advances have been achieved in super-resolution imaging. The latest commonly used ultrafast plane-wave ultrasound Doppler imaging of the brain and microbubble-based super-resolution ultrasound imaging have been applied to the imaging of cerebral microvessels and blood flow in small animals such as mice but have not been applied to in vivo imaging of the cerebral microvessels in monkeys and larger animals. In China, preliminary research results have been obtained using super-resolution imaging in certain fields but rarely in fundamental and clinical experiments on large animals. In recent years, we have conducted a joint study with the Xi'an Jiaotong University to explore the application and performance of this new technique in the diagnosis of cerebrovascular diseases in large animals.Objective: To explore the characteristics and advantages of microbubble-based super-resolution ultrasound imaging of intracranial vessels in rhesus monkeys compared with conventional transcranial ultrasound.Methods: First, the effectiveness and feasibility of the super-resolution imaging technique were verified by modular simulation experiments. Then, the imaging parameters were adjusted based on in vitro experiments. Finally, two rhesus monkeys were used for in vivo experiments of intracranial microvessel imaging.Results: Compared with conventional plane-wave imaging, super-resolution imaging could measure the inner diameters of cerebral microvessels at a resolution of 1 mm or even 0.7 mm and extract blood flow information. In addition, it has a better signal-to-noise ratio (5.625 dB higher) and higher resolution (~30-fold higher). The results of the experiments with rhesus monkeys showed that microbubble-based super-resolution ultrasound imaging can achieve an optimal resolution at the micron level and an imaging depth >35 mm.Conclusion: Super-resolution imaging can realize the monitoring imaging of high-resolution and fast calculation of microbubbles in the process of tissue damage, providing an important experimental basis for the clinical application of non-invasive transcranial ultrasound.

Ultrasound imaging of preterm brain injury: fundamentals and updates.

Neurosonography has become an essential tool for diagnosis and serial monitoring of preterm brain injury. Preterm infants are at significantly higher risk of hypoxic-ischemic injury, intraventricular hemorrhage, periventricular leukomalacia and post-hemorrhagic hydrocephalus. Neonatologists have become increasingly dependent on neurosonography to initiate medical and surgical interventions because it can be used at the bedside. While brain MRI is regarded as the gold standard for detecting preterm brain injury, neurosonography offers distinct advantages such as its cost-effectiveness, diagnostic utility and convenience. Neurosonographic signatures associated with poor long-term outcomes shape decisions regarding supportive care, medical or behavioral interventions, and family members' expectations. Within the last decade substantial progress has been made in neurosonography techniques, prompting an updated review of the topic. In addition to the up-to-date summary of neurosonography, this review discusses the potential roles of emerging neurosonography techniques that offer new functional insights into the brain, such as superb microvessel imaging, elastography, three-dimensional ventricular volume assessment, and contrast-enhanced US.

Small G1 type III gastric neuroendocrine cell tumor showing scirrhous invasion and lymph node metastasis

A 42-year-old woman underwent upper endoscopy for screening. EGD revealed a raised lesion with a central depression in the lesser curvature of the lower body of the stomach (A). Magnified endoscopy with narrow-band imaging showed that most of the surface of the tumor had a normal pattern. However, in the central depression, the pit structures were disappearing, the microvessel image was slightly irregular, and dilatated cyan subepithelial vessels were seen there with magnified endoscopy with narrow-band imaging (B). The biopsy result revealed a gastric neuroendocrine tumor (NET). The serum gastrin level was 116 pg/mL, and test results for antiparietal cell antibody and Helicobacter pylori infection were negative. Therefore, the NET was diagnosed as a type III gastric NET. We performed endoscopic submucosal dissection for the tumor. However, the tumor was adhered to the muscle layer; therefore, it was difficult to dissect the tumor (C). The tumor diameter was 8 mm. NET was observed in the mucosa and submucosa (D, H&E, org. mag. ×100); in particular, the tumor cells infiltrated into the submucosa with strong fibrosis, like scirrhous (E, H&E, org. mag. ×100, F, α-smooth muscle actin, orig. mag. ×100), resulting in incomplete resection. Notably, the Ki67 index of the tumor was 2%; therefore, this tumor was classified as NET G1. Additional surgical resection revealed no residual tumor; however, 2 lymph node metastases were observed.

Dietary tomato inhibits angiogenesis in TRAMP prostate cancer but is not protective with a Western-style diet in this pilot study

Prostate cancer (PCa) remains the second most diagnosed cancer worldwide. Higher body weight is associated with chronic inflammation, increased angiogenesis, and treatment-resistant tumor phenotypes. Dietary tomato reduces PCa risk, which may be due to tomato inhibition of angiogenesis and disruption of androgen signaling. This pilot study investigated the interplay between tomato powder (TP), incorporated into control (CON) and obesogenic (OB) diets, and PCa tumor growth and blood perfusion over time in a transgenic model of PCa (TRAMP). Ultrasound microvessel imaging (UMI) results showed good agreement with gold-standard immunohistochemistry quantification of endothelial cell density, indicating that this technique can be applied to non-invasively monitor tumor blood perfusion in vivo. Greater body weight was positively associated with tumor growth. We also found that TP significantly inhibited prostate tumor angiogenesis but that this inhibition differentially affected measured outcomes depending on CON or OB diets. TP led to reduced tumor growth, intratumoral inflammation, and intratumoral androgen-regulated gene expression (srd5a1, srd5a2) when incorporated with the CON diet but greater tumor growth and intratumoral gene expression when incorporated with the OB diet. Results from this study show that protective benefits from dietary tomato are lost, or may become deleterious, when combined with a Western-style diet.

Dietary Tomato Inhibits Tumor Angiogenesis in the TRAMP Model of Prostate Cancer but Is Not Protective With a Western-Style Diet

Abstract Objectives The objective of this study was to investigate the interplay between tomato powder (TP), incorporated into control (CON) and obesogenic (OB) diets, and PCa tumor growth and blood perfusion over time in a transgenic model of PCa. We hypothesized that TP would be protective against PCa growth. Methods Diets (either CON [17.2% kcal from fat] or OB [44.6% kcal from fat] both with and without 10% TP) were fed to transgenic adenocarcinoma of the mouse prostate (TRAMP) mice (n = 5/dietary group) from weaning. Tumor growth was monitored by weekly ultrasound scanning, at which time novel ultrasound microvessel images (UMI) were captured to quantitatively measure tumor blood perfusion over time. Animals were euthanized after 5 weeks of tumor growth, and tissues were collected for measurement of protein (HIF-1α, TNFα) and gene (ar, srd5a1, srd5a2) expression. Data were analyzed to determine differences between CON diets (without TP + with 10% TP) and OB diets (without TP + with 10% TP) and to evaluate the impact of 10% TP on outcome measures both independent of TP (No TP vs. TP) as well as within CON and OB diets (interaction effect of diet*TP) by mixed model ANCOVA with body weight as a covariate. Results UMI results showed good agreement with gold-standard immunohistochemistry quantification of endothelial cell density, indicating that this technique can be applied to non-invasively and longitudinally monitor tumor blood perfusion in vivo. Greater body weight (P = 0.029) and OB diets (P = 0.008) were associated with earlier age at tumor detection, and greater body weight was positively associated with tumor growth (P = 0.001). TP significantly inhibited prostate tumor angiogenesis (P = 0.043), but this inhibition differentially affected measured outcomes depending on CON or OB diets. TP led to reduced tumor growth (P = 0.004), intratumoral inflammation (TNFα; P = 0.019), and intratumoral androgen-regulated gene expression (srd5a1, srd5a2; P = 0.030 and P = 0.016, respectively) when incorporated with the CON diet but greater tumor growth and intratumoral gene expression when incorporated with the OB diet. Conclusions Results from this study show that protective benefits from dietary tomato are lost, or may become deleterious, when combined with a Western-style diet. Funding Sources CA was supported by the NIH NIBIB. MRL and PS were partially supported by NIH NCI.

Super-resolution ultrasound localization microscopy based on a high frame-rate clinical ultrasound scanner: an in-human feasibility study

Non-invasive detection of microvascular alterations in deep tissues in vivo provides critical information for clinical diagnosis and evaluation of a broad-spectrum of pathologies. Recently, the emergence of super-resolution ultrasound localization microscopy (ULM) offers new possibilities for clinical imaging of microvasculature at capillary level. Currently, the clinical utility of ULM on clinical ultrasound scanners is hindered by the technical limitations, such as long data acquisition time, high microbubble (MB) concentration, and compromised tracking performance associated with low imaging frame-rate. Here we present a robust in-human ULM on a high frame-rate (HFR) clinical ultrasound scanner to achieve super-resolution microvessel imaging using a short acquisition time (<10 s). Ultrasound MB data were acquired from different human tissues, including a healthy liver and a diseased liver with acute-on-chronic liver failure, a kidney, a pancreatic tumor, and a breast mass using an HFR clinical scanner. By leveraging the HFR and advanced processing techniques including sub-pixel motion registration, MB signal separation, and Kalman filter-based tracking, MBs can be robustly localized and tracked for ULM under the circumstances of relatively high MB concentration associated with standard clinical MB administration and limited data acquisition time in humans. Subtle morphological and hemodynamic information in microvasculature were shown based on data acquired with single breath-hold and free-hand scanning. Compared with contrast-enhanced power Doppler generated based on the same MB dataset, ULM showed a 5.7-fold resolution improvement in a vessel based on a linear transducer, and provided a wide-range blood flow speed measurement that is Doppler angle-independent. Microvasculatures with complex hemodynamics can be well-differentiated at super-resolution in both normal and pathological tissues. This preliminary study implemented the ultrafast in-human ULM in various human tissues based on a clinical scanner that supports HFR imaging, indicating the potentials of the technique for various clinical applications. However, rigorous validation of the technique in imaging human microvasculature (especially for those tiny vessel structure), preferably with a gold standard, is still required.

Fast Acoustic Steering Via Tilting Electromechanical Reflectors (FASTER): A Novel Method for High Volume Rate 3-D Ultrasound Imaging.

The 3-D ultrasound imaging is essential for a wide range of clinical applications in diagnostic and interventional cardiology, radiology, and obstetrics for prenatal imaging. 3-D ultrasound imaging is also pivotal for advancing technical developments of emerging imaging technologies, such as elastography, blood flow imaging, functional ultrasound (fUS), and super-resolution microvessel imaging. At present, however, existing 3-D ultrasound imaging methods suffer from low imaging volume rate, suboptimal imaging quality, and high costs associated with 2-D ultrasound transducers. Here, we report a novel 3-D ultrasound imaging technique, fast acoustic steering via tilting electromechanical reflectors (FASTER), which provides both high imaging quality and fast imaging speed while at low cost. Capitalizing upon unique water immersible and fast-tilting microfabricated mirror to scan ultrafast plane waves in the elevational direction, FASTER is capable of high volume rate, large field-of-view (FOV) 3-D imaging with conventional 1-D transducers. In this article, we introduce the fundamental concepts of FASTER and present a series of calibration and validation studies for FASTER 3-D imaging. In a wire phantom and tissue-mimicking phantom study, we demonstrated that FASTER was capable of providing spatially accurate 3-D images with a 500-Hz imaging volume rate and an imaging FOV with a range of 48° (20 mm at 25-mm depth) in the elevational direction. We also showed that FASTER had comparable imaging quality with conventional mechanical translation-based 3-D imaging. The principles and results presented in this study establish the technical foundation for the new paradigm of high volume rate 3-D ultrasound imaging based on ultrafast plane waves and fast-tilting, water-immersible microfabricated mirrors.

Improved Ultrasound Microvessel Imaging Using Deconvolution with Total Variation Regularization

Singular value decomposition-based clutter filters can robustly reject tissue clutter, allowing for detection of slow blood flow in imaging microvasculature. However, to identify microvessels, high ultrasound frequency must be used to increase the spatial resolution at the expense of shorter depth of penetration. Deconvolution using Tikhonov regularization is an imaging processing method widely used to improve spatial resolution. The ringing artifact of Tikhonov regularization, though, can produce image artifacts such as non-existent microvessels, which degrade image quality. Therefore, a deconvolution method using total variation is proposed in this study to improve spatial resolution and mitigate the ringing artifact. Performance of the proposed method was evaluated using chicken embryo brain, ex ovo chicken embryo chorioallantoic membrane and tumor data. Results revealed that the reconstructed power Doppler (PD) images are substantially improved in spatial resolution compared with original PD images: the full width half-maximum (FWHM) of the cross-sectional profile of a microvessel was improved from 132 to 83 µm. Two neighboring microvessels that were 154 µm apart were better separated using the proposed method than conventional PD imaging. Additionally, 223 FWHMs measured from the cross-sectional profiles of 223 vessels were used to determine the improvement in FWHM with the proposed method statistically. The mean ± standard deviation of the FWHM without and with the proposed method was 233.19 ± 85.08 and 172.31 ± 75.11 μm, respectively; the maximum FWHM without and with the proposed method was 693.01 and 668.69 μm; and the minimum FWHM without and with the proposed method was 73.92 and 45.74 μm. There were statistically significant differences between FWHMs with and without the proposed method according to the rank-sum test, p < 0.0001. The contrast-to-noise ratio improved from 1.06 to 4.03 dB with use of the proposed method. We also compared the proposed method with Tikhonov regularization using ex ovo chicken embryo chorioallantoic membrane data. We found that the proposed method outperformed Tikhonov regularization as false microvessels appeared using the Tikhonov regularization but not with the proposed method. These results indicate that the proposed method is capable of providing more robust PD images with higher spatial resolution and higher contrast-to-noise ratio.

Narrow-band Imaging Examination of Microvascular Architecture of Subcapsular Hepatic Tumors

BackgroundIntraoperative ultrasonography is the golden standard method for evaluation of liver tumors during hepatectomy. However, in laparoscopic surgery, accurate assessment of tumors may be difficult, particularly if the lesion is located nearby the liver surface because of the challenges in handling the intraoperative ultrasound and the lack of tactile sensation. In this study, we demonstrate the preliminary results of examining the microvascular architecture of subcapsular hepatic tumors using laparoscopic narrow-band imaging (NBI) to distinguish between malignant and benign tumors. Materials and MethodsThirty-five lesions were examined by NBI during laparoscopic hepatectomy for the presence of abnormal microvasculature on the liver surface in relation to hepatic tumors from January 2016 to August 2018. The microvascular findings were correlated with tumor localization and pathological diagnosis. ResultsThe 35 examined nodules included 11 hepatocellular carcinoma, 18 colorectal liver metastasis, and six benign nodules. The mean tumor diameter was 26.3 (3-70) mm, and the distance from the liver surface to the tumor was 0.5 (0-5) mm. Microvessels on the liver surface were clearly visualized by NBI, consistent with malignant tumor localization. The tumors were thoroughly examined for the presence of three pathological microvascular features (enlargement, tortuosity, and heterogeneity). Abnormal microvascular patterns were found in 90.9% of hepatocellular carcinoma and 77.8% of colorectal liver metastasis, whereas neither normal sites nor benign lesions displayed microvascular abnormality. ConclusionsThis study suggests that observing the microvessel image on the liver surface by NBI could be useful in tumor localization and differentiation between benign and malignant lesions.

Non-contrast-enhanced ultrafast ultrasound Doppler imaging of spinal cord micro-vessels

With the advantages of non-radiation and low-cost, ultrasound imaging has been widely used in clinical diagnosis. However, due to the compromise between temporal and spatial resolution, the traditional ultrasound imaging method which collects images line by line fails to obtain the images at a high frame rate. Ultrafast ultrasound imaging method based on the plane-wave emission can achieve a high frame rate with the capability for instantaneous hemodynamic imaging of neurovascular response. Besides, by the coherent compounding of the echo signals received from emitting a set of tilting plane-waves, the image quality can be improved in terms of resolution, contrast and signal-to-noise ratio (SNR). Considering the fact that received signals are the mixture of echo signals from the low-speed soft tissue and high-speed blood flow, a clutter filtering method is used to remove the signals of soft tissue. In this study, the ultrafast ultrasound sequence of emission and reception is designed to image the spinal cord by using the groups of multiple steering-angle plane-waves. The so-called f-k migration algorithm based on an exploding reflector model (ERM) is used for coherent plane-wave compounding. Eigenvalue decomposition (EVD) is then applied to tissue and blood signal extraction. The static tissue signals correspond to eigenvectors with low Doppler frequency shift and large magnitude eigenvalue while the high-speed blood flow signals correspond to eigenvectors with high Doppler frequency shift and small eigenvalue. Therefore, frequency and amplitude thresholds can be applied to the accurate separation of the blood component and the tissue component. After the signal extraction, the hemodynamic imaging of blood vessels can thus be obtained from the power Doppler results. The experiments are carried out by using a programmable ultrasonic array system and a high-frequency linear array transducer L22-14vX with a central frequency of 15.625 MHz. The sample acquisition frequency is set to be 62.5 MHz. In rat experiments &lt;i&gt;in vivo&lt;/i&gt;, 14040 angle-stilting images per second are compounded into 520 images, each of which is compounded from 27 tilting images (the tilting angles ranging from –10° to 10°). The experiments are conducted on the anesthetized rats with part of the vertebral plate removed. The ultrafast B-mode images are acquired from a 14.0 mm ×12.7 mm region-of-interest. The 520 frames acquired in one second are processed by the clutter filter based on eigenvalue decomposition and Doppler shift analysis. The eigenvectors and eigenvalues corresponding to the soft tissue are discarded. The power Doppler images of the spinal cord micro-vessels are obtained. The experimental results indicate that the ultrafast ultrasound Doppler imaging method is effective for monitoring the hemodynamic variation in spinal cord. The micro-hemorrhage can be identified from the power Doppler images. The quantitative results indicate that the SNR increases with the steering angles increasing. Compared with the results obtained by using 9 steering angles, 5 dB SNR enhancement can be obtained by using the 27 steering angles. In conclusion, the ultrafast ultrasound Doppler technology has the potential applications in spinal cord microvascular imaging and hemodynamic evaluation of neurovascular function of spinal cord.