Imaging Methods for Ultrasound Contrast Agents

Super-resolution ultrasound imaging of ischaemia flow: An in silico study

Super-resolution ultrasound (SRU) is a new ultrasound imaging mode that promises to facilitate the detection of microvascular disease by providing new vascular bio-markers that are directly linked to microvascular pathophysiology, thereby augmenting current knowledge and potentially enabling new treatment. Such a capability can be developed through thorough understanding as articulated by means of mathematical models. In this study, a 2D numerical flow model is adopted for generating flow adaptation in response to ischaemia, in order to determine the ability of SRU to register the resulting flow perturbations. The flow model results demonstrate that variations in flow behaviour in response to locally induced ischaemia can be significant throughout the entire vascular bed. Measured velocities have variations that are dependent on the location of ischaemia, with median values ranging between 2-7 mms-1. Moreover, the distinction between healthy and ischaemic networks are recorded accurately in the SRU results showing excellent agreement between SRU maps and the model. Up to 7-fold spatial resolution improvement to conventional contrast ultrasound was achieved in microbubble localisation while the detection precision and recall was consistently above 98%. The microbubble tracking precision was of a similar accuracy, whereas the recall was reduced (77%) under varying ischaemic impacted flow. Further, regions with velocities up to 30 mms-1 are in excellent agreement with SRU maps, while at regions that include a proportion of higher velocities, the median velocity values are within 1.28%-3.32% of the ground-truth. In conclusion, SRU is a highly promising methodology for the direct measurement of microvascular flow dynamics and may provide a valuable tool for the understanding and subsequent modelling of behaviour in the vascular bed.

The effect of micro-vessel viscosity on the resonance response of a two-microbubble system

Clinical ultrasound contrast agent microbubbles remain intravascular and are between 1-8 µm in diameter, with a volume-weighted mean size of 2-3 µm. Despite their worldwide clinical utility as a diagnostic contrast agent, and their continued and ongoing success as a local therapeutic vector, the fundamental interplay between microbubbles - including bubble-bubble interaction and the effects of a neighboring viscoelastic vessel wall, remain poorly understood. In this work, we developed a finite element model to study the physics of the complex system of two different-sized bubbles (2 and 3 µm in diameter) confined within a viscoelastic vessel from a resonance response perspective (3-12 MHz). Here, we focus on the effect of micro-vessel wall viscosity on the resulting vibrational activity of the two-bubble system. The larger bubble (3 µm) was not influenced by its smaller companion bubble, and we observed a significant dampening effect across all transmit frequencies when confined within the vessel of increasing viscosity, an expected result. However, the smaller bubble (2 µm) was highly influenced by its larger neighboring bubble, including the induction of a strong low-frequency resonant response - resulting in transmit frequency windows in which its response in a lightly damped vessel far exceeded its vibration amplitude when unconfined. Further, micro-vessel wall dynamics closely mimic the frequency-dependence of the adjacent bubbles. Our findings imply that for a system of multi-bubbles within a viscoelastic vessel, the larger bubble physics dominates the system by inducing the smaller bubble and the vessel wall to follow its vibration - an effect that can be amplified within a lightly damped vessel. These findings have important implications for contrast-enhanced ultrasound imaging and therapeutic applications.

The Clinical Utility of Liver-Specific Ultrasound Contrast Agents During Hepatocellular Carcinoma Imaging

Hepatocellular carcinoma (HCC) is the most common form of hepatic malignancy, with high mortality rates recorded globally. Early detection through clinical biomarkers, medical imaging and histological assessment followed by rapid intervention are integral for positive patient outcomes. Although contrast-enhanced computed tomography scans and magnetic resonance imaging are recognised as the reference standard for the diagnosis and staging of HCC in international guidelines, ultrasound (US) examination is recommended as a screening tool for patients at risk. Contrast-enhanced US (CEUS) elevates the standard of an US examination using US contrast agents (UCAs), capable of diagnosing focal liver lesions with high efficacy. Most UCAs are purely intravascular, offering clinicians a dynamic representation of a lesions' arterial phase vascular kinetics, which is seldom seen in such detail during computed tomography or magnetic resonance imaging assessments. Despite its benefits, there is incongruity between international societies on the role of CEUS in the HCC clinical pathway. The transient nature of pure blood-pool agents is suggested to be insufficient to justify CEUS as a primary modality due to the inability to consistently perform whole liver imaging, alongside disputes regarding its capabilities to differentiate HCC from intrahepatic cholangiocarcinoma. A sinusoidal phase UCA affords clinicians the opportunity to perform whole liver imaging through Kupffer cell uptake in addition to visualising lesion vascular kinetics in the arterial and portal venous phases. Therefore, the purpose of this review was to examine the role of CEUS in the HCC clinical pathway in its current practice and observe how a Kupffer cell sinusoidal phase UCA may supplement contemporary diagnostic techniques through a multi-modality, multi-agent approach.

Polydisperse Versus Monodisperse Microbubbles: A Simulation Study for Contrast-Enhanced Ultrasound Imaging

OBJECTIVE

Contrast-enhanced ultrasound (CEUS) presents distinct advantages in diagnostic echography. Utilizing microbubbles (MBs) as conventional contrast agents enhances vascular visualization and organ perfusion, facilitating real-time, non-invasive procedures. There is a current tendency to replace traditional polydisperse MBs with novel monodisperse formulations in an attempt to optimize contrast enhancement and guarantee consistent behavior and reliable imaging outcomes. This study investigates the contrast enhancement achieved using various-sized monodisperse MBs and their influence on non-linear imaging artifacts observed in traditional CEUS.

METHODS

To explore the differences between monodisperse and polydisperse populations without excessive experimentation, numerical simulations are employed for delivering precise, objective and expeditious results. The iterative non-linear contrast source (INCS) method has previously demonstrated efficacy when simulating ultrasound propagation in large populations in which each bubble has individual properties and several orders of multiple scattering are significant. Therefore, this method is employed to realistically simulate both monodisperse and polydisperse MBs.

RESULTS

Our findings in CEUS imaging indicate that scattering from resonant monodisperse MBs is 11.8 dB stronger than scattering from polydisperse MBs. Furthermore, the amplitude of non-linear imaging artifacts downstream of the monodisperse population is 19.4 dB stronger compared with polydisperse suspension.

CONCLUSION

Investigating the impact of multiple scattering on polydisperse populations compared with various monodisperse suspensions has revealed that monodisperse MBs are more effective contrast agents, especially when at resonance. Despite the strong signal-to-noise ratio of monodisperse populations, imaging artifacts caused by non-linear wave propagation are also enhanced, resulting in further mis-classification of MBs as tissue.

Comparison of contrast-enhanced ultrasound imaging (CEUS) and super-resolution ultrasound (SRU) for the quantification of ischaemia flow redistribution: a theoretical study

The study of microcirculation can reveal important information related to pathology. Focusing on alterations that are represented by an obstruction of blood flow in microcirculatory regions may provide an insight into vascular biomarkers. The current in silico study assesses the capability of contrast enhanced ultrasound (CEUS) and super-resolution ultrasound imaging (SRU) flow-quantification to study occlusive actions in a microvascular bed, particularly the ability to characterise known and model induced flow behaviours. The aim is to investigate theoretical limits with the use of CEUS and SRU in order to propose realistic biomarker targets relevant for clinical diagnosis. Results from CEUS flow parameters display limitations congruent with prior investigations. Conventional resolution limits lead to signals dominated by large vessels, making discrimination of microvasculature specific signals difficult. Additionally, some occlusions lead to weakened parametric correlation against flow rate in the remainder of the network. Loss of correlation is dependent on the degree to which flow is redistributed, with comparatively minor redistribution correlating in accordance with ground truth measurements for change in mean transit time,dMTT(CEUS,R = 0.85; GT,R = 0.82) and change in peak intensity,dIp(CEUS,R = 0.87; GT,R = 0.96). Major redistributions, however, result in a loss of correlation, demonstrating that the effectiveness of time-intensity curve parameters is influenced by the site of occlusion. Conversely, results from SRU processing provides accurate depiction of the anatomy and dynamics present in the vascular bed, that extends to individual microvessels. Correspondence between model vessel structure displayed in SRU maps with the ground truth was>91%for cases of minor and major flow redistributions. In conclusion, SRU appears to be a highly promising technology in the quantification of subtle flow phenomena due ischaemia induced vascular flow redistribution.

A Comprehensive and Repeatable Contrast-Enhanced Ultrasound Quantification Approach for Clinical Evaluations of Tumor Blood Flow

OBJECTIVE

The aim of this study is to define a comprehensive and repeatable contrast-enhanced ultrasound (CEUS) imaging protocol and analysis method to quantitatively assess lesional blood flow. Easily repeatable CEUS evaluations are essential for longitudinal treatment monitoring. The quantification method described here aims to provide a structure for future clinical studies.

MATERIALS AND METHODS

This retrospective analysis study included liver CEUS studies in 80 patients, 40 of which contained lesions (primarily hepatocellular carcinoma, n = 28). Each patient was given at least 2 injections of a microbubble contrast agent, and 60-second continuous loops were acquired for each injection to enable evaluation of repeatability. For each bolus injection, 1.2 mL of contrast was delivered, whereas continuous, stationary scanning was performed. Automated respiratory gating and motion compensation algorithms dealt with breathing motion. Similar in size regions of interest were drawn around the lesion and liver parenchyma, and time-intensity curves (TICs) with linearized image data were generated. Four bolus transit parameters, rise time (RT), mean transit time (MTT), peak intensity (PI), and area under the curve (AUC), were extracted either directly from the actual TIC data or from a lognormal distribution curve fitted to the TIC. Interinjection repeatability for each parameter was evaluated with coefficient of variation. A 95% confidence interval was calculated for all fitted lognormal distribution curve coefficient of determination (R2) values, which serves as a data quality metric. One-sample t tests were performed between values obtained from injection pairs and between the fitted lognormal distribution curve and direct extraction from the TIC calculation methods to establish there were no significant differences between injections and measurement precision, respectively.

RESULTS

Average interinjection coefficient of variation with both the fitted curve and direct calculation of RT and MTT was less than 21%, whereas PI and AUC were less than 40% for lesion and parenchyma regions of interest. The 95% confidence interval for the R2 value of all fitted lognormal curves was [0.95, 0.96]. The 1-sample t test for interinjection value difference showed no significant differences, indicating there was no relationship between the order of the repeated bolus injections and the resulting parameters. The 1-sample t test between the values from the fitted lognormal distribution curve and the direct extraction from the TIC calculation found no statistically significant differences (α = 0.05) for all perfusion-related parameters except lesion and parenchyma PI and lesion MTT.

CONCLUSIONS

The scanning protocol and analysis method outlined and validated in this study provide easily repeatable quantitative evaluations of lesional blood flow with bolus transit parameters in CEUS data that were not available before. With vital features such as probe stabilization ideally performed with an articulated arm and an automated respiratory gating algorithm, we were able to achieve interinjection repeatability of blood flow parameters that are comparable or surpass levels currently established for clinical 2D CEUS scans. Similar values and interinjection repeatability were achieved between calculations from a fitted curve or directly from the data. This demonstrated not only the strength of the protocol to generate TICs with minimal noise, but also suggests that curve fitting might be avoided for a more standardized approach. Utilizing the imaging protocol and analysis method defined in this study, we aim for this methodology to potentially assist clinicians to assess true perfusion changes for treatment monitoring with CEUS in longitudinal studies.

Principle of contrast-enhanced ultrasonography

Sonazoid, an ultrasound contrast agent, has been covered by insurance in Japan since January 2007 for the diagnosis of hepatic mass lesions and is widely used for diagnosing not only primary liver cancer but also liver metastases such as those from breast cancer and colorectal cancer. Contrast-enhanced ultrasound for breast mass lesions has been covered by insurance since August 2012 after phase II and phase III clinical trials showed that the diagnostic performance was significantly superior to that of B-mode and contrast-enhanced magnetic resonance imaging. This paper describes the principles of imaging techniques in contrast-enhanced ultrasonography including the filter, pulse inversion, amplitude modulation, and amplitude-modulated pulse inversion methods. The pulse inversion method, which visualizes the second-harmonic component using the nonlinear scattering characteristics of the contrast agent, is widely used regardless of the contrast agent and target organ because of its high resolution. Sonazoid has a stiffer shell and requires a higher acoustic amplitude than Sonovue to generate nonlinear vibrations. The higher transmitted sound pressure generates more tissue harmonic components. Since pulse inversion allows visualization of the tissue harmonic components, amplitude modulation and amplitude-modulated pulse inversion, which include few tissue harmonic components, are primarily used. Amplitude modulation methods detect nonlinear signals from the contrast agent in the fundamental band. The mechanism of the amplitude modulation is considered to be changes in the echo signal's phase depending on the sound pressure. Since the tissue-derived component is minor in amplitude modulation methods, good contrast sensitivity can be obtained.

Safety of contrast-enhanced ultrasound using microbubbles in human pregnancy: A scoping review

INTRODUCTION

Successful placentation is crucial for fetal development and maintaining a healthy pregnancy. Placental insufficiency can cause a variety of obstetric complications. Despite the many efforts to enhance diagnosing placental insufficiency, no imaging technique has proven satisfactory. A promising imaging technique is contrast-enhanced ultrasound (CEUS) using microbubbles which has proven capable of (micro)vascular imaging. Its use for placental vascularization assessment in human pregnancies remains constrained by limited evidence and safety concerns. This scoping review aims to demonstrate the safety of CEUS used in human pregnancy in the published literature to date.

MATERIAL AND METHODS

A systematic search using PubMed, Medline, Embase, and Cochrane databases was performed. All studies where contrast-enhanced ultrasound was used in pregnant humans were included. Studies, where there was a planned termination of pregnancy, were excluded. To assess the safety of CEUS during pregnancy, relevant outcomes were divided into the following 3 categories; fetal outcome, maternal outcome, and pregnancy and neonatal outcomes.

RESULTS

A total of 13 articles were included, in which 256 women underwent CEUS during pregnancy. No clinically significant maternal or fetal adverse events or negative pregnancy or neonatal outcomes associated with CEUS were described.

CONCLUSION

Based on our findings, we consider expanding the knowledge of this promising diagnostic technique in future larger clinical studies to be safe and relevant.

Characterizing Sentinel Lymph Node Status in Breast Cancer Patients Using a Deep-Learning Model Compared With Radiologists' Analysis of Grayscale Ultrasound and Lymphosonography

ABSTRACT

The objective of the study was to use a deep learning model to differentiate between benign and malignant sentinel lymph nodes (SLNs) in patients with breast cancer compared to radiologists' assessments.Seventy-nine women with breast cancer were enrolled and underwent lymphosonography and contrast-enhanced ultrasound (CEUS) examination after subcutaneous injection of ultrasound contrast agent around their tumor to identify SLNs. Google AutoML was used to develop image classification model. Grayscale and CEUS images acquired during the ultrasound examination were uploaded with a data distribution of 80% for training/20% for testing. The performance metric used was area under precision/recall curve (AuPRC). In addition, 3 radiologists assessed SLNs as normal or abnormal based on a clinical established classification. Two-hundred seventeen SLNs were divided in 2 for model development; model 1 included all SLNs and model 2 had an equal number of benign and malignant SLNs. Validation results model 1 AuPRC 0.84 (grayscale)/0.91 (CEUS) and model 2 AuPRC 0.91 (grayscale)/0.87 (CEUS). The comparison between artificial intelligence (AI) and readers' showed statistical significant differences between all models and ultrasound modes; model 1 grayscale AI versus readers, P = 0.047, and model 1 CEUS AI versus readers, P < 0.001. Model 2 r grayscale AI versus readers, P = 0.032, and model 2 CEUS AI versus readers, P = 0.041.The interreader agreement overall result showed κ values of 0.20 for grayscale and 0.17 for CEUS.In conclusion, AutoML showed improved diagnostic performance in balance volume datasets. Radiologist performance was not influenced by the dataset's distribution.

What is the place of ultrasound in MSK imaging?

During the past four decades, ultrasound has become popular as an imaging modality applied to the musculoskeletal (MSK) system, particularly outside the USA, due to its low cost, accessibility, and lack of ionizing radiation. A basic requirement in performing these examinations is to have a core group of radiologists and ultrasound technologists with expertise in MSK ultrasound. The extent to which ultrasound will be part of the imaging offered by a particular radiology practice or in an academic institution will vary according to expertise, availability, and reimbursements. A brief discussion of the technical capabilities of the current generation of ultrasound scanners will be followed by a description of some of the more prevalent MSK ultrasound imaging applications. The extent to which training to perform these exams within and outside of Radiology plays a role is discussed. Applications that are unique to ultrasound, such as dynamic evaluation of musculoskeletal anatomy and some, US-guided interventions are an important part of MSK imaging. Ultrasound is increasingly important in the assessment of superficial structures, such as tendons, small joints, and peripheral nerves. These applications help to establish the place of ultrasound as an important part of the Radiologists approach to MSK imaging. Outside of radiology, for a variety of clinical subspecialties, ultrasound already plays an integral role in MSK imaging.

Functionalized monodisperse microbubble production: microfluidic method for fast, controlled, and automated removal of excess coating material

Functionalized monodisperse microbubbles have the potential to boost the sensitivity and efficacy of molecular ultrasound imaging and targeted drug delivery using bubbles and ultrasound. Monodisperse bubbles can be produced in a microfluidic flow focusing device. However, their functionalization and sequential use require removal of the excess lipids from the bubble suspension to minimize the use of expensive ligands and to avoid competitive binding and blocking of the receptor molecules. To date, excess lipid removal is performed by centrifugation, which is labor intensive and challenging to automate. More importantly, as we show, the increased hydrostatic pressure during centrifugation can reduce bubble monodispersity. Here, we introduce a novel automated microfluidic 'washing' method. First, bubbles are injected in a microfluidic chamber 1 mm in height where they are left to float against the top wall. Second, lipid-free medium is pumped through the chamber to remove excess lipids while the bubbles remain located at the top wall. Third, the washed bubbles are resuspended and removed from the device into a collection vial. We demonstrate that the present method can (i) reduce the excess lipid concentration by 4 orders of magnitude, (ii) be fully automated, and (iii) be performed in minutes while the size distribution, functionality, and acoustic response of the bubbles remain unaffected. Thus, the presented method is a gateway to the fully automated production of functionalized monodisperse microbubbles.

A Prospective Multicenter Study on the Additive Value of Contrast-Enhanced Ultrasound for Biopsy Decision of Ultrasound BI-RADS 4 Breast Lesions

OBJECTIVE

The main aim of this study was to determine whether the use of contrast-enhanced ultrasound (CEUS) could improve the categorization of suspicious breast lesions based on the Breast Imaging Reporting and Data System (BI-RADS), thereby reducing the number of benign breast lesions referred for biopsy.

METHODS

This prospective study, conducted between January 2017 and December 2018, enrolled consenting patients from eight teaching hospitals in China, who had been diagnosed with solid breast lesions classified as BI-RADS 4 using conventional ultrasound. CEUS was performed within 1 wk of diagnosis for reclassification of breast lesions. Histopathological results obtained from core needle biopsies or surgical excision samples served as the reference standard. The simulated biopsy rate and cancer-to-biopsy yield were used to compare the accuracy of CEUS and conventional ultrasound (US).

RESULTS

Among the 1490 lesions diagnosed as BI-RADS 4 with conventional ultrasound, 486 malignant and 1004 benign lesions were confirmed based on histology. Following CEUS, 2, 395, and 211 lesions were reclassified as CEUS-based BI-RADS 2, 3, and 5, respectively, while 882 (59%) remained as BI-RADS 4. The actual cancer-to-biopsy yield based on US was 32.6%, which increased to 43.4% when CEUS-based BI-RADS 4A was used as the cut-off point to recommend biopsy. The simulated biopsy rate decreased to 73.4%. Overall, in this preselected BI-RADS 4 population, only 2.5% (12/486) of malignant lesions would have been miscategorized as BI-RADS 3 using CEUS-based reclassification. The diagnostic accuracy, sensitivity, and specificity of contrast-enhanced ultrasound reclassification were 57.65%, 97.53%, and 38.35%, respectively.

CONCLUSION

Our collective findings indicate that CEUS is a valuable tool in further triage of BI-RADS category 4 lesions and facilitates a reduction in the number of biopsies while increasing the cancer-to-biopsy yield.

Nonlinear sound-sheet microscopy: imaging opaque organs at the capillary and cellular scale

Light-sheet fluorescence microscopy has revolutionized biology by visualizing dynamic cellular processes in three dimensions. However, light scattering in thick tissue and photobleaching of fluorescent reporters limit this method to studying thin or translucent specimens. Here we show that non-diffractive ultrasonic beams used in conjunction with a cross-amplitude modulation sequence and nonlinear acoustic reporters enable fast and volumetric imaging of targeted biological functions. We report volumetric imaging of tumor gene expression at the cm 3 scale using genetically encoded gas vesicles, and localization microscopy of currently uncharted cerebral capillary networks using intravascular microbubble contrast agents. Nonlinear sound-sheet microscopy provides a ∼64x acceleration in imaging speed, ∼35x increase in imaged volume and ∼4x increase in classical imaging resolution compared to the state-of-the-art in biomolecular ultrasound.

A Systematic Study on Long-acting Nanobubbles: Current Advancement and Prospects on Theranostic Properties

Delivery of diagnostic drugs via nanobubbles (NBs) has shown to be an emerging field of study. Due to their small size, NBs may more easily travel through constricted blood vessels and precisely target certain bodily parts. NB is considered the major treatment for cancer treatment and other diseases which are difficult to diagnose. The field of NBs is dynamic and continues to grow as researchers discover new properties and seek practical applications in various fields. The predominant usage of NBs in novel drug delivery is to enhance the bioavailability, and controlled drug release along with imaging properties NBs are important because they may change interfacial characteristics including surface force, lubrication, and absorption. The quick diffusion of gas into the water was caused by a hypothetical film that was stimulated and punctured by a strong acting force at the gas/water contact of the bubble. In this article, various prominent aspects of NBs have been discussed, along with the long-acting nature, and the theranostical aspect which elucidates the potential marketed drugs along with clinical trial products. The article also covers quality by design aspects, different production techniques that enable method-specific therapeutic applications, increasing the floating time of the bubble, and refining its properties to enhance the prepared NB's quality. NB containing both analysis and curing properties makes it special from other nano-carriers. This work includes all the possible methods of preparing NB, its application, all marketed drugs, and products in clinical trials.

A review of ultrasound contrast media

Efforts have been made over the last five decades to create effective ultrasonic contrast media (UCM) for cardiac and noncardiac applications. The initial UCM was established in the 1980s, following publications from the 1960s that detailed the discovery of ultrasonic contrast enhancement using small gaseous bubbles in echocardiographic examinations. An optimal contrast agent for echography should possess the following characteristics: non-toxicity, suitability for intravenous injection, ability to traverse pulmonary, cardiac, and capillary circulations, and stability for recirculation. Definity, Optison, Sonazoid, and SonoVue are examples of current commercial contrast media. These contrast media have shown potential for various clinical reasons, both on-label and off-label. Several possible UCMs have been developed or are in progress. Advancements in comprehending the physical, chemical, and biological characteristics of microbubbles have significantly improved the visualization of tumor blood vessels, the identification of areas with reduced blood supply, and the enhanced detection of narrowed blood vessels. Innovative advances are expected to enhance future applications such as ultrasonic molecular imaging and therapeutic utilization of microbubbles.

Micro-ultrasound based characterization of cerebrovasculature following focal ischemic stroke and upon short-term rehabilitation

Notwithstanding recanalization treatments in the acute stage of stroke, many survivors suffer long-term impairments. Physical rehabilitation is the only widely available strategy for chronic-stage recovery, but its optimization is hindered by limited understanding of its effects on brain structure and function. Using micro-ultrasound, behavioral testing, and electrophysiology, we investigated the impact of skilled reaching rehabilitation on cerebral hemodynamics, motor function, and neuronal activity in a rat model of focal ischemic stroke. A 50 MHz micro-ultrasound transducer and intracortical electrophysiology were utilized to characterize neurovascular changes three weeks following focal ischemia elicited by endothelin-1 injection into the sensorimotor cortex. Sprague-Dawley rats were rehabilitated through tray reaching, and their fine skilled reaching was assessed via the Montoya staircase. Focal ischemia led to a sustained deficit in forelimb reaching; and increased tortuosity of the penetrating vessels in the perilesional cortex; with no lateralization of spontaneous neuronal activity. Rehabilitation improved skilled reaching; decreased cortical vascularity; was associated with elevated peri- vs. contralesional hypercapnia-induced flow homogenization and increased perilesional spontaneous cortical neuronal activity. Our study demonstrated neurovascular plasticity accompanying rehabilitation-elicited functional recovery in the subacute stage following stroke, and multiple micro-ultrasound-based markers of cerebrovascular structure and function modified in recovery from ischemia and upon rehabilitation.

Contrast-Enhanced Ultrasound and Conventional Ultrasound Characteristics of Breast Cancer With Different Molecular Subtypes

BACKGROUND

Identifying molecular subtypes of breast cancer (BC) is of great significance in selecting optimal treatment strategy. Different molecular subtypes of BC have various vascular distribution characteristics. Contrast-enhanced ultrasound (CEUS) can dynamically display the microcirculation of tumor. This study intends to explore the conventional ultrasound and CEUS characteristics of different molecular subtypes of BC.

METHODS

During this prospective study, 86 patients with BC who were divided into Luminal A (LA), Luminal B (LB), HER2 over-expression (H2), and triple-negative (TN). The CEUS qualitative and quantitative characteristics of BC with different molecular subtypes was explored, as well as the conventional ultrasound features. In addition, the diagnostic efficiency of CEUS quantitative parameters in differentiating molecular subtypes of BC was analyzed.

RESULTS

Our study found that the Adler grade differed significantly among 4 molecular subtypes (P < .05). The enhancement speed, enhancement degree and size after enhancement of 4 molecular subtypes were statistically different (P < .05). The wash in slope (WIS), peak intensity (PI), and wash-in area under the curve (WiAUC) differed significantly among 4 subtypes (P < .05). The diagnostic efficiency of PI was better for detecting LA and H2 subtype with the areas under the receiver operating characteristic curve was 0.778 and 0.734, respectively.

CONCLUSION

Different molecular subtypes of BC have different CEUS and conventional ultrasound characteristics. CEUS can provide valuable imaging basis for precise clinical diagnosis and individualized therapy of BC with different molecular subtypes.

Tips and tricks for a correct interpretation of contrast-enhanced ultrasound

Although contrast-enhanced ultrasound (CEUS) is a widespread and easily manageable technique, image interpretation errors can occur due to the operator's inexperience and/or lack of knowledge of the frequent pitfalls, which may cause uncertain diagnosis and misdiagnosis. Indeed, knowledge of the basic physical and technical principles of ultrasound is needed both to understand sonographic image findings and to evaluate the potential and limits of the method. Like the B-mode ultrasound, the quality of the CEUS examination is also subject not only to the adequate manual skill of the operator but also to his/her deep knowledge of the technique which improves the quality of the image helping avoid misleading artifacts. In this review, the main parameters influencing a CEUS examination will be described by taking into account the most common errors and pitfalls and their possible solutions.

Sensitivity improvement of subharmonic-based pressure measurement using phospholipid-coated monodisperse microbubbles

The use of the subharmonic signal from microbubbles exposed to ultrasound is a promising safe and cost-effective approach for the non-invasive measurement of blood pressure. Achieving a high sensitivity of the subharmonic amplitude to the ambient overpressure is crucial for clinical applications. However, currently used microbubbles have a wide size distribution and diverse shell properties. This causes uncertainty in the response of the subharmonic amplitude to changes in ambient pressure, which limits the sensitivity. The aim of this study was to use monodisperse microbubbles to improve the sensitivity of subharmonic-based pressure measurements. With the same shell materials and gas core, we used a flow-focusing microfluidic chip and a mechanical agitation method to fabricate monodisperse (∼2.45-µm mean radius and 4.7 % polydisperse index) and polydisperse microbubbles (∼1.51-µm mean radius and 48.4 % polydisperse index), respectively. We varied the ultrasound parameters (i.e., the frequency, peak negative pressure (PNP) and pulse length), and found that there was an optimal excitation frequency (2.8 MHz) for achieving maximal subharmonic emission for monodisperse microbubbles, but not for polydisperse microbubbles. Three distinct regimes (occurrence, growth, and saturation) were identified in the response of the subharmonic amplitude to increasing PNP for both monodisperse and polydisperse microbubbles. For the polydisperse microbubbles, the subharmonic amplitude decreased either monotonically or non-monotonically with ambient overpressure, depending on the PNP. By contrast, for the monodisperse microbubbles, there was only a monotonic decrease at all PNPs. The maximum sensitivity (1.18 dB/kPa, R2 = 0.97) of the subharmonic amplitude to ambient overpressure for the monodisperse microbubbles was ∼6.5 times higher than that for the polydisperse microbubbles (0.18 dB/kPa, R2 = 0.88). These results show that monodisperse microbubbles can achieve a more consistent response of the subharmonic signal to changes in ambient overpressure and greatly improve the measurement sensitivity.

Quantitative analysis of contrast-enhanced ultrasound in neoadjuvant treatment of locally advanced rectal cancer: a retrospective study

Purpose

To explore the clinical value of contrast-enhanced ultrasound (CEUS) quantitative analysis in the evaluation and prognosis of neoadjuvant chemoradiotherapy for locally advanced rectal cancer (LARC).

Methods

Eighty-three consecutive patients undergoing neoadjuvant chemoradiotherapy and total mesorectal excision for LARC were retrospectively included. According to pathological results, patients were categorized into complete or incomplete response groups. Differences in ultrasonic parameters, pathological results, and clinical data between groups were evaluated. The cutoff point for a complete response as determined by quantitative analysis of CEUS was assessed using a receiver operating characteristic curve; additionally, overall survival (OS) and progression-free survival (PFS) were analyzed.

Results

Of the 83 patients, 12 (14.5%) achieved a complete response and 71 (85.5%) did not. There were significant between-group differences in carcinoembryonic antigen (CEA) levels, differentiation degree, proportion of tumor occupying the lumen, anterior-posterior and superior-inferior diameters of the lesion, and intensity of enhancement (P<0.05). CEUS quantitative analysis showed significant between-group differences in peak intensity (PI) and area under the curve (AUC) values (P<0.05). The OS and PFS of patients with high PI, high AUC value, and poorly differentiated cancer were significantly worse than those with low PI, low AUC values, and moderately to highly differentiated cancer (P<0.05). High CEA levels (hazard ratio: 1.02, 95% confidence interval: 1.01-1.04; P=0.002) and low differentiation (2.72, 1.12-6.62; P=0.028) were independent risk factors for PFS and OS.

Conclusions

CEUS can predict the response to neoadjuvant treatment in patients with LARC. CEUS quantitative analysis is helpful for clinical prognosis.

Subharmonic resonance of phospholipid coated ultrasound contrast agent microbubbles

Phospholipid encapsulated ultrasound contrast agents have proven to be a powerful addition in diagnostic imaging and show emerging applications in targeted therapy due to their resonant and nonlinear scattering. Microbubble response is affected by their intrinsic (e.g. bubble size, encapsulation physics) and extrinsic (e.g. boundaries) factors. One of the major intrinsic factors at play affecting microbubble vibration dynamics is the initial phospholipid packing of the lipid encapsulation. Here, we examine how the initial phospholipid packing affects the subharmonic response of either individual or a system of two closely-placed microbubbles. We employ a finite element model to investigate the change in subharmonic resonance under 'small' and 'large' radial excursions. For microbubbles ranging between 1.5 and 2.5 µm in diameter and in its elastic state (σ0 = 0.01 N/m), we demonstrate up to a 10 % shift towards lower frequencies in the peak subharmonic response as the radial excursion increases. However, for a bubble initially in its buckled state (σ0 = 0 N/m), we observe a maximum shift of 8 % towards higher frequencies as the radial excursion increases over the same range of bubble sizes - the opposite trend. We studied the same scenario for a system of two individual microbubbles for which we saw similar results. For microbubbles that are initially in their elastic state, in both cases of a) two identically sized bubbles and b) a bubble in proximity to a smaller bubble, we observed a 6 % and 9 % shift towards lower frequencies respectively; while in the case of a neighboring larger bubble no change in subharmonic resonance frequency was observed. Microbubbles that are initially in a buckled state exert no change, 5 % and 19 % shift towards higher frequencies, in two-bubble systems consisting of a) same-size, b) smaller, and c) larger neighboring bubble respectively. Furthermore, we examined the effect of two adjacent bubbles with non-equal initial phospholipid states. The results presented here have important implications in ultrasound contrast agent applications.

Enhancing medical ultrasound imaging through fractional mathematical modeling of ultrasound bubble dynamics

The classical mathematical modeling of ultrasound acoustic bubble is so far using to improve the medical imaging quality. A clear and visible medical ultrasound image relies on bubble's diameter, wavelength and intensity of the scattered sound. A bubble with diameter much smaller than the sound wavelength is regarded as highly efficient source of sound scattering. The dynamical equation for a medical ultrasound bubble is primarily modeled in classical integer-order differential equation. Then a reduction of order technique is used to convert the modeled dynamic equation for the bubble surface into a system of incommensurate fractional-orders. The incommensurate fractional-order values are calculated directly, by using Riemann stability region. On the basis of stability the convergence and accuracy of the numerical scheme is also discussed in detail. It has been found that the system will remain stable and chaotic for the incommensurate values α1<0.737 and α2<2.80, respectively.

Higher Order Singular Value Decomposition Filter for Contrast Echocardiography

Assessing the coronary circulation with contrast-enhanced echocardiography has high clinical relevance. However, it is not being routinely performed in clinical practice because the current clinical tools generally cannot provide adequate image quality. The contrast agent's visibility in the myocardium is generally poor, impaired by motion and nonlinear propagation artifacts. The established multipulse contrast schemes (MPCSs) and the more experimental singular value decomposition (SVD) filter also fall short to solve these issues. Here, we propose a scheme to process amplitude modulation/amplitude-modulated pulse inversion (AM/AMPI) echoes with higher order SVD (HOSVD) instead of conventionally summing the complementary pulses. The echoes from the complementary pulses form a separate dimension in the HOSVD algorithm. Then, removing the ranks in that dimension with dominant coherent signals coming from tissue scattering would provide the contrast detection. We performed both in vitro and in vivo experiments to assess the performance of our proposed method in comparison with the current standard methods. A flow phantom study shows that HOSVD on AM pulsing exceeds the contrast-to-background ratio (CBR) of conventional AM and an SVD filter by 10 and 14 dB, respectively. In vivo porcine heart results also demonstrate that, compared to AM, HOSVD improves CBR in open-chest acquisition (up to 19 dB) and contrast ratio (CR) in closed-chest acquisition (3 dB).

Contrast-Enhanced Ultrasound Feasibility in Assessing Carotid Plaque Vulnerability-Narrative Review

The risk assessment for carotid atherosclerotic lesions involves not only determining the degree of stenosis but also plaque morphology and its composition. Recently, carotid contrast-enhanced ultrasound (CEUS) has gained importance for evaluating vulnerable plaques. This review explores CEUS's utility in detecting carotid plaque surface irregularities and ulcerations as well as intraplaque neovascularization and its alignment with histology. Initial indications suggest that CEUS might have the potential to anticipate cerebrovascular incidents. Nevertheless, there is a need for extensive, multicenter prospective studies that explore the relationships between CEUS observations and patient clinical outcomes in cases of carotid atherosclerotic disease.

Musculoskeletal ultrasound: a technical and historical perspective

During the past four decades, musculoskeletal ultrasound has become popular as an imaging modality due to its low cost, accessibility, and lack of ionizing radiation. The development of ultrasound technology was possible in large part due to concomitant advances in both solid-state electronics and signal processing. The invention of the transistor and digital computer in the late 1940s was integral in its development. Moore's prediction that the number of microprocessors on a chip would grow exponentially, resulting in progressive miniaturization in chip design and therefore increased computational power, added to these capabilities. The development of musculoskeletal ultrasound has paralleled technical advances in diagnostic ultrasound. The appearance of a large variety of transducer capabilities and rapid image processing along with the ability to assess vascularity and tissue properties has expanded and continues to expand the role of musculoskeletal ultrasound. It should also be noted that these developments have in large part been due to a number of individuals who had the insight to see the potential applications of this developing technology to a host of relevant clinical musculoskeletal problems. Exquisite high-resolution images of both deep and small superficial musculoskeletal anatomy, assessment of vascularity on a capillary level and tissue mechanical properties can be obtained. Ultrasound has also been recognized as the method of choice to perform a large variety of interventional procedures. A brief review of these technical developments, the timeline over which these improvements occurred, and the impact on musculoskeletal ultrasound is presented below.

Imaging in inflammatory arthritis: progress towards precision medicine

Imaging techniques such as ultrasonography and MRI have gained ground in the diagnosis and management of inflammatory arthritis, as these imaging modalities allow a sensitive assessment of musculoskeletal inflammation and damage. However, these techniques cannot discriminate between disease subsets and are currently unable to deliver an accurate prediction of disease progression and therapeutic response in individual patients. This major shortcoming of today's technology hinders a targeted and personalized patient management approach. Technological advances in the areas of high-resolution imaging (for example, high-resolution peripheral quantitative computed tomography and ultra-high field MRI), functional and molecular-based imaging (such as chemical exchange saturation transfer MRI, positron emission tomography, fluorescence optical imaging, optoacoustic imaging and contrast-enhanced ultrasonography) and artificial intelligence-based data analysis could help to tackle these challenges. These new imaging approaches offer detailed anatomical delineation and an in vivo and non-invasive evaluation of the immunometabolic status of inflammatory reactions, thereby facilitating an in-depth characterization of inflammation. By means of these developments, the aim of earlier diagnosis, enhanced monitoring and, ultimately, a personalized treatment strategy looms closer.

Controlled Hyperthermia With High-Intensity Focused Ultrasound and Ultrasound Contrast Agent Microbubbles in Porcine Liver

OBJECTIVE

The objective of this work was to study microbubble-enhanced temperature elevation with high-intensity focused ultrasound (HIFU) at different acoustic pressures and under image guidance. The microbubbles were administered with either local or vascular injections (that mimic systemic injections) in perfused and non-perfused ex vivo porcine liver under ultrasound image guidance.

METHODS

Porcine liver was insonified for 30 s with a single-element HIFU transducer (0.9 MHz, 0.413 ms, 82% duty cycle, focal pressures of 0.6-3.5 MPa). Contrast microbubbles were injected either locally or through the vasculature. A needle thermocouple at the focus measured temperature elevation. Diagnostic ultrasound (Philips iU22, C5-1 probe) guided placement of the thermocouple and delivery of microbubbles and monitored the procedure in real time.

RESULTS

At lower acoustic pressures (0.6 and 1.2 MPa) in non-perfused liver, inertial cavitation of the injected microbubbles led to greater temperatures at the focus compared with HIFU-only treatments. At higher pressures (2.4 and 3.5 MPa) native inertial cavitation in the tissue (without injecting microbubbles) resulted in temperature elevations similar to those after injecting microbubbles. The heated area was larger when using microbubbles at all pressures. In the presence of perfusion, only local injections provided a sufficiently high concentration of microbubbles necessary for significant temperature enhancement.

CONCLUSION

Local injections of microbubbles provide a higher concentration of microbubbles in a smaller area, avoiding acoustic shadowing, and can lead to higher temperature elevation at lower pressures and increase the size of the heated area at all pressures.

A Diagnostic Model for Breast Lesions With Enlarged Enhancement Extent on Contrast-Enhanced Ultrasound Improves Malignancy Prediction

OBJECTIVE

The aim of the work described here was to develop a diagnostic model based on contrast-enhanced ultrasound (CEUS) features to improve performance in predicting the probability of malignancy for breast lesions with an enlarged enhancement extent on CEUS.

METHODS

In total, 299 consecutive patients who underwent CEUS examination and had confirmed pathological results were retrospectively enrolled. Among the 299 patients, an enlarged enhancement extent on CEUS was found in 142 patients. In this special cohort, we analyzed the association of malignant pathologic results with perfusion patterns emphatically by reclassifying the patterns.

RESULTS

A diagnostic model was developed and presented as a nomogram, assessed with discrimination and calibration. Receiver operating characteristic (ROC) curve analysis revealed that the areas under the curves of the conventional perfusion and modified perfusion patterns were 0.58 and 0.76 (p < 0.001), respectively. A diagnostic model was built and exhibited good discrimination with a C-index of 0.95 (95% confidence interval: 0.91-0.98), which was confirmed to be 0.93 via internal bootstrapping validation.

CONCLUSION

The nomogram based on CEUS features provides radiologists with a quantitative tool to predict the probability of malignancy in this special cohort of breast lesions.

Contrast-Enhanced Ultrasonography for Acute Kidney Injury: A Systematic Review and Meta-Analysis

OBJECTIVE

The aim of the work described here was to provide an evidence-based evaluation of contrast-enhanced ultrasonography (CEUS) in acute kidney injury (AKI) and assess variations in renal microperfusion with CEUS quantitative parameters in patients at a high risk of developing AKI.

METHODS

A meta-analysis and systematic review were conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, and the Embase, MEDLINE, Web of Science and the Cochrane Library databases were used to search the relevant articles systematically (2000-2022). Studies using CEUS to assess renal cortical microcirculation in AKI were included.

RESULTS

Six prospective studies (374 patients) were included. The overall quality of included studies was moderate to high. CEUS measures, maximum intensity (standard mean difference [SMD]: -1.37, 95% confidence interval [CI]: -1.64 to -1.09) and wash-in rate (SMD: -0.77, 95% CI: -1.09 to -0.45) were lower in the AKI+ group than in the AKI- group, and mean transit time (SMD: 0.76, 95% CI: 0.11-1.40) and time to peak (SMD: 1.63, 95% CI: 0.99-2.27) were higher in the AKI+ group. Moreover, maximum intensity and wash-in rate values changed before creatinine changed in the AKI+ group.

CONCLUSION

Patients with AKI had reduced microcirculatory perfusion, prolonged perfusion time and a reduced rising slope in the renal cortex, which occurred before serum creatinine changes. And they could be measured using CEUS, indicating that CEUS could help in the diagnosis of AKI.

Ultrasound stiffness and perfusion markers correlate with tumor volume responses to immunotherapy

Immunotherapy has revolutionized the treatment of dozens of cancers and became a standard of care for some tumor types. However, the majority of patients do not benefit from current immunotherapeutics and many develop severe toxicities. Therefore, the identification of biomarkers to classify patients as likely responders or non-responders to immunotherapy is a timely task. Here, we test ultrasound imaging markers of tumor stiffness and perfusion. Ultrasound imaging is non-invasive and clinically available and can be used both for stiffness and perfusion evaluation. In this study, we employed syngeneic orthotopic models of two breast cancers, a fibrosarcoma and melanoma, to demonstrate that ultrasound-derived measures of tumor stiffness and perfusion (i.e., blood volume) correlate with the efficacy of immune checkpoint inhibition (ICI) in terms of changes in primary tumor volume. To modulate tumor stiffness and perfusion and thus, get a range of therapeutic outcomes, we employed the mechanotherapeutic tranilast. Mechanotherapeutics combined with ICI are advancing through clinical trials, but biomarkers of response have not been tested until now. We found the existence of linear correlations between tumor stiffness and perfusion imaging biomarkers as well as strong linear correlations between the stiffness and perfusion markers with ICI efficacy on primary tumor growth rates. Our findings set the basis for ultrasound imaging biomarkers predictive of ICI therapy in combination with mechanotherapeutics. STATEMENT OF SIGNIFICANCE: Hypothesis: Monitoring Tumor Microenvironment (TME) mechanical abnormalities can predict the efficacy of immune checkpoint inhibition (ICI) and provide biomarkers predictive of response. Tumor stiffening and solid stress elevation are hallmarks of tumor patho-physiology in desmoplastic tumors. They induce hypo-perfusion and hypoxia by compressing tumor vessels, posing major barriers to immunotherapy. Mechanotherapeutics is a new class of drugs that target the TME to reduce stiffness and improve perfusion and oxygenation. In this study, we show that measures of stiffness and perfusion derived from ultrasound shear wave elastography and contrast enhanced ultrasound can provide biomarkers of tumor response.

CNN-based automatic segmentations and radiomics feature reliability on contrast-enhanced ultrasound images for renal tumors

Objective

To investigate the feasibility and efficiency of automatic segmentation of contrast-enhanced ultrasound (CEUS) images in renal tumors by convolutional neural network (CNN) based models and their further application in radiomic analysis.

Materials and methods

From 94 pathologically confirmed renal tumor cases, 3355 CEUS images were extracted and randomly divided into training set (3020 images) and test set (335 images). According to the histological subtypes of renal cell carcinoma, the test set was further split into clear cell renal cell carcinoma (ccRCC) set (225 images), renal angiomyolipoma (AML) set (77 images) and set of other subtypes (33 images). Manual segmentation was the gold standard and serves as ground truth. Seven CNN-based models including DeepLabV3+, UNet, UNet++, UNet3+, SegNet, MultilResUNet and Attention UNet were used for automatic segmentation. Python 3.7.0 and Pyradiomics package 3.0.1 were used for radiomic feature extraction. Performance of all approaches was evaluated by the metrics of mean intersection over union (mIOU), dice similarity coefficient (DSC), precision, and recall. Reliability and reproducibility of radiomics features were evaluated by the Pearson coefficient and the intraclass correlation coefficient (ICC).

Results

All seven CNN-based models achieved good performance with the mIOU, DSC, precision and recall ranging between 81.97%-93.04%, 78.67%-92.70%, 93.92%-97.56%, and 85.29%-95.17%, respectively. The average Pearson coefficients ranged from 0.81 to 0.95, and the average ICCs ranged from 0.77 to 0.92. The UNet++ model showed the best performance with the mIOU, DSC, precision and recall of 93.04%, 92.70%, 97.43% and 95.17%, respectively. For ccRCC, AML and other subtypes, the reliability and reproducibility of radiomic analysis derived from automatically segmented CEUS images were excellent, with the average Pearson coefficients of 0.95, 0.96 and 0.96, and the average ICCs for different subtypes were 0.91, 0.93 and 0.94, respectively.

Conclusion

This retrospective single-center study showed that the CNN-based models had good performance on automatic segmentation of CEUS images for renal tumors, especially the UNet++ model. The radiomics features extracted from automatically segmented CEUS images were feasible and reliable, and further validation by multi-center research is necessary.

Ultrasonic Characterization of Ibidi μ-Slide I Luer Channel Slides for Studies With Ultrasound Contrast Agents

Understanding and controlling the ultrasound contrast agent (UCA)'s response to an applied ultrasound pressure field are crucial when investigating ultrasound imaging sequences and therapeutic applications. The magnitude and frequency of the applied ultrasonic pressure waves affect the oscillatory response of the UCA. Therefore, it is important to have an ultrasound compatible and optically transparent chamber in which the acoustic response of the UCA can be studied. The aim of our study was to determine the in situ ultrasound pressure amplitude in the ibidi μ -slide I Luer channel, an optically transparent chamber suitable for cell culture, including culture under flow, for all microchannel heights (200, 400, 600, and [Formula: see text]). First, the in situ pressure field in the 800- [Formula: see text] high channel was experimentally characterized using Brandaris 128 ultrahigh-speed camera recordings of microbubbles (MBs) and a subsequent iterative processing method, upon insonification at 2 MHz, 45° incident angle, and 50-kPa peak negative pressure (PNP). Control studies in another cell culture chamber, the CLINIcell, were compared with the obtained results. The pressure amplitude was -3.7 dB with respect to the pressure field without the ibidi μ -slide. Second, using finite-element analysis, we determined the in situ pressure amplitude in the ibidi with the 800- [Formula: see text] channel (33.1 kPa), which was comparable to the experimental value (34 kPa). The simulations were extended to the other ibidi channel heights (200, 400, and [Formula: see text]) with either 35° or 45° incident angle, and at 1 and 2 MHz. The predicted in situ ultrasound pressure fields were between -8.7 and -1.1 dB of the incident pressure field depending on the listed configurations of ibidi slides with different channel heights, applied ultrasound frequencies, and incident angles. In conclusion, the determined ultrasound in situ pressures demonstrate the acoustic compatibility of the ibidi μ -slide I Luer for different channel heights, thereby showing its potential for studying the acoustic behavior of UCAs for imaging and therapy.

Assessment of Transarterial Chemoembolization Using Super-resolution Ultrasound Imaging and a Rat Model of Hepatocellular Carcinoma

OBJECTIVE

Hepatocellular carcinoma (HCC) is a highly prevalent form of liver cancer diagnosed annually in 600,000 people worldwide. A common treatment is transarterial chemoembolization (TACE), which interrupts the blood supply of oxygen and nutrients to the tumor mass. The need for repeat TACE treatments may be assessed in the weeks after therapy with contrast-enhanced ultrasound (CEUS) imaging. Although the spatial resolution of traditional CEUS has been restricted by the diffraction limit of ultrasound (US), this physical barrier has been overcome by a recent innovation known as super-resolution US (SRUS) imaging. In short, SRUS enhances the visible details of smaller microvascular structures on the 10 to 100 µm scale, which unlocks a host of new clinical opportunities for US.

METHODS

In this study, a rat model of orthotopic HCC is introduced and TACE treatment response (to a doxorubicin-lipiodol emulsion) is assessed using longitudinal SRUS and magnetic resonance imaging (MRI) performed at 0, 7 and 14 d. Animals were euthanized at 14 d for histological analysis of excised tumor tissue and determination of TACE response, that is, control, partial response or complete response. CEUS imaging was performed using a pre-clinical US system (Vevo 3100, FUJIFILM VisualSonics Inc.) equipped with an MX201 linear array transducer. After administration of a microbubble contrast agent (Definity, Lantheus Medical Imaging), a series of CEUS images were collected at each tissue cross-section as the transducer was mechanically stepped at 100 μm increments. SRUS images were formed at each spatial position, and a microvascular density metric was calculated. Microscale computed tomography (microCT, OI/CT, MILabs) was used to confirm TACE procedure success, and tumor size was monitored using a small animal MRI system (BioSpec 3T, Bruker Corp.).

RESULTS

Although there were no differences at baseline (p > 0.15), both microvascular density levels and tumor size measures from the complete responder cases at 14 d were considerably lower and smaller, respectively, than those in the partial responder or control group animals. Histological analysis revealed tumor-to-necrosis levels of 8.4%, 51.1% and 100%, for the control, partial responder and complete responder groups, respectively (p < 0.005).

CONCLUSION

SRUS imaging is a promising modality for assessing early changes in microvascular networks in response to tissue perfusion-altering interventions such as TACE treatment of HCC.

New Technologies in the Assessment of Carotid Stenosis: Beyond the Color-Doppler Ultrasound-High Frame Rate Vector-Flow and 3D Arterial Analysis Ultrasound

Atherosclerotic plaque in the carotid artery is the main cause of ischemic stroke, with a high incidence rate among people over 65 years. A timely and precise diagnosis can help to prevent the ischemic event and decide patient management, such as follow up, medical, or surgical treatment. Presently, diagnostic imaging techniques available include color-Doppler ultrasound, as a first evaluation technique, computed tomography angiography, which, however, uses ionizing radiation, magnetic resonance angiography, still not in widespread use, and cerebral angiography, which is an invasively procedure reserved for therapeutically purposes. Contrast-enhanced ultrasound is carving out an important and emerging role which can significantly improve the diagnostic accuracy of an ultrasound. Modern ultrasound technologies, still not universally utilized, are opening new horizons in the arterial pathologies research field. In this paper, the technical development of various carotid artery stenosis diagnostic imaging modalities and their impact on clinical efficacy is thoroughly reviewed.

Microbubble-Assisted Ultrasound for Drug Delivery to the Retina in an Ex Vivo Eye Model

Drug delivery to the retina is one of the major challenges in ophthalmology due to the biological barriers that protect it from harmful substances in the body. Despite the advancement in ocular therapeutics, there are many unmet needs for the treatment of retinal diseases. Ultrasound combined with microbubbles (USMB) was proposed as a minimally invasive method for improving delivery of drugs in the retina from the blood circulation. This study aimed to investigate the applicability of USMB for the delivery of model drugs (molecular weight varying from 600 Da to 20 kDa) in the retina of ex vivo porcine eyes. A clinical ultrasound system, in combination with microbubbles approved for clinical ultrasound imaging, was used for the treatment. Intracellular accumulation of model drugs was observed in the cells lining blood vessels in the retina and choroid of eyes treated with USMB but not in eyes that received ultrasound only. Specifically, 25.6 ± 2.9% of cells had intracellular uptake at mechanical index (MI) 0.2 and 34.5 ± 6.0% at MI 0.4. Histological examination of retinal and choroid tissues revealed that at these USMB conditions, no irreversible alterations were induced at the USMB conditions used. These results indicate that USMB can be used as a minimally invasive targeted means to induce intracellular accumulation of drugs for the treatment of retinal diseases.

Update of Contrast-enhanced Ultrasound in Musculoskeletal Medicine: Clinical Perspectives - A Review

Contrast-enhanced ultrasound (CEUS) uses an intravascular contrast agent to enhance blood flow signals and assess microcirculation in different parts of the human body. Over the past decade, CEUS has become more widely applied in musculoskeletal (MSK) medicine, and the current review aims to systematically summarize current research on the application of CEUS in the MSK field, focusing on 67 articles published between January 2001 and June 2021 in online databases including PubMed, Scopus, and Embase. CEUS has been widely used for the clinical assessment of muscle microcirculation, tendinopathy, fracture nonunions, sports-related injuries, arthritis, peripheral nerves, and tumors, and can serve as an objective and quantitative evaluation tool for prognosis and outcome prediction. Optimal CEUS parameters and diagnostic cut off values for each disease category remain to be confirmed.

QCM-D Investigations on Cholesterol-DNA Tethering of Liposomes to Microbubbles for Therapy

Lipid-shelled microbubbles (MBs) offer potential as theranostic agents, capable of providing both contrast enhancement in ultrasound imaging as well as a route for triggered drug release and improved localized drug delivery. A common motif in the design of such therapeutic vehicles is the attachment of the drug carrier, often in the form of liposomes, to the microbubble. Traditionally, such attachments have been based around biotin-streptavidin and maleimide-PDP chemistries. Comparatively, the use of DNA-lipid tethers offers potential advantage. First, their specificity permits the construction of more complex architectures that might include bespoke combinations of different drug-loaded liposomes and/or targeting groups, such as affimers or antibodies. Second, the use of dual-lipid tether strategies should increase the strength of the individual tethers tethering the liposomes to the bubbles. The ability of cholesterol-DNA (cDNA) tethers for conjugation of liposomes to supported lipid bilayers has previously been demonstrated. For in vivo applications, bubbles and liposomes often contain a proportion of polyethylene glycol (PEG) to promote stealth-like properties and increase lifetimes. However, the associated steric effects may hinder tethering of the drug payload. We show that while the presence of PEG reduced the tethering affinity, cDNA can still be used for the attachment of liposomes to a supported lipid bilayer (SLB) as measured via QCM-D. Importantly, we show, for the first time, that QCM-D can be used to study the tethering of microbubbles to SLBs using cDNA, signified by a decrease in the magnitude of the frequency shift compared to liposomes alone due to the reduced density of the MBs. We then replicate this tethering interaction in the bulk and observe attachment of liposomes to the shell of a central MB and hence formation of a model therapeutic microbubble.

Recent Development of Rhenium-Based Materials in the Application of Diagnosis and Tumor Therapy

Rhenium (Re) is widely used in the diagnosis and treatment of cancer due to its unique physical and chemical properties. Re has more valence electrons in its outer shell, allowing it to exist in a variety of oxidation states and to form different geometric configurations with many different ligands. The luminescence properties, lipophilicity, and cytotoxicity of complexes can be adjusted by changing the ligand of Re. This article mainly reviews the development of radionuclide 188Re in radiotherapy and some innovative applications of Re as well as the different therapeutic approaches and imaging techniques used in cancer therapy. In addition, the current application and future challenges and opportunities of Re are also discussed.

Generalized mathematical framework for contrast-enhanced ultrasound imaging with pulse inversion spectral deconvolution

A generalized mathematical framework for performing contrast-enhanced ultrasound (CEUS) imaging is introduced. Termed pulse inversion spectral deconvolution (PISD), this CEUS approach is founded on Gaussian derivative functions (GDFs). PISD pulses are used to form two inverted pulse sequences, which are then used to filter backscattered ultrasound (US) data for isolation of the nonlinear (NL) microbubble (MB) signal component. An US scanner equipped with a linear array transducer was used for data acquisition. With a vascular flow phantom perfused with MBs, data was collected using PISD and NL-based CEUS imaging. The role of wide-beam transmit aperture size (32 or 64 elements) was also evaluated using an US pulse frequency of 6.25 MHz. Image enhancement was quantified by a contrast-to-noise ratio (CNR). Preliminary in vivo data was collected in the hindlimb and kidney of healthy rats. Overall, in vitro wide-beam CEUS imaging using an aperture size of 64 elements yielded improved CNR values. Specifically, PISD-based CEUS imaging produced CNR values of 37.3 dB. For comparison, CNR values obtained using B-mode US or NL approaches were 2.1 and 12.1 dB, respectively. In vivo results demonstrated that PISD-based CEUS imaging improved vascular visualization compared to the NL imaging strategy.

A Single-Shot Harmonic Imaging Approach Utilizing Deep Learning for Medical Ultrasound

Tissue Harmonic Imaging (THI) is an invaluable tool in clinical ultrasound owing to its enhanced contrast resolution and reduced reverberation clutter in comparison to fundamental mode imaging. However, harmonic content separation based on high pass filtering suffers from potential contrast degradation or lower axial resolution due to spectral leakage. Whereas nonlinear multi-pulse harmonic imaging schemes, such as amplitude modulation and pulse inversion, suffer from a reduced framerate and comparatively higher motion artifacts due to the necessity of at least two pulse echo acquisitions. To address this problem, we propose a deep-learning-based single-shot harmonic imaging technique capable of generating comparable image quality to pulse amplitude modulation methods, yet at a higher framerate and with fewer motion artifacts. Specifically, an asymmetric convolutional encoder-decoder structure is designed to estimate the combination of the echoes resulting from the half-amplitude transmissions using the echo produced from the full amplitude transmission as input. The echoes were acquired with the checkerboard amplitude modulation technique for training. The model was evaluated across various targets and samples to illustrate generalizability as well as the possibility and impact of transfer learning. Furthermore, for possible interpretability of the network, we investigate if the latent space of the encoder holds information on the nonlinearity parameter of the medium. We demonstrate the ability of the proposed approach to generate harmonic images with a single firing that are comparable to those from a multi-pulse acquisition.

Contrast-Enhanced Ultrasound with Optimized Aperture Patterns and Bubble Segmentation Based on Echo Phase

Amplitude modulation (AM) suppresses tissue signals and detects microbubble signals in contrast-enhanced ultrasound (CEUS) and is often implemented with checkerboard apertures. However, possible crosstalk between transmitting and non-transmitting array elements may compromise tissue suppression in AM. Using AM aperture patterns other than the conventional checkerboard approach (one on, one off) may reduce the degree of crosstalk and increase the contrast-to-tissue-ratio (CTR) compared with conventional AM. Furthermore, previous studies have reported that the phase difference between the echoes in AM pulsing sequences may be used to segment tissue and microbubbles and improve tissue signal suppression and the CTR of CEUS images. However, the CTR of the image produced by alternative AM aperture patterns and the effect of segmentation approach on these alternative apertures have not been investigated. We evaluated a number of AM aperture patterns to find an optimal AM aperture pattern that provides the highest CTR. We found that the aperture that uses alternating groups of two elements, AM2, had the highest CTR for the probe evaluated. In addition, a segmentation technique based on echo phase differences (between the full and half-pulses, ΔΦAM, between the complementary half-pulses, ΔΦhalf, and the maximum of the two ΔΦmax) was also considered in the AM aperture optimization process. The segmentation approach increases the CTR by about 25 dB for all apertures. Finally, AM2 segmented with ΔΦmax had a 7-dB higher CTR in a flow phantom and a 6-dB higher contrast in a perfused pig liver than conventional AM segmented with ΔΦAM, and it is the optimal transmit aperture design.

Quantitative tissue perfusion imaging using nonlinear ultrasound localization microscopy

Ultrasound localization microscopy (ULM) is a recent advancement in ultrasound imaging that uses microbubble contrast agents to yield vascular images that break the classical diffraction limit on spatial resolution. Current approaches cannot image blood flow at the tissue perfusion level since they rely solely on differences in velocity to separate tissue and microbubble signals; lower velocity microbubble echoes are removed during high pass wall filtering. To visualize blood flow in the entire vascular tree, we have developed nonlinear ULM, which combines nonlinear pulsing sequences with plane-wave imaging to segment microbubble signals independent of their velocity. Bubble localization and inter-frame tracking produces super-resolved images and, with parameters derived from the bubble tracks, a rich quantitative feature set that can describe the relative quality of microcirculatory flow. Using the rat spinal cord as a model system, we showed that nonlinear ULM better resolves some smaller branching vasculature compared to conventional ULM. Following contusion injury, both gold-standard histological techniques and nonlinear ULM depicted reduced in-plane vessel length between the penumbra and contralateral gray matter (-16.7% vs. -20.5%, respectively). Here, we demonstrate that nonlinear ULM uniquely enables investigation and potential quantification of tissue perfusion, arguably the most important component of blood flow.

A multi-pulse ultrasound technique for imaging of thick-shelled microbubbles demonstrated in vitro and in vivo

Contrast enhanced ultrasound is a powerful diagnostic tool and ultrasound contrast media are based on microbubbles (MBs). The use of MBs in drug delivery applications and molecular imaging is a relatively new field of research which has gained significant interest during the last decade. MBs available for clinical use are fragile with short circulation half-lives due to the use of a thin encapsulating shell for stabilization of the gas core. Thick-shelled MBs can have improved circulation half-lives, incorporate larger amounts of drugs for enhanced drug delivery or facilitate targeting for use in molecular ultrasound imaging. However, methods for robust imaging of thick-shelled MBs are currently not available. We propose a simple multi-pulse imaging technique which is able to visualize thick-shelled polymeric MBs with a superior contrast-to-tissue ratio (CTR) compared to commercially available harmonic techniques. The method is implemented on a high-end ultrasound scanner and in-vitro imaging in a tissue mimicking flow phantom results in a CTR of up to 23 dB. A proof-of-concept study of molecular ultrasound imaging in a soft tissue inflammation model in rabbit is then presented where the new imaging technique showed an enhanced accumulation of targeted MBs in the inflamed tissue region compared to non-targeted MBs and a mean CTR of 13.3 dB for stationary MBs. The presence of fluorescently labelled MBs was verified by confocal microscopy imaging of tissue sections post-mortem.

Microbubble-Assisted Ultrasound for Imaging and Therapy of Melanoma Skin Cancer: A Systematic Review

Recent technological developments in ultrasound (US) imaging and ultrasound contrast agents (UCAs) have improved diagnostic confidence in echography. In the clinical management of melanoma, contrast-enhanced ultrasound (CEUS) imaging complements conventional US imaging (i.e., high-resolution US and Doppler imaging) for clinical examination and therapeutic follow-up. These developments have set into motion the combined use of ultrasound and UCAs as a new modality for drug delivery. This modality, called sonoporation, has emerged as a non-invasive, targeted and safe method for the delivery of therapeutic drugs into melanoma. This review focuses on the results and prospects of using US and UCAs as dual modalities for CEUS imaging and melanoma treatment.

The influence of inter-bubble spacing on the resonance response of ultrasound contrast agent microbubbles

Ultrasound-driven microbubbles, typically between 1 and 8 µm in diameter, are resonant scatterers that are employed as diagnostic contrast agents and emerging as potentiators of targeted therapies. Microbubbles are administered in populations whereby their radial dynamics - key to their effectiveness - are greatly affected by intrinsic (e.g. bubble size) and extrinsic (e.g. boundaries) factors. In this work, we aim to understand how two neighbouring microbubbles influence each other. We developed a finite element model of a system of two individual phospholipid-encapsulated microbubbles vibrating in proximity to each other to study the effect of inter-bubble distance on microbubble radial resonance response. For the case of two equal-sized and identical bubbles, each bubble exhibits a decrease between 7 and 10% in the frequency of maximum response (f_MR) and an increase in amplitude of maximum response (A_MR) by 9-11% as compared to its isolated response in free-space, depending on the bubble size examined. For a system of two unequal-sized microbubbles, the large bubble shows no significant change, however the smaller microbubble shows an increase in f_MR by 7-11% and a significant decrease in A_MR by 38-52%. Furthermore, in very close proximity the small bubble shows a secondary off-resonance peak at the corresponding f_MR of its larger companion microbubble. Our work suggests that frequency-dependent microbubble response is greatly affected by the presence of another bubble, which has implications in both imaging and therapy applications. Furthermore, our work suggests a mechanism by which nanobubbles show significant off-resonance vibrations in the clinical frequency range, a behaviour that has been observed experimentally but heretofore unexplained.

Ultrasound Responsive Smart Implantable Hydrogels for Targeted Delivery of Drugs: Reviewing Current Practices

Over the last two decades, the process of delivering therapeutic drugs to a patient with a controlled release profile has been a significant focus of drug delivery research. Scientists have given tremendous attention to ultrasound-responsive hydrogels for several decades. These smart nanosystems are more applicable than other stimuli-responsive drug delivery vehicles (ie UV-, pH- and thermal-, responsive materials) because they enable more efficient targeted treatment via relatively non-invasive means. Ultrasound (US) is capable of safely transporting energy through opaque and complex media with minimal loss of energy. It is capable of being localized to smaller regions and coupled to systems operating at various time scales. However, the properties enabling the US to propagate effectively in materials also make it very difficult to transform acoustic energy into other forms that may be used. Recent research from a variety of domains has attempted to deal with this issue, proving that ultrasonic effects can be used to control chemical and physical systems with remarkable specificity. By obviating the need for multiple intravenous injections, implantable US responsive hydrogel systems can enhance the quality of life for patients who undergo treatment with a varied dosage regimen. Ideally, the ease of self-dosing in these systems would lead to increased patient compliance with a particular therapy as well. However, excessive literature has been reported based on implanted US responsive hydrogel in various fields, but there is no comprehensive review article showing the strategies to control drug delivery profile. So, this review was aimed at discussing the current strategies for controlling and targeting drug delivery profiles using implantable hydrogel systems.

Quantitative Analysis of Renal Perfusion in Rhabdomyolysis-Induced Acute Kidney Injury Using Contrast-Enhanced Ultrasound: An Experimental Study

The aim of this study was to evaluate renal perfusion changes in rats with acute kidney injury induced by rhabdomyolysis, using quantitative parameters obtained with contrast-enhanced ultrasound (CEUS). Sprague-Dawley (SD) rats were randomly divided into an experimental group (n = 40) and a control group (n = 20). Each group was further divided into four subgroups (0.5-, 6-, 24- and 72-h groups). Time-intensity curves and related quantitative parameters of the renal cortex and medulla were obtained by CEUS, and the contrast characteristics analyzed for different time points. In the experimental group, the CEUS quantitative parameters for the renal medulla of time to peak (TTP), descending time/2 (DT/2) and area under the curve (AUC) increased, whereas ascending slope (AS) and descending slope (DS) decreased. Similarly, renal cortical AS, DS and AUC in the experimental group differed significantly from those in the control group. With respect to the CEUS quantitative parameters for the renal cortex, AUC increased, and AS and DS decreased. These parameters differed significantly between the experimental and control groups. CEUS is sensitive to change in renal perfusion in rhabdomyolysis-induced acute kidney injury and, thus, has diagnostic value.

A Comparison of the Sensitivity of Contrast-Specific Imaging Modes on Clinical and Preclinical Ultrasound Scanners

Ultrasonic contrast agents are used routinely to aid clinical diagnosis. All premium- and mid-range scanners utilise contrast-specific imaging techniques to preferentially isolate and display the nonlinear signals generated from the microbubbles when insonated with a series of ultrasound pulses. In this manuscript the abilities of four premium ultrasound scanners to detect and display the ultrasound signal from two commercially available contrast agents—SonoVue and DEFINITY^®—are compared. A flow phantom was built using tubes with internal diameters of 1.6 mm and 3.2 mm, suspended at depths of 1, 5 and 8 cm and embedded in tissue-mimicking material. Dilute solutions of SonoVue and DEFINITY^® were pumped through the phantom at 0.25 mL/s and 1.5 mL/s. Four transducers were used to scan the tubes—a GE Logiq E9 (C2-9) curvilinear probe, a Philips iU22 L9-3 linear array probe, an Esaote MyLab Twice linear array LA523 (4–13 MHz) and a Fujifilm VisualSonics Vevo3100 MX250 (15–30 MHz) linear array probe. We defined a new parameter to compare the ability of the ultrasound scanners to display the contrast enhancement. This was defined as the ratio of grey-scale intensity ratio in contrast-specific imaging mode relative to the B-mode intensity from the same region-of-interest within the corresponding B-mode image. The study demonstrated that the flow rates used in this study had no effect on the contrast-specific imaging mode to B-mode (CSIM-BM) ratio for the three clinical scanners studied, with SonoVue demonstrating broadly similar CSIM-BM ratios across all 3 clinical scanners. DEFINITY^® also displayed similar results to SonoVue except when insonated with the Esaote MyLab Twice LA523 transducer, where it demonstrated significantly higher CSIM-BM ratios at superficial depths.

The evolving role of contrast-enhanced ultrasound in urology: a review

PURPOSE

Ultrasound's versatility and ease of use has expanded its application in many clinical settings. Technological advancements with contrast-enhanced ultrasound (CEUS) have allowed high quality imaging similar to CT or MRI with lower risk of contrast toxicity and radiation exposure. In this review article we examine the development of CEUS and its vast applications in the field of urology.

METHODS

A PubMed literature search was performed using keywords: contrast enhanced ultrasound, prostate cancer, renal cancer, and multiparametric ultrasound.

RESULTS

The development of CEUS has improved transrectal ultrasound imaging with increased detection of prostate cancer (PCa). Further enhancements of CEUS such as subharmonic imaging (SHI), flash replenishment imaging (FRI) and contrast ultrasound dispersion imaging (CUDI) allow improved PCa diagnosis. CEUS has also emerged as an important tool in characterizing suspicious renal mass without compromising renal function with contrast imaging.

CONCLUSION

CEUS has modernized imaging and diagnosis of prostate and renal cancer. Future advancements and utilization of CEUS will allow its expansion into other urological subspecialties.