Microbubble contrast agent SonoVue: An efficient medium for the preoperative lymphatic mapping of thyroid carcinoma

Objective: To assess the value of microbubble contrast agent SonoVue in the thorough preoperative lymphatic mapping of patients with thyroid carcinoma, including the lymphatic drainage region, the detection of sentinel lymph node (SLN), and the diagnosis of lymph node metastasis (LNM). Materials and methods: 55 patients with 62 thyroid malignancies proved by surgical pathology (59 papillary thyroid carcinomas and three medullary thyroid carcinomas) who underwent preoperative lymphatic contrast-enhanced ultrasound (LCEUS) with microbubble contrast agent SonoVue were enrolled. All LNM were confirmed by pathology. The location of thyroid lesions, ultrasonic features of lymph nodes, lymphatic drainage region, and detection of SLN were assessed. The diagnostic performance (sensitivity, specificity, positive predictive value, negative predictive value and accuracy) of different parameters for the LNM diagnosis was calculated. Results: SonoVue effectively demonstrated the lymphatic drainage region for all enrolled thyroid carcinomas. The most common lymphatic drainage region for thyroid carcinomas was region VI (93.55%), followed by region III (62.90%), region IV (48.39%) and region II (4.84%). When divided by the lesion location, the most common lymphatic drainage regions for the nodule in isthmus, superior lobe and inferior lobe of the thyroid were region VI, region III, and region VI respectively. SLN was detected in 96.77% (60/62) of cases. The two cases without SLN demonstration had pathologically proven LNM. The most common sonographic sign of LNM was perfusion defect (54.17%). The diagnostic accuracy of SonoVue in central and lateral compartment LNM was 86.67% and 91.67%, respectively. Conclusion: Microbubble contrast agent SonoVue is a valuable imaging contrast medium for thorough preoperative lymphatic mapping in patients with thyroid carcinoma, including the lymphatic drainage region, the detection of SLN, and the diagnosis of LNM. LCEUS with SonoVue alone has limitations of false negatives when there is lymphatic vessel obstruction and may need to be combined with other ultrasound modalities.

Contrast-enhanced ultrasound imaging of acute changes in pancreatic cancer following targeted hyaluronan treatment

The purpose of this study was to monitor acute changes in pancreatic tumor perfusion with contrast-enhanced ultrasound (CEUS) imaging following targeted hyaluronan (HA) treatment. Intratumoral accumulation of HA is one of contributing factors that can lead to an increased tumor interstitial pressure (TIP). These elevated TIP levels can hinder delivery of chemotherapeutic drugs and cause treatment failure. For this study, pancreatic cancer-bearing mice were imaged at baseline and again at 2 h after intravenous administration of physiological saline (control group) or PEGPH20, which targets HA (therapy group). CEUS data were collected for 5 min and the temporal sequence was first analyzed using a singular value filter (SVF) to remove any background clutter signal. Given the time history of contrast agent flow, a tumor perfusion parametric analysis was performed. A series of morphological image operations was applied to quantify structural features of the tumor angiogenic network including vessel count, density, length, diameter, tortuosity, and branching points. After imaging, animals were euthanized, and tumors excised for histological processing. Acute microvascular changes were found at 2 h after drug administration as confirmed by CEUS imaging. Further, histologic analysis of tumor sections revealed lower HA accumulation in the therapy group animals. Overall, these findings suggest that CEUS imaging of acute changes in tumor perfusion may help identify an optimal window whereby follow-up chemotherapeutic drug dosing would be more effective.

The Most Appropriate Time Delay after Microbubble Contrast Agent Intravenous Injection to Maximize Liver Metastasis Conspicuity on Contrast-Enhanced Ultrasound

PURPOSE

To identify the most appropriate time delay after microbubble contrast agent injection to maximize liver metastasis conspicuity on contrast-enhanced ultrasound (CEUS).

METHODS

Twenty-five consecutive patients (12 male and 13 female; age: 50 ± 13 years) with a known primary tumor and evidence of liver metastases on unenhanced ultrasound (US) underwent CEUS. CEUS consisted of continuous liver parenchyma scanning during arterial (15-35 s after microbubble injection), portal venous (40-120 s), and late phase (from 120 s up to microbubble disappearance). Subjective conspicuity index (ranging from 1 to 5) and objective conspicuity index (I_lesion-I_liver/I_liver, I = signal intensity) were calculated on reference frames selected on arterial phase and every 20 s on portal venous and late phase.

RESULTS

A total number of 40 liver metastases were identified after microbubble injection. The highest liver metastasis conspicuity was observed on early portal venous phase (40-60 s after microbubble injection) both on visual (mean subjective conspicuity index ± standard deviation [SD] = 4.36 ± 0.75, reader 1; 4.25 ± 0.65, reader 2) and quantitative analysis (mean objective conspicuity index ± SD = -0.99 ± 0.001).

CONCLUSION

The early portal venous phase (40-60 s after microbubble injection) provides the best liver metastases' conspicuity after microbubble contrast agent injection.

Can Contrast-Enhanced Sonography Detect Bowel Wall Fibrosis in Mixed Inflammatory and Fibrotic Crohn Disease Lesions in an Animal Model?

OBJECTIVES

To determine whether contrast-enhanced sonographic quantitative perfusion parameters can detect bowel wall fibrosis in the setting of mixed inflammatory and fibrotic lesions in a Crohn disease animal model.

METHODS

This study was approved by the institutional Committee on the Use and Care of Animals. Multiple (range, 1-5) 2,4,6-trinitrobenzenesulfonic acid-ethanol enemas were used to create intestinal inflammatory lesions with variable fibrosis in female Lewis rats. Low-mechanical index contrast-enhanced sonography was performed 3 days after the final enema using a 0.2-mL bolus of sulfur hexafluoride microbubbles injected through a tail vein. Contrast-enhanced sonographic data were analyzed with software that converts video data into echo-power (linearized) data. Colorectal lesions were scored for histopathologic inflammation and fibrosis; bowel wall collagen was quantified by Western blotting. The Spearman correlation was used to assess associations between contrast-enhanced sonographic quantitative parameters and bowel wall collagen; the Kruskal-Wallis test was used to compare continuous results between histopathologic groups.

RESULTS

Thirty-one animals were included in our analysis. Animals were placed into 3 histopathologic cohorts: (1) severe bowel wall inflammation/minimal or no fibrosis (n = 11); (2) severe bowel wall inflammation/moderate fibrosis (n = 9); and (3) severe bowel wall inflammation/severe fibrosis (n = 11). Western blotting showed a significant difference in bowel wall collagen between histopathologic cohorts (P = .0001). There was no correlation between any contrast-enhanced sonographic quantitative parameter and bowel wall collagen (P > .05). There was no difference between histopathologic cohorts for any contrast-enhanced sonographic quantitative parameter (P > .05).

CONCLUSIONS

Contrast-enhanced sonographic quantitative perfusion parameters failed to effectively detect bowel wall fibrosis in the setting of superimposed inflammation in a Crohn disease animal model.

3-D Ultrasound Localization Microscopy for Identifying Microvascular Morphology Features of Tumor Angiogenesis at a Resolution Beyond the Diffraction Limit of Conventional Ultrasound

Angiogenesis has been known as a hallmark of solid tumor cancers for decades, yet ultrasound has been limited in its ability to detect the microvascular changes associated with malignancy. Here, we demonstrate the potential of 'ultrasound localization microscopy' applied volumetrically in combination with quantitative analysis of microvascular morphology, as an approach to overcome this limitation. This pilot study demonstrates our ability to image complex microvascular patterns associated with tumor angiogenesis in-vivo at a resolution of tens of microns - substantially better than the diffraction limit of traditional clinical ultrasound, yet using an 8 MHz clinical ultrasound probe. Furthermore, it is observed that data from healthy and tumor-bearing tissue exhibit significant differences in microvascular pattern and density. Results suggests that with continued development of these novel technologies, ultrasound has the potential to detect biomarkers of cancer based on the microvascular 'fingerprint' of malignant angiogenesis rather than through imaging of blood flow dynamics or the tumor mass itself.

Biophysical insight into mechanisms of sonoporation

This study presents a unique approach to understanding the biophysical mechanisms of ultrasound-triggered cell membrane disruption (i.e., sonoporation). We report direct correlations between ultrasound-stimulated encapsulated microbubble oscillation physics and the resulting cellular membrane permeability by simultaneous microscopy of these two processes over their intrinsic physical timescales (microseconds for microbubble dynamics and seconds to minutes for local macromolecule uptake and cell membrane reorganization). We show that there exists a microbubble oscillation-induced shear-stress threshold, on the order of kilopascals, beyond which endothelial cellular membrane permeability increases. The shear-stress threshold exhibits an inverse square-root relation to the number of oscillation cycles and an approximately linear dependence on ultrasound frequency from 0.5 to 2 MHz. Further, via real-time 3D confocal microscopy measurements, our data provide evidence that a sonoporation event directly results in the immediate generation of membrane pores through both apical and basal cell membrane layers that reseal along their lateral area (resealing time of ∼<2 min). Finally, we demonstrate the potential for sonoporation to indirectly initiate prolonged, intercellular gaps between adjacent, confluent cells (∼>30-60 min). This real-time microscopic approach has provided insight into both the physical, cavitation-based mechanisms of sonoporation and the biophysical, cell-membrane-based mechanisms by which microbubble acoustic behaviors cause acute and sustained enhancement of cellular and vascular permeability.

Quantitative Nonlinear Contrast-Enhanced Ultrasound of the Breast

OBJECTIVE

Breast cancer is the most frequent type of cancer among women (25% of all cancers). The angiogenic process that fuels the growth of tumors is a potential early indicator for differentiating between malignant and benign tumors. Recently, the use of microbubble-based contrast agents combined with ultrasound has allowed the development of contrast agent-specific imaging modes that provide visualization of tumor neovascularity.

CONCLUSION

Contrast-enhanced Doppler, harmonic, and subharmonic imaging are some of the imaging modes that have been investigated for visualizing and quantifying the vascularity in breast tumors.

Potential use of microbubbles (MBs) as contrast material in x-ray dark field (DF) imaging: How does the DF signal change with the characteristic parameters of the MBs?

One of the most exciting aspects of the grating based x-ray differential phase contrast (DPC) acquisition method is the concurrent generation of the so-called dark field (DF) signal, along with the classical absorption signal and the novel DPC signal. The DF signal is associated with local distribution of small angle scatterers in an image object, while the absorption signal and DPC signal are often used to characterize the relatively uniform structure of the image object. Besides the endogenous image contrast, exogenous contrast media are often used in x-ray imaging to locally enhance the image signal. This paper proposes a potential contrast medium for DF signal enhancement: microbubbles (MBs). MBs have already been developed for clinical use in ultrasound imaging, and recent experimental studies have shown that MBs may also enhance the DF signal, although it remained unclear how the physical characteristics of the MBs quantitatively impact the DF signal. In this paper, a systematic study was performed to investigate the quantitative relationships between the DF signal and the following properties of MBs: size, concentration, shell thickness, size uniformity, and whether gold nanoparticles were attached. The experimental results demonstrated that, an increased MB size (about 4 microns) may generate a stronger DF signal for our DPC imaging system; additionally, a moderately increased shell thickness and the use of gold nanoparticles on the shell surface also resulted in further enhancement of the DF signal. These findings may provide critical information needed for using MBs as the contrast agent of x-ray DF imaging.

Quantitative contrast-enhanced ultrasound imaging: a review of sources of variability

Ultrasound provides a valuable tool for medical diagnosis offering real-time imaging with excellent spatial resolution and low cost. The advent of microbubble contrast agents has provided the additional ability to obtain essential quantitative information relating to tissue vascularity, tissue perfusion and even endothelial wall function. This technique has shown great promise for diagnosis and monitoring in a wide range of clinical conditions such as cardiovascular diseases and cancer, with considerable potential benefits in terms of patient care. A key challenge of this technique, however, is the existence of significant variations in the imaging results, and the lack of understanding regarding their origin. The aim of this paper is to review the potential sources of variability in the quantification of tissue perfusion based on microbubble contrast-enhanced ultrasound images. These are divided into the following three categories: (i) factors relating to the scanner setting, which include transmission power, transmission focal depth, dynamic range, signal gain and transmission frequency, (ii) factors relating to the patient, which include body physical differences, physiological interaction of body with bubbles, propagation and attenuation through tissue, and tissue motion, and (iii) factors relating to the microbubbles, which include the type of bubbles and their stability, preparation and injection and dosage. It has been shown that the factors in all the three categories can significantly affect the imaging results and contribute to the variations observed. How these factors influence quantitative imaging is explained and possible methods for reducing such variations are discussed.

The antivascular action of physiotherapy ultrasound on a murine tumor: role of a microbubble contrast agent

This study investigated whether a microbubble-containing ultrasound contrast agent had a role in the antivascular action of physiotherapy ultrasound on tumor neovasculature. Ultrasound images (B-mode and contrast-enhanced power Doppler [0.02 mL Definity]) were made of 22 murine melanomas (K1735(22)). The tumor was insonated (I(SATA) = 1.7 W cm(-2), 1 MHz, continuous output) for 3 min and the power Doppler observations of the pre- and postinsonation tumor vascularities were analyzed. Significant reductions (p = 0.005 for analyses of color-weighted fractional area) in vascularity occurred when a contrast-enhanced power Doppler study occurred before insonation. Vascularity was unchanged in tumors without a pretherapy Doppler study. Histologic studies revealed tissue structural changes that correlated with the ultrasound findings. The underlying etiology of the interaction between the physiotherapy ultrasound beam, the microbubble-containing contrast agent and the tumor neovasculature is unknown. It was concluded that contrast agents play an important role in the antivascular effects induced by physiotherapy ultrasound.