The Dependence of Glomerular Capillary Hemorrhage Induced by Contrast Enhanced Diagnostic Ultrasound on Microbubble Diameter

Enhancement of Tumor Perfusion and Antiangiogenic Therapy in Murine Models of Clear Cell Renal Cell Carcinoma Using Ultrasound-Stimulated Microbubbles

OBJECTIVE

To explore the effect of ultrasound-stimulated microbubble cavitation (USMC) on enhancing antiangiogenic therapy in clear cell renal cell carcinoma.

MATERIALS AND METHODS

We explored the effects of USMC with different mechanical indices (MIs) on tumor perfusion, 36 786-O tumor-bearing nude mice were randomly assigned into four groups: (i) control group, (ii) USMC0.25 group (MI = 0.25), (iii) USMC1.4 group (MI = 1.4) (iv) US1.4 group (MI = 1.4). Tumor perfusion was assessed by contrast-enhanced ultrasound (CEUS) before the USMC treatment and 30 min, 4h and 6h after the USMC treatment, respectively. Then we evaluated vascular normalization(VN) induced by low-MI (0.25) USMC treatment, 12 tumor-bearing nude mice were randomly divided into two groups: (i) control group (ii) USMC0.25 group. USMC treatment was performed, and tumor microvascular imaging and blood perfusion were analyzed by MicroFlow imaging (MFI) and CEUS 30 min after each treatment. In combination therapy, a total of 144 tumor-bearing nude mice were randomly assigned to six groups (n = 24): (i) control group, (ii) USMC1.4 group, (iii) USMC0.25 group, (iv) bevacizumab(BEV) group, (v) USMC1.4 +BEV group, (vi) USMC0.25 +BEV group. BEV was injected on the 6th, 10th, 14th, and 18th d after the tumors were inoculated, while USMC treatment was performed 24 h before and after every BEV administration. We examined the effects of the combination therapy through a series of experiments.

RESULTS

Tumor blood perfusion enhanced by USMC with low MI (0.25)could last for more than 6h, inducing tumor VN and promoting drug delivery. Compared with other groups, USMC0.25+BEV combination therapy had the strongest inhibition on tumor growth, led to the longest survival time of the mice.

CONCLUSION

The optimized USMC is a promising therapeutic approach that can be combined with antiangiogenic therapy to combat tumor progression.

Enhanced Sonothrombolysis Induced by High-Intensity Focused Acoustic Vortex

High-intensity focused ultrasound (HIFU) thrombolysis provides a targeted and non-invasive therapy for thrombosis-related diseases. Rapid thrombolysis and restoration of blood flow are vital to reduce the disability and death rate. The objective of this study was to explore the feasibility of using a high-intensity focused acoustic vortex (HIFAV) to enhance sonothrombolysis. The in vitro clots were treated with HIFU with a peak negative pressure (PNP) of 2.86 MPa (HIFU A) or 3.27 MPa (HIFU B) or HIFAV with a PNP of 2.14 MPa. The results revealed that HIFAV thrombolysis could achieve a significantly higher efficiency than HIFU (HIFAV: 65.4%, HIFU A: 24.1%, HIFU B: 31.6%, p < 0.01), even at a lower intensity. The average size of the debris particles generated in HIFAV thrombolysis was similar to that in HIFU. Additionally, the cavitation activities were found to be more intense in HIFAV thrombolysis. Although the efficiency of HIFAV thrombolysis was higher when the pulse repetition frequency increased from 100 to 500 Hz (41.4% vs. 65.4%, p < 0.05), it decreased when the PRF reached 1000 Hz (29.9%). Lastly, it was found that increasing the duty cycle from 5% to 15% led to a higher efficiency in HIFAV thrombolysis (40.3% vs. 75.2%, p < 0.001). This study illustrated that HIFAV provided enhanced thrombolysis and that its efficiency could be further increased by optimizing the ultrasound parameters.

Ultrasound Contrast: Gas Microbubbles in the Vasculature

Gas-filled microbubbles are currently in clinical use as blood pool contrast agents for ultrasound imaging. The goal of this review is to discuss the trends and issues related to these relatively unusual intravascular materials, which are not small molecules per se, not polymers, not even nanoparticles, but larger micrometer size structures, compressible, flexible, elastic, and deformable. The intent is to connect current research and initial studies from 2 to 3 decades ago, tied to gas exchange between the bubbles and surrounding biological medium, in the following areas of focus: (1) parameters of microbubble movement in relation to vasculature specifics; (2) gas uptake and loss from the bubbles in the vasculature; (3) adhesion of microbubbles to target receptors in the vasculature; and (4) microbubble interaction with the surrounding vessels and tissues during insonation.Microbubbles are generally safe and require orders of magnitude lower material doses than x-ray and magnetic resonance imaging contrast agents. Application of microbubbles will soon extend beyond blood pool contrast and tissue perfusion imaging. Microbubbles can probe molecular and cellular biomarkers of disease by targeted contrast ultrasound imaging. This approach is now in clinical trials, for example, with the aim to detect and delineate tumor nodes in prostate, breast, and ovarian cancer. Imaging of inflammation, ischemia-reperfusion injury, and ischemic memory is also feasible. More importantly, intravascular microbubbles can be used for local deposition of focused ultrasound energy to enhance drug and gene delivery to cells and tissues, across endothelial barrier, especially blood-brain barrier.Overall, microbubble behavior, stability and in vivo lifetime, bioeffects upon the action of ultrasound and resulting enhancement of drug and gene delivery, as well as targeted imaging are critically dependent on the events of gas exchange between the bubbles and surrounding media, as outlined in this review.

Application of Contrast-Enhanced Ultrasound in the Differential Diagnosis of Different Molecular Subtypes of Breast Cancer

To explore the value of contrast-enhanced ultrasound (CEUS) in the differential diagnosis of molecular subtypes of breast cancer. Sixty-two cases of breast cancer were divided into luminal epithelium A or B subtype (luminal A/B), Her-2 over-expression subtype and triple negative subtype (TN). CEUS and routine ultrasonography were performed for all patients before surgery. (1) The luminal epithelium subtype contrast enhancement pattern was more likely to present with radial edge (76.92%, p < 0.05) and low perfusion (69.23%, p < 0.05). The maximum intensity (IMAX) was lower in the luminal epithelium subtype (p < 0.05). (2) The Her-2 over-expression subtype contrast enhancement pattern was more likely to present with centripetal enhancement (93.75%, p < 0.05) and perfusion defect (75.0%, p < 0.05), and the time to peak (TTP) was shorter (80.0%, p < 0.05). (3) The contrast enhancement pattern of the triple negative subtype was shown to have a clear boundary. Compared to the other two subtypes, the triple negative subtype did not have significantly different perfusion parameters (p > 0.05). (4) Our study showed that the areas under the ROC curve for radial edge, low perfusion and IMAX for the luminal epithelium subtype breast lesions were 76.5%, 75.6%, and 82.1%, respectively. Additionally, the areas under the ROC curve for centripetal enhancement, perfusion defect and TTP for the Her-2 over-expression subtype breast lesions were 68.6%, 92.4%, and 97.8%, respectively. The sensitivity, specificity, and diagnostic accuracy of clear boundaries in detecting triple negative subtype breast lesions were 90.5%, 80.0%, and 91.9%, respectively.

Tumor perfusion enhancement by ultrasound stimulated microbubbles potentiates PD-L1 blockade of MC38 colon cancer in mice

Cancer immunotherapy holds tremendous promise as a strategy for eradicating solid tumors, and its therapeutic effect highly relies on sufficient CD8⁺ T cells infiltration. Here, we demonstrate that ultrasound stimulated microbubble cavitation (USMC) promotes tumor perfusion, thereby increasing CD8⁺ T cells infiltration and anti-PD-L1 antibody delivery, then further enhancing the PD-L1 blockade of MC38 colon cancer in mice. Firstly, we optimized the mechanic index (MI) of ultrasound, and found that USMC with MI of 0.4 (equal to peak negative pressure of 0.8 MPa) significantly improved the peak intensity and area under curve of tumor contrast-enhanced ultrasound. Also, flow cytometry exhibited higher percentage of infiltrating CD8⁺ T cells in the USMC (MI = 0.4)-treated tumors than that of the control. We further explored the combination therapy of optimized USMC with anti-PD-L1 antibody. The combination therapy enhanced tumor perfusion and even led to the tumor vascular normalization. More importantly, flow cytometry showed that the combination not only increased the percentage and absolute number of tumor infiltrating CD8⁺ T cells, but also promoted the expression of Ki67 as well as the secretions of IFN γ and granzyme B, therefore, the combination therapy achieved greater tumor growth inhibition and longer survival than that of the monotherapies. These suggest that USMC is a promising therapeutic modality for combining immune checkpoint blockade against solid tumors.

Ultrasound Contrast Agent Modeling: A Review

Ultrasound is extensively used in medical imaging, being safe and inexpensive and operating in real time. Its scope of applications has been widely broadened by the use of ultrasound contrast agents (UCAs) in the form of microscopic bubbles coated by a biocompatible shell. Their increased use has motivated a large amount of research to understand and characterize their physical properties as well as their interaction with the ultrasound field and their surrounding environment. Here we review the theoretical models that have been proposed to study and predict the behavior of UCAs. We begin with a brief introduction on the development of UCAs. We then present the basics of free-gas-bubble dynamics upon which UCA modeling is based. We review extensively the linear and non-linear models for shell elasticity and viscosity and present models for non-spherical and asymmetric bubble oscillations, especially in the presence of surrounding walls or tissue. Then, higher-order effects such as microstreaming, shedding and acoustic radiation forces are considered. We conclude this review with promising directions for the modeling and development of novel agents.

Capillary Hemorrhage Induced by Contrast-Enhanced Diagnostic Ultrasound in Rat Intestine

Contrast-enhanced diagnostic ultrasound (CEDUS) can lead to microvascular injury and petechial hemorrhage by the cavitational mechanism of ultrasonic bioeffects. Capillary hemorrhage has been noted in the heart and kidney, which are common targets of CEDUS examination. CEDUS has also become useful for monitoring intestinal inflammation. In the 1990s, the risk of intestinal microvascular hemorrhage was investigated both for incidental exposure by lithotripter shockwaves and for contrast agent microbubbles acting as cavitation nuclei with laboratory pulsed ultrasound systems. This study was initiated to update the risk assessment for intestine exposed to diagnostic imaging simulating CEDUS. The abdomens of anesthetized rats were scanned by a 1.6 MHz phased array probe during infusion of microbubble suspensions simulating Definity ultrasound contrast agent. Dual image frames were triggered intermittently, and the output power was varied to assess the exposure response. Petechiae counts in small intestine mucosa and muscle layers increased with increasing trigger interval from 2 s to 10 s, indicative of a slow refill after microbubble destruction. The counts increased with increasing output above a threshold of 1.4 MPa peak rarefactional pressure amplitude. Petechiae were also seen in Peyer's patches, and occult blood was detected in many affected segments of intestine. These results are consistent with early laboratory pulsed-ultrasound results.

Hepatocyte Injury Induced by Contrast-Enhanced Diagnostic Ultrasound

OBJECTIVES

Contrast-enhanced diagnostic ultrasound (US) has a potential to induce localized biological effects. The potential for contrast-enhanced diagnostic US bioeffects in liver were researched, with guidance from a report by Yang et al (Ultrasonics 2012; 52:1065-1071).

METHODS

Contact and standoff scanning was performed for 10 minutes with a diagnostic US phased array at 1.6 MHz during bolus injection or infusion of a contrast agent at a high dose. The impact of the imaging on rat liver was investigated by measuring enzyme release, microvascular leakage, and staining of injured hepatocytes.

RESULTS

The results showed liver enzyme release at 30 minutes, indicating liver injury, and elevated extraction of Evans blue dye, indicating microvascular leakage. In addition, Evans blue and trypan blue vital-staining methods revealed scattered stained cells within the US scan plane. For the Evans blue method, fluorescent cell counts in frozen sections were greatest for standoff exposure with contrast infusion. The count decreased strongly with depth for bolus injection, which was probably reflective of the high attenuation noted for this agent delivery method.

CONCLUSIONS

The results qualitatively confirmed the report by Yang et al and additionally showed hepatocyte vital staining. Research is needed to determine the threshold for the effects and the contrast agent dose response.

Influence of Microbubble Size and Pulse Amplitude on Hepatocyte Injury Induced by Contrast-Enhanced Diagnostic Ultrasound

Recent research has found that contrast-enhanced diagnostic ultrasound (CEDUS) has the potential to induce localized injury in the liver, with clearly observable effects for contrast agent doses higher than the recommended dose and maximal mechanical index values. This study was undertaken to assess effects with intermittent exposure at lower contrast doses of infusion and at reduced output to determine thresholds. In addition, microbubble (MB) suspensions with enhanced content of larger MBs were tested. Exposure from a phased array probe (GE Vivid 7 Dimension, GE Vingmed Ultrasound, Horten, Norway) was applied at 1.6 MHz and 1-s intermittent frame trigger for 10 min with infusion of MB suspension with normal (1.8 µm), medium (3.1 µm) and large (5.3 µm) mean MB diameters. The bio-effect endpoint was the count of hepatocytes stained with Evans blue dye in frozen sections. For the normal MBs, the count increased for clinically relevant infusion dosages, but leveled off above 20 µL/kg/min. The evidence of injury declined with time from 30 min to 4 h and was lacking at 24 h. The exposure thresholds in terms of peak rarefactional pressure amplitude, divided by the square root of frequency (in situ mechanical index) were 1.7, 1.3 and 1.2 for the normal-, medium- and large-sized MB suspensions. The enhanced efficacy for larger MBs lends support to the two-criterion model for cavitational microvascular injury during CEDUS. Overall, CEDUS in liver appears to have markedly less potential for induction of tissue injury than has been reported in other tissues, which indicates a satisfactory safety profile for CEDUS using recommended parameters in normal liver.