Activation, aggregation and adhesion of platelets exposed to high-intensity focused ultrasound

A power-triggered preparation strategy of nano-structured inorganics: sonosynthesis

Ultrasound irradiation covers many chemical reactions crucially aiming to design and synthesize various structured materials as an enduring trend in frontier research studies. Here, we focus on the latest progress of ultrasound-assisted synthesis and present the basic principles or mechanisms of sonosynthesis (or sonochemical synthesis) from ultrasound irradiation in a brand new way, including primary sonosynthesis, secondary sonosynthesis, and synergetic sonosynthesis. This current review describes in detail the various sonochemical synthesis strategies for nano-structured inorganic materials and the unique aspects of products including the size, morphology, structure, and properties. In addition, the review points out the probable challenges and technological potential for future advancement. We hope that such a review can provide a comprehensive understanding of sonosynthesis and emphasize the great significance of structured materials synthesis as a power-induced strategy broadening the updated applications of ultrasound.

Tuning the Interfacial Properties of Fluorous Colloids Toward Ultrasound Programmable Bioactivity

Liquid-in-liquid emulsions are kinetically stable colloids that undergo liquid-to-gas phase transitions in response to thermal or acoustic stimuli. Perfluorocarbons (PFCs) are preferred species as their highly fluorinated nature imparts unique properties that are unparalleled by nonfluorinated counterparts. However, traditional methods to prepare PFC emulsions lack the ability to precisely tune the thermodynamic stability of the fluorous-water interphase and consequently control their vaporization behavior. Here, we report a privileged fluoroalkanoic acid that undergoes concentration-dependent assembly on the surfaces of fluorous droplets to modulate interfacial tension. This allows for the rational formulation of orthogonal PFC droplets that can be programmed to vaporize at specified ultrasound powers. We exploit this behavior in two exemplary biomedical settings by developing emulsions that aid ultrasound-mediated hemostasis and enable bioorthogonal delivery of molecular sensors to mammalian cells. Mechanistic insights gained from these studies can be generalized to tune the thermodynamic interfacial equilibria of PFC emulsions toward designing controllable tools for precision medicine.

Therapeutic application of contrast ultrasound in ST elevation myocardial infarction: Role in coronary thrombosis and microvascular obstruction

In the past few decades, cardiac ultrasound has become a widely available, easy-to-use diagnostic tool in many scenarios in acute cardiac care. The introduction of microbubbles extended its diagnostic value. Not long thereafter, several investigators explored the therapeutic potential of contrast ultrasound on thrombus dissolution. Despite large improvements in therapeutic options, acute ST elevation myocardial infarction remains one of the main causes of mortality and morbidity in the western world. The therapeutic effect of contrast ultrasound on thrombus dissolution might prove to be a new, effective treatment strategy in this group of patients. With the recent publication of human studies scrutinising the therapeutic options of ultrasound and microbubbles in ST elevation myocardial infarction, we have entered a new stage in this area of research. This therapeutic effect is based on biochemical effects both at macrovascular and microvascular levels, of which the exact working mechanisms remain to be elucidated in full. This review will give an up-to-date summary of our current knowledge of the therapeutic effects of contrast ultrasound and its potential application in the field of ST elevation myocardial infarction, along with its future developments.

Hemostatic mechanism underlying microbubble-enhanced non-focused ultrasound in the treatment of a rabbit liver trauma model

The aim of our study was to investigate the hemostatic mechanism underlying microbubble-enhanced non-focused ultrasound treatment of liver trauma. Thirty rabbits with liver trauma were randomly divided into three groups-the microbubble-enhanced ultrasound (MEUS; further subdivided based on exposure intensity into MEUS1 [0.11 W/cm²], MEUS2 [0.55 W/cm²], and MEUS3 [1.1 W/cm²]), ultrasound without microbubbles (US), and microbubbles without ultrasound (MB) groups. The pre- and post-treatment bleeding weight and visual bleeding scores were evaluated. The serum liver enzyme concentrations as well as the blood perfusion level represented by mean peak contrast intensity (PI) ratio in the treatment area were analyzed. The hemostatic mechanism was evaluated by histological and transmission electron microscopic examination of liver tissue samples. The MEUS subgroups 1-3 (grade 0-1, grade 0-2, and grade 1-2, respectively) exhibited significantly lower post-treatment visual bleeding scores than the US and MB groups (both, grade 3-4; all, P < 0.05). Subgroups MEUS1 (0.346 ± 0.345 g) and MEUS2 (2.232 ± 2.256 g) exhibited significantly lower post-treatment bleeding weight than the US and MB groups (5.698 ± 1.938 and 5.688 ± 2.317 g, respectively; all, P < 0.05). Additionally, MEUS subgroups 1-3 exhibited significantly lower post-treatment blood perfusion levels (PI ratios, 0.64 ± 0.085, 0.73 ± 0.045, and 0.84 ± 0.034, respectively) than the US and MB groups (PI ratios, 1.00 ± 0.005 and 0.99 ± 0.005, respectively; all, P < 0.05). In the MEUS group, hepatic cells became edematous and compressed the hepatic sinus and associated blood vessels. However, the serum liver enzyme levels were not significantly altered. Microbubble-enhanced non-focused ultrasound does not significantly affect blood perfusion and liver function and can be used to induce rapid hemostasis in case of liver trauma.

Effects of Low-Intensity Continuous Ultrasound on Hematological Parameters of Rats

BACKGROUND

Low intensity ultrasound (US) has some well-known bio-effects which are of great importance to be considered. Objective: We conducted the present study to investigate the effects of low intensity continuous ultrasound on blood cells count in rat.

METHODS

Rats were anesthetized and blood samples were collected before US exposure. Then, they were exposed to US with nominal intensity of 0.2 W/cm2 at frequency of 3 MHz for a period of 10 minutes and this protocol was repeated for 7 days. Twenty four hours after the last US exposure, secondary blood samples were collected and the changes in blood parameters were evaluated.

RESULTS

Analysis revealed that platelets, hematocrit (HCT) and hemoglobin (HGB) were significantly different between experimental and sham groups but no difference between sham and control groups was observed. The results show that HCT and HGB of exposed rats were significantly reduced. Conclusion: This study shows that low intensity US may lead to side effects for hematological parameters such as reduction in the levels of HGB and HCT.

Targeted gene delivery to the synovial pannus in antigen-induced arthritis by ultrasound-targeted microbubble destruction in vivo

The purpose of this study was to optimize an ultrasound-targeted microbubble destruction (UTMD) technique to improve the in vivo transfection efficiency of the gene encoding enhanced green fluorescent protein (EGFP) in the synovial pannus in an antigen-induced arthritis rabbit model. A mixture of microbubbles and plasmids was locally injected into the knee joints of an antigen-induced arthritis (AIA) rabbits. The plasmid concentrations and ultrasound conditions were varied in the experiments. We also tested local articular and intravenous injections. The rabbits were divided into five groups: (1) ultrasound+microbubbles+plasmid; (2) ultrasound+plasmid; (3) microbubble+plasmid; (4) plasmid only; (5) untreated controls. EGFP expression was observed by fluorescent microscope and immunohistochemical staining in the synovial pannus of each group. The optimal plasmid dosage and ultrasound parameter were determined based on the results of EGFP expression and the present and absent of tissue damage under light microscopy. The irradiation procedure was performed to observe the duration of the EGFP expression in the synovial pannus and other tissues and organs, as well as the damage to the normal cells. The optimal condition was determined to be a 1-MHz ultrasound pulse applied for 5 min with a power output of 2 W/cm(2) and a 20% duty cycle along with 300 μg of plasmid. Under these conditions, the synovial pannus showed significant EGFP expression without significant damage to the surrounding normal tissue. The EGFP expression induced by the local intra-articular injection was significantly more increased than that induced by the intravenous injection. The EGFP expression in the synovial pannus of the ultrasound+microbubbles+plasmid group was significantly higher than that of the other four groups (P<0.05). The expression peaked on day 5, remained detectable on day 40 and disappeared on day 60. No EGFP expression was detected in the other tissues and organs. The UTMD technique can significantly enhance the in vivo gene transfection efficiency without significant tissue damage in the synovial pannus of an AIA model. Thus, this could become a safe and effective non-viral gene transfection procedure for arthritis therapy.

The Advantages and Disadvantages of Methods Used to Control Liver Bleeding: A Review

Context:

Despite advancements in the science of surgery, minimizing bleeding from parenchymal tissue of the liver continues to be one of the challenges surgeons are facing to protect patients’ lives. However, the number of surgeries needing incisions in the liver tissue, e.g. metastatectomy, is constantly increasing.

Evidence Acquisition:

A MEDLINE and conventional search of the past 50 years of the medical literature was performed to identify relevant articles on hemostasis in the liver parenchymal tissue.

Results:

The studies that have been published on hemostasis in the liver parenchymal tissue can be classified into 3 categories: 1. surgical procedures; 2. methods affecting body hemodynamic; 3. pharmacological methods. The purpose of these studies are to identify the best therapeutic approaches that not only minimize the bleeding, but also save the maximum amount of the liver tissue and minimize the use of partial liver resections.

Conclusions:

The excessive blood loss and the long time needed to control the bleeding during liver surgery impose several side effects and complications on patients. Topical hemostatic agents such as ferric chloride, potassium aluminum sulfate (alum) and aluminum chloride are safely applicable in patients. These agents might be used along with other current methods to minimize the blood loss and the need for blood products during liver surgeries.

Deep Bleeder Acoustic Coagulation (DBAC)-part II: in vivo testing of a research prototype system

Background

Deep Bleeder Acoustic Coagulation (DBAC) is an ultrasound image-guided high-intensity focused ultrasound (HIFU) method proposed to automatically detect and localize (D&L) and treat deep, bleeding, combat wounds in the limbs of soldiers. A prototype DBAC system consisting of an applicator and control unit was developed for testing on animals. To enhance control, and thus safety, of the ultimate human DBAC autonomous product system, a thermal coagulation strategy that minimized cavitation, boiling, and non-linear behaviors was used.

Material and methods

The in vivo DBAC applicator design had four therapy tiles (Tx) and two 3D (volume) imaging probes (Ix) and was configured to be compatible with a porcine limb bleeder model developed in this research. The DBAC applicator was evaluated under quantitative test conditions (e.g., bleeder depths, flow rates, treatment time limits, and dose exposure time limits) in an in vivo study (final exam) comprising 12 bleeder treatments in three swine. To quantify blood flow rates, the “bleeder” targets were intact arterial branches, i.e., the superficial femoral artery (SFA) and a deep femoral artery (DFA). D&L identified, characterized, and targeted bleeders. The therapy sequence selected Tx arrays and determined the acoustic power and Tx beam steering, focus, and scan patterns. The user interface commands consisted of two buttons: “Start D&L” and “Start Therapy.” Targeting accuracy was assessed by necropsy and histologic exams and efficacy (vessel coagulative occlusion) by angiography and histology.

Results

The D&L process (Part I article, J Ther Ultrasound, 2015 (this issue)) executed fully in all cases in under 5 min and targeting evaluation showed 11 of 12 thermal lesions centered on the correct vessel subsection, with minimal damage to adjacent structures. The automated therapy sequence also executed properly, with select manual steps. Because the dose exposure time limit (t_dose ≤ 30 s) was associated with nonefficacious treatment, 60-s dosing and dual-dosing was also pursued. Thrombogenic evidence (blood clotting) and collagen denaturation (vessel shrinkage) were found in necropsy and histologically in all targeted SFAs. Acute SFA reductions in blood flow (20–30 %) were achieved in one subject, and one partial and one complete vessel occlusion were confirmed angiographically. The complete occlusion case was achieved with a dual dose (90 s total exposure) with focal intensity ≈500 W/cm² (spatial average, temporal average).

Conclusions

While not meeting all in vivo objectives, the overall performance of the DBAC applicator was positive. In particular, D&L automation workflow was verified during each of the tests, with processing times well under specified (10 min) limits, and all bleeder branches were detected and localized. Further, gross necropsy and tissue examination confirmed that the HIFU thermal lesions were coincident with the target vessel locations in over 90 % of the multi-array dosing treatments. The SFA/DFA bleeder models selected, and the protocols used, were the most suitable practical model options for the given DBAC anatomical and bleeder requirements. The animal models were imperfect in some challenging aspects, including requiring tissue-mimicking material (TMM) standoffs to achieve deep target depths, thereby introducing device-tissue motion, with resultant imaging artifacts. The model “bleeders” involved intact vessels, which are subject to less efficient heating and coagulation cascade behaviors than true puncture injuries.

Generation of Autologous Platelet-Rich Plasma by the Ultrasonic Standing Waves

Platelet-rich plasma (PRP) is a volume of autologous plasma that has a higher platelet concentration above baseline. It has already been approved as a new therapeutic modality and investigated in clinics, such as bone repair and regeneration, and oral surgery, with low cost-effectiveness ratio. At present, PRP is mostly prepared using a centrifuge. However, this method has several shortcomings, such as long preparation time (30 min), complexity in operation, and contamination of red blood cells (RBCs). In this paper, a new PRP preparation approach was proposed and tested. Ultrasound waves (4.5 MHz) generated from piezoelectric ceramics can establish standing waves inside a syringe filled with the whole blood. Subsequently, RBCs would accumulate at the locations of pressure nodes in response to acoustic radiation force, and the formed clusters would have a high speed of sedimentation. It is found that the PRP prepared by the proposed device can achieve higher platelet concentration and less RBCs contamination than a commercial centrifugal device, but similar growth factor (i.e., PDGF-ββ). In addition, the sedimentation process under centrifugation and sonication was simulated using the Mason-Weaver equation and compared with each other to illustrate the differences between these two technologies and to optimize the design in the future. Altogether, ultrasound method is an effective method of PRP preparation with comparable outcomes as the commercially available centrifugal products.

Real-time feedback of histotripsy thrombolysis using bubble-induced color Doppler

Histotripsy thrombolysis is a non-invasive, drug-free, image-guided therapy that fractionates blood clots using well-controlled acoustic cavitation alone. Real-time quantitative feedback is highly desired during histotripsy thrombolysis treatment to monitor the progress of clot fractionation. Bubble-induced color Doppler (BCD) monitors the motion after cavitation generated by each histotripsy pulse, which has been found in gel and ex vivo liver tissue to be correlated with histotripsy fractionation. We investigated the potential of BCD to quantitatively monitor histotripsy thrombolysis in real time. To visualize clot fractionation, transparent three-layered fibrin clots were developed. Results indicated that a coherent motion follows the cavitation generated by each histotripsy pulse with a push and rebound pattern. The temporal profile of this motion expands and saturates as treatment progresses. A strong correlation exists between the degree of histotripsy clot fractionation and two metrics extracted from BCD: time of peak rebound velocity (tPRV) and focal mean velocity at a fixed delay (Vf,delay). The saturation of clot fractionation (i.e., treatment completion) matches well the saturations detected using tPRV and Vf,delay. The mean Pearson correlation coefficients between the progression of clot fractionation and the two BCD metrics were 93.1% and 92.6%, respectively. To validate BCD feedback in in vitro clots, debris volumes from histotripsy thrombolysis were obtained at different therapy doses and compared with Vf,delay. There is also good agreement between the increasing and saturation trends of debris volume and Vf,delay. Finally, a real-time BCD feedback algorithm to predict complete clot fractionation during histotripsy thrombolysis was developed and tested. This work illustrates the potential of BCD to monitor histotripsy thrombolysis treatment in real time.

An overview of the influence of therapeutic ultrasound exposures on the vasculature: high intensity ultrasound and microbubble-mediated bioeffects

It is well established that the interaction of ultrasound with soft tissues can induce a wide range of bioeffects. One of the most important and complex of these interactions in the context of therapeutic ultrasound is with the vasculature. Potential vascular effects range from enhancing microvascular permeability to inducing vascular damage and vessel occlusion. While aspects of these effects are broadly understood, the development of improved approaches to exploit these effects and gain a more detailed mechanistic understanding is ongoing and largely anchored in preclinical research. Here a general overview of this established yet rapidly evolving topic is provided, with a particular emphasis on effects arising from high-intensity focused ultrasound and microbubble-mediated exposures.

Prediction and suppression of HIFU-induced vessel rupture using passive cavitation detection in an ex vivo model

Background

Occlusion of blood vessels using high-intensity focused ultrasound (HIFU) is a potential treatment for arteriovenous malformations and other neurovascular disorders. However, attempting HIFU-induced vessel occlusion can also cause vessel rupture, resulting in hemorrhage. Possible rupture mechanisms include mechanical effects of acoustic cavitation and heating of the vessel wall.

Methods

HIFU exposures were performed on 18 ex vivo porcine femoral arteries with simultaneous passive cavitation detection. Vessels were insonified by a 3.3-MHz focused source with spatial-peak, temporal-peak focal intensity of 15,690–24,430 W/cm² (peak negative-pressure range 10.92–12.52 MPa) and a 50% duty cycle for durations up to 5 min. Time-dependent acoustic emissions were recorded by an unfocused passive cavitation detector and quantified within low-frequency (10–30 kHz), broadband (0.3–1.1 MHz), and subharmonic (1.65 MHz) bands. Vessel rupture was detected by inline metering of saline flow, recorded throughout each treatment. Recorded emissions were grouped into ‘pre-rupture’ (0–10 s prior to measured point of vessel rupture) and ‘intact-vessel’ (>10 s prior to measured point of vessel rupture) emissions. Receiver operating characteristic curve analysis was used to assess the ability of emissions within each frequency band to predict vessel rupture.

Based on these measurements associating acoustic emissions with vessel rupture, a real-time feedback control module was implemented to monitor acoustic emissions during HIFU treatment and adjust the ultrasound intensity, with the goal of maximizing acoustic power delivered to the vessel while avoiding rupture. This feedback control approach was tested on 10 paired HIFU exposures of porcine femoral and subclavian arteries, in which the focal intensity was stepwise increased from 9,117 W/cm² spatial-peak temporal-peak (SPTP) to a maximum of 21,980 W/cm², with power modulated based on the measured subharmonic emission amplitude. Time to rupture was compared between these feedback-controlled trials and paired controller-inactive trials using a paired Wilcoxon signed-rank test.

Results

Subharmonic emissions were found to be the most predictive of vessel rupture (areas under the receiver operating characteristic curve (AUROC) = 0.757, p < 10^-16) compared to low-frequency (AUROC = 0.657, p < 10^-11) and broadband (AUROC = 0.729, p < 10^-16) emissions. An independent-sample t test comparing pre-rupture to intact-vessel emissions revealed a statistically significant difference between the two groups for broadband and subharmonic emissions (p < 10^-3), but not for low-frequency emissions (p = 0.058).

In a one-sided paired Wilcoxon signed-rank test, activation of the control module was shown to increase the time to vessel rupture (T_- = 8, p = 0.0244, N = 10). In one-sided paired t tests, activation of the control module was shown to cause no significant difference in time-averaged focal intensity (t = 0.362, p = 0.363, N = 10), but was shown to cause delivery of significantly greater total acoustic energy (t = 2.037, p = 0.0361, N = 10).

Conclusions

These results suggest that acoustic cavitation plays an important role in HIFU-induced vessel rupture. In HIFU treatments for vessel occlusion, passive monitoring of acoustic emissions may be useful in avoiding hemorrhage due to vessel rupture, as shown in the rupture suppression experiments.

High-intensity focused ultrasound ablation: an effective and safe treatment for secondary hypersplenism

OBJECTIVE

Hypersplenism is a common disease. The conventional treatment is splenectomy and partial splenic embolization; however, both of them have high complication rates and technical defects. Therefore, safer and more effective techniques should be considered for the treatment of hypersplenism. High-intensity focused ultrasound (HIFU) may provide an effective and safe way for treatment of hypersplenism. Therefore, we conducted this study to assess the safety and efficacy of HIFU in treatment of secondary hypersplenism.

METHODS

A total of 28 patients who suffered from secondary hypersplenism were treated with HIFU ablation. All patients who underwent HIFU were closely followed-up over a year. MRI scan was performed, and the spleens were observed. Blood counts and liver function tests were also carried out.

RESULTS

In the follow-up process, the levels of white blood cells and platelets in the blood after HIFU were significantly higher than those before HIFU, liver function also improved after HIFU treatment. In addition, the symptoms were ameliorated significantly or even disappeared. The MRI showed that the ablation area had turned into a non-perfused volume, and after 12 months of HIFU ablation, the ablated area shrank evidently; the sunken spleen formed a lobulated shape and the splenic volume decreased.

CONCLUSION

HIFU ablation is a safe, effective and non-invasive approach for secondary hypersplenism.

ADVANCES IN KNOWLEDGE

For the first time we used HIFU ablation to treat secondary hypersplenism. It not only expands indications of HIFU but also provides better choice for the treatment of secondary hypersplenism.

Pathophysiological mechanisms of high-intensity focused ultrasound-mediated vascular occlusion and relevance to non-invasive fetal surgery

High-intensity focused ultrasound (HIFU) is a non-invasive technology, which can be used occlude blood vessels in the body. Both the theory underlying and practical process of blood vessel occlusion are still under development and relatively sparse in vivo experimental and therapeutic data exist. HIFU would however provide an alternative to surgery, particularly in circumstances where serious complications inherent to surgery outweigh the potential benefits. Accordingly, the HIFU technique would be of particular utility for fetal and placental interventions, where open or endoscopic surgery is fraught with difficulty and likelihood of complications including premature delivery. This assumes that HIFU could be shown to safely and effectively occlude blood vessels in utero. To understand these mechanisms more fully, we present a review of relevant cross-specialty literature on the topic of vascular HIFU and suggest an integrative mechanism taking into account clinical, physical and engineering considerations through which HIFU may produce vascular occlusion. This model may aid in the design of HIFU protocols to further develop this area, and might be adapted to provide a non-invasive therapy for conditions in fetal medicine where vascular occlusion is beneficial.

Hemostatic effects of microbubble-enhanced low-intensity ultrasound in a liver avulsion injury model

OBJECTIVES

Microbubble-enhanced therapeutic ultrasound (MEUS) can block the blood flow in the organs. The aim of this study was to evaluate the hemostatic effect of microbubble-enhanced pulsed, low-intensity ultrasound in a New Zealand White rabbit model of avulsion trauma of the liver. The therapeutic ultrasound (TUS) transducer was operated with the frequency of 1.2 MHz and an acoustic pressure of 3.4 MPa. Microbubble-(MB) enhanced ultrasound (MEUS) (n = 6) was delivered to the distal part of the liver where the avulsion was created. Livers were treated by TUS only (n = 4) or MB only (n = 4) which served as controls. Bleeding rates were measured and contrast enhanced ultrasound (CEUS) was performed to assess the hemostatic effect, and liver hemoperfusion before and after treatment. Generally, bleeding rates decreased more than 10-fold after the treatment with MEUS compared with those of the control group (P<0.05). CEUS showed significant declines in perfusion. The peak intensity value and the area under the curve also decreased after insonation compared with those of the control group (P<0.05). Histological examination showed cloudy and swollen hepatocytes, dilated hepatic sinusoids, perisinusoidal spaces with erythrocyte accumulation in small blood vessels, obvious hemorrhage around portal areas and scattered necrosis in liver tissues within the insonation area of MEUS Group. In addition, necrosis was found in liver tissue 48 h after insonation. We conclude that MEUS might provide an effective hemostatic therapy for serious organ trauma such as liver avulsion injury.

Cavitation distribution within large phantom vessel and mechanical damage formed on surrounding vessel wall

Blood vessel is one of the most important targets encountered during focused ultrasound (FU) therapy. The lasting high temperature caused by continuous FU can result in structural modification of small vessel. For the vessel with a diameter larger than 2mm, convective cooling can significantly weaken the thermal effect of FU. Meanwhile, the continued presence of ultrasound will cause repetitive cavitation and acoustic microstreaming, making comprehension of continuous wave induced cavitation effect in large vessels necessary. The Sonoluminescence (SL) method, mechanical damage observation and high-speed camera were used in this study to investigate the combination effect of ultrasound contrast agents (UCAs) and continuous FU in large phantom vessels with a diameter of 10mm without consideration of thermal effect. When the focus was positioned at the proximal wall, cylindrical hole along the acoustic axis opposite the ultrasound wave propagation direction was observed at the input power equal to or greater than 50 W. When the focus was located at the distal wall, only small tunnels can be found. The place where the cylindrical hole formed was corresponding to where bubbles gathered and emitted brilliant light near the wall. Without UCAs neither such bright SL nor cylindrical hole can be found. However, the UCAs concentration had little influence on the SL distribution and the length of cylindrical hole. The SL intensity near the proximal vessel wall and the length of the cylindrical hole both increased with the input power. It is suggested that these findings need to be considered in the large vessel therapy and UCAs usage.

High-intensity focused ultrasound ablation for treatment of hepatocellular carcinoma and hypersplenism: preliminary study

The purpose of this work was to preliminarily investigate the efficacy and safety of high-intensity focused ultrasound treatment of hepatocellular carcinoma and hypersplenism. Nine patients with hepatocellular carcinoma complicated by hypersplenism (5 male and 4 female; median age, 56 years; range, 51-66 years) were treated with ultrasound-guided high-intensity focused ultrasound. Complications were recorded. Laboratory examination and magnetic resonance imaging were used to evaluate the efficacy. After high-intensity focused ultrasound treatment, mean spleen ablation ± SD of 28.76% ± 6.1% was discovered; meanwhile, the white blood cell count, platelet count, and liver function of the patients were substantially improved during the follow-up period. In addition, symptoms such as epistaxis and gingival bleeding were ameliorated or even eliminated, and the quality of life was improved. Follow-up imaging showed a nonperfused volume in the spleen and an absence of a tumor blood supply at the treated lesions in the liver. For the first time to our knowledge, high-intensity focused ultrasound ablation was used to treat hepatocellular carcinoma complicated by hypersplenism. High-intensity focused ultrasound may be an effective and safe alternative for treatment of hepatocellular carcinoma complicated by hypersplenism, but further studies are necessary to clarify the mechanisms.

Rapid ultrasonic stimulation of inflamed tissue with diagnostic intent

Previous studies have observed that individual pulses of intense focused ultrasound (iFU) applied to inflamed and normal tissue can generate sensations, where inflamed tissue responds at a lower intensity than normal tissue. It was hypothesized that successively applied iFU pulses will generate sensation in inflamed tissue at a lower intensity and dose than application of a single iFU pulse. This hypothesis was tested using an animal model of chronic inflammatory pain, created by injecting an irritant into the rat hind paw. Ultrasound pulses were applied in rapid succession or individually to rats' rear paws beginning at low peak intensities and progressing to higher peak intensities, until the rats withdrew their paws immediately after iFU application. Focused ultrasound protocols consisting of successively and rapidly applied pulses elicited inflamed paw withdrawal at lower intensity and estimated tissue displacement values than single pulse protocols. However, both successively applied pulses and single pulses produced comparable threshold acoustic dose values and estimates of temperature increases. This raises the possibility that temperature increase contributed to paw withdrawal after rapid iFU stimulation. While iFU-induction of temporal summation may also play a role, electrophysiological studies are necessary to tease out these potential contributors to iFU stimulation.

Creating brain lesions with low-intensity focused ultrasound with microbubbles: a rat study at half a megahertz

Low-intensity focused ultrasound was applied with microbubbles (Definity, Lantheus Medical Imaging, North Billerica, MA, USA; 0.02 mL/kg) to produce brain lesions in 50 rats at 558 kHz. Burst sonications (burst length: 10 ms; pulse repetition frequency: 1 Hz; total exposure: 5 min; acoustic power: 0.47-1.3 W) generated ischemic or hemorrhagic lesions at the focal volume revealed by both magnetic resonance imaging and histology. Shorter burst time (2 ms) or shorter sonication time (1 min) reduced the probability of lesion production. Longer pulses (200 ms, 500 ms and continuous wave) caused significant near-field damage. Using microbubbles with focused ultrasound significantly reduced acoustic power levels and, therefore, avoided skull heating issues and potentially can extend the treatable volume of transcranial focused ultrasound to brain tissues close to the skull.

Hemorrhage control of liver injury by short electrical pulses

Trauma is a leading cause of death among young individuals globally and uncontrolled hemorrhage is the leading cause of preventable death. Controlling hemorrhage from a solid organ is often very challenging in military as well as civilian setting. Recent studies demonstrated reversible vasoconstriction and irreversible thrombosis following application of microseconds-long electrical pulses. The current paper describes for the first time reduction in bleeding from the injured liver in rat and rabbit model in-vivo. We applied short (25 and 50 µs) electrical pulses of 1250 V/cm to rats and rabbit liver following induction of standardized penetrating injury and measured the amount of bleeding into the abdominal cavity one hour post injury. We found a 60 and 36 percent reduction in blood volume in rats treated by 25 µs and 50 µs, respectively (P<0.001). Similar results were found for the rabbit model. Finite element simulation revealed that the effect was likely non-thermal. Histological evaluation found local cellular injury with intravascular thrombosis. Further research should be done to fully explore the mechanism of action and the potential use of short electric pulses for hemorrhage control.

Spatiotemporal evolution of cavitation dynamics exhibited by flowing microbubbles during ultrasound exposure

Ultrasound and microbubble-based therapies utilize cavitation to generate bioeffects, yet cavitation dynamics during individual pulses and across consecutive pulses remain poorly understood under physiologically relevant flow conditions. SonoVue(®) microbubbles were made to flow (fluid velocity: 10-40 mm/s) through a vessel in a tissue-mimicking material and were exposed to ultrasound [frequency: 0.5 MHz, peak-rarefactional pressure (PRP): 150-1200 kPa, pulse length: 1-100,000 cycles, pulse repetition frequency (PRF): 1-50 Hz, number of pulses: 10-250]. Radiated emissions were captured on a linear array, and passive acoustic mapping was used to spatiotemporally resolve cavitation events. At low PRPs, stable cavitation was maintained throughout several pulses, thus generating a steady rise in energy with low upstream spatial bias within the focal volume. At high PRPs, inertial cavitation was concentrated in the first 6.3 ± 1.3 ms of a pulse, followed by an energy reduction and high upstream bias. Multiple pulses at PRFs below a flow-dependent critical rate (PRF(crit)) produced predictable and consistent cavitation dynamics. Above the PRF(crit), energy generated was unpredictable and spatially biased. In conclusion, key parameters in microbubble-seeded flow conditions were matched with specific types, magnitudes, distributions, and durations of cavitation; this may help in understanding empirically observed in vivo phenomena and guide future pulse sequence designs.

Ablation of synovial pannus using microbubble-mediated ultrasonic cavitation in antigen-induced arthritis in rabbits

To investigate the ablative effectiveness of microbubble-mediated ultrasonic cavitation for treating synovial pannus and to determine a potential mechanism using the antigen-induced arthritis model (AIA). Ultrasonic ablation was performed on the knee joints of AIA rabbits using optimal ultrasonic ablative parameters. Rabbits with antigen-induced arthritis were randomly assigned to 4 groups: (1) the ultrasound (US) + microbubble group; (2) the US only group; (3) the microbubble only group, and (4) the control group. At 1 h and 14 days after the first ablation, contrast-enhanced ultrasonography (CEUS) monitoring and pathology synovitis score were used to evaluate the therapeutic effects. Synovial necrosis and microvascular changes were also measured. After the ablation treatment, the thickness of synovium and parameters of time intensity curve including derived peak intensity and area under curve were measured using CEUS, and the pathology synovitis score in the ultrasound + microbubble group was significantly lower than that found in the remaining groups. No damage was observed in the surrounding normal tissues. The mechanism underlying the ultrasonic ablation was related to microthrombosis and microvascular rupture that resulted in synovial necrosis. The results suggest that microbubble-mediated ultrasonic cavitation should be applied as a non-invasive strategy for the treatment of synovial pannus in arthritis under optimal conditions.

Platelet-targeted microbubbles inhibit re-occlusion after thrombolysis with transcutaneous ultrasound and microbubbles

Microbubbles (MBs) can augment the acoustic cavitation' (US), thereby facilitating the thrombolysis of external ultrasound. But we observed re-thrombosis after successful thrombolysis by MBs and transcutaneous ultrasound in an endothelium injury model. This study was designed to explore whether platelet-targeted MBs can prevent the reformation of thrombi. Arterial injury was induced in canine femoral arteries with balloon, and the arteries were completely thrombotically occluded. The arteries were treated with intra-arterial MBs or platelet-targeted MBs (TMB) and transcutaneous low frequency ultrasound (LFUS) to achieve complete thrombolysis. The arterial flow was monitored with angiogram for 4h following treatment. Results showed that both MBs and TMBs produced successful dissolution of clots in the presence of ultrasound. The re-occlusion began to occur 1h after thrombolysis in MB/LFUS treatment, and 7 of 8 arteries were re-occluded within 3h. Most of the arteries (7 of 8) in the TMB/LFUS group remained patent for 4h following treatment. The flow tended to decrease after thrombolysis in MB/LFUS treatment. These results indicated that platelet-targeted microbubbles were beneficial in preventing re-thrombosis in vivo and microbubbles served as good carrier of thrombolytic and anticoagulation drugs.

Non-invasive pulsed cavitational ultrasound for fetal tissue ablation: feasibility study in a fetal sheep model

OBJECTIVES

Currently available fetal intervention techniques rely on invasive procedures that carry inherent risks. A non-invasive technique for fetal intervention could potentially reduce the risk of fetal and obstetric complications. Pulsed cavitational ultrasound therapy (histotripsy) is an ablation technique that mechanically fractionates tissue at the focal region using extracorporeal ultrasound. In this study, we investigated the feasibility of using histotripsy as a non-invasive approach to fetal intervention in a sheep model.

METHODS

The experiments involved 11 gravid sheep at 102-129 days of gestation. Fetal kidney, liver, lung and heart were exposed to ultrasound pulses (< 10 µs) delivered by an external 1-MHz focused ultrasound transducer at a 0.2-1-kHz pulse-repetition rate and 10-16 MPa peak negative pressure. Procedures were monitored and guided by real-time ultrasound imaging. Treated organs were examined by gross and histological inspection for location and degree of tissue injury.

RESULTS

Hyperechoic, cavitating bubble clouds were successfully generated in 19/31 (61%) treatment attempts in 27 fetal organs beneath up to 8 cm of overlying tissue and fetal bones. Histological assessment confirmed lesion locations and sizes corresponding to regions where cavitation was monitored, with no lesions found when cavitation was absent. Inability to generate cavitation was primarily associated with increased depth to target and obstructing structures such as fetal limbs.

CONCLUSION

Extracorporeal histotripsy therapy successfully created targeted lesions in fetal sheep organs without significant damage to overlying structures. With further improvements, histotripsy may evolve into a viable technique for non-invasive fetal intervention procedures.

Therapeutic opportunities in biological responses of ultrasound

The therapeutic benefits of several existing ultrasound-based therapies such as facilitated drug delivery, tumor ablation and thrombolysis derive largely from physical or mechanical effects. In contrast, ultrasound can also trigger various time-dependent biochemical responses in the exposed biological milieu. Several biological responses to ultrasound exposure have been previously described in the literature but only a handful of these provide therapeutic opportunities. These include the use of ultrasound for healing of soft tissues and bones, the use of ultrasound for inducing non-necrotic tumor atrophy as well as for potentiation of chemotherapeutic drugs, activation of the immune system, angiogenesis and suppression of phagocytosis. A review of these therapeutic opportunities is presented with particular emphasis on their mechanisms. Overall, this review presents the increasing importance of ultrasound's role as a biological sensitizer enabling novel therapeutic strategies.

Hemostasis and sealing of air leaks in the lung using high-intensity focused ultrasound

BACKGROUND

Operative management of parenchymal lung injury can be complicated by persistent hemorrhage and air leak, which might require resection. Techniques that preserve parenchyma are associated with improved survival. High-intensity focused ultrasound (HIFU) has been demonstrated as a useful method for hemostasis in experimental solid organ injuries. We wished to investigate whether this could be applied to lung injuries.

METHODS

An intraoperative HIFU device (frequency of 5.7 MHz, acoustic power of 65 W), equipped with a titanium coupler, was used. Incisions (average length of 2.5 cm, and depth of 5 mm) were made in the lungs of 11 pigs, which created both parenchymal hemorrhage and air leakage. In treatment experiments, 70 incisions were sealed with HIFU. The HIFU application started within 10 seconds of inducing the injury. Hemostasis was assessed by visual observation of sealed incisions. The possible air leakage was determined by submersing the sealed incision under the layer of water and observing for air bubble formation. In control experiments, five incisions were left untreated to monitor air leaks and bleeding for 2 minutes.

RESULTS

Hemostasis and pneumostasis (sealing of air leaks) of the treated incisions were achieved in 51 +/- 37 seconds (mean +/- SD) (range of 10-210 seconds) of HIFU application time. Over 95% of incisions were hemostatic within 2 minutes of HIFU application. The treatment time was not dependent on the incision length or depth. In control experiments, the air leaking and bleeding were still present at 2 minutes after the injury.

CONCLUSION

Intraoperative HIFU might provide an effective method of hemostasis and control of air leaks from lacerations caused by trauma.

Role of acoustic cavitation in the delivery and monitoring of cancer treatment by high-intensity focused ultrasound (HIFU)

Acoustic cavitation has been shown to play a key role in a wide array of novel therapeutic ultrasound applications. This paper presents a brief discussion of the physics of thermally relevant acoustic cavitation in the context of high-intensity focussed ultrasound (HIFU). Models for how different types of cavitation activity can serve to accelerate tissue heating are presented, and results suggest that the bulk of the enhanced heating effect can be attributed to the absorption of broadband acoustic emissions generated by inertial cavitation. Such emissions can be readily monitored using a passive cavitation detection (PCD) scheme and could provide a means for real-time treatment monitoring. It is also shown that the appearance of hyperechoic regions (or bright-ups) on B-mode ultrasound images constitutes neither a necessary nor a sufficient condition for inertial cavitation activity to have occurred during HIFU exposure. Once instigated at relatively large HIFU excitation amplitudes, bubble activity tends to grow unstable and to migrate toward the source transducer, causing potentially undesirable pre-focal damage. Potential means of controlling inertial cavitation activity using pulsed excitation so as to confine it to the focal region are presented, with the intention of harnessing cavitation-enhanced heating for optimal HIFU treatment delivery. The role of temperature elevation in mitigating bubble-enhanced heating effects is also discussed, along with other bubble-field effects such as multiple scattering and shielding.

Hemorrhage control using high intensity focused ultrasound

Hemorrhage control is a high priority task in advanced trauma care, because hemorrhagic shock can result in less than a minute in cases of severe injuries. Hemorrhage was found to be solely responsible for 40-50% of traumatic civilian and battlefield deaths in recent years. The majority of these deaths were due to abdominal and pelvic injuries with hidden and inaccessible bleeding of solid organs such as liver, spleen, and kidneys, as well as major blood vessels. High intensity focused ultrasound (HIFU) offers a promising method for hemorrhage control. An important advantage of HIFU is that it can deliver energy to deep regions of tissue where hemorrhage is occurring, allowing cauterization at depth of parenchymal tissues, or in difficult-to-access anatomical regions, while causing no or minimal biological effects in the intervening and surrounding tissues. Moreover, HIFU can cause both thermal and mechanical effects that are shown to work synergistically for rapid hemorrhage control. The major challenges of this method are in development of bleeding detection techniques for accurate localization of the injury sites, delivery of large HIFU doses for profuse bleeding cases, and ensuring safety when critical structures are in the vicinity of the injury. Future developments of acoustic hemostasis technology are anticipated to be for applications in peripheral vascular injuries where an acoustic window is usually available, and for applications in the operating room on exposed organs.

Image-guided acoustic hemostasis for hemorrhage in the posterior liver

We investigated the use of ultrasound image-guided high intensity focused ultrasound (HIFU) to stop bleeding from injuries in the posterior liver. A HIFU transducer with focal length of 3.5 cm and frequency of 3.2 MHz was integrated with an intraoperative high-resolution ultrasound-imaging probe. Wedge tissue extractions, 30-mm long, 5-mm wide and 8-mm deep, were made in the posterior liver surface of five pigs to induce bleeding. The device was positioned on the anterior surface of the liver and HIFU was applied using ultrasound image-guidance. Hemostasis was achieved in 66 +/- 18 s (mean +/- standard deviation) for 17 HIFU treatments. During 7 min of sham HIFU treatment, none of the control incisions (n = 7) became hemostatic. Ultrasound image-guided HIFU offers a promising method for hemostasis in surgical settings in which the hemorrhage site is hidden and/or not accessible.

Therapeutic applications of ultrasound

Therapeutic applications of ultrasound predate its use in imaging. A range of biological effects can be induced by ultrasound, depending on the exposure levels used. At low levels, beneficial, reversible cellular effects may be produced, whereas at high intensities instantaneous cell death is sought. Therapy ultrasound can therefore be broadly divided into "low power" and "high power" applications. The "low power" group includes physiotherapy, fracture repair, sonophoresis, sonoporation and gene therapy, whereas the most common use of "high power" ultrasound in medicine is probably now high intensity focused ultrasound. Therapeutic effect through the intensity spectrum is obtained by both thermal and non-thermal interaction mechanisms. At low intensities, acoustic streaming is likely to be significant, but at higher levels, heating and acoustic cavitation will predominate. While useful therapeutic effects are now being demonstrated clinically, the mechanisms by which they occur are often not well understood.

Hemorrhage control in arteries using high-intensity focused ultrasound: a survival study

High-intensity focused ultrasound (HIFU) has been shown to provide an effective method for hemorrhage control of blood vessels in acute animal studies. The objective of the current study was to investigate the long-term effects of HIFU-induced hemostasis in punctured arteries. The femoral arteries ( approximately 2mm in diameter) of 25 adult anesthetized rabbits were surgically exposed, and either punctured and treated with HIFU (n=15), served as control (no puncture and no HIFU application: n=7), or were punctured and left untreated (n=3). Treated animals were allowed to recover, and examined and/or sacrificed on days 0, 1, 3, 7, 14, 28, and 60 after treatment to obtain ultrasound images and samples of blood and tissue. Hemostasis (arrest of bleeding) was achieved in all 15 of the HIFU-treated arteries. Eleven of the arteries were patent after HIFU treatment, and four arteries were occluded, as determined by Doppler ultrasound. The median HIFU application time to achieve hemostasis was 20s (range 7-55 s) for the patent arteries and 110 s (range 50-134 s) for the occluded arteries. In untreated animals, bleeding had not stopped after 120 s. One of the occluded arteries had reopened by day 14. No immediate or delayed re-bleeding was observed after HIFU treatment. Maximal blood flow velocities were similar in HIFU-treated patent vessels and control vessels. No significant difference in hematocrits was found between HIFU-treated and control groups at different time points after the procedure. Light microscopy observations of the HIFU-treated arteries showed disorganization of adventitia, and coagulation and thinning of the tunica media. The general organization of the adventitia and tunica media recovered to normal appearance within 28 days, with some thinning of the tunica media observed up to day 60. Neointimal hyperplasia was observed on days 14 and 28. The results show that HIFU can produce effective and long-term (up to 60 days) hemostasis of punctured femoral arteries while preserving normal blood flow and vessel wall structure in the majority of vessels.

Vascular effects induced by combined 1-MHz ultrasound and microbubble contrast agent treatments in vivo

Previous in vivo studies have demonstrated that microvessel hemorrhages and alterations of endothelial permeability can be produced in tissues containing microbubble-based ultrasound contrast agents when those tissues are exposed to MHz-frequency pulsed ultrasound of sufficient pressure amplitudes. The general hypothesis guiding this research was that acoustic (viz., inertial) cavitation, rather than thermal insult, is the dominant mechanism by which such effects arise. We report the results of testing five specific hypotheses in an in vivo rabbit auricular blood vessel model: (1) acoustic cavitation nucleated by microbubble contrast agent can damage the endothelia of veins at relatively low spatial-peak temporal-average intensities, (2) such damage will be proportional to the peak negative pressure amplitude of the insonifying pulses, (3) damage will be confined largely to the intimal surface, with sparing of perivascular tissues, (4) greater damage will occur to the endothelial cells on the side of the vessel distal to the source transducer than on the proximal side and (5) ultrasound/contrast agent-induced endothelial damage can be inherently thrombogenic, or can aid sclerotherapeutic thrombogenesis through the application of otherwise subtherapeutic doses of thrombogenic drugs. Auricular vessels were exposed to 1-MHz focused ultrasound of variable peak pressure amplitude using low duty factor, fixed pulse parameters, with or without infusion of a shelled microbubble contrast agent. Extravasation of Evans blue dye and erythrocytes was assessed at the macroscopic level. Endothelial damage was assessed via scanning electron microscopy (SEM) image analysis. The hypotheses were supported by the data. We discuss potential therapeutic applications of vessel occlusion, e.g., occlusion of at-risk gastric varices.

Effects of high intensity focused ultrasound on vascular endothelial growth factor in melanoma bearing mice

This study was to investigate the effects of high intensity focused ultrasound on vascular endothelial growth factor. A B16 melanoma model was adopted in our study. Melanoma bearing mice were randomly divided into two groups: HIFU group and surgery group. While the control group was only injected with isovolumetric normal saline solution and treated as the surgery group. We detected VEGF both in tissues and sera through immunohistochemical method and ELISA respectively. Tissues were sampled pre- and at the 3rd day post-operation in HIFU group and blood samples were taken pre- and at the 1st, 3rd, and 7th day post-operation in all the groups. As a result, in the tissues, VEGF was expressed in 80% melanomas, but none was detected in the targeted area after HIFU treatment. In the sera, there was a decreasing tendency of serum-VEGF concentrations in group HIFU and surgery after operation, while that in the control group increased after operation. The levels in the HIFU group on day 1, 3, and 7 postoperatively were all lower than that in the surgery group respectively (79.16 pg/ml vs 91.59 pg/ml; 33.64 pg/ml vs 49.39 pg/ml; 30.37 pg/ml vs 46.68 pg/ml), but there wasn't any significant difference (P > 0.05). So HIFU can destroy VEGF in the targeted area and maybe have less of an effect on serum-VEGF than surgery.

Intra-operative acoustic hemostasis of liver: production of a homogenate for effective treatment

OBJECTIVE

We have shown that High-Intensity Focused Ultrasound (HIFU) can effectively control bleeding from injuries to solid organs such as liver, spleen, and lung. Achievement of hemostasis was augmented when a homogenate of tissue and blood was formed. The objective of this study was to investigate quantitatively the effect of homogenate production on HIFU application time for hemostasis. Possible mechanisms involved in homogenate production were also studied.

METHODS

Ten anesthetized rabbits had laparotomy and liver exposure. Liver incisions, 15-25 mm long and 3-4 mm deep, were made followed immediately by HIFU application. Two electrical powers of 80 and 100 W corresponding to focal acoustic intensities of 2264 and 2829 W/cm(2), respectively were used. Tissue and homogenate temperatures were measured. Smear and histological tissue sample analysis using light microscopy were performed.

RESULTS

In treatments with homogenate formation, hemostasis was achieved in 76+/-1.3 s (Mean+/-Standard Error Mean: SEM) at 80 W. In treatments without homogenate formation (at 80 W), hemostasis was achieved in 106+/-0.87 s. At 100 W, hemostasis was achieved in 46+/-0.3 s. The time required for homogenate formation, at 80 and 100 W were 60+/-2.5 and 23+/-0.3 s, respectively. The homogenate temperature was 83 degrees C (SEM 0.6 degrees C), and the non-homogenate tissue temperature at the treatment site was 60 degrees C (SEM 0.4 degrees C). The smear and histological analysis showed significant blood components and cellular debris in the homogenate, with some intact cells.

CONCLUSION

The HIFU-induced homogenate of blood and tissue resulted in a statistically significant shorter HIFU application time for hemostasis. The incisions with homogenate had higher temperatures as compared to incisions without homogenate. Further studies of the correlation between homogenate formation and temperature must be done, as well as studies on the long-term effects of homogenate in achieving hemostasis.

Bubble dynamics and size distributions during focused ultrasound insonation

The deposition of ultrasonic energy in tissue can cause tissue damage due to local heating. For pressures above a critical threshold, cavitation will occur, inducing a much larger thermal energy deposition in a local region. The present work develops a nonlinear bubble dynamics model to numerically investigate bubble oscillations and bubble-enhanced heating during focused ultrasound (HIFU) insonation. The model is applied to calculate two threshold-dependent phenomena occurring for nonlinearly oscillating bubbles: Shape instability and growth by rectified diffusion. These instabilities in turn are shown to place physical boundaries on the time-dependent bubble size distribution, and thus the thermal energy deposition.

The relation between cavitation and platelet aggregation during exposure to high-intensity focused ultrasound

Our previous study showed that high-intensity focused ultrasound (HIFU) is capable of producing "primary acoustic hemostasis" in the form of ultrasound (US)-induced platelet activation, aggregation and adhesion to a collagen-coated surface. In the current study, 1.1 MHz continuous-wave HIFU was used to investigate the role of cavitation as a mechanism for platelet aggregation in samples of platelet-rich plasma. A 5 MHz passive cavitation detector was used to monitor cavitation activity and laser aggregometry was used to measure platelet aggregation. Using spatial average intensities from 0 to 3350 W/cm2, the effects of HIFU-induced cavitation on platelet aggregation were investigated by enhancing cavitation activity through use of US contrast agents and by limiting cavitation activity through use of an overpressure system. Our results show that increased cavitation activity lowers the intensity threshold to produce platelet aggregation and decreased cavitation activity in the overpressure system raises the intensity threshold for platelet aggregation.

Liver hemostasis with high-intensity ultrasound: repair and healing

OBJECTIVE

Previous studies have shown that high-intensity focused ultrasound can effectively control bleeding from injuries of liver, spleen, and blood vessels. This study investigated long-term hemostasis and tissue repair after high-intensity focused ultrasound treatment in liver.

METHODS

A total of 21 rabbits were randomly assigned to 2 groups: high-intensity focused ultrasound treatment (n = 14) and sham treatment (n = 7). All animals had sterile laparotomy and liver exposure. The high-intensity focused ultrasound-treated animals received liver incisions, 20 to 25 mm long and 4 to 6 mm deep, followed immediately by high-intensity focused ultrasound application until complete hemostasis was achieved. After recovery, sonographic images, blood samples, and histologic samples were collected immediately and on days 1, 3, 7, 14, 28, and 60 after treatment.

RESULTS

All 14 liver injuries were hemostatic after an average +/- SD of 78 +/- 44 seconds of high-intensity focused ultrasound application, with no rebleeding at any time point after the treatment. Subsequent blood analysis showed no significant difference in serial hematologic or coagulation measures between the high-intensity focused ultrasound and sham groups. Alanine aminotransferase and aspartate aminotransferase levels increased immediately after surgery by as much as 285% up to day 3 and returned to normal values by day 7. Hematocrit and white blood cell counts showed no statistically significant difference from normal values at all time points. Histologic examination up to 60 days after treatment revealed scarring and liver tissue regeneration at the treatment site.

CONCLUSIONS

High-intensity focused ultrasound appears to provide long-lasting hemostasis of acute liver injury. Healing and repair mechanisms after high-intensity focused ultrasound application appear to be intact.

Endothelial cell injury and platelet aggregation induced by contrast ultrasonography in the rat hepatic sinusoid

OBJECTIVE

To determine whether contrast ultrasonography can affect the sinusoidal cells and platelets of the liver by using ultrastructural analysis in vivo.

METHODS

Fifteen Wistar rats were placed into the following 5 groups of 3 rats each: 3 control groups comprising a sham operation group, a contrast agent injection-alone group, and an ultrasound exposure-alone group; and 2 contrast agent injection with ultrasound exposure groups, split according to excision time. After a dose of an echo contrast agent (100 mg/kg of body weight) was administered through the femoral vein, the rats that received injections were subjected to ultrasound for the first minute, no ultrasound for the next 4 minutes, and then ultrasound sweep scanning for 10 seconds. The rats were perfused via the heart with cold physiologic saline containing 2% paraformaldehyde and 2.5% glutaraldehyde solution buffered with 0.1-mol/L phosphate. The livers of the rats in 4 of the groups were excised immediately. The livers of the rats in 1 of the 2 contrast agent with ultrasound exposure groups were excised by the same procedure 5 hours after they received the injections. All specimens were studied with light and electron microscopy.

RESULTS

Platelet aggregation and injury to endothelial cells were more severe in the contrast agent injection and ultrasound exposure groups than in the other groups.

CONCLUSIONS

Contrast ultrasonography can cause platelet aggregation and endothelial cell damage in the rat hepatic sinusoid.

The emergent role of focal liver ablation techniques in the treatment of primary and secondary liver tumours

Only 20% of patients with primary or secondary liver tumours are suitable for resection because of extrahepatic disease or the anatomical distribution of their disease. These patients could be treated by ablation of the tumour, thus preserving functioning liver. This study presents a detailed review of established and experimental ablation procedures. The relative merits of each technique will be discussed and clinical data regarding the efficacy of the techniques evaluated. A literature search from 1966 to 2003 was undertaken using Medline, Pubmed and Web of Science databases. Keywords were Hepatocellular carcinoma, liver metastases, percutaneous ethanol injection, cryotherapy, microwave coagulation therapy, radiofrequency ablation, interstitial laser photocoagulation, focused high-intensity ultrasound, hot saline injection, electrolysis and acetic acid injection. Ablative techniques offer a promising therapeutic modality to treat unresectable tumours. Large-scale randomised controlled trials are required before widespread acceptance of these techniques can occur.

High-intensity focused US: a potential new treatment for GI bleeding

BACKGROUND

High-intensity focused US has been shown to achieve hemostasis in lacerated large veins and arteries. High-intensity focused US was studied as a potential endoscopic treatment for GI bleeding.

METHODS

A segment of the auricular vein of the rabbit was lacerated longitudinally and then treated with a high-intensity focused US transducer driven at 3.9 MHz (focal intensity of 750 W/cm(2)) in 15 animals until hemostasis was achieved. Sham treatment was delivered to 3 vessels. Rabbits were euthanized on days 0, 2, 7, 14, and 28 to allow for histologic evaluation of the response to treatment.

RESULTS

Hemostasis was achieved in all treated vessels and in none of the sham treatments. Mean treatment time was 13 seconds. Histology initially demonstrated acute thermal injury with subsequent thrombus formation and chronic inflammation leading to replacement of the vessel by fibrous scar tissue.

CONCLUSIONS

High-intensity focused US causes hemostasis in acutely bleeding veins and results in occlusion of treated vessel with subsequent granulation tissue formation.

Inertial cavitation dose and hemolysis produced in vitro with or without Optison

Gas-based contrast agents (CAs) increase ultrasound (US)-induced bioeffects, presumably via an inertial cavitation (IC) mechanism. The relationship between IC dose (ICD) (cumulated root mean squared [RMS] broadband noise amplitude; frequency domain) and 1.1-MHz US-induced hemolysis in whole human blood was explored with Optison; the hypothesis was that hemolysis would correlate with ICD. Four experimental series were conducted, with variable: 1. peak negative acoustic pressure (P-), 2. Optison concentration, 3. pulse duration and 4. total exposure duration and Optison concentration. P- thresholds for hemolysis and ICD were approximately 0.5 MPa. ICD and hemolysis were detected at Optison concentrations >/= 0.01 V%, and with pulse durations as low as four or two cycles, respectively. Hemolysis and ICD evolved as functions of time and Optison concentration; final hemolysis and ICD values depended on initial Optison concentration, but initial rates of change did not. Within series, hemolysis was significantly correlated with ICD; across series, the correlation was significant at p < 0.001.

In vitro platelet activation by an echo contrast agent

OBJECTIVE

We investigated whether an ultrasonic echo contrast agent containing microbubbles (Levovist [SH U 508A]; Schering AG, Berlin, Germany) could in routine use activate platelets.

METHODS

Levovist and its main component, galactose, were mixed with separate samples of whole blood (1.5-75 mg/mL) from 5 healthy volunteers to form a 1-mL suspension sample. After in vitro exposure to ultrasound emitted from a commercial ultrasonic scanner at a pulse frequency of 3.5 MHz with a mechanical index of 1.9 and an exposure duration of 5 minutes, 5 microL of the sample was incubated for 20 minutes with the fluorescein isothiocyanate-labeled CD61 antibody, which is a platelet-specific antigen, and the phycoerythrin-labeled CD62P (P-selectin) antibody, an activation-specific antigen, both on the platelet surface. After more than 30 minutes of fixing in 1% paraformaldehyde, flow cytometric analysis was performed.

RESULTS

The percentage of CD62P-expressing platelets increased according to the concentrations of Levovist and galactose, which showed almost equal effects. Ultrasound exposure did not enhance the effect except at the highest concentration of Levovist (75 mg/mL).

CONCLUSIONS

In vitro, a galactose-based echo contrast agent could not activate the platelets at its routine concentration.

Spleen hemostasis using high-intensity ultrasound: survival and healing

BACKGROUND

Previous studies have shown that high-intensity focused ultrasound (HIFU) can effectively control bleeding of incised livers and spleens and punctured vessels. This current study investigated the long-term safety of HIFU in splenic hemostasis.

METHODS

A total of 21 rabbits were randomly assigned to two groups: HIFU treatment (n = 14), and sham treatment (n = 7). All animals underwent sterile laparotomy and splenic exposure. The HIFU-treated animals received splenic incisions, 8 to 10 mm long and 4 to 5 mm deep, and immediate 9.6-MHz HIFU until hemostasis was achieved. After recovery, ultrasound images, blood samples, and histologic samples were collected on days 0, 1, 3, 7, 14, 28, and 60.

RESULTS

All 14 splenic injuries were hemostatic after an average of 96 seconds of HIFU application. There was evidence of rebleeding in one animal between days 3 and 7 posttreatment. Subsequent blood analysis showed no significant difference in serial hematologic or coagulation measures between HIFU and sham groups. Histologic examination up to 60 days posttreatment revealed scarring and spleen tissue regeneration at the treatment site.

CONCLUSION

HIFU provides an effective and safe method of achieving hemostasis after acute splenic injury.

Phonophoresis: efficiency, mechanisms and skin tolerance

Phonophoresis or sonophoresis is the use of ultrasound to increase percutaneous absorption of a drug. The technique has been widely used in sports medicine since the sixties. Controlled studies in humans in vivo have demonstrated absence or mild effects of the technique with the parameters currently used (frequency 1-3 MHz, intensity 1-2 W/cm(2), duration 5-10 mins, continuous or pulse mode). However, it was demonstrated in 1995 that administration of macromolecules with conserved biological activity was feasible in animals in vivo using low frequency ultrasound. This led to new research into this method of transdermal administration. The aim of this review is to present the main findings published with low frequency and high frequency ultrasound over the last ten years, and to discuss the respective roles of thermal, cavitational and non-cavitational effects on the reduction of the skin barrier. Particular attention is paid to the biological effects on living skin which might be of importance for tolerance and practical use in humans.