The Effect of Laser and Ultrasound Synchronization in Photo-Mediated Ultrasound Therapy

Ultrasound-assisted laser therapy for selective removal of melanoma cells

The current study explores the potential of ultrasound-assisted laser therapy (USaLT) to selectively destroy melanoma cells. The technology was tested on an ex vivo melanoma model, which was established by growing melanoma cells in chicken breast tissue. Ultrasound-only and laser-only treatments were used as control groups. USaLT was able to effectively destroy melanoma cells and selectively remove 66.41% of melanoma cells in the ex vivo tumor model when an ultrasound peak negative pressure of 2 MPa was concurrently applied with a laser fluence of 28 mJ/cm2 at 532 nm optical wavelength for 5 min. The therapeutic efficiency was further improved with the use of a higher laser fluence, and the treatment depth was improved to 3.5 mm with the use of 1,064 nm laser light at a fluence of 150 mJ/cm2. None of the laser-only and ultrasound-only treatments were able to remove any melanoma cells. The treatment outcome was validated with histological analyses and photoacoustic imaging. This study opens the possibility of USaLT for melanoma that is currently treated by laser therapy, but at a much lower laser fluence level, hence improving the safety potential of laser therapy.

Real-Time Cavitation Monitoring During Optical Coherence Tomography Guided Photo-Mediated Ultrasound Therapy of the Retina

OBJECTIVE

Photo-mediated ultrasound therapy (PUT) is a novel antivascular therapeutic modality based on cavitation-induced bioeffects. During PUT, synergistic combinations of laser pulses and ultrasound bursts are used to remove the targeted microvessels selectively and precisely without harming nearby tissue. In the current study, an integrated system combining PUT and spectral domain optical coherence tomography (SD-OCT) was developed, where the SD-OCT system was used to guide PUT by detecting cavitation in real time in the retina of the eye.

METHOD

We first examined the capability of SD-OCT in detecting cavitation on a vascular-mimicking phantom and compared the results with those from a passive cavitation detector. The performance of the integrated system in treatment of choroidal microvessels was then evaluated in rabbit eyes in vivo.

RESULTS

During the in vivo PUT experiments, several biomarkers at the subretinal layer in the rabbit eye were identified on OCT images. The findings indicate that, by evaluating biomarkers of treatment effect, real-time SD-OCT monitoring could help to avoid micro-hemorrhage, which is a potential major side effect.

CONCLUSION

Real-time OCT monitoring can thus improve the safety and efficiency of PUT in removing the retinal and choroidal microvasculature.

Cutaneous Hypervascularization Treatment Using Photo-Mediated Ultrasound Therapy

Photo-mediated ultrasound therapy (PUT) is a cavitation-based, highly selective antivascular technique. In this study, the effectiveness and safety of PUT on cutaneous vascular malformation was examined through in vivo experiments in a clinically relevant chicken wattle model, whose microanatomy is similar to that of port-wine stain and other hypervascular dermal diseases in humans. Assessed by optical coherence tomography angiography, the blood vessel density in the chicken wattle decreased by 73.23% after one session of PUT treatment in which 0.707 J/cm2 fluence laser pulses were applied concurrently with ultrasound bursts (n = 7, P < .01). The effectiveness of removing blood vessels in the skin at depth up to 1 mm was further assessed by H&E-stained histology at multiple time points, which included days 1, 3, 7, 14, and 21 after treatment. Additional immunohistochemical analyses with CD31, caspase-3, and Masson's trichrome stains were performed on day 3 after treatment. The results show that the PUT-induced therapeutic effect was confined and specific to blood vessels only, whereas unwanted collateral damage in other skin tissues such as collagen was avoided. The findings from this study demonstrate that PUT can efficiently and safely remove hypervascular dermal capillaries using laser fluence at a level that is orders of magnitude smaller than that used in conventional laser treatment of vascular lesions, thus offering a safer alternative technique for clinical management of cutaneous vascular malformations.

Choroidal neovascularization removal with photo-mediated ultrasound therapy

BACKGROUND

Age-related macular degeneration (AMD) is a major cause of irreversible central vision loss. The main reason for lost vision due to AMD is choroidal neovascularization (CNV). In the clinic, current treatments for CNV include photodynamic therapy, laser photocoagulation, and anti-vascular endothelial growth factor (VEGF) therapy.

PURPOSE

This study evaluates a novel treatment technique combining synchronized nanosecond laser pulses and ultrasound bursts, namely photo-mediated ultrasound therapy (PUT) as a potential treatment method for CNV, for its efficacy and safety in the treatment of CNV via the experiments in a clinically-relevant rabbit model in vivo.

METHODS

CNV was created by subretinal injection of Matrigel and vascular endothelial growth factor (M&V) in 10 New Zealand white rabbits. Six rabbits were used in the PUT group. In the control groups, two rabbits were treated by laser-only, and two rabbits were treated by ultrasound-only. The treatment efficacy was evaluated through fundus photography and fluorescein angiography (FA) longitudinally for up to 4 weeks. Rabbits were sacrificed for histopathology 3 months after treatment to examine the safety of PUT.

RESULTS

The fluorescein leakage on FA was quantified to longitudinally evaluate treatment outcome. Compared with baseline, the relative intensity index was reduced by 26.57% ± 8.66% at 3 days after treatment, 27.24% ± 6.21% at 1 week after treatment, 27.79% ± 2.61% at 2 weeks after treatment, and 32.12% ± 3.23% at 4 weeks after treatment, all with a statistically significant difference of p < 0.01. The comparison between the relative intensity indexes from the two control groups (laser-only treatment and ultrasound-only treatment) did not show any statistically significant difference at all time points. Safety evaluation at 3 months with histopathology demonstrated that the PUT did not result in morphologic changes to the neurosensory retina.

CONCLUSIONS

This study introduces PUT for the first time for the treatment of CNV. The results demonstrated good efficacy and safety of PUT to treat CNV in a clinically-relevant rabbit model. With a single session of treatment, PUT can safely reduce the leakage of CNV for at least 1 month after treatment.

A review on photo-mediated ultrasound therapy

Photo-mediated ultrasound therapy (PUT) is a novel therapeutic technique based on the combination of ultrasound and laser. The underlying mechanism of PUT is the enhanced cavitation effect inside blood vessels. The enhanced cavitation activity can result in bio-effects such as reduced perfusion in microvessels. The reduced perfusion effect in microvessels in the eye has the potential to control the progression of eye diseases such as diabetic retinopathy and age-related macular degeneration. Several in vivo studies have demonstrated the feasibility of PUT in removing microvasculature in the eye using rabbit eye model and vasculature in the skin using rabbit ear model. Numerical studies using a bubble dynamics model found that cavitation is enhanced during PUT due to the dramatic increase in size of air/vapor nuclei in blood. In addition, the study conducted to model cavitation dynamics inside a blood vessel during PUT found stresses induced on the vessel wall during PUT are higher than that at normal physiological levels, which may be responsible for bio-effects. The concentration of vasodilators such as nitric oxide and prostacyclin were also found to be affected during PUT in an in vitro study, which may limit blood perfusion in vessels. The main advantage of PUT over conventional techniques is non-invasive, precise, and selective removal of microvessels with high efficiency at relatively low energy levels of ultrasound and laser, without affecting the nearby structures. However, the main limitation of vessel rupture/hemorrhage needs to be overcome through the development of real-time monitoring of treatment effects during PUT. In addition to the application in removing microvessels, PUT-based techniques were also explored in treating other diseases. Studies have found a combination of ultrasound and laser to be effective in removing blood clots inside veins, which has the potential to treat deep-vein thrombosis. The disruption of atherosclerotic plaque using combined ultrasound and laser was also tested, and the feasibility was demonstrated.

Development of a micro-Raman system for in vivo studying the mechanism of laser biological effects

The laser irradiation on organism will produce a series of biological effects, which can be used for basic medical research, diagnosis and treatments of diseases. However, the mechanism of this biological effects is still unclear. As a sensitive molecular monitoring technique, Raman spectroscopy has became a very popular detection method in biomedical research especially in vivo study. In this paper, we present a compact and flexible micro-Raman system for in vivo studying the mechanism of laser biological effects. The system has the two functions of laser induction and Raman measurement, which can realize the micro-area radiation of laser and simultaneously collect the corresponding Raman spectra in vivo. The detection method provided by this home-built system is able to deepen the understanding of laser biological effects mechanism at molecular level, so it is expected that the system is significant for the treatments and diagnosis of diseases in the near future.

A feasibility study on removing lipid deposition in atherosclerotic plaques with ultrasound-assisted laser ablation

Objective. Atherosclerosis is the buildup of fats, cholesterol, and other substances on the inner walls of arteries. It can affect arteries of heart, brain, arms, legs, pelvis and kidney, resulting in ischemic heart disease, carotid artery disease, peripheral artery disease and chronic kidney disease. Laser-based treatment techniques like laser atherectomy can be used to treat many common atherosclerostic diseases. However, the use of laser-based treatment remains limited due to the high risk of complications and low efficiency in removing atherosclerostic plaques as compared with other treatment methods. In this study, we developed a technology that used high intensity focused ultrasound to assist laser treatment in the removal of the lipid core of atherosclerotic plaques.Approach. The fundamental mechanism to disrupt atherosclerostic plaque was to enhance the mechanical effect of cavitation during laser/ultrasound therapy. To promote cavitation, spatiotemporally synchronized ultrasound bursts of 2% duty cycle at 0.5 MHz and nanosecond laser pulses at 532 nm wavelength were used. Experiments were first performed on pig belly fat samples to titrate ultrasound and laser parameters. Then, experiments were conducted on human plaque samples, where the lipid depositions of the plaques were targeted.Main results. Our results showed that fat tissue could be removed with an ultrasound peak negative pressure (PNP) of 2.45 MPa and a laser radiant exposure as low as 3.2 mJ mm-2. The lipid depositions on the atherosclerostic plaques were removed with laser radiant exposure of 16 mJ mm-2in synchronizing with an ultrasound PNP of 5.4 MPa. During all the experiments, laser-only and ultrasound-only control treatments at the same energy levels were not effective in removing the lipid.Significance. The results demonstrated that the addition of ultrasound could effectively reduce the needed laser power for atherosclerotic plaque removal, which will potentially improve treatment safety and efficiency of current laser therapies.

High speed photo-mediated ultrasound therapy integrated with OCTA

Photo-mediated Ultrasound Therapy (PUT), as a new anti-vascular technique, can promote cavitation activity to selectively destruct blood vessels with a significantly lower amount of energy when compared to energy level required by other laser and ultrasound treatment therapies individually. Here, we report the development of a high speed PUT system based on a 50-kHz pulsed laser to achieve faster treatment, decreasing the treatment time by a factor of 20. Furthermore, we integrated it with optical coherence tomography angiography (OCTA) for real time monitoring. The feasibility of the proposed OCTA-guided PUT was validated through in vivo rabbit experiments. The addition of OCTA to PUT allows for quantitative prescreening and real time monitoring of treatment response, thereby enabling implementation of individualized treatment strategies.

Aspects of Antiviral Strategies Based on Different Phototherapy Approaches: Hit by the Light

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) which caused the COVID-19 pandemic spreading around the world from late 2019, served as a ruthless reminder of the threat viruses pose to global public health. The synthesis of new antiviral drugs, as well as repurposing existing products, is a long-term ongoing process which has challenged the scientific community. One solution could be an effective, accessible, and rapidly available antiviral treatment based on phototherapy (PT). PT has been used to treat several diseases, and relies on the absorption of light by endogenous molecules or exogenous photosensitizers (PS). PT has often been used in cancer treatment and prophylaxis, and as a complement to established chemotherapy and immunotherapy in combined therapeutic strategy. Besides significant applications in anticancer treatment, studies have demonstrated the beneficial impact of PT on respiratory, systemic, emerging, and oncogenic viral infections. The aim of this review was to highlight the potential of PT to combat viral infections by summarizing current progress in photodynamic, photothermal, and photoacoustic approaches. Attention is drawn to the virucidal effect of PT on systemic viruses such as the human immunodeficiency virus and human herpes viruses, including the causative agent of Kaposi sarcoma, human herpes virus (HHV8). PT has good potential for disinfection in anti-norovirus research and against pandemic viruses like SARS-CoV-2.

A 3D finite element model to study the cavitation induced stresses on blood-vessel wall during the ultrasound-only phase of photo-mediated ultrasound therapy

Photo-mediated ultrasound therapy (PUT) is a novel technique utilizing synchronized ultrasound and laser to generate enhanced cavitation inside blood vessels. The enhanced cavitation inside blood vessels induces bio-effects, which can result in the removal of micro-vessels and the reduction in local blood perfusion. These bio-effects have the potential to treat neovascularization diseases in the eye, such as age-related macular degeneration and diabetic retinopathy. Currently, PUT is in the preclinical stage, and various PUT studies on in vivo rabbit eye models have shown successful removal of micro-vessels. PUT is completely non-invasive and particle-free as opposed to current clinical treatments such as anti-vascular endothelial growth factor therapy and photodynamic therapy, and it precisely removes micro-vessels without damaging the surrounding tissue, unlike laser photocoagulation therapy. The stresses produced by oscillating bubbles during PUT are responsible for the induced bio-effects in blood vessels. In our previous work, stresses induced during the first phase of PUT due to combined ultrasound and laser irradiation were studied using a 2D model. In this work, stresses induced during the third or last phase of PUT due to ultrasound alone were studied using a 3D finite element method-based numerical model. The results showed that the circumferential and shear stress increased as the bubble moves from the center of the vessel toward the vessel wall with more than a 16 times increase in shear stress from 1.848 to 31.060 kPa as compared to only a 4 times increase in circumferential stress from 211 to 906 kPa for a 2 µm bubble placed inside a 10 µm vessel on the application of 1 MHz ultrasound frequency and 130 kPa amplitude. In addition, the stresses decreased as the bubble was placed in smaller sized vessels with a larger decrease in circumferential stress. The changes in shear stress were found to be more dependent on the bubble-vessel wall distance, and the changes in circumferential stress were more dependent on the bubble oscillation amplitude. Moreover, the bubble shape changed to an ellipsoidal with a higher oscillation amplitude in the vessel's axial direction as it was moved closer to the vessel wall, and the bubble oscillation amplitude decreased drastically as it was placed in vessels of a smaller size.

Photo-mediated ultrasound therapy for the treatment of retinal neovascularization in rabbit eyes

Objectives

Retinal neovascularization (RNV) is the growth of abnormal microvessels on the retinal surface and into the vitreous, which can lead to severe vision loss. By combining relatively low‐intensity ultrasound and nanosecond‐pulse‐duration laser, we developed a novel treatment method, namely photo‐mediated ultrasound therapy (PUT), which holds a potential to remove RNV with minimal or no damage to the adjacent tissues.

Methods

RNV was created in both albino and pigmented rabbits (n = 10) through a single intravitreal injection with DL‐α‐aminoadipic acid. RNV was treated with PUT 8 weeks postinjection. After PUT treatment, animals were evaluated longitudinally for up to 6 weeks. Treatment outcomes were evaluated through fundus photography, red‐free fundus photography, fluorescein angiography (FA), and histopathology.

Results

In both albino and pigmented rabbits, there were no leakage in the treatment area immediately after PUT treatment as demonstrated by FA, indicating the cessation of blood perfusion of the RNV in the treated area. The fluorescence leakage did not recover in albino rabbits during the 6‐week posttreatment monitoring period, and only 9.9 ± 9.8% of the neovascularization remained at the end of 6 weeks. In the pigmented rabbits, the fluorescence leakage partially returned, but the level of leakage decreased over time during the 6‐week posttreatment monitoring period, and only 10.8 ± 9.8% of the neovascularization remained at the end of 6 weeks. Histology demonstrated removal of vasculature without damage to the surrounding neurosensory retina.

Conclusions

These results demonstrate that PUT could precisely remove RNV without damage to the surrounding neurosensory retina in both rabbit strains.

Effect of Photo-Mediated Ultrasound Therapy on Nitric Oxide and Prostacyclin from Endothelial Cells

Several studies have investigated the effect of photo-mediated ultrasound therapy (PUT) on the treatment of neovascularization. This study explores the impact of PUT on the release of the vasoactive agents nitric oxide (NO) and prostacyclin (PGI₂) from the endothelial cells in an in vitro blood vessel model. In this study, an in vitro vessel model containing RF/6A chorioretinal endothelial cells was used. The vessels were treated with ultrasound-only (0.5, 1.0, 1.5 and 2.0 MPa peak negative pressure at 0.5 MHz with 10% duty cycle), laser-only (5, 10, 15 and 20 mJ/cm² at 532 nm with a pulse width of 5 ns), and synchronized laser and ultrasound (PUT) treatments. Passive cavitation detection was used to determine the cavitation activities during treatment. The levels of NO and PGI₂ generally increased when the applied ultrasound pressure and laser fluence were low. The increases in NO and PGI₂ levels were significantly reduced by 37.2% and 42.7%, respectively, from 0.5 to 1.5 MPa when only ultrasound was applied. The increase in NO was significantly reduced by 89.5% from 5 to 20 mJ/cm², when only the laser was used. In the PUT group, for 10 mJ/cm² laser fluence, the release of NO decreased by 76.8% from 0.1 to 1 MPa ultrasound pressure. For 0.5 MPa ultrasound pressure in the PUT group, the release of PGI₂ started to decrease by 144% from 15 to 20 mJ/cm² laser fluence. The decreases in NO and PGI₂ levels coincided with the increased cavitation activities in each group. In conclusion, PUT can induce a significant reduction in the release of NO and PGI₂ in comparison with ultrasound-only and laser-only treatments.

Photo-Mediated Ultrasound Therapy for the Treatment of Corneal Neovascularization in Rabbit Eyes

Purpose

Corneal neovascularization (CNV) is the invasion of new blood vessels into the avascular cornea, leading to reduced corneal transparency and visual acuity, impaired vision, and even blindness. Current treatment options for CNV are limited. We developed a novel treatment method, termed photo-mediated ultrasound therapy (PUT), that combines laser and ultrasound, and we tested its feasibility for treating CNV in a rabbit model.

Methods

A suture-induced CNV model was established in New Zealand White rabbits, which were randomly divided into two groups: PUT and control. For the PUT group, the applied light fluence at the corneal surface was estimated to be 27 mJ/cm² at 1064-nm wavelength with a pulse duration of 5 ns, and the ultrasound pressure applied on the cornea was 0.43 MPa at 0.5 MHz. The control group received no treatment. Red-free photography and fluorescein angiography were utilized to evaluate the efficiency of PUT. Safety was evaluated by histology and immunohistochemistry. For comparison with the PUT safety results, conventional laser photocoagulation (LP) treatment was performed with standard clinical parameters: 532-nm continuous-wave (CW) laser with 0.1-second pulse duration, 450-mW power, and 75-µm spot size.

Results

In the PUT group, only 1.8% ± 0.8% of the CNV remained 30 days after treatment. In contrast, 71.4% ± 7.2% of the CNV remained in the control group after 30 days. Safety evaluations showed that PUT did not cause any damage to the surrounding tissue.

Conclusions

These results demonstrate that PUT is capable of removing CNV safely and effectively in this rabbit model.

Translational Relevance

PUT can remove CNV safely and effectively.

Removing Subcutaneous Microvessels Using Photo-Mediated Ultrasound Therapy

BACKGROUND AND OBJECTIVES

We have developed a novel anti-vascular technique, termed photo-mediated ultrasound therapy (PUT), which utilizes nanosecond duration laser pulses synchronized with ultrasound bursts to remove the microvasculature through cavitation. The objective of the current study is to explore the potential of PUT in removing subcutaneous microvessels.

STUDY DESIGN/MATERIALS AND METHODS

The auricular blood vessels of two New Zealand white rabbits were treated by PUT with a peak negative ultrasound pressure of 0.45 MPa at 0.5 MHz, and a laser fluence of 0.056 J/cm2 at 1064 nm for 10 minutes. Blood perfusion in the treated area was measured by a commercial laser speckle imaging (LSI) system before and immediately after treatment, as well as at 1 hour, 3 days, 2 weeks, and 4 weeks post-treatment. Perfusion rates of 38 individual vessels from four rabbit ears were tracked during this time period for longitudinal assessment.

RESULTS

The measured perfusion rates of the vessels in the treated areas, as quantified by the relative change in perfusion rate, showed a statistically significant decrease for all time points post-treatment (P < 0.001). The mean decrease in perfusion is 50.79% immediately after treatment and is 32.14% at 4 weeks post-treatment. Immediately after treatment, the perfusion rate decreased rapidly. Following this, there was a partial recovery in perfusion rate up to 3 days post-treatment, followed by a plateau in the perfusion from 3 days to 4 weeks.

CONCLUSIONS

This study demonstrated that a single PUT treatment could significantly reduce blood perfusion by 32.14% in the skin for up to 4 weeks. With unique advantages such as low laser fluence as compared with photothermolysis and agent-free treatment as compared with photodynamic therapy, PUT holds the potential to be developed into a new tool for the treatment of cutaneous vascular lesions. Lasers Surg. Med. © 2020 Wiley Periodicals, LLC.