Enhanced cavitation activity in a slab-shaped optical absorber during photo-mediated ultrasound therapy.

Recently, new studies have shown that combined laser and ultrasound, or photo-mediated ultrasound therapy (PUT), can enhance cavitation in optically absorptive targets to disrupt tissues through photoacoustic (PA) effect. These studies, including both experimental and theoretical investigations, have largely focused on blood vessels, which are modeled as cylindrically-shaped optical absorbers for PA wave generation and propagation. However, in many clinical situations, target tissues may not be cylindrically-shaped. In this paper we investigated the effect of PUT on a slab-shaped optical absorber, much larger than the size of the laser beam or the ultrasound focal point. Our results demonstrated that laser light could generate a PA wave that could enhance cavitation not only at the surface of a slab, but also at depths when combined with ultrasound, suggesting that PUT may be effective in enhancing cavitation in a large range of soft tissues. Our results also demonstrated that the cavitation enhancement was based on the optical absorption of the targeted tissue, allowing for self-targeting treatments when optical contrast is present. Additionally, we demonstrated that for the greatest cavitation enhancement in deeper layers a focused laser beam geometry would be most effective.

Enhanced laser surface ablation with an integrated photoacoustic imaging and high intensity focused ultrasound system.

BACKGROUND AND OBJECTIVE: Combined laser and ultrasound treatments have been found to have synergistic effects, which may be of particular note in dermatology. We aim to investigate the potential of this technology for dermatology through in vitro and ex vivo experiments. METHODS: In vitro tissue phantoms made of agar and tattoo ink and tattooed ex vivo chicken breast tissue were used. An integrated photoacoustic imaging and high intensity focused ultrasound (HIFU) system, using a 5-ns tunable OPO laser system and a 5 MHz HIFU transducer, was used to perform photoacoustic analysis to identify the optical contrast, and perform combined laser and ultrasound ablation. On the tissue phantoms, lines of ablation were created under various operating conditions. The samples were then quantified to determine the level of ablation. Same procedures were performed on the tattooed chicken breast tissue and the tattoo was removed by using combined laser and ultrasound. RESULTS: Ablation in the in vitro tissue phantoms was observed with properly synchronized laser and ultrasound while no ablation was found with either laser or ultrasound alone. Increases to the intensity or pulse duration of ultrasound caused an increase in ablation to the samples. The tattoo was removed from the ex vivo chicken breast using combined laser and ultrasound with a radiant exposure of 1.2 J/cm2 while laser and ultrasound alone were unable to remove the tattoo. CONCLUSIONS: We determined that by supplementing nanosecond laser pulses with ultrasound, ablation, and tattoo removal can be achieved at laser radiant exposures levels would otherwise be ineffective. The area of ablation can be adjusted through changes in the intensity and duration of the ultrasound burst with a constant laser intensity. Additionally, the system can be used to perform photoacoustic analysis of the tissue to estimate the relative optical absorbance at various available wavelengths, allowing for pretreatment analysis. Lasers Surg. Med. 9999:1-9, 2019. © 2019 Wiley Periodicals, Inc.

Treatment of post-traumatic joint contracture in a rabbit model using pulsed, high intensity laser and ultrasound.

Post-traumatic joint contracture induced by scar tissues following a surgery or injury can leave patients in a permanent state of pain and disability, which is difficult to resolve by current treatments. This randomized controlled trial examines the therapeutic effect of pulsed high-intensity laser (PHIL) and pulsed high-intensity focused ultrasound (PHIFU) for post-traumatic joint contracture due to arthrofibrosis. The peak power levels of both PHIL and PHIFU are much higher than that of laser or ultrasound currently used in physical therapy, while short pulses are utilized to prevent damage. To test the effectiveness of these treatments, a rabbit knee model for joint contracture was established. Twenty-one rabbits were split into four groups: untreated control (n = 5), PHIL (n = 5), PHIFU (n = 5), and a PHIL + PHIFU group (n = 6). Maximum extension of the surgically modified rabbit knee was compared to that of the contralateral control knee over the course of 16 weeks. The rabbits in the untreated control group maintained a relatively consistent level of joint contracture, while every rabbit in each of the treatment groups had improved range of motion, eventually leading to a restoration of normal joint extension. Average recovery time was 7.6 ± 1.5 weeks for the PHIL treatment group, 9.8 ± 3.7 weeks for the PHIFU group, and 8.0 ± 2.2 weeks for the combined treatment group. Histopathology demonstrated reduced density and accelerated resorption of scar tissues in the treated knee joints. This study provides evidence that both PHIL and PHIFU are effective in treating post-traumatic joint contracture in rabbits and warrant further investigation into the underlying mechanisms to optimize PHIL and PHIFU based treatments in a larger number of animals.

Laser-Activated Bioprobes with High Photothermal Conversion Efficiency for Sensitive Photoacoustic/Ultrasound Imaging and Photothermal Sensing.

Laser-activated bioprobes with high photothermal conversion efficiency (IRPDA@PFH NDs) based on biocompatible IR-780 doped polydopamine perfluorocarbon nanodroplets (NDs) were developed. When protected by gelatin microspheres, their near-spherical morphologies can be easily observed with transmission electron microscope. Doping IR-780 (3 w/w % of added dopamine hydrochloride) can significantly enhance near-infrared (NIR) absorption and photothermal conversion efficiency to 57.7%. The enhanced NIR absorption and nonradiative relaxation are preferred to stronger photoacoustic (PA) signals and higher PA imaging definition; ultrasound (US) signals also increase more than 2.5 times because of easier phase change of NDs. These bioprobes had sensitive PA/US imaging capability with highly effective substitute utilizations, in which polydopamine was used either as a PA contrast or a photothermal agent. Perfluorocarbon can be used as an US contrast agent and temperature indicator. More importantly, the gray value increments of US increase with temperature in a general range from 35 to 55 °C. Especially, an approximate linear increasing of gray value in the optimized photothermal therapy (PTT) range from 35 °C to 50 °C could be used for the temperature monitoring and control of PTT. During PTT, the heated regions and the extent of photothermal heating can be visualized by US imaging. These findings indicate their great potential for biosensing and PTT monitoring.

Novel rabbit model of moderate knee contracture induced by direct capsular damage.

The treatment of joint contracture continues to represent a challenging problem in orthopedic surgery and rehabilitation medicine. Existing animal models of knee contracture for evaluating new treatments are mostly created by extensive joint tissue damage with Kirschner-wire immobilization which requires a second surgery to remove Kirschner-wires. This study aimed to develop a less invasive rabbit model of moderate knee contracture through a single surgery. Skeletally mature New Zealand White rabbits had their right knee operated to create surgical damage to the posterior capsule under direct visualization. Operated knees were then held in a flexed position by suturing the superficial flexion muscles with absorbable sutures. The flexion contracture (net extension loss) was determined by comparing the extension angles between the operated and non-operated knees from 8 to 24 weeks post-surgery. The flexion contracture of the operated knees was significantly greater (p < 0.01/0.001) than the non-operated knees at each weekly measurement. The mean flexion contractures were 22° at 8 weeks, 19° at 16 weeks, and 18° at 24 weeks. No significant differences in the severity of flexion contracture were observed between 8-week and each of the following weeks, suggesting that the flexion contracture was essentially stabilized by 8 weeks post-surgery. Histopathologic analyses demonstrated intra-articular and peri-articular scar formation. This less invasive rabbit model of moderate knee contracture is more quickly established through a single surgery with lower risk of surgical complications compared to the previously reported invasive models, and could be an alternative animal model for joint contracture research. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2687-2695, 2018.