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

Abstract

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.

The feasibility of ultrasound‐assisted endovascular laser thrombolysis in an acute rabbit thrombosis model

“…The USELT is based on our earlier developed PUT technology. The high selectivity, precision, and safety of PUT technology have been demonstrated in our previous studies 30‐33 . Our current in vivo study demonstrated that USELT utilizing laser pulses with a fluence of 8 mJ/cm 2 at 532‐nm wavelength and ultrasound bursts with a peak negative pressure of 1.3 MPa at 0.5 MHz were effective for thrombolysis (shown in Figures 3, 5 and 6.…”

“…Note that USELT is based on the synergistic effect between the light pulse and the ultrasound burst. Strong cavitation will only be induced at the location where laser and ultrasound energy overlap and are properly synchronized 30 . Due to the low applied ultrasound energy intensity, ultrasound alone is not capable of producing cavitation on the vessel wall and surrounding tissues (shown in Figure 3, ultrasound only; Figure 4, ultrasound only; Figure 5d‐f; Figure 6, ultrasound only; Figure 7a).…”

“…We have developed a novel hybrid technology, based on the combination of light and ultrasound, namely ultrasound‐assisted endovascular laser thrombolysis (USELT), to safely and efficiently dissolve the blood clots in the vein. The USELT system is based on our earlier developed photo‐mediated ultrasound therapy (PUT) technology 30‐33 . Both technologies use combination of ultrasound and laser to generate enhanced cavitation.…”

“…The USELT system is based on our earlier developed photo-mediated ultrasound therapy (PUT) technology. [30][31][32][33] Both technologies use combination of ultrasound and laser to generate enhanced cavitation. In PUT, both laser and ultrasound are applied noninvasively, [34][35][36][37][38][39] whereas in USELT the laser is delivered directly to the clot using an endovascular laser catheter.…”

On the attenuation of ultrasound by pure black tattoo ink

“…Ultrasonic imaging has been used to monitor dermatological tattoo complications [9,10]. In addition to laser ablation [11], ultrasound has also been experimentally applied for tattoo removal [12,13]. The high-intensity focussed ultrasound used for this purpose ablates the tissue in or near the transducer focus, irrespective of the presence of ink.…”