Atherectomy using a solid-state laser at 355 nm wavelength.

Peripheral arterial disease (PAD), caused by atherosclerotic processes, is allied with an increased risk of ischemic events, limb loss, and death. Recently, the use of a solid-state laser at 355 nm within a hybrid catheter was suggested for that purpose. In this work, short nanosecond pulses of a solid-state laser at 355 nm delivered through a hybrid catheter, composed of optical fibers and a blunt mechanical blade, are used to conduct a pre-clinical study and two clinical cases. The pre-clinical study consisted of an atherosclerotic calcified cadaveric leg and a porcine in vivo trial within the iliac artery, respectively. The clinical cases include chronic total occlusions with a calcified lesion. The occluded cadaveric leg is recanalized successfully and no evidence of thermal necrosis is indicated in the histopathology analysis of the porcine study. No arterial wall damage is demonstrated on the animals' treated arteries and no significant impact on blood count and biochemistry analysis is noted in the animal trial. Successful recanalization of the occluded arteries followed by balloon angioplasty is obtained in both clinical cases. Our work constitutes a proof of concept for using a solid-state pulsed laser at 355 nm in atherectomy.

Shaping photomechanical effects in tissue ablation using 355 nm laser pulses.

We investigate the influence of the cladding diameter of an optical delivery fiber on the ablation dynamics of porcine aorta immersed in tetracycline antibiotic solution using 355 nm nanosecond pulses. We manipulate the pressure transients by enforcing a rear rigid interface (applied by an enlargement of the cladding diameter) to the ablated area, which leads to enhanced ablation efficiency along with a reduction in tissue disruption effects. Numerical simulations, based on the finite elements method, are used to study the propagation of the pressure transients within the suggested scheme. Ultrasonic transducers are used for measuring the increased pressure in front of the fiber's facet and the reduced pressure at the fiber's circumference in the presence of large diameter cladding. The increase and decrease are both found to be by a factor of ˜1.8. The width of the cavitation bubble is measured by high-speed photography. An enlargement of 13.8% is demonstrated, at the expense of backward expansion along the fiber's axis. A histopathological in vitro study demonstrates an average enhancement of 12.27% in the diameter of the ablated crater, as well as significant reduction in the disruption effects. Our study sheds light on the potential to improve the ablation efficiency without additional energy cost, along with attaining improved safety for interventional medical procedures.

Selective tissue ablation using laser radiation at 355 nm in lead extraction by a hybrid catheter; a preliminary report.

BACKGROUND: Current lead extraction (LE) devices can harm the blood vessel endothelium, increasing the risk of perforation. OBJECTIVE: Proof of concept for using a solid-state pulsed laser at 355 nm with a hybrid catheter in LE. METHODS: A hybrid catheter was used comprising optical fibers for the delivery of 355 nm laser pulses at 30 Hz and 6 J/cm(2) combined with a blunt mechanical blade. Specific parameters were chosen to enable selectivity in ablation, thereby reducing the risk of blood vessel perforation. The design exploits differences in the mechanical properties of the fibrotic tissue and the normal blood vessel. Ex vivo ablation was performed to evaluate a hybrid catheter operation on various tissues. Two ex/in vivo pig studies used a free-floating electrode to which three bovine tendon pieces were glued. Finally, two in vivo dog model studies were performed on specimens with 4-5-year-old pacing lead implants, followed by a histopathology study. RESULTS: Catheter penetration rate in the ex vivo experiments was 0.1 mm/seconds for bovine tendon, 0.025 mm/seconds for porcine superior vena cava and 0.033 mm/seconds for porcine aorta. In the ex/in vivo pig study, the three tissue blocks were successfully dissected. In the in vivo dog study, the two leads were successfully extracted. In all in vivo tests, hemodynamic stability was maintained. Gross histopathology did not reveal any injury. CONCLUSIONS: Ablation using 355 nm laser pulses in combination with a mechanical blunt blade may potentially constitute a viable alternative for LE.

Effect of spatial coherence on damage occurrence in multimode optical fibers.

We investigate the influence of spatial coherence on damage occurrence in highly multimode optical fibers using ultraviolet (UV) nanosecond pulses, with the aim of delivering high fluence in the UV. In some cases, the optical damage is initiated below the fiber facet damage threshold and takes place along the propagation path; such damage is believed to be caused by local constructive interference, creating "hot spots." In order to reduce the degree of spatial coherence, we used a large-diameter core (1.5 mm) fiber as a mode scrambler. Different lengths of this large core fiber were used to deliver energy to a fiber core with a smaller diameter (0.6 mm), in which the damage occurrence was observed. The experimental results indicate that there is a correlation between the degree of spatial coherence and the occurrence of optical damages, typically observed a few millimeters from the fiber facet. Numerical simulations, based on the beam-propagation method, support the degradation of spatial coherence, due to the excitation of high-order modes. Finally, by degrading the spatial coherence of the beam, we establish a new record by delivering more than 100 mJ via a 1.5 mm core diameter fiber in the UV, corresponding to ∼26 times the critical power for self-focusing. Our work sheds light on the ability to deliver high energies of nanosecond-pulsed UV laser radiation through multimode optical fibers.

Chalcogenide waveguides on a sapphire substrate for mid-IR applications.

We report on the fabrication of arsenic tri-sulfide chalcogenide strip waveguides on a sapphire substrate, suitable for guiding 0.55-5 µm wavelengths. Propagation losses measured using the Fabry-Perot resonator technique are 2.78 dB/cm. The chalcogenide layer refractive index dispersion is evaluated by measuring the transmission as a function of wavelength prior to waveguide fabrication. Numerical simulations are used to compare between silica and sapphire substrates for mid-IR transmittance and to calculate the waveguide's effective refractive index in a suggested design. The use of a low-loss sapphire substrate redefines the mid-IR boundaries of chalcogenide waveguides for linear and nonlinear applications.

Wavelength conversion of nanosecond pulses to the mid-IR in photonic crystal fibers.

We investigate degenerate four wave mixing with nanosecond pulses in fused silica photonic crystal fibers. Phase-matching curves are calculated taking into account the material and waveguide dispersion. Experiments with a nanosecond pulsed Nd:YAG pump laser and relatively short fiber lengths show more than an octave spanning conversion to idler and signal wavelengths at 3.105 µm and 0.642 µm, respectively. Conversion efficiency depends on the fiber length and pump intensity and is limited in our experiments by damage of the fiber input facet. Our results represent a new stretch towards the limit of the silica transmission window in the mid-infrared (IR).