Egészségügy | Bőrgyógyászat » Sabotinov-Stoykova - Copper-bromide Laser System for Treatment of Dermatological Malformations

Copper-bromide laser system for treatment of dermatological malformations Ognian Sabotinov*, Elena Stoykova Central Laboratory for Optical Storage and Processing of Information, Acad. G Bonchev Str, Bl101, PO Box 95, 1113 Sofia, Bulgaria ABSTRACT The work presents a cosmetic CuBr laser system for treatment of various cutaneous vascular malformations (operating wavelength 578.2 nm, output power 3 W) and pigmented lesions (operating wavelength 511 nm, output power 6 W) Simultaneous emission at both wavelengths (output power 9 W) can be used for precise ablation of cutaneous lesions. The system is provided with a fiberoptic delivery system and a hand-piece, which forms a convergent beam with a diameter of the laser spot 0.4 mm in the focal plane A built-in CPU sets and controls all operational modes by using an intracavity polychromatic acousto-optic modulator or a mechanical shutter. The laser irradiation can be emitted within a preset temporal interval with variable duration from 15 to

950 ms. The controllable interval for thermal relaxation of the irradiated tissue can be varied from 20 to 1000 ms. The controllable radiant exposures vary from 5 to 100 J/cm2 for the yellow light and from 10 to 100 J/cm2 for the green light. Monte-Carlo modeling has been used to compare the volumetric energy deposition at 532, 578.2 and 585 nm The model simulates photon migration for the case of a portwine stain birthmark within a skin layer with embedded cylindrical small blood vessels of varying size, which are randomly distributed at different depths. Optical properties (absorption coefficient, scattering coefficient, anisotropy factor, and index of refraction) of epidermal tissue, dermis and blood were chosen from the literature. Keywords: Copper-bromide lasers, Monte-Carlo simulation, treatment of vascular malformations. I. INTRODUCTION During the recent years lasers are successfully used to treat blood vessel growths, portwine stain birthmarks, malformations of skin blood

vessels known as hemangiomas, enlarged blood vessels on the face known as telangiectasia, and the “red nose” syndrome that occurs as a result of acne rosacea or nasal surgery1. The treatment of vascular malformations relies on the strong absorption of laser light by oxyhemoglobin that leads to selective injury of the ecstatic blood vessels in the dermis without damaging the adjacent tissue. Actual literature values give absorption peaks for oxyhemoglobin at 420 nm, 540 nm, and 577 nm and deoxyhemoglobin peaks at 430 nm and 555 nm. The peak at 577 nm makes especially appropriate use of Copper-bromide lasers which emit at 510.6 and 5782 nm and which have already been shown to be effective light sources in dermatology and photodynamic therapy1. This work presents a cosmetic CuBr laser system2 with a possibility for fast optical shuttering and wavelength selection. To evaluate the volumetric energy deposition inside the tissue, we performed a Monte-Carlo simulation of photon migration

within a two-layered model of skin with embedded blood vessels for the wavelength of 578.2 nm The volumetric energy deposition has been compared with energy delivery at 532 and 585 nm, which are also frequently used wavelengths for treatment of the cutaneous vascular malformations. Optical properties (absorption coefficient, scattering coefficient, anisotropy factor, and index of refraction) of epidermal tissue, dermis and blood were chosen from the literature3. The simulation was performed in a 3D case considering the blood vessels as parallel to the tissue surface and located at different depths. * aesthetic lasers@issp.basbg II. CuBr LASER SYSTEM The developed CuBr cosmetic laser system can operate at 510.6 nm with output power of 6 W and at 5782 nm with output power of 9 W. The emission at the first wavelength is suitable for the treatment of various pigmented lesions whereas the emission at the second wavelength, which is close to one of the main absorption peaks of the

oxyhemoglobin, can be used to destroy cutaneous vascular malformations by selective phototermolysis. Simultaneous emission at both wavelengths (output power 9 W) permits precise ablation of cutaneous lesions. The system is provided with a fiberoptic delivery system and a hand-piece, which forms a convergent beam with a diameter of the laser spot 0.4 mm in the focal plane A built-in CPU sets and controls all operational modes by using an intracavity polychromatic acousto-optic modulator (PCAOM) or a mechanical shutter. The PCAOM is inserted in a low-intensity section of a classical confocal negative unstable resonator2,3. The PCAOM controls the optical seeding that initiates the laser emission. Depending on the electric RF signal that feeds the PCAOM, a feedback can be created for each of the spectral lines 510.6 nm and 5782 nm separately, as well as for both of them simultaneously This permits spectrally selective control of laser generation. This makes it possible to stop and to

restart the laser generation at the desired wavelength at a speed restricted only by the time required for the acoustic wave to cross the optical beam diameter. More than that, by controllable interruption of the RF power, a fast optical shutter for the laser generation can be created. Thus, laser irradiation can be emitted within a preset temporal interval with variable duration from 15 to 950 ms. To check the beam quality, we measured intensity distribution within the emitted laser beam for the different regimes of operation in the focal plane of a 1 m focal-length lens with a CCD camera Spiricon LBA 300 at the same pumping conditions. The spatial distributions of the output laser beam showed neither power losses nor worsening of the beam quality in comparison with the classical scheme without the modulator. In addition, PCAOM insertion inside the cavity resulted in a 99% linearly polarized laser output. The angle of divergence calculated from the measurements is of the order of

0.11-012 mrad The controllable interval for thermal relaxation of the irradiated tissue can be varied from 20 to 1000 ms. The controllable radiant exposures vary from 5 to 100 J/cm2 for the yellow light and from 10 to 100 J/cm2 for the green light. III. SIMULATION To evaluate the volumetric energy deposition inside the blood vessels at different wavelengths, we performed a MonteCarlo simulation of photon migration within a two-layered model of skin with embedded blood vessels. Efficiency of energy deposition in skin tissue with embedded one or more blood vessels has been addressed in many studies3,5-7. In Ref. 3 this efficiency is studied for a single vessel assuming Beer-Lambert propagation inside it; the influence of the adjacent vessels on the energy delivery into the targeted vessel is introduced by increase of the mean dermis absorption. In Ref.5 and 6 the cases of a single vessel and of a 2D random distribution of many vessels with the same radius are modeled using

delta-scattering technique. In Ref7 a 3D tissue sample model is constructed on the basis of many histological slices. Table 1 Coefficient Wavelength, nm Epidermis Dermis Blood 532 21 2.2 266 µa, cm-1 577 19 2.2 354 585 18 2.4 191 532 530 156 473 µs, cm-1 577 475 210 468 585 470 205 467 532 0.77 0.77 0.995 g 577 0.787 0.787 0.995 585 0.79 0.79 0.995 We modeled propagation of a collimated circular laser beam that was normal to the tissue surface with radius 0.3 mm and uniform distribution of photon density within the beam cross-section. The Z-axis entered the tissue at the beam center; X and Y axes were on the tissue surface. As in the most of simulations, the thickness of the epidermis in our model was accepted equal to 60 µm while the dermis was modeled as a homogeneous semi-infinite medium. The radii of the blood vessels varied from 20 to 100 µm. Optical properties of skin constituents – absorption coefficient, µa, scattering coefficient, µs, and anisotropy factor,

g, - were taken from the literature (Table 1) for different wavelengths. We accepted that the values of µa, µs, and g at 578.2 nm were practically the same as at 577 nm A Henyey-Greenstein scattering phase function and refractive index of 1.37 were assumed throughout all types of tissue The blood vessels were modeled as infinite cylinders parallel to the Y-axis, which were randomly distributed at different depths in the X-Z plane. Photon migration was modeled in a 3D case using a variance-reduction Monte-Carlo code8 and delta-scattering technique6 due to the fact that no reflections occur at tissue interfaces except at the entrance of the laser beam. 0.04 200 Epidermis 160 0.02 578.2 nm X, cm Fig.1 Monte-Carlo simulation of the spatial distribution of the absorbed energy in the X-Z plane in the dermal layer with three embedded blood vessels. The blood vessels are modeled as infinite cylinders oriented along the Y axis and located at different depths with centers on the beam

axis. The number of the launched photon packets is 1000000. For better visualization of the obtained distributions in the region of the dermis, the highest level in the map is chosen to be equal to 40 % of the mean absorption within the epidermis. 120 0.00 80 Blood vessels -0.02 Dermis -0.04 0.00 0.02 0.04 0.06 0.08 40 0.10 0 Depth, cm 0.08 0.07 Depth, cm 0.06 578.2 nm Dermis Blood vessels 0.05 Fig.2 Monte-Carlo simulation of the spatial distribution of the absorbed energy in the X-Z plane. The number of the launched photon packets is 1000000. For better visualization of the obtained distributions in the region of the dermis, the highest level in the map is chosen to be equal to 15 % of the mean absorption within the epidermis. 0.04 0.03 Cluster of vessels The results of simulation are presented in Figs.13 Figure 1 shows energy deposition in the X-Z plane for three blood vessels with radius of 30 0.02 µm located at 0.02, 003 and 005 cm under the tissue surface on

the beam axis. As it should be Epidermis 0.01 expected, the epidermis absorbs a large portion of the launched photons. Only for the vessel at 0.02 cm the fraction of absorbed energy is higher 0.00 -0.04 -003 -002 -001 000 001 002 003 004 than in the epidermis. Obviously, the decrease in X, cm energy deposition in the deeper located vessels is 400 350 300 250 200 150 100 50 0 due not only to the exponential attenuation of the fluence with depth but to the screening caused by the vessel that is closest to the surface. Figure 2 depicts energy deposition for many blood vessels that are randomly distributed at different depths. Some of the vessels form clusters As it can be seen, for vessels that are located no deeper than 0.025 cm, the fraction of the absorbed energy is higher or comparable to that in the epidermal layer Figure 3 compares energy deposition for three wavelengths for vessels with radius of 50 µm located at 0.03, 006 and 008 cm below the surface. The best result is

obtained for irradiation at 5782 nm, especially at the greatest depth of 008 cm However, due to the high absorption of blood, energy deposition in larger vessels as those in Fig.3 is non-uniform and for this reason less effective compared to smaller vessels in Fig.1 and 2 For large vessels only the outer layer of the vessel is injured. It can be accepted, that deposition is uniform for vessels with radius less than 30 µm This effect is most pronounced at 578.2 nm The screening caused by the upper located vessels is also stronger for this wavelength 0.02 0.02 532 nm 0.02 578.2 nm 420.00 585 nm 360.00 X, cm 300.00 0.00 0.00 240.00 0.00 180.00 120.00 60.00 -0.02 0.01 0.02 0.03 0.04 -0.02 0.01 0.02 0.02 0.03 0.04 -0.02 0.01 0.02 0.02 0.03 0.04 0.02 0.00 45.00 40.00 X, cm 35.00 30.00 0.00 0.00 25.00 0.00 20.00 15.00 10.00 5.00 -0.02 0.04 0.05 0.06 -0.02 0.04 0.02 0.05 -0.02 0.04 0.06 0.02 0.05 0.00 0.06 0.02 12.50 X, cm 10.00 0.00 0.00

7.50 0.00 5.00 2.50 -0.02 0.08 0.09 Depth, cm 0.10 -0.02 0.08 0.09 Depth, cm 0.10 -0.02 0.00 0.08 0.09 0.10 Depth, cm Fig.3 Monte-Carlo simulation of the spatial distribution of the absorbed energy in the X-Z plane in the dermal layer with embedded blood vessels. The blood vessels are modeled as infinite cylinders oriented along the Y axis and located at different depths with centers on the beam axis. Beam radius is 03 mm; the number of launched photon packets is 1000000 The contour maps correspond to irradiation at 532 nm in the left column, to 578.2 nm in the middle column and to 585 nm in the right column CONCLUSION In conclusion, we described a Copper-Bromide system for medical applications with effective way for optical shuttering and wavelength selection which permits to control the output characteristics of the emission. We obtained that the energy deposition is most effective for blood vessels with radius less than 30 µm which are located up to 0.025 cm

in depth. For the larger vessels photons are stopped in the outer layer of the vessel The vessels located at greater depth are screened by the vessels above them. Comparison of energy delivery for irradiation at 5782 nm with irradiation at 532 and 585 nm showed that the wavelength of 578.2 nm is most beneficial at targeting deeply located vessels due to the high absorption peak of blood at 577 nm. ACKNOWLEDGMENT The authors would like to thank the National Science Fund to the Ministry of Education and Science of Bulgaria, Project Ph1313. REFERENCES 1. L. Y Chong, H Chan, Handbook of Dermatology & Venereology Hong Kong: Social Hygiene Service, pp 169-183, 1997. 2. O. Sabotinov, N Minkovski, E Stoykova, R Salimbeni, “Fast optical shuttering and wavelength selection in Copper vapor lasers and Copper bromide lasers by intracavity polychromatic acousto-optic modulation”, to be printed in IEEE Journal of Quantum Electronics. 3. W. Verkruysse, JW Pickering, JF Beek, M Keijzer,

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