The role of skin optics in planning proper dosimetry for radiant energy delivered by lasers and conventional light sources is presented. The optical properties of the epidermis, dermis, and cutaneous blood are summarized. The ability of laser pulses at 577-nm wavelength to penetrate into and around a large blood vessel is studied using Monte Carlo simulations. The variation in laser penetration for variable beam diameters and variable vessel depths in presented. The distinction between TOTAL PULSE ENERGY versus PULSE ENERGY DENSITY is illustrated. The topic of this paper is especially pertinent to laser therapy for portwine stain lesions.

As the temperature of heated tissues approach 100 degree(s)C the pathological results of laser irradiation become dominated by the effects of phase changes in tissue water. The tissue effects include tissue desication and, as the temperature passes 100 degree(s)C, steam vacuole formation with expansion and rupture of the vacuoles producing tissue defects without loss of dry tissue mass, the so-called 'popcorn effect'. More rapid rates of steam formation result in explosive rupture of the vacuoles with expulsion of tissue fragments producing ablation, a loss of dry tissue mass. Water-dominated photothermal tissue effects are dependent on (1) diffusion of water vapor in tissues at temperatures below 100 degree(s)C, (2) rate of steam formation over 100 degree(s)C, (3) the mechanical properties of the heated tissues over time and (4) the anatomy of the 'native' target tissue.

The purpose of this study is to determine whether the extent of injury induced in blood vessels can be increased by : (a) increasing the number of sites per unit irradiation area, and (b) modifying the irradiation sequence, without compromising selectivity and specificity. Irradiation parameters comprising a wavelength of 585 nm, a pulse duration of 360 microsecond(s) , a spotsize of 3-5 mm diameter, and an energy density range of 7.0-7.5 cm-2 is applied in vivo on an albino pig. The results demonstrated that up to one third overlap of irradiated sites is tolerated without causing irreversible alteration in the epidermis and dermis. Injury remains confined predominantly to vascular tissues, and increases in severity as the sites become closer. Besides site density, the degree of injury also depends on the location of the site (center, boundary, or corner) within the irradiated matrix. These observations concur with inferences from surface temperature measurements made on an in vitro model. Another method for increasing injury is to irradiate in small clusters rather than point by point along a line.

Kinetic models of thermal damage in tissues can be used to describe histologic end points obtained with laser irradiation. In this study, thermographic measurements of skin surface temperature distributions during laser impingement were used to derive a temperature history for the lesion site. Lesions were evaluated at 48 h after laser irradiation to determine the radius of purpura formation. The temperature histories at the maximum radius of purpura formation (threshold temperatures) were analyzed and plotted on Arrhenius axes to estimate rate coefficients for the process. As expected, transient in vivo thermal history data yielded a noisy Arrhenius plot; however, estimates of the appropriate rate coefficients for purpura formation in vivo could be made.

Quantitative histologic markers of thermal damage in collagen include changes of intensity and color shifts of birefringent images and hyalinization of collagen fibers using transmission polarizing microscopy (TPM) and light microscopy (LM). These changes are seen in routinely prepared paraffin histologic sections stained with dyes readily available in most pathology and histology laboratories. The quantitative histologic markers of thermal damage have been used to map extent of thermal injury and promise to be useful for investigations of the mechanisms of photothermal laser-tissue interactions.

While both wavelength and pulse duration are of equal importance in ensuring selective and specific localization of injury to vascular tissues, it is increasingly apparent that pulse duration is the more dominant factor in determining clearance of hyperpigmented skin. This paper examines how different pulse durations stimulated different injury mechanisms; and consequently explains how effective elimination of vascular and pigmentary abnormalities involve vastly varying physical processes that are pulse duration dependent.

Selective damage of epidermal pigment cells induced by 504 nm pulsed dye laser at different pulse durations and fluence on black pig skin was examined electron microscopically. Epidermal melanosomes were satisfactorily disrupted at shorter pulse duration (100 ns). Epidermal blister formation and necrosis were seen at 2 days postirradiation, and reepithelization was evident at 7 days postirradiation in all specimens. Repigmentation was evident 21 to 56 days after irradiation. Histological pigmentary incontinence was evident at 2 days and persisted until 56 days postirradiation. This phenomenon was observed more frequently in skin exposed to longer pulse duration and at low fluences. Optimal parameters required to induce epidermal melanosome disruption using the 504 nm pulsed dye laser will be discussed.

Skin cancers are most common cancers in human populations, with more than 550,000 new cases annually in the United States, representing at least 30% of annual primary cancer diagnosed. It has been well recognized that solar ultraviolet radiation is the predominant causal factor in cutaneous carcinogenesis in humans. The risk degree of solar ultraviolet radiation in terms of inducing skin cancers in humans varies among the population. Some of factors, such as an individual's skin type, are beyond one's control. But many of others are manageable. Among them are outdoor activity patterns and all factors related including spectrum of the ultraviolet radiation, intensity of the ultraviolet radiation and total exposure time. This paper will discuss the factors affecting the risk degree of solar ultraviolet radiation-induced skin cancers in humans and present a novel method and sensing device in order to help in preventing such cancers in humans.

The justifaction of method of the laser PUVA (LPUVA) therapy, the description of an UVA therapeutic system, the preliminary results of using the nitrogen gas laser as an UVA source for LPUVA chamber and in some other fields of application in dermatology are given.

Over the last seven years, I and several co-investigators have studied the vascular welding potential of the milliwatt CO2 laser. It has become clear that there are definite limitations to this method of vascular repair which has hindered its advancement into the clinical arena. The thrust of this review is to highlight these limitations and thereby clarify what future direction might be considered.

Over the last seven years, I and several co-investigators have studied the vascular welding potential of the milliwatt CO2 laser. It has become clear that there are definite limitations to this method of vascular repair which has hindered its advancement into the clinical arena. The thrust of this review is to highlight these limitations and thereby clarify what future direction might be considered.

Tissue fusion by laser energy is an intriguing and very promising new applications for laser technology. In comparison to using high laser energy to ablate tissue as in the angioplasty application, laser tissue fusion is possible in any soft tissue by delivering appropriate low levels of energy to the opposed tissue surfaces. This technology is particularly appealing for vascular applications in making sutureless blood vessel anastomosisand for securing the endpoints of endarterectomies and dissection planes. Although there have been limited evaluations of this technology, the preliminary experimental and clinical data is very promising for continued development and application. Vascular tissue fusion or welding by lasers is performed by directing a low energy beam at the opposed edges of the repair. The energy is applied by moving the beam back and forth along the fusion line or, in certain cases, by delivering the energy in "spot" applications. Vessel sealing is apparent in the majority of fusions to the trained eye, as is nonunion caused by inadequate energy delivery, or tissue coagulation or vaporization from excessive energy exposure. Laser repairs can be fashioned in time intervals comparable to or slightly longer than those required for suture repairs. Precision of tissue apposition at the time of fusion is a critical parameter which affects the rate of healing and tensile strength of tissue welds. A gap between the vessel edges or blood at the interface compromises weld strength.

This study investigated the use of a computerized 1 .3 micron Nd:YAG laser to seal approximated wound edges in pig skin. The medical laser system used was the DLS Type 1 , 1 .32 micron Nd:YAG laser (Laser Surgery Software, Inc.). The purpose of this study was to evaluate the effectiveness of laser assisted skin closure using the DLS YAG laser in a large animal model. Effectiveness was judged on the basis of wound dehiscence, infection, unusual healing result and consistency of results. Comparative cosmetic result was also evaluated. In this study, the DLS YAG laser was used to close scalpel-induced, full-thickness wounds. The pig model was chosen for its many integumentary similarities to man. Controls included scalpel-induced wounds closed using suture, staple and some with norepair. After adequate anesthesia was achieved, the dorsum of Yucutan pigs (approximately 75- 100 pounds) each was clipped with animal hair clippers from the shoulder area to the hind legs. The area was then shaved with a razor blade, avoiding any inadvertent cuts or abrasions of the skin. The dorsum was divided into four rows of four parallel incisions made by a #15 scalpel blade. Full-thickness incisions, 9 cm long, were placed over the dorsum of the pigs and then closed either with one loosely approximating Prolene" suture (the "no repair' group), multiple interrupted 6-0 nylon sutures, staples or laser. The experimental tissue sealing group consisted of 1 69 laser assisted closures on 1 3 pigs. Sutured control wounds were closed with 6-0 nylon, full thickness, simple, interrupted sutures. Eight sutures were placed 1 cm apart along the 9 cm incision. Stapled control wounds were approximated using two evenly spaced 3-0 VicryP' sub-dermal sutures and the dermis closed using Proximate' skin staples. Eight staples were placed 1 cm apart along the 9 cm incision. The no-repair incisions were grossly approximated using a single 2-0 Prolene full thickness, simple, interrupted suture located at the center of the 9 cm incision. Experimental wounds were approximated using two evenly spaced subdermal 3.0 Vicryl' sutures and the dermis closed by laser sealing using the DLS YAG laser. Wounds were examined daily for the first seven days and followed for up to 20 months postoperatively. To facilitate wound edge approximation, surgical tape that is relatively transparent to 1.3 micron irradiation was used to hold the wound edges approximated while laser application occurred. Surgical tape was also applied to the "no-repair" suture and staple closures at the end of each procedure.

A simple thermodynamic approach to tissue 'welding' was studied. Fresh bovine tendon (67% type I collagen) was sectioned into disk shaped pieces, pairs of which were inserted between bowed glass coverslips and wrapped in aluminum foil. The packets were heated in a waterbath according to two protocols. In group I, packets were tested for four minutes at temperatures between 55-65 degree(s)C, in 1 degree(s)C intervals. In group II, the packets were kept at 62 degree(s)C for 4 minutes while the rate of cooling was altered. The force necessary to separate the tendon disks was then measured. The optimal temperature for tissue bonding (group I) was 62 degree(s)C (598 gm/in2). Stress values below 250 gm/in2 could be achieved without heat application and were considered non-welds. Group II showed that the faster the sample cools, the stronger the bond. Several conclusions can be postulated. The narrow temperature region necessary for tissue 'welding' strongly suggests that melting of type I collagen fibrils is involved. Bonding presumably occurs at 62 degree(s)C by allowing (alpha) -strands from the collagen super-helix molecule to form new, random connections. Group II results suggest that trans-incisional reannealing of unraveled helices does not play a role in tissue bonding. Rapid cooling allows less time for extended helix reformation; same-side a-helix reannealing may inhibit effective welds by reducing sites for trans-incisional visco-elastic bonding. Although the exact nature and optimization of thermal tissue 'welds' remains unclear, the behavior of collagen appears to play a central role.

Clinical application of laser vascular anastomosis in inhibited by a lack of understanding of its mechanism. Whether tissue fusion results from covalent or non-covalent bonding of collagen and other structural proteins is unknown. We compared electrophoretic mobility of collagen in laser treated and untreated specimens of rat tail tendon (>90% type I collagen) and rabbit aorta. Welding was performed, using tissue shrinkage as the clinical endpoint, using the 808 nm diode laser (power density 14 watts/cm2) and topical indocyanine green dye (max absorption 805 nm). Collagen was extracted with 8 M urea (denaturing), 0.5 M acetic acid (non-denaturing) and acetic acid/pepsin (cleaves non- helical protein). Mobility patterns on gel electrophoresis (SDS-PAGE) after urea or acetic acid extraction were identical in the lasered and control tendon and vessel (confirmed by optical densitometry), revealing no evidence of formation of novel covalent bonds. Alpha and beta band intensity was diminished in pepsin incubated lasered specimens compared with controls (optical density ratio 0.00 +/- 9 tendon, 0.65 +/- 0.12 aorta), indicating the presence of denatured collagen. With the laser parameters used, collagen is denatured without formation of covalent bonds, suggesting that non-covalent interaction between denatured collagen molecules may be responsible for the weld. Based on this mechanism, welding parameters can be chosen which produce collagen denaturation without cell death.

In previous investigations it was found that prostaglanding E1 (PGE1) and Bradiquinine (B), liberated in the inflammatory process, produced a significant increment on the Plasma fibrition Level (PFL), indicative of inflammatory process. The mentioned increment was completely abolished by the irradiation with HeNe laser in the area of infection of the mentioned substances. In the current investigation it was studied the effect of HeNe laser radiation on the P.F.L. of rats injected with another substance related with the inflammatory process and tissular injury: Thromboxane (Tx). It is though that the signal to increase P.F.L. is though an adrenal and an extra adrenal pathways. To study it we injected normal and medullectomized animals and both showed marked increment of P.F.L. Then we repeated the experiment but followed immediately by HeNe laser radiation and we noted a complete blockage of the P.F.L. increment in both groups which suggest that the effect is extra-adrenal. All substances were injected I.M. once daily X 3 days. Immediately after injection the area was irradiated with HeNe laser, 1.5 J total energy. In the normal, non injected non irradiated animals the P.F.L. reached 210.3 + 1.15 mg%. The single injection of Tx did not modify the P.F.L. compared with the previous group. The HeNe irradiation alone did not modify the P.F.L. in the animals injected with Tx only. The animals injected with PGE1+B showed a marked increment of P.F.L. to 337.6 + 14.5 mg%; the HeNe laser radiation completely abolished the increment (231 + 22.3 mg%). But in the animals injected with PGE1+B+Tx, the P.F.L. reached even larger values: 375.2 + 15.3 mg%. The HeNe laser radiation produced a partial blockage in P.F.L. increment (270.3 +/- 13.4 mg%). Showing a significant difference (p < 0.001) compared with normal rats or with rats injected with PGE1+B+Tx without radiation. In conclusion Tx potentiate the effect of PGE+B on the P.F.L. The HeNe laser blocks completely the interaction of PGE1+B on the P.F.L. but only partially the interaction PGE(subscript 1+B+Tx.

We report the clinical observation of the effect on 53 surgical cases with Helium-Neon laser local irradiation therapy. Of those cases 15 were suffered from chronic and acute infection, 5 were traumatic, 15 of hemangioma had been treated by solid CO freezing therapy and sclerosing injection previously. 18 cases were received incisional irradiation postoperatively. All showed remarkable results. There were no infection, and the healing process was shortened by Helium-Neon laser local irradiation for 2-3 days. The results showed that the curative rate was 88.68%, the marked effective rate was 9.43%, and the fair was 1.89$. We emphasize that because of the characteristic of anatomical physiology and histology in children. so the result in children is better than in adults. Thus, we strongly recommend using Helium-Laser local irradiation in surgical pediatric field. It is reliable, safe, painless, convenient, economic, and no side effects at all.

The effect of 632 nm and 360 nm light on NIH fibroblast cells was examined. Mitosis counts of irradiated cells at various energy doses were taken. Scanning Electron Micrographs of these cells enriched and nonenriched with porphyrins were studied. It is suggested that low-level laser therapy (LLLT) in the visible and in the far infrared region is due to cell respiration stimulation by either the endogenous porphyrins in the cell, or by the cytochromes.

We used the Monte Carlo method to evaluate UV-A radiation penetration through human skin (epidermis and dermis). Calculations were performed for multilayered medium, refractive indices mismatch on boundaries of the sample and finite width of incident beam. The fluence rate distributions of UV-A radiation (wavelength 337 nm) within tissue are presented. In order to optimize the laser PUVA treatment of psoriasis were have developed the mathematical model of the dynamics of cell processed within epidermis. The task of optimal control for PUVA treatment is formulated

Laser tissue soldering techniques allow reinforcement of sutured repairs and may be a useful adjunct in reducing anastomotic bleeding. Initial results of our clinical trial with laser solder reinforcement are reported. Twenty-one patients underwent standard polytetraflouroethylene (PTFE) graft arteriovenous fistula (AVF) creation. In 11 patients thrombin soaked gelatin sponges were placed around the anastomoses and in 10 laser reinforcement was accomplished. Three lasers were used: KTP (532 nm, power density 4.1 W/cm2, spot size .5 cm), CO2 (10,600 nm, power density 14.1 W/cm2, spot size .3 cm), and diode (805 nm, power density 9.6 W/cm2, spot size .2 cm). The solder consisting of 0.4 cc hyaluronate, 0.2 cc albumin, and 3 drops of the appropriate laser enhancing dye (fluorescein for KTP, indocyanine green for the diode, water for CO2) was applied to the target tissues prior to laser exposure. The laser was directed over the tissue in a sweeping motion until the solder had desiccated. Several lessons are evident from our experience. First, over exposure to the laser results in solder charring and ineffective reinforcement. Greater laser exposure with less undesired solder damage is achieved if dye is added to the solder. Second, the solder should be spread over the target in a thin layer to facilitate controlled desiccation and tissue bonding. Additional layers can be applied as required. Although improvements in the solder and laser technique are required, these early results demonstrate a potential clinical use for laser soldered reinforcement during vascular anastomoses.

Stress-strain profiles of welded tissue provide additional means of analysing and comparing laser soldering to alternative anastoinosing techniques. Three groups were created in a rabbit model: (1) nonincised control aortic tissue, (2) longitudinal aortotomies repaired with a 808 nm diodelaser (power density 4.8 watts/cm2) after topical application of fibrinogen mixed with indocyanine green dye (peak absorption 805 nm) , and (3) aortotomies repaired with 6-0 polypropylene suture in a running fashion. The rabbits were sacrificed on 0,l,7,and 28 postoperative days and the fresh aortic specimens were strained until disruption in order to produce a stress-strain profile graph. No significant differences were noted between sutured and bonded aorta at any time interval. Nonincised (which served as a control) aortic tissuewithstood significantly higher stress (p<.05) than both sutured and bonded groups at the time of creation. By seven days after operation, no significant differences were noted between any of the three groups. The only significant difference in modulus (stretchability) identified the sutured aorta to be more rigid than the nonincised group (p<.05). Both sutured and laser bonded anastoinoses are weaker than control aorta initially; however, after an early critical period, both treatments achieve the strength of control aorta. By one nionth post-operatively, sutured anastomoses have the disadvantage of creating a less distensible anastomosis.