【正文】 a large number of photons was used to create the desired beam pro?le. Second, the vertical ink layer was modeled as an in?nite absorber extending from the skin surface to the base of the dermis with a uniform thickness of 100 m. The experimentally measured absorption coef?cient for the ink, was 3500 cm. Even though histologic analysis of the welds showed variable staining of the tissue with a lateral thickness varying from 40 to 100 m, since the ink layer thickness was much greater than the probability that a photon could cross the ink layer was negligible, and the assumption that was in?nite is reasonable. Third, the skin was modeled as a single dermal tissue layer with the assumption that the epidermis and subcutaneous tissue have optical properties similar to that of the dermis. Finally, even though the optical properties of tissue are known to be temperaturedependent, with the dermal scattering coef?cient initially increasing with temperature for temperatures less than 60 C then decreasing sharply at higher temperatures and the dermal absorption coef?cient decreasing with increasing temperature , the optical properties in this model were assumed to be static. This assumption, which avoided a plete opticalthermal model, will result in a slight underestimation of the penetration depth of the photons in the dermis. The optical properties of guinea pig skin at a wavelength of have not been well characterized. The optical properties for human, pig, and rat dermis were therefore. piled from several sources. The optical properties used in the Monte Carlo simulations are listed in Table II. Note that in the experimental irradiations, the irradiance was held constant at 127 . For the simulated irradiations, the mean irradiance over the fullwidth, halfmaximum of each beam was constant (10 photons per 1mmdiameter area). The grid element size in the tissue was ?xed at 100 m, and the dimensions of the tissue (length width depth) were cm cm cm, respectively. The tissue thickness was, in part, chosen based on the knowledge that human skin may be thicker than guinea pig skin, ranging in thickness from 1 to 4 mm. Simulations were run on a Pentium 133 MHz PC puter (Micron, Nampa, ID)running Microsoft Windows 95 (Microsoft, Redmond, WA)III. RESULTSA. ExperimentsHistologic analysis showed that only shallow welds were achieved using a 1mmdiameter laser irradiation area. Thermal denaturation was observed only to a depth of 570100 (.,n=7) or 30% of the average dermal thickness of 1900200 , see Table III. Thermal denaturation lateral to the incision was limited to near the tissue surface. An image of a weld created with a 1mmdiameter spot is shown in.When the laser spot diameter was increased to 2 mm, thermal denaturation was observed down to the middle layers of the dermis, as show. The thermal denaturation extended to an average depth of (n=7)(p) or 50% of the dermal thickness. This depth was signi?cantly greater than achieved with a 1mmdiameter spot Signi?cantly more lateral thermal denaturation was also measured at the surface of the skin, m, than for the 1mmdiameter spot.Increasing the spot diameter to 4 mm resulted in welds with an average depth of (n=7) , or 80% of the dermal thickness。 Laser Technology, 1999: 411 418.17 A. C. Hadenfeldt, K. Sayood. Compression of Colorm apped Images. IEEET ransactions on Geoscience and Remote Sensing 1994, 32(3): 534541.附錄A 英文原文Laser Tissue Welding: Laser Spot Size and Beam Pro?le StudiesAbstract：This paper evaluates the effect of laser spot diameter and beam pro?le on the shape of the thermal denaturation zone produced during laser tissue welding. 2cmlong fullthickness incisions were made on the epilated backs of guinea pigs in vivo. India ink was used as an absorber and clamps were used to appose the incision edges. Welding was performed using continuouswave , Nd:YAG laser radiation scanned over the incisions to produce 100ms pulses. Laser spot diameters of 1, 2, 4, and 6 mm were studied, with powers of 1, 4, 16, and 36 W, respectively. The irradiance remained constant at 127 Monte Carlo simulations were also conducted to examine .the effect of laser spot size and beam pro?le on the distribution of photons absorbed in the tissue. The laser spot diameter was varied from 1 to 6 mm. Gaussian, ?attop, dual Gaussian, and dual ?attop beam pro?les were studied. The experimental results showed that 1, 2, 4, and 6mmdiameter spots produced thermal denaturation to an average depth of 570, 970, 1470, and 1900 m, respectively. Monte Carlo simulations demonstrated that the most uniform distribution of photon absorption is achieved using large diameter dual ?attop beams. Index Terms— Denaturation, laser biomedical applications, laser materialsprocessing applications, laser welding, Monte Carlo methods, optical propagation.MATERIALS AND METHODSA. ExperimentsIn vivo welding of skin incisions was performed at constant irradiance to investigate the effect of various laser spot sizes (1, 2, 4, and 6mmdiameter FWHM) on the extent of thermal denaturation at the weld site. Adult female albino guinea pigs (Hartley, age 7–8 weeks, weight 400–500 grams) were shaved then epilated with a chemical depilator (Nair,CarterWallace, Inc., New York, NY). Each guinea pig was anesthetized with atropine ( mg/kg), ketamine (30 mg/kg), and xylazine (2 mg/kg) administered by intraperitoneal injection. 1% lidocaine with 1:100000 epinephrine was used as a local anesthetic at each incision site. 2cmlong, fullthickness incisions were made parallel to the spine with a scalpel. Four incisions were made on the back of each guinea pig. Approximately 2–5 l of India ink (black India Rapidograph ink, 3080F, 100nm particle diameter, KohINoor, Bloomsbury, NJ) were applied to the wound edges with a micropipette. The animal was then placed prone on a translation stage, in preparation for surgery. Clamps were used to temporarily appos