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Background. The diagnostic ability of algorithms developed for the Multispectral Digital Colposcope (MDC) is highly dependent on the quality of the image. The field of objective medical image quality analysis has great potential but has not been well exploited. Various researchers have reported different measures of image quality but with an existence of a reference image. The quality of an image can be attributed to several sources of errors, a few of which would be inclusion of presence of extraneous components, improper illumination, or an image out of focus. This can be due to motion artifact or the region of interest out of the focal plane. Methods. With spectroscopic measurements, assessment of data quality has been used by our group in the past to avoid hardware errors at the time of acquisition. We are currently developing algorithms that will help identify hardware and acquisition errors to the clinician in under a few seconds. Results. Minimizing these errors not only provides quality images for a diagnostic algorithm, but reduces the necessity for complex and time intensive post-processing software for enhancing the images. Conclusion. We propose a no reference image quality system specifically designed for MDC that can be modified to similar spectroscopic imaging applications.

Background. Devices using fluorescence spectroscopy to differentiate high grade squamous intraepithelial lesions from normal tissue in the cervix have shown some diagnostic efficacy. Measurements from these devices produce large amounts of complex, multi-factored data. The purpose of this study is to isolate the effects of the particular care providers and equipment operators who are involved in taking measurements. Methods. Data from spectroscopic measurements of the Phase II study of 850 patients with abnormal Papancicolau smears were used. The data were subject to a Principal Components Analysis and to MANOVA to control for variables that are known to affect outcomes. Results. The analysis showed significant provider effects from both devices and significant operator effects from one device. Conclusion. We will repeat a similar analysis on data from a screening trial, on the combined diagnostic and screening study, and on the reflectance data. In the future, we hope to be able to design devices that address provider and operator effects.

Background and Objectives Two wavelengths, 585 and 595 nm, are currently common options for treating vascular malformations such as port-wine stains (PWS). Controversy exists as to which wavelength induces greater photothermal damage to the blood vessels and subsequent resolution of the malformations. Study Design/Materials and Methods We irradiated normal, human skin in vivo at 585 and 595 nm wavelengths using fluences of 10–30 J/cm2 with a 1.5 millisecond laser pulse. The level of purpura, total vascular damage, maximum coagulation depth (MCD), and perivascular damage were quantified by gross observation and histological analysis. Results Results demonstrated that 585 nm light caused greater purpura, vascular damage, maximum coagulation depth, and perivascular damage than 595 nm. Purpura showed a positive correlation with total vascular damage to a certain extent beyond which the total vascular damage did not change. For equivalent purpura, 585 and 595 nm produced no statistically significant difference in vascular damage. The difference in the laser-induced vascular damage between 585 and 595 nm, although statistically significant, was no more than 50%. Conclusions The bathochromic (red) shift and formation of met-hemoglobin, which reduces the 585 nm light absorption and increases that of 595 nm compared to native oxy-hemoglobin, play a considerable role in creating more parity in vascular damage between the two wavelengths than would be expected based on their respective “native” absorption coefficients alone. Lasers Surg. Med. 36:117–123, 2005. © 2005 Wiley-Liss, Inc.

Cryogen spray cooling (CSC) reduces epidermal damage during laser treatment of various dermatoses. The goal of this study was to determine the heat removal mechanism in skin and quantify the amount in response to CSC. Thermocouples were imbedded in four model substrates with a range of thermal diffusivities, greater than three orders of magnitude in difference, to measure the temperature profiles in response to CSC and sapphire contact cooling, which removes heat completely by conduction. An algorithm solving an inverse heat conduction problem was subsequently used to quantify the amount of heat removal from the substrates using the measured temperatures. The interface thermal conductance and internal temperatures within the substrates were computed by a finite difference algorithm that solved the heat conduction equation. Results verify a marked increase in heat removal and interface thermal conductance with increasing thermal diffusivity. By estimation from the model substrate results, heat removal and interface thermal conductance values for skin were obtained. Data demonstrate that during CSC, evaporation is the dominant heat transfer mechanism in materials with higher thermal diffusivities; however, conductive cooling dominates in substrates with lower thermal diffusivities such as skin.

Background and Objective Cryogen spray cooling (CSC) is an effective method to reduce or eliminate non-specific injury to the epidermis during laser treatment of various dermatological disorders. In previous CSC investigations, fuel injectors have been used to deliver the cryogen onto the skin surface. The objective of this study was to examine cryogen atomization and heat removal characteristics of various cryogen delivery devices. Study Design/Materials and Methods Various cryogen delivery device types including fuel injectors, atomizers, and a device currently used in clinical settings were investigated. Cryogen mass was measured at the delivery device output orifice. Cryogen droplet size profiling for various cryogen delivery devices was estimated by optically imaging the droplets in flight. Heat removal for various cryogen delivery devices was estimated over a range of spraying distances by temperature measurements in an skin phantom used in conjunction with an inverse heat conduction model. Results A substantial range of mass outputs were measured for the cryogen delivery devices while heat removal varied by less than a factor of two. Droplet profiling demonstrated differences in droplet size and spray density. Conclusions Results of this study show that variation in heat removal by different cryogen delivery devices is modest despite the relatively large difference in cryogen mass output and droplet size. A non-linear relationship between heat removal by various devices and droplet size and spray density was observed. Lasers Surg. Med. 28:103–112, 2001. © 2001 Wiley-Liss, Inc.

With the development of fluorescence spectroscopy, multicenter clinical trials are becoming more common both in the academic and commercial arenas. To ensure the quality of quantitative and device independent results, standardization of the tissue spectra is essential for the comparison of data from various groups. An added concern is the potential degradation of instrumentation during a trial which may affect the instrument's ability to accurately represent the tissue spectra. Our group has recently completed a Phase II clinical trial for the detection of cervical neoplasia using two different generations of spectroscopic devices at multiple sites. Both positive and negative optical standards were used to calibrate the tissue spectra as well as aid in the diagnosis of potential instrumentation problems during the trial. We have also conducted a cross validation study of fiber optic probes, spectroscopic devices, and optical standards for the latest generation of devices. The spectroscopic data of optical standards were analyzed for both the clinical trial and cross validation studies. Results demonstrated perceptible differences in optical standards data between the two generations of spectroscopy devices in the clinical trial, as well as the cross validation study with multiple devices of the same generation. Although the spectra were unexpectedly different, tissue spectra measured with the different systems can be empirically corrected by use of the various optical standards. Device performance during the clinical trial also was a concern; however, with the use of optical calibration standards, instrumentation problems were easily identified. To eliminate the problems associated with instrumentation, we have recently developed real-time quality assurance software to assess the optical calibration standards immediately after acquisition.

Measurement quality assurance plans for optical devices should be a mandatory part of grant funding submissions and should explicitly affect scoring during review. These should include calibration strategy, standards selection strategy, performance verification plan, performance validation plan and thorough preclinical performance validation. A multispectral digital colposcope (MDC) has been designed to collect image data from patients as part of an NIH sponsored clinical trial, based on a technology assessment model. Calibration strategy, standards selection and performance verification methods are presented that may be used as a template for smaller groups or more limited studies. With the MDC, red green and blue fluorescence images are captured under ultraviolet light excitation and red and green images are captured under blue light excitation. Red, green and blue reflectance images are captured under broadband white light illumination from a metal halide lamp in three modes - ordinary reflectance, and with polarized illumination in combination with parallel and cross-polarized filtered imaging. The highly automated system was designed to collect images of the cervix prior to and following the application of acetic acid. Three systems have been built and will be operated in clinics in Vancouver, Canada, Houston, Texas and other locations in the developed and developing world including Nigeria. The system is designed with a comprehensive set of calibration and performance verification standards, based on our experience with large scale multi-center spectroscopy clinical trials and measurements are made frequently prior to and following patient measurements. Automated performance verification procedures are being designed based on measurements made during pilot studies to facilitate larger clinical trials.

Introduction. A study was designed to assess variability between different fluorescence spectroscopy devices. Measurements were made with all combinations of three devices, four probes, and thee sets of standards trays. Additionally, we made three measurements on the same day over 2 days for the same combination of device, probe, and standards tray to assess reproducibility over a day and across days. Materials and methods. The devices consisted of light sources, fiber-optics, and cameras. We measured thirteen standards and present the data from the frosted cuvette, water, and rhodamine standards. A preliminary analysis was performed with the data that were wavelength calibrated and background subtracted; however, the system has not been corrected for systematic intensity variations caused by the devices. Two analyses were performed on the rhodamine, water, and frosted cuvette standards data. The first one is based on first clustering the measurements and then looking for association between the 5 factors (device, probe, standards tray, day, measurement number) using chi-squared tests on the cross-tabulation of cluster and factor level. This showed that only device and probe were significant. We then did an analysis of variance to assess the percent variance explained by each factor that was significant from the chi-squared analysis. Results. The data were remarkably similar across the different combinations of factors. The analysis based on the clusters showed that sometimes devices alone, probes alone, but most often combinations of device and probe caused significant differences in measurements. The analysis showed that time of day, location of device, and standards trays do not vary significantly; whereas the devices and probes account for differences in measurement. We expected this type of significance using unprocessed data since the processing corrects for differences in devices. However, this analysis on raw data is useful to explore what combination of device and probe measurements should be targeted for further investigation. This experiment affirms that online quality control is necessary to obtain the best excitation–emission matrices from optical spectroscopy devices. Conclusion. The fact that the device and probe are the primary sources of variability indicates that proper correction for the transfer function of the individual devices should make the measurements essentially equivalent.

Background and Objectives Successful laser treatment of cutaneous hyper-vascular lesions requires appropriate laser irradiation parameters for selective photothermolysis of ectatic dermal blood vessels as well as appropriate cooling parameters for epidermal protection based on an individual patient basis. Using the rabbit ear as an in vivo model for dermal vasculature, we investigated the influences of laser wavelength (585 nm vs. 595 nm) and cryogen spray cooling with various spurt durations on the laser-induced thermal injury to dermal blood vessels. Wound healing response was also evaluated in 2 hours and 4 days. Study Design/Materials and Methods Flashlamp-pumped pulsed dye laser ScleroPlus™ (operated at the wavelength of 585 or 595 nm) was used for the comparison between the influences of two wavelengths (585 nm vs. 595 nm). R134-a cryogen spurts with the durations from 50 to 300 milliseconds were sprayed onto the sites to be irradiated and terminated 20 milliseconds before the onset of the laser pulses. In vivo rabbit ear was used as the model for cutaneous hyper-vascular lesions. Totally 10 New Zealand Albino white rabbits were experimented and in each rabbit ear six to seven sites were irradiated. Five animals were sacrificed 2 hours after the irradiation, and the remaining five sacrificed 4 days after the irradiation. Thermal injury to the blood vessel was assessed by hematoxylin and eosin stained histological sections and confirmed by an apoptosis assay. Results When the radiant exposures were above 10 J/cm2, 595 nm wavelength induced equivalent or more severe thermal injury to dermal blood vessels than 585 nm. Cryogen spray cooling with the spurt durations above 100 milliseconds resulted in increased depth of the most superficial thermal injury to dermal blood vessels than without cooling, indicating that superficial blood vessels were non-specifically cooled by the cryogen spurts applied at these parameters. Laser-induced thermal injury was significantly healed in the rabbit ear vasculature at 4 days post irradiation. Conclusions Given sufficient radiant exposure, 595 nm wavelength can induce equivalent or more severe vascular injury compared with 585 nm. Cryogen spray cooling with the spurt durations above 100 ms may impair the photocoagulation of superficial blood vessels. Irreversible thermal injury to blood vessel can be achieved only when the basement membrane of blood vessel wall is irreversibly damaged. Lasers Surg. Med. 37:210–218, 2005. © 2005 Wiley-Liss, Inc.

Background and Objectives Laser irradiation is the current modality for treatment of cutaneous hypervascular malformations such as port wine stains and telangiectasia. Although cryogen spray cooling (CSC) is used to protect the epidermis from non-specific laser-induced thermal damage in moderately-pigmented skin types, individuals with high melanin content are still at risk for epidermal damage using the current laser irradiation and CSC parameters. The objective of this study was to investigate the influence of the spray Weber number (1,100 or 5,100) on epidermal protection and examine vascular coagulation in response to pulsed dye laser irradiation. Study Design/Materials and Methods Normal, in vivo human skin from eight subjects of Fitzpatrick skin types I–V were precooled with either low or high Weber number cryogen sprays and subsequently irradiated with a pulsed dye laser at 595 nm. Analysis of gross purpura, morphological vascular damage, and apoptosis of the vascular walls were performed. Results Results demonstrated a high Weber number spray of 5,100 decreased the level of epidermal damage in darker and moderate pigmented individuals compared to a Weber number spray of 1,100. This study also established a positive correlation between gross purpura and the level of vessel wall apoptosis. Conclusions This study has demonstrated that CSC with a high Weber number spray can decrease nonspecific thermal damage to the epidermis in response to laser irradiation in vivo. We have also established a positive correlation between gross purpura and the level of vessel wall apoptosis. Lasers Surg. Med. © 2005 Wiley-Liss, Inc.

Indocyanine Green (ICG) is clinically used as a fluorescent dye for imaging purposes. Its rapid circulation kinetics and minimal toxicity has prompted investigation into ICG's utility as a photosentitizer for therapeutic applications. Traditionally, optically mediated tumor therapy has focused on photodynamic therapy, which employs a photochemical mechanism resulting from the absorption of low intensity CW laser light by localized photosensitizers such as Photofrin II, Benzoporphyrin Derivative (BPD), ICG. Treatment of cutaneous vascular malformations such as port-wine stains, on the other hand, is based on a photothermal mechanism resulting from the absorption of high intensity pulsed laser light by hemoglobin. In this study, we compared the effectiveness of combining photochemical and photothermal mechanisms during application of ICG in conjunction with laser irradiation with the intention that the combined approach may lead to a reduction in the threshold dose of pulsed laser light required to treat hypervascular malformations. The blood vessels in rabbit ears were used as an in vivo model for targeted vasculature. Irradiation of the ears with IR light (λ=785 nm, Δτ = 3 min, Io = 120 mW) was used to elicit photochemical damage, while photothermal damage was brought about using pulses from a ruby laser (λ=694 nm, τ = 3 ms) with different fluences. For the combined modality, photochemical damage was induced first and followed by photothermal irradiation. This modality was compared with photothermal irradiation alone. The effectiveness of each irradiation scheme was assessed using histopathological analysis. We present preliminary data that suggests that pretreatment with photodynamic therapy before photothermal coagulation results in more severe vascular damage with lower photothermal fluence levels. The results of this study provide the foundation work for further exploration of the therapeutic potentials of photochemical and photothermal effects during application of ICG in conjunction with laser irradiation.

Near-infrared wavelengths are absorbed less by epidermal melanin, and penetrate deeper into human skin dermis and blood than visible wavelengths. Therefore, laser irradiation using near-infrared wavelengths may improve the therapeutic outcome of cutaneous hyper-vascular malformations in moderately to heavily pigmented skin patients and those with large-sized blood vessels or blood vessels extending deeply into the skin. A mathematical model composed of a Monte Carlo algorithm to estimate the distribution of absorbed light, numerical solution of a bio-heat diffusion equation to calculate the transient temperature distribution, and a damage integral based on an empirical Arrhenius relationship to quantify the tissue damage was utilized to investigate the opto-thermal response of human skin to near-infrared and visible laser irradiations in conjunction with cryogen spray cooling. In addition, the thermal effects of a single continuous laser pulse and micropulse-composed laser pulse profiles were compared. Simulation results indicated that a 940 nm wavelength induces improved therapeutic outcome compared with a 585 and 595 nm wavelengths for the treatment of patients with large-sized blood vessels and moderately to heavily pigmented skin. On the other hand, a 585 nm wavelength shows the best efficacy in treating small-sized blood vessels, as characterized by the largest laser-induced blood vessel damage depth compared with 595 and 940 nm wavelengths. Dermal blood content has a considerable effect on the threshold incident dosage for epidermal damage, while the effect of blood vessel size is minimal. For the same macropulse duration and incident dosage, a micropulse-composed pulse profile results in higher peak temperature at the basal layer of skin epidermis than an ideal single continuous pulse profile.

Cryogen spray cooling (CSC) is an effective method to reduce or eliminate epidermal damage during laser treatment of various dermatoses. This study sought to determine the effects of specific cryogen properties on heat removal. Heat removal was quantified using an algorithm that solved an inverse heat conduction problem from internal temperature measurements made within a skin phantom. A nondimensional parameter, the Weber number, characterized the combined effects of droplet velocity, diameter, and surface tension. CSC experiments with laser irradiation were conducted on ex vivo human skin samples to assess the effect of Weber number on epidermal protection. An empirical relationship between heat removal and the difference in droplet temperature and the substrate, droplet velocity, and diameter was obtained. Histological sections of irradiated ex vivo human skin demonstrated that sprays with higher Weber numbers increased epidermal protection. Results indicate that the cryogen film acts as an impediment to heat transfer between the impinging droplets and the substrate. This study offers the importance of Weber number in heat removal and epidermal protection.

Background and Objectives The cochlea is the part of the inner ear that transduces sound waves into neural signals. The basilar membrane, a connective tissue sheet within the cochlea, is tonotopically tuned based on the spatial variation of its mass, stiffness, and damping. These biophysical properties are mainly defined by its constituent collagen fibers. We sought to assess the effect of laser irradiation on collagen within the basilar membrane using histological analysis. Study Design/Materials and Methods Four excised guinea pig cochleae were stained with trypan blue. From these, two were irradiated with a 600 nm pulsed dye laser and two were used as controls. Collagen organization was visualized using polarization microscopy. Results Laser irradiation reduced the birefringence within the basilar membrane as well as within other stained collagen-containing structures. Larger reductions in birefringence were measured when more laser pulses were given. The effects were similar across all turns of each cochlea. Conclusions Laser irradiation causes immediate alterations in collagen organization within the cochlea that can be visualized with polarization microscopy. These alterations may affect cochlear tuning. Ongoing research is aimed at analyzing the effect of laser irradiation on cochlear function. It is conceivable that this technique may have therapeutic benefits for patients with high-frequency sensorineural hearing loss. Lasers Surg. Med. 35:174–180, 2004. © 2004 Wiley-Liss, Inc.

Near-infrared wavelengths are absorbed less by epidermal melanin mainly located at the basal layer of epidermis (dermo-epidermal junction), and penetrate deeper into human skin dermis and blood than visible wavelengths. Therefore, laser irradiation using near-infrared wavelength may improve the therapeutic outcome of cutaneous hyper-vascular malformations in moderately to heavily pigmented skin patients and those with large-sized blood vessels or blood vessels extending deeply into the skin. A mathematical model composed of a Monte Carlo algorithm to estimate the distribution of absorbed light followed by numerical solution of a bio-heat diffusion equation was utilized to investigate the thermal response of human skin to near-infrared laser irradiation, and compared it with that to visible laser irradiation. Additionally, the effect of skin surface cooling on epidermal protection was theoretically investigated. Simulation results indicated that 940 nm wavelength is superior to 810 and 1064 nm in terms of the ratio of light absorption by targeted blood vessel to the absorption by the basal layer of epidermis, and is more efficient than 595 nm wavelength for the treatment of patients with large-sized blood vessels and moderately to heavily pigmented skin. Dermal blood content has a considerable effect on the laser-induced peak temperature at the basal layer of epidermis, while the effect of blood vessel size is minimum.

Cryogen spray cooling (CSC) is an effective method to minimize epidermal damage during laser treatment of various cutaneous anomalies such as port wine stains, excess hair, and facial rhytides. Radiometric temperature measurements provide a noninvasive method to estimate the skin surface temperature. Since the infrared absorption spectrum of the cryogen film has remained unknown, assumptions for those values may lead to inaccurate temperature estimations. We have constructed several high-pressure infrared transparent cuvettes to determine the absorption coefficient of room temperature R-134a in liquid phase using Fourier Transform Infrared Spectroscopy (FTIR) in the 2.5 - 14 μm spectral bandwidth. Results demonstrate that liquid R-134a has several absorption bands in the infrared, with those between 7 - 10.5 and 11.5 - 12.5 μm being the most prominent. Additionally, the absorption coefficient at two common radiometric bands, 3 - 5 and 7 - 11 μm differ by four orders of magnitude. Results of this study will lead to further improvements in interpreting radiometric temperature measurements when using CSC.

Cryogen spray cooling (CSC) reduces epidermal damage during laser treatment of various dermatoses. The goal of this study was to determine the instantaneous surface heat removal from skin by CSC. Thermocouples were imbedded in four substrates with a range of thermal diffusivities, greater than three orders of magnitude in difference, to measure internal temperature profiles in response to CSC. An inverse heat conduction model was subsequently used to quantify the instantaneous heat removal from the substrates using the measured temperatures. The ratio of the average values of the instantaneous heat removal among pairs of substrates was plotted as a function of the ratio of the thermal diffusivity among the pairs. The resulting correlation was then used to estimate the instantaneous heat removal from skin. This work will aid in the modeling of heat transfer in skin during laser irradiation in conjunction with CSC.

We have investigated the utilization of high incident fluence, long pulse laser irradiation in conjunction with cryogen spray cooling (CSC) on ex-vivo human skin. Abdominal skin samples of different types (Fitzpatrick type I-VI) were obtained from patients undergoing the trans-rectus myocutaneous flap procedures. Each skin type was irradiated with a Candela Vbeam/spl trade/ laser (wavelength /spl lambda/=595 nm) at incident dosages of D/sub /spl theta//=6, 10, 15, 20 J/cm/sup 2/, pulse durations of /spl tau//sub laser/=1.5, 10, 40 ms, without and with CSC. Preliminary results indicate that lightly pigmented skins can sustain higher incident fluence levels than those currently used in therapeutic settings. While the incident dosage of the laser pulse remains the same, longer pulse duration can decrease the degree of epidermal thermal injury.

Background and Objectives Improved laser treatment of cutaneous hypervascular lesions is expected by utilizing higher incident dosages, longer pulse durations and longer wavelengths than those currently used in clinical settings. However, simply increasing the incident dosage will also increase the risk of nonspecific thermal injury to the epidermis due to light absorption by melanin. In this study, we investigated the thermal response of human skin epidermis to 595-nm wavelength laser irradiation at high incident dosages (up to 20 J/cm2) and long pulse durations (up to 40 milliseconds) in conjunction with cryogen spray cooling (CSC) using ex-vivo human skin samples. Study Design/Materials and Methods The Candela V-beam™ laser (595-nm wavelength) was used in the experiments. Ex-vivo human skin samples (Fitzpatrick types I–VI) were irradiated at the incident dosages D0 = 4, 6, 10, 15, and 20 J/cm2, laser pulse durations τlaser = 1.5, 10, and 40 milliseconds, without and with CSC (refrigerant-134A, spurt duration τCSC = 100 milliseconds). Thermal injury to the epidermis was evaluated by histological observations. Results Under the same incident dosage, longer pulse durations led to reduced thermal injury to the epidermis. Without CSC, no demonstrable thermal injury to the epidermis was observed in skin types I–II irradiated at the incident dosage as high as 15 J/cm2, and in skin types III–IV at 10 J/cm2. When CSC was applied, no evidence of thermal injury to the epidermis was present in skin types I–II even when irradiated at the maximum available incident dosage of the laser system (20 J/cm2). In skin types III–IV, no demonstrable thermal injury to the epidermis was observed when using incident dosage as high as 15 J/cm2 in conjunction with CSC. In skin type VI, thermal injury to the epidermis could not be avoided even at the setting D0 = 4 J/cm2, τlaser = 40 milliseconds in conjunction with CSC. Conclusions For a given incident dosage, longer pulse durations help reduce thermal injury to the epidermis. When a 100-millisecond cryogen spurt is applied, thermal injury to the epidermis can be prevented in ex-vivo skin types I–IV when irradiated at higher incident dosages (15–20 J/cm2) than those currently used in clinical settings. Further studies on optimizing the CSC parameters in conjunction with the laser irradiation parameters are needed to protect skin types V–VI from thermal injury to the epidermis. Lasers Surg. Med. 33:16–24, 2003. © 2003 Wiley-Liss, Inc.

Improved laser treatment of port wine stains is expected by utilizing higher incident dosages, longer pulse durations, and longer wavelengths than those currently used in clinical settings. However, higher incident dosages also increase the risk of nonspecific thermal injury to the epidermis. Using ex-vivo human skin samples, we investigated the thermal respone of human skin epidermis in different skin types ot 595-nm wavelength laser irradiation at high incident dosages (up to 20 J/cm2) and long pulse durations (1.5 to 40 milliseconds) in conjunction with cryogen spray cooling (CSC). Human skin samples (Fitzpatrick types I-VI) from consenting adult females undergoing trans-rectus abdominis myocutaneoues flap procedures were irradiated at the incident dosages D0=4, 6, 10, 15, and 20 J/cm2, pulse durations τlaser=1.5, 10, and 40 milliseconds without and with CSC (Refrigerant-134A, spurt duration τCSC=100 milliseconds). Thermal injury to the epidermis was evaluated by histological observations. Experimental results showed that thermal injury to the epidermis could not be avoided in skin type VI even at D0 = 4 J/cm2 in conjunction with CSC. However, CSC allowed utilization of high incident dosages (15 - 20 J/cm2) in skin types I-IV. Under the same incident dosage, longer pulse durations led to decreased degree of thermal injury to the epidermis. Threshold values for irradiation parameters that resulted in thermal injury to the epidermis for each skin type were obtained.

Cryogen spray cooling (CSC) is an effective method to minimize epidermal damage during laser treatment of various cutaneous anomalies such as port wine stains, excess hair, and facial rhytides. In this study, we investigated the effects of the cryogen film thickness on heat removal, and laser light transmission through the film. Surfactants were added to the cryogen (R-134a) to decrease the film height by reducing the surface tension, and the resulting heat removal from an in vitro skin phantom was estimated using an algorithm that solved an inverse heat conduction problem. Transmission of light through the cryogen film sprayed onto a glass cover slip was measured by an energy meter at wavelengths of 595, 755, 1064, and 1450 nm. Normalized film height was negatively correlated (r < -0.65) to heat removal for relatively short spraying distances (50 mm). Reducing the cryogen film height may offer an approach to increase heat removal. Values of light transmission were in the range of 70 – 95% for the lasers using various durations of cryogen spurts and delays.

Cryogen spray cooling (CSC) is a technique to protect the epidermis from non-specific thermal injury during laser treatment of various dermatoses. Successful application of CSC in conjunction with laser treatment of heavily pigmented individuals, and high radiant exposures which may be required for effective therapeutic outcomes, requires enhancement of heat removal. We have investigated the thermal mechanisms, and effects of droplet size, density and velocity on heat removal during CSC. Our results suggest that although the inherent thermal diffusivity of skin may be a limiting factor in heat removal, parameters such as droplet size, density, and velocity are important, and should be optimized for maximum heat removal.

The cochlea is the mammalian organ of hearing. Its predominant vibratory element, the basilar membrane, is tonotopically tuned, based on the spatial variation of its mass and stiffness. The constituent collagen fibers of the basilar membrane affect its stiffness. Laser irradiation can induce collagen remodeling and deposition in various tissues. We tested whether similar effects could be induced within the basilar membrane. Trypan blue was perfused into the scala tympani of anesthetized mice to stain the basilar membrane. We then irradiated the cochleas with a 694-nm pulsed ruby laser at 15 or 180 Jcm(2). The mice were sacrificed 14 to 16 days later and collagen organization was studied. Polarization microscopy revealed that laser irradiation increased the birefringence within the basilar membrane in a dose-dependent manner. Electron microscopy demonstrated an increase in the density of collagen fibers and the deposition of new fibrils between collagen fibers after laser irradiation. As an assessment of hearing, auditory brainstem response (ABR) thresholds were found to increase moderately after 15 Jcm(2) and substantially after 180 Jcm(2). Our results demonstrate that collagen remodeling and new collagen deposition occurs within the basilar membrane after laser irradiation in a similar fashion to that found in other tissues.

In the context of clinical trials, calibration protocols for optical instruments that ensure measurement accuracy and the ability to carry out meaningful comparisons of data acquired from multiple instruments are required. A series of calibration standards and procedures are presented to assess technical feasibility of optical devices for cervical precancer detection. Measurements of positive and negative standards, and tissue are made with two generations of research grade spectrometers. Calibration accuracy, ability of standards to correct and account for changes in experimental conditions, and device components are analyzed. The relative frequency of measured calibration standards is investigated retrospectively using statistical analysis of trends in instrument performance. Fluorescence measurements of standards and tissue made with completely different spectrometers show good agreement in intensity and lineshape. Frequency of wavelength calibration standards is increased to every 2 h to compensate for thermal drifts in grating mount. Variations in illumination energy detected between standards and patient measurements require probe redesign to allow for simultaneous acquisition of illumination power with every patient measurement. The use of frequent and well-characterized standards enables meaningful comparison of data from multiple devices and unambiguous interpretation of experiments among the biomedical optics community.

Background and Objective: Cryogen spray cooling (CSC) is a method used to protect the epidermis from non-specific thermal injury that may occur as a result of various dermatological laser procedures. However, better understanding of cryogen deposition and skin thermal response to CSC is needed to optimize the technique. Study Design/Materials and Methods: Temperature measurements and video imaging were carried out on an epoxy phantom as well as human skin during CSC with and without simultaneous application of airflow which was intended to accelerate cryogen evaporation from the substrate surface. An inverse thermal conduction model was used to estimate heat flux and total heat removed. Results: Lifetime of the cryogen film deposited on the surface of skin and epoxy phantom lasted several hundred milliseconds beyond the spurt, but could be reduced to the spurt duration by application of airflow. Values over 100 J/cm 3 were estimated for volumetric heat removed from the epidermis using CSC. Conclusions: ‘‘Film cooling’’ instead of ‘‘evaporative cooling’’ appears to be the dominant mode of CSC on skin. Estimated values of heat removed from the epidermis suggest that a cryogen spurt as long as 200 milliseconds is required to counteract heat generated by high laser fluences (e.g., in treatment of port wine stains) in patients with high concentration of epidermal melanin. Additional cooling beyond spurt termination can be avoided by simultaneous application of airflow, although it is unclear at the moment if avoiding the additional cooling would be beneficial in the actual clinical situation. Lasers Surg. Med. 28:477‐486, 2001. fl 2001 Wiley-Liss, Inc.