Filtered Xenon Arc Lamp Research Articles

Coating and Interface Degradation of Coated steel, Part 2: Accelerated Laboratory Tests

In a previous paper, it was demonstrated that the measurement of cathodic delamination by the Scanning Kelvin Probe can assess the interface stability of poly(vinyl butyral) (PVB) coated steel after field exposure. This technique was utilized to characterize the degradation of the polymer/metal interface in several outdoor climates. In this paper, the effects of environmental factors on the interface degradation were investigated in the laboratory. The mechanisms measured in the field were reproduced to provide input in the development of an appropriate accelerated test for PVB coated steel. The ASTM B117 and G154 standardized tests were investigated individually and sequentially. The interface stability improved after 24h of ASTM G154 exposure. After 144h of exposure to ASTM G154 exposure, polymer oxidation took place simultaneously with interface degradation. The condensation phase of the ASTM G154 test was responsible for the interface improvement while the ultraviolet radiation triggered the interface degradation. Pre-exposure to ASTM G154 delayed wet de-adhesion during ASTM B117 exposure. After wet de-adhesion caused by 6h of ASTM B117, exposure to ASTM G154 for 24h increased the interface stability. The effects of ultraviolet radiation, relative humidity, temperature and environment on interface degradation were investigated in a special chamber. Humidity was the primary factor found to influence the interface improvement during G154 exposure. A wet/dry salt fog cycle with irradiation by an ultraviolet or filtered xenon arc lamp around room temperature was suggested to reproduce the competition between the interface improvement and the interface degradation that takes place in the field.

Parameters influencing the accuracy and practical applicability of UV indicator cards

In order to evaluate the potential hazard for the skin and the eye presented by solar ultraviolet radiation, and to take appropriate precautions, it is necessary to characterise the biological effective irradiance or dose. Recently, inexpensive UV indicator cards became available that in principle would provide an attractive means to roughly indicate the local level of erythemal solar UV irradiance. We have characterised the properties of a number of different types of UV indicator cards. Several parameters which may influence the colour of the cards were examined with both outdoor trials under solar UV as well as indoor trials using a filtered xenon arc lamp. Our findings show that the tested cards do not give an appropriate estimation of the effective irradiance due to their spectral sensitivity and their temperature dependence. The application area of the tested UV indicator cards is therefore limited to certain temperature ranges and to seasons where a certain ratio between solar UV-A and solar UV-B occurs.

Validation of a semiautomated method of minimal erythema dose testing for narrowband ultraviolet B phototherapy

The most widely used method for establishing the minimal erythema dose (MED) before narrowband ultraviolet (UV) B phototherapy is time-consuming, inconvenient and may yield inconsistent results. To assess the equivalence of MED assessment using a filtered xenon arc lamp UV source, a semiautomated MED tester, and a UV-opaque template method of MED determination with a panel of TL-01 311-nm UVB fluorescent tubes. Secondly, to gauge the current usage of MED testing, and the method used, in a large sample of U.K. phototherapy units. Thirdly, to assess variation in UV output of the semiautomated skin tester immediately after switching on to identify optimum warm-up time. Finally, to assess reproducibility of MED testing by assessing within-patient variability and interobserver variability of MED test results. Sixty-five patients about to undergo UVB phototherapy had their MED determined using three different methods. Within each patient we compared the values of MED determined by a semiautomated Durham MED tester, a panel of narrowband UVB lamps with a UV-opaque template constructed by a phototherapist, and a 310-nm filtered xenon arc lamp with a liquid light guide. MED test results were assessed by clinical evaluation using a 6500 K colour temperature examination lamp. The output of the semiautomated MED tester was measured by spectroradiometer over a period of 20 min in order to identify the time to steady output. Reproducibility of MED testing with the semiautomated MED tester was carried out in 25 normal volunteers. All MEDs were assessed by at least two independent observers. A postal questionnaire was sent to 78 U.K. phototherapy units to assess routine practice concerning MED testing prior to narrowband UVB phototherapy. The semiautomated MED tester showed consistency with the panel method (r = 0.92, panel MED = -0.57 + 1.14 x Durham MED). The semiautomated MED tester produced a slightly lower MED result than the panel MED. Reproducibility tests showed high interobserver agreement (kappa value = 0.79), and high consistency for successive day testing (kappa value = 0.79). Questionnaires were returned from 67 of 78 phototherapy units (85%) and revealed that 19 units (28%) were routinely using MED testing prior to UVB therapy. This study has shown the Durham MED tester to be a convenient, valid and reproducible method for determining patient MED values prior to narrowband UVB phototherapy when used under carefully controlled lighting, by experienced observers.

Sunscreen lotions prevent ultraviolet radiation-induced suppression of antitumor immune responses.

Exposure to subcarcinogenic doses of ultraviolet (UV) radiation suppresses tumor immunity, thus permitting the emergence and growth of highly immunogenic skin cancers in mice. Sunscreens prevent UV carcinogenesis; however, there are conflicting reports regarding their ability to block UV-induced tumor immune suppression. In this study we critically evaluated the effects of UV spectrum and dose on the tumor immune protective capacity of 4 marketed sunscreen lotions with labeled sun protection factors (SPF) 8-45. Effective tumor immune suppression doses (TISD), i.e., the lowest dose tested to induce outgrowth of transplanted nonmelanoma skin tumors in 100% of UV-exposed C3H mice, were established for 3 different UV sources. TISD were significantly lower for unfiltered (FS) and Kodacel-filtered (KFS) UVB-type FS20 sunlamps compared with a filtered xenon arc lamp solar simulator. Sunscreen tumor immune protection levels matched those predicted by their labeled SPF when sunscreen-protected mice were exposed to a fixed TISD of solar simulator UV radiation. SPF 30 and 45 sunscreens also blocked activation of tumor antigen-specific suppressor T-lymphocytes in mice exposed to solar simulator UV radiation. In comparison, sunscreens with SPF > or = 15 provided partial to complete protection, as measured by tumor incidence, for mice exposed to UV radiation from KFS. All sunscreens tested reduced tumor growth rates in KFS UV-exposed mice. None of the sunscreens tested provided measurable tumor immune protection for mice exposed to FS UV radiation. Thus, sunscreen lotions provide an extent of tumor immune protection consistent with their labeled SPF when appropriate testing conditions are employed.

Clinical evaluation of a method for detecting superficial surgical transitional cell carcinoma of the bladder by light-induced fluorescence of protoporphyrin IX following the topical application of 5-aminolevulinic acid: preliminary results.

In bladder cancer, conventional white light endoscopic examination of the bladder does not provide adequate information about the presence of "flat" urothelial lesions such as carcinoma in situ. In the present investigation, we examine a new technique for the photodetection of such lesions by the imaging of protoporphyrin IX (PpIX) fluorescence following topical application of 5-aminolevulinic acid (ALA). Several hours after bladder instillation of an aqueous solution of ALA in 34 patients, a Krypton ion laser or a filtered Xenon arc-lamp was used to excite PpIX fluorescence. Tissue samples for histological analysis were taken while observing the bladder wall either by means of a video camera, or by direct endoscopic observation. A good correlation was found between the PpIX fluorescence and the histopathological diagnosis. On a total of 215 biopsies, 143 in fluorescent and 72 in nonfluorescent areas, all visible tumors on white light cytoscopy appeared in a bright red fluorescence with the photodetection technique. In addition, this method permitted to discover 47 unsuspected carcinomatous lesions on white light observation, among which 40% were carcinoma in situ. PpIX fluorescence induced by instillation into the bladder of 5-ALA is an efficient method of mapping the mucosa in bladder carcinoma.

Ultraviolet spectral energy differences affect the ability of sunscreen lotions to prevent ultraviolet-radiation-induced immunosuppression.

Acute exposure to UV radiation causes immunosuppression of contact hypersensitivity (CH) responses. Past studies conducted with unfiltered sunlamps emitting nonsolar spectrum UV power (wavelengths below 295 nm) or using excessive UV doses have suggested sunscreens may not prevent UV-induced immunosuppression in mice. This study was thus designed to evaluate critically the effects of different UV energy spectra on the immune protection capacity of sunscreen lotions. Minimum immune suppression doses (MISD), i.e. the lowest UV dose to cause approximately 50% suppression of the CH response to dinitrofluorobenzene in C3H mice, were established for three artificial UV sources. The MISD for each UV source was 0.25 kJ/m2 for unfiltered FS20 sunlamps (FS), 0.90 kJ/m2 for Kodacel-filtered FS20 sunlamps (KFS), which do not emit UV power at wavelengths < 290 nm, and 1.35 kJ/m2 for a 1000 W filtered xenon arc lamp solar simulator. Using MISD as baseline, sunscreens with labeled sun protection factors (SPF) of 4, 8, 15 and 30 were tested with each UV source to establish their relative immune protection factors. The immune protection factor of each sunscreen exceeded its labeled SPF in tests conducted with the solar simulator, which has a UV power spectrum (295-400 nm) similar to that of sunlight. Conversely, sunscreen immune protection factors were significantly less than the labeled SPF in tests conducted with FS and KFS. Comparison of the immunosuppression effectiveness spectra showed that relatively small amounts of nonsolar spectrum UV energy, i.e. UVC (200-290 nm) and/or shorter wavelength UVB (between 290 and 295 nm), produced by FS and KFS contributes significantly to the induction of immunosuppression. For example, 36.3% and 3.5% of the total immunosuppressive UV energy from FS and KFS, respectively, lies below 295 nm. Sunscreen absorption spectra showed that transmission of immunosuppressive UV energy below 295 nm for FS was at least eight-fold higher than that for KFS. Compared to the solar simulator UV spectrum the transmission of nonsolar immunosuppressive UV energy through sunscreens was > 15-fold higher for FS and > or = 1.5-fold higher for KFS. These data demonstrate that relevant evaluations of sunscreen immune protection can only be obtained when tests are conducted with UV sources that produce UV power spectra similar to that of sunlight and UV doses are employed that are based on established MISD.

Intratumor temperature measurements during photodynamic therapy.

Abstract Photodynamic therapy has been under investigation as a form of cancer treatment for a number of years. This procedure uses a light source of 630 nm to photoactivate the drug, Photofrin II. Researchers in the past have reported temperature increases during photodynamic therapy, by measuring surface temperature of the tumor or a single point temperature within the tumors. Three temperature points within the tumors have been measured in this study, to quantify the temperature distribution within the lesion. These temperatures were measured for photodynamic therapy treated mice and control mice receiving an exposure to the treatment light without the drug. The use of a filtered xenon arc lamp for the 630 nm light source produced larger temperature increases and thermal gradients within the tumors, than when an Argon dye laser was employed. This temperature increase is due in part to the broad wavelength output of this filtered lamp. When this thermal effect is present during PDT treatment, researchers have observed the development of shock proteins resulting in the induction of thermotolerance and resistance to subsequence hyperthermia treatments. Using the filtered arc lamp, mice receiving photodynamic therapy treatments displayed consistently higher temperature increases than control mice. The use of an argon dye laser, with sufficient air cooling of the tumor, can eliminate this thermal effect. It has been demonstrated that the use of filtered lamps produce thermal effects which cannot be eliminated, demonstrating that lasers should be the primary source of light used to photoirradiate animals for photodynamic therapy studies. The intratumor temperature increases should be documented at multiple positions, to determine the amount of thermotolerance which can be induced. When photodynamic therapy is followed with a subsequent hyperthermia treatment, this induced thermotolerance can then be taken into consideration.

Induction of reproducible brain infarction by photochemically initiated thrombosis.

We have used a photochemical reaction in vivo to induce reproducible thrombosis leading to cerebral infarction in rats. After the intravenous injection of rose bengal, a potent photosensitizing dye, an ischemic lesion was formed by irradiating the left parietal convexity of the exposed skull for 20 minutes with green light (560 nm) from a filtered xenon arc lamp. Animals were allowed to survive from 30 minutes to 15 days after irradiation. Early microscopic alterations within the irradiated zone included the formation of thrombotic plugs and adjacent red blood cell stasis within pial and parenchymal vessels. Scanning electron microscopy revealed frequent platelet aggregates adhering to the vascular endothelium, often resulting in vascular occlusion. Carbon-black brain perfusion demonstrated that occlusion of vascular channels progressed after irradiation and was complete within 4 hours. Histopathological examination at 1, 5, and 15 days revealed that the associated infarct evolved reproducibly through several characteristic stages, including a phase of massive macrophage infiltration. Although cerebral infarction in this model is initiated by thrombosis of small blood vessels, the fact that the main pathological features of stroke are consistently reproduced should permit its use in assessing treatment regimens. Further, the capability of producing infarction in preselected cortical regions may facilitate the study of behavioral, functional, and structural consequences of acute and chronic stroke.