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PubMed2006

Pheomelanin and eumelanin in human skin determined by high-performance liquid chromatography and its relation to in vivo reflectance measurements.

BACKGROUND/PURPOSE: Clinical experience has shown that red haired, fair-skinned people have an increased frequency of skin cancer and in addition a relatively high content of pheomelanin and low content of eumelanin in their skin. Of these, eumelanin is presumed photoprotective, and pheomelanin phototoxic. Thus, a fast, easy, and non-invasive method for determining skin content of eumelanin and pheomelanin was sought. METHODS: Skin reflectance measurements using a UV-Optimize apparatus were performed before taking suction blisters of the same skin area. Each skin sample was freeze dried and submitted to alkaline hydrogen peroxide degradation. Two eumelanin degradation compounds:Pyrrole-2,3-dicarboxylic acid (PDCA) and pyrrole-2,3,5-tricarboxylic acid (PTCA), and two pheomelanin degradation compounds: Thiazole-4,5-dicarboxylic acid (TDCA) and 1,3-thiazole-2,4,5-tricarboxylic acid (TTCA) were determined in a single chromatographic analysis. Each degradation compound was correlated to reflectance measurements of red (660 nm), green (555 nm), and blue (488 nm) light and additionally correlated to the pigmentation % and redness % given by UV-Optimize. RESULTS: Neither of the investigated parameters were significantly correlated to either PDCA or TTCA. Contrarily, a highly significant correlation was found for the eumelanin marker, PTCA (r2=0.79, P<0.0001). The pheomelanin marker, TDCA, was likewise found to be significantly correlated (r2=0.43, P<0.0001). CONCLUSION: Based on the coefficients of determination it was concluded that in vivo spectrophotometric reflectance measurements of human skin were highly useful for determining the eumelanin content of skin and to classify the pheomelanin content of skin non-invasively. This may be used individually and in population-based studies.

Adolescent↗

PubMed1990

Immediate pigment darkening: visual and reflectance spectrophotometric analysis of action spectrum.

Immediate pigment darkening (IPD) occurs in human skin upon exposure to ultraviolet-A and visible radiation. The spectral changes that occur during IPD were measured with a rapid scanning reflectance spectrophotometer (RS) which employs optical fiber bundles for delivery and detection of light between 400 and 750 nm. The radiation dose dependence and wavelength dependence (334-549 nm irradiation) of IPD were studied by both the classical visual grading method and by spectrophotometric scoring using the RS system. The spectral changes that occur at long wavelengths with IPD mimic the natural absorption spectrum of melanin. Therefore, the IPD was scored in terms of the apparent change in melanin optical density, using the method Kollias and Baqer [Photochem. Photobiol. 43, 49-54 (1986)], based on reflectance in the 620-720 nm range. The nonlinearity of the visual grading method is demonstrated. The degree of IPD is first-order with respect to delivered dose and saturates after high doses. The maximum amount of IPD attained at saturation is greater for shorter wavelengths. Extrapolation of the reflectance data suggests the longest wavelength capable of eliciting IPD is about 470 nm.

Adult↗

PubMed1995

In vivo spectrophotometric evaluation of neoplastic and non-neoplastic skin pigmented lesions. III. CCD camera-based reflectance imaging.

Reflectance spectroscopy, which allows an objective evaluation of the color of surfaces, has recently been proposed as a useful tool to discriminate cutaneous melanoma from other pigmented cutaneous lesions. A novel spectrophotometric system based on the use of a charge coupled device camera provided with a set of interference filters has been developed to acquire images of cutaneous pigmented lesions at selected wavelengths ranging from 420 to 1040 nm. For each filter, an image was captured, digitized by a frame grabber and stored in a personal computer to perform off-line data handling. Reflectance images were acquired of 22 cutaneous pigmented lesions including melanoma and dysplastic, compound and junctional nevus. From each spectral image, three parameters, i.e. mean reflectance, variegation index and lesion area; were derived at the corresponding wavelength. The wavelength dependence of the three parameters was significantly different when melanoma was compared to the other investigated lesions. Although preliminary, our results suggest that telespectrophotometry gives useful information and could be utilized as an aid in the clinical diagnosis of cutaneous pigmented lesions.

Humans↗

PubMed1997

Accuracy of noninvasive in vivo measurements of photosensitizer uptake based on a diffusion model of reflectance spectroscopy.

This study compares the photosensitizer concentration measured noninvasively in vivo by diffuse reflectance spectroscopy with the results of postmortem tissue solubilization and fluorometric assay. The reflectance spectrometer consists of a fiber optic surface probe, spectrometer and charge-coupled device (CCD) array detector. The surface probe has eight detection fibers separated from the light source fiber by distances ranging from 0.85 to 10 mm. The imaging spectrometer disperses the light from each detector fiber onto the two-dimensional CCD array, while maintaining spatial separation of each individual spectrum. A single exposure of the CCD therefore captures the reflectance spectrum ar eight distances and over a range of 300 nm. From the spectra, the tissue's optical scattering and absorption coefficients are determined using a diffusion model of light propagation. Changes in the tissue absorption are used to estimate the photosensitizer concentration. Normal New Zealand White rabbits were injected with aluminum phthalocyanine tetrasulfonate (AlPcS4) and probe measurements made 24 h after injection on the dorsal skin, on muscle after surgically turning the skin back and on liver. For skin, the noninvasive estimate to proportional to the true concentration but low by a factor of 3. Based on Monte Carlo modeling of multilayered systems, this underestimate is attributed to the layered structure of the skin and nonuniform AlPcS4 distribution. A comparison of the noninvasive concentration estimates to the postmortem assay results finds good agreement for liver tissue even though application of the diffusion model is not strictly justified.

Animals↗

PubMed1998

A "reader's theater" intervention to managing grief: posttherapy reflections by a family and clinical team.

The sudden and accidental death of a child can be one of the most devastating events in the life of a family. This paper describes one couple's reflections of their grief and mourning following the death of their adolescent son as well as the clinical team's reflections of therapy. The uniqueness of this paper is that it offers a "reader's theater" intervention that enabled further change to occur. The clinical team used a belief model, emphasizing that altering constraining beliefs is at the heart of healing from such tragedies as sudden death (Wright, Watson, & Bell, 1996). This approach is operationalized through therapeutic conversations between family members, clinician, and clinical team. Interventions such as reflecting teams, therapeutic letters, and "homework tasks" were used to modify or challenge constraining beliefs of both the family members and the clinical team members. However, the intent to co-author a paper with this couple provided the serendipity intervention of a "reader's theater" that further served to identify, affirm, and solidify facilitating beliefs.

Adolescent↗

PubMed1988

Relation between trans-synovial flow and plasma osmotic pressure, with an estimation of the albumin reflection coefficient in the rabbit knee.

The volume of synovial fluid in a joint correlates inversely with plasma colloid osmotic pressure (COP). The inferred influence of plasma osmotic forces on trans-synovial flow was investigated directly here, in isolated perfused hindquarters of sixteen rabbits. Flow of intra-articularly infused Krebs solution across the synovial lining of the cannulated knee was recorded at controlled intra-articular pressure (18 cmH2O). Colloid osmotic pressure in the synovial microcirculation was varied by perfusion with oxygenated red cells resuspended in albumin solution or plasma from an extra-corporeal system at constant perfusion pressure. Studies in vitro showed that the COP versus concentration curve for commercial bovine albumin samples was variable and not reliably described by a widely used polynomial. The rate of trans-synovial absorption Qs was a positive linear function of intravascular COP pi p (r = 0.936, P less than 0.001, n = 83). The average slope dQs/d pi p was 0.20 microliter min-1 cmH2O-1 (S.E. +/- 0.01 microliter min-1 cmH2O-1), the slope depending on hydraulic conductance and osmotic reflection coefficient. Trans-synovial flow was a negative linear function of synovial capillary pressure (Pc). Absolute slope dQs/d pi p was on average only 78% of dQs/dPc in the same joint. The osmotic reflection coefficient of the blood-joint barrier to serum albumin was estimated from these slopes as 0.78-0.81 (S.E.M. +/- 0.06). Vascular perfusion with a hyperosmolar solution of glucose, sucrose or NaCl generated a transient, rapidly decaying osmotic absorption from the joint cavity, with a half-life of 17-60 s. A reversed osmotic transient occurred on reperfusion with isotonic fluid. It was concluded that the blood-joint barrier, which comprises fenestrated endothelium and synovial intima, approximates to an imperfect semipermeable membrane for albumin solutions, justifying the application of Starling's hypothesis to trans-synovial flow. For small solutes the tissues form a highly permeable but nevertheless slightly osmotically reflective membrane.

Animals↗

PubMed1988

Filtration coefficient and osmotic reflection coefficient to albumin in rabbit submandibular gland capillaries.

1. The isolated perfused submandibular salivary gland of the rabbit has been used in order to make estimates of the filtration coefficient (Kf) and reflection coefficient (sigma d) of the capillary wall to albumin. 2. An isogravimetric preparation was used and in paired experiments the value for Kf obtained in glands perfused with albumin-Krebs solution, 0.96 +/- 0.086 (mean +/- S.E. of mean) ml min-1 mmHg-1 100 g-1, was not significantly different from that in blood-perfused glands, 0.90 +/- 0.15. 3. On analysing the data for reflection coefficient, it was concluded that the above values underestimated Kf by about 30%; using corrected values for Kf, osmotic reflection coefficients were determined from the weight changes following a sudden change in the oncotic pressure of the perfusate. The value for sigma d to albumin lay between 0.79 and 1.0, the lower value being obtained after the Kf correction. 4. The high hydraulic conductivity, combined with sieving properties comparable to those in continuous capillaries, is consistent with other data on fenestrated capillaries. 5. Finally, it was observed that, while the Kf value calculated from the initial flux rate was similar whether measured during fluid efflux from or influx into the microvasculature, on returning to the initial conditions after raising osmotic pressure, efflux was now more rapid than influx. This phenomenon is discussed in relation to readjustment of Starling forces and the possible existence of an asymmetric double membrane in the capillary, interstitium system and cells of the salivary gland.

Albumins↗

PubMed2004

Filtration rate dependence of hyaluronan reflection by joint-to-lymph barrier: evidence for concentration polarisation.

Hyaluronan (HA), a component of synovial fluid, buffers fluid loss from joints. To explain this, a quantitative theory for HA concentration polarisation at a partially sieving synovial lining was developed. The theory predicts a fall in HA reflected fraction R with increased filtration rate. To test this, knees of anaesthetised rabbits were infused with HA and fluorescein-dextran (FD) at constant trans-synovial filtration rates of 6-89 microl min(-1). Samples of femoral lymph, mixed intra-articular fluid and subsynovial fluid after >/= 3 h were analysed by high-performance liquid chromatography. R was calculated as (1 - downstream/upstream concentration), using [FD] to adjust for joint lymph dilution in femoral lymph. Intra-articular HA concentration after >/= 3 h, 0.47 +/- 0.02 mg ml(-1) (mean +/-s.e.m., n= 31), exceeded the infusate concentration, 0.20 mg ml(-1), while subsynovial and lymph [HA] were reduced relative to [FD]. The changes in [HA] demonstrated synovial molecular sieving of HA. R from cavity to lymph (R(lymph)) fell monotonically from 0.93 at 6 microl min(-1) to 0.14 at 89 microl min(-1) (P < 0.0001, regression analysis, n= 33). R values calculated from the intra-articular HA accumulation (R(asp)) or the low subsynovial concentrations (R(syn)) were similar negative functions of filtration rate. R for lymphatic capillary endothelium (R(endo)), calculated from lymph/subsynovial concentration ratios, was effectively zero (-0.03 +/- 0.18, n= 21), confirming that synovium, not initial lymphatic endothelium, is the reflection site. Logarithmic linearisation of the results evaluated the synovial HA reflection coefficient as 0.91. In conclusion, the existence of concentration polarisation during joint fluid drainage was supported by the demonstration of a negative relation between filtration rate and R(lymph), R(asp) and R(syn).

Algorithms↗

PubMed2002

Reflectance spectroscopy for in vivo detection of cervical precancer.

Optical technologies, in particular fluorescence spectroscopy, have shown the potential to provide improved detection methods for cervical neoplasia that are sensitive and cost effective through accurate, objective, instantaneous point-of-care diagnostic tools. The specific goals of this study were to analyze reflectance spectra of normal and neoplastic cervical tissue in vivo and to evaluate the data for use in diagnostic algorithm development. Spectroscopic measurements were obtained at four distinct source-detector separations from 324 sites in 161 patients. As the source-detector separation increases, greater tissue depth is probed. The average spectra of each diagnostic class differed at all source-detector separations, with the greatest differences occurring at the smallest source-detector separations. Algorithms, based on principal-component analysis and Mahalanobis distance classification, were developed and evaluated for all combinations of source-detector separations relative to the gold standard of colposcopically directed biopsy. The diagnostic combination of squamous normal versus high-grade squamous intraepithelial lesions gave good discrimination with a sensitivity of 72% and a specificity of 81%; discrimination of columnar normal versus high-grade squamous intraepithelial lesions also was good, with sensitivity of 72% and specificity of 83%. Thus, reflectance spectroscopy appears promising for in vivo detection of cervical precancer. Strategies that combine fluorescence and reflectance spectroscopy may enhance the discrimination capabilities.

Female↗

PubMed2003

Reflectance-based determination of optical properties in highly attenuating tissue.

Accurate data on in vivo tissue optical properties in the ultraviolet A (UVA) to visible (VIS) range are needed to elucidate light propagation effects and to aid in identifying safe exposure limits for biomedical optical spectroscopy. We have performed a preliminary study toward the development of a diffuse reflectance system with maximum fiber separation distance of less than 2.5 mm. The ultimate objective is to perform endoscopic measurement of optical properties in the UVA to VIS. Optical property sets with uniformly and randomly distributed values were developed within the range of interest: absorption coefficients from 1 to 25 cm(-1) and reduced scattering coefficients from 5 to 25 cm(-1). Reflectance datasets were generated by direct measurement of Intralipid-dye tissue phantoms at lambda=675 nm and Monte Carlo simulation of light propagation. Multivariate calibration models were generated using feed-forward artificial neural network or partial least squares algorithms. Models were calibrated and evaluated using simulated or measured reflectance datasets. The most accurate models developed-those based on a neural network and uniform optical property intervals-were able to determine absorption and reduced scattering coefficients with root mean square errors of +/-2 and +/-3 cm(-1), respectively. Measurements of ex vivo bovine liver at 543 and 633 nm were within 5 to 30% of values reported in the literature. While our technique for determination of optical properties appears feasible and moderately accurate, enhanced accuracy may be achieved through modification of the experimental system and processing algorithms.

Algorithms↗

PubMed2003

Near-infrared thermo-optical response of the localized reflectance of intact diabetic and nondiabetic human skin.

We observed a difference in the thermal response of localized reflectance signal of human skin between type 2 diabetics and nondiabetics. We investigated the use of this thermo-optical behavior as the basis for a noninvasive method for the determination of the diabetic status of a subject. We used a two-site temperature differential method, which is predicated upon the measurement of localized reflectance from two areas on the surface of the skin. Each of these areas is subjected to a different thermal perturbation. The response of localized reflectance to temperature perturbation was measured and used in a classification algorithm. We used a discriminant function to classify subjects as diabetic or nondiabetic. In a prediction set of twenty-four noninvasive tests collected from six diabetic and six nondiabetic subjects, the sensitivity ranged between 73 and 100%, and the specificity ranged between 75 and 100%, depending on the thermal conditions and the probe-skin contact time. The difference in the thermo-optical response of the skin of the two groups is explained in terms of a difference in the response of cutaneous microcirculation, which is manifested as a difference in the near-infrared light absorption. Another factor is the difference in the temperature response of the scattering coefficient between the two groups, which may be caused by cutaneous structural differences induced by nonenzymatic glycation of skin protein fibers, and possibly by the difference in blood cell aggregation.

Algorithms↗

PubMedDate not supplied

Modulation of an optical needle's reflectivity alters the average photon path through scattering media.

We introduce the concept of deliberate placement of absorbers to alter the average path of photons through tissue for a biomedical optical device. By changing the reflectivity of a needle that separates a source and detector, the average photon path through a turbid medium can be changed. Totally reflective needles have photon scattering density functions similar to a point source and detector in an infinite medium. An absorbing needle moves the average photon path of photons that reach the detector away from the needle. Thus, by modulating the reflectivity of the needle, it is possible to modify the sensitive volume, and simple tomography data should be possible. These results are confirmed by Monte Carlo simulations and experiment. Experiments include moving a black target relative to an optical "needle" and measuring the resulting intensity and phase lag of light reaching a detector at the distal end of the needle.

Biopsy↗

PubMedDate not supplied

Reflection spectroscopy of atherosclerotic plaque.

Heart disease is the primary cause of death in the western world. Many of these deaths are caused by the rupture of vulnerable plaque. Vulnerable plaques are characterized by a large lipid core covered by a thin fibrous cap. One method for detecting these plaques is reflection spectroscopy. Several studies have investigated this method using statistical methods. A more analytic and quantitative study might yield more insight into the sensitivity of this detection modality. This is the approach taken in this work. Reflectance spectra in the spectral region from 400 to 1700 nm are collected from 77 measurement points from 23 human aortas. A measure of lipid content in a plaque based on reflection spectra is presented. The measure of lipid content is compared with the thickness of the lipid core, determined from histology. Defining vulnerable plaque as having a lipid core >500 microm and fibrous cap <500 microm, vulnerable plaques are detected with a sensitivity of 88% and a specificity of 94%. Although the method can detect lipid content, it is not very sensitive to the thickness of the fibrous cap. Another detection modality is necessary to detect this feature.

Algorithms↗

PubMedDate not supplied

In vivo confocal scanning laser microscopy: comparison of the reflectance and fluorescence mode by imaging human skin.

Optical, noninvasive methods have become efficient in vivo tools in dermatological diagnosis and research. From these promising imaging techniques, only the confocal scanning laser microscopy (CSLM) provides visualization of subsurface skin structures with resolutions similar to those of light microscopy. Skin annexes, as well as cutaneous cells from different epidermal layers, can be distinguished excellently. Currently, two forms of application have been established in dermatological practice: the reflectance mode, predominantly in the clinical field, and the fluorescence mode in dermatological research. Differences in both methods exist in the preparative protocol, in maximum imaging depth and, particularly, in the gain of contrast extraction. The reflectance mode demonstrates naturally occurring tissue components, whereas the fluorescent CSLM achieves contrast by administering fluorescence dye, representing the dynamic distribution pattern of the dye's fluorescent emission. Therefore, the reflectance and fluorescent modes highlight various skin microstructures, providing dissimilar in vivo confocal images of the skin. This permits different predications and information on the state of the tissue. We report the advantages and disadvantages of both optical imaging modes. The comparison was drawn by scanning human skin in vivo. Representative images in varying depths were obtained and analyzed; preparation procedures are shown and discussed.

Humans↗

PubMedDate not supplied

Hemodialysis monitoring in whole blood using transmission and diffuse reflection spectroscopy: A pilot study.

Visible and near infrared transmission and diffuse reflection spectroscopy were used to monitor changes in whole blood resulting from hemodialysis treatment for end-stage renal disease. Blood samples from 8 patients on chronic hemodialysis therapy were measured in the 500- to 1700-nm wavelength range immediately before and after a single treatment. Principal component scores characteristic of each spectrum were derived, and mean pre- and posttreatment scores of the first principal component indicated a significant treatment-dependent change in both optical transmission (P = 0.004) and diffuse reflection (P < 0.001). Significant treatment-induced change persisted (P < 0.05) when the first four principal components were used to account for >97% of the treatment-dependent spectral variation. Some blood spectral changes expressed in terms of difference spectra (posttreatment - pretreatment) were consistent with standard clinical indicators of weight reduction, urea reduction, and potassium change, with probable origins at a molecular level. The results indicate the feasibility of using optical transmission and diffuse reflection spectroscopy to characterize clinically relevant blood changes for the future development of more comprehensive indicators of hemodialysis efficacy and long-term clinical outcomes. Moreover, the optical techniques employed are adaptable for potential online monitoring of blood changes during the hemodialysis treatment.

Adult↗

PubMed2004

Hemoglobin oxygen saturations in phantoms and in vivo from measurements of steady-state diffuse reflectance at a single, short source-detector separation.

We present a method for the analysis of steady state diffuse reflectance spectra obtained from vascularized tissue or from tissue simulating phantoms at a single, short source-detector separation. This method uses reasonable assumptions about the structure of the reduced scattering spectrum and basis absorption spectra for oxy- and deoxyhemoglobin, which dominate tissue absorption in the visible region of the spectrum. Using a hybrid P3-diffusion description of light propagation, described originally by Hull and Foster [J. Opt. Soc. Am. A 18, 584-599 (2001)] and suitable for short (approximately 1 mm) source-detector separations and optical properties of tissue at visible wavelengths, we create a forward model of the diffuse reflectance with four free parameters. We demonstrate that this model is able to recover accurately the hemoglobin concentrations and scattering properties from synthetic data generated by Monte Carlo simulation and from reflectance spectra acquired from tissue-simulating phantoms containing intact human erythrocytes. We show also that the method is capable of monitoring carbogen-induced changes in murine tumor oxygenation in vivo. The successful implementation of single, short detector separations enables the measurement of intratumor heterogeneities in hemoglobin oxygen saturation and responses to carbogen using a simple fiber-based probe design.

Algorithms↗

PubMed2005

Noninvasive reflection spectra provide quantitative information about the spatial distribution of skin chromophores.

In this work, a new method of analyzing noninvasive reflection spectra is presented. The approach explicitly models the inhomogeneity of chromophore distributions in living tissues and thus extracts not only apparent chromophore concentrations but also relative chromophore distributions in tissues. Furthermore, it works with spectra obtained with short source-detector separations where the diffusion theory of light transport through turbid media is not valid, and formerly presented methods thus fail. The effect of inhomogeneously distributed chromophores in a multicompartment model of tissues on measured reflection spectra is explained and an algorithm to deconvolute tissue spectra based on this model is presented. It is evaluated using simulated spectra and measurements on phantoms, which are made up of partially printed pieces of paper to simulate inhomogeneous dye distributions. Its applicability to real tissue is proven using reflection spectra obtained with 130 microm source-detector separation from a hemoperfusion stop experiment. The proposed model accurately determines apparent chromophore concentrations and corresponding distributions in simulated spectra and phantoms. Regarding real tissue spectra, the results correspond to former publications and the spectral reconstruction yields only minimal residuals, indicating a complete and accurate spectral deconvolution. In conclusion, the presented approach is a suitable extension and amendment to existing models of light transport through inhomogeneous samples.

Algorithms↗

PubMedDate not supplied

A diffusion theory model of spatially resolved, steady-state diffuse reflectance for the noninvasive determination of tissue optical properties in vivo.

A model based upon steady-state diffusion theory which describes the radial dependence of diffuse reflectance of light from tissues is developed. This model incorporates a photon dipole source in order to satisfy the tissue boundary conditions and is suitable for either refractive index matched or mismatched surfaces. The predictions of the model were compared with Monte Carlo simulations as well as experimental measurements made with tissue simulating phantoms. The model describes the reflectance data accurately to radial distances as small as 0.5 mm when compared to Monte Carlo simulations and agrees with experimental measurements to distances as small as 1 mm. A nonlinear least-squares fitting procedure has been used to determine the tissue optical properties from the radial reflectance data in both phantoms and tissues in vivo. The optical properties derived for the phantoms are within 5%-10% of those determined by other established techniques. The in vivo values are also consistent with those reported by other investigators.

Diffusion↗