Optical signature of nerve tissue-Exploratory ex vivo study comparing optical, histological, and molecular characteristics of different adipose and nerve tissues.

BACKGROUND: During several anesthesiological procedures, needles are inserted through the skin of a patient to target nerves. In most cases, the needle traverses several tissues-skin, subcutaneous adipose tissue, muscles, nerves, and blood vessels-to reach the target nerve. A clear identification of the target nerve can improve the success of the nerve block and reduce the rate of complications. This may be accomplished with diffuse reflectance spectroscopy (DRS) which can provide a quantitative measure of the tissue composition. The goal of the current study was to further explore the morphological, biological, chemical, and optical characteristics of the tissues encountered during needle insertion to improve future DRS classification algorithms. METHODS: To compare characteristics of nerve tissue (sciatic nerve) and adipose tissues, the following techniques were used: histology, DRS, absorption spectrophotometry, high-resolution magic-angle spinning nuclear magnetic resonance (HR-MAS NMR) spectroscopy, and solution 2D 13 C-1 H heteronuclear single-quantum coherence spectroscopy. Tissues from five human freshly frozen cadavers were examined. RESULTS: Histology clearly highlights a higher density of cellular nuclei, collagen, and cytoplasm in fascicular nerve tissue (IFAS). IFAS showed lower absorption of light around 1200 nm and 1750 nm, higher absorption around 1500 nm and 2000 nm, and a shift in the peak observed around 1000 nm. DRS measurements showed a higher water percentage and collagen concentration in IFAS and a lower fat percentage compared to all other tissues. The scattering parameter (b) was highest in IFAS. The HR-MAS NMR data showed three extra chemical peak shifts in IFAS tissue. CONCLUSION: Collagen, water, and cellular nuclei concentration are clearly different between nerve fascicular tissue and other adipose tissue and explain some of the differences observed in the optical absorption, DRS, and HR-NMR spectra of these tissues. Some differences observed between fascicular nerve tissue and adipose tissues cannot yet be explained but may be helpful in improving the discriminatory capabilities of DRS in anesthesiology procedures. Lasers Surg. Med. 50:948-960, 2018. © 2018 The Authors. Lasers in Surgery and Medicine Published by Wiley Periodicals, Inc.

Nerve detection using optical spectroscopy, an evaluation in four different models: In human and swine, in-vivo, and post mortem.

OBJECTIVE: Identification of peripheral nerve tissue is crucial in both surgery and regional anesthesia. Recently, optical tissue identification methods are presented to facilitate nerve identification in transcutaneous procedures and surgery. Optimization and validation of such techniques require large datasets. The use of alternative models to human in vivo, like human post mortem, or swine may be suitable to test, optimize and validate new optical techniques. However, differences in tissue characteristics and thus optical properties, like oxygen saturation and tissue perfusion are to be expected. This requires a structured comparison between the models. STUDY DESIGN: Comparative observational study. METHODS: Nerve and surrounding tissues in human (in vivo and post mortem) and swine (in vivo and post mortem) were structurally compared macroscopically, histologically, and spectroscopically. Diffuse reflective spectra were acquired (400-1,600 nm) after illumination with a broad band halogen light. An analytical model was used to quantify optical parameters including concentrations of optical absorbers. RESULTS: Several differences were found histologically and in the optical parameters. Histologically nerve and adipose tissue (subcutaneous fat and sliding fat) showed clear similarities between human and swine while human muscle enclosed more adipocytes and endomysial collagen. Optical parameters revealed model dependent differences in concentrations of ß-carotene, water, fat, and oxygen saturation. The similarity between optical parameters is, however, sufficient to yield a strong positive correlation after cross model classification. CONCLUSION: This study shows and discusses similarities and differences in nerve and surrounding tissues between human in vivo and post mortem, and swine in vivo and post mortem; this could support the discussion to use an alternative model to optimize and validate optical techniques for clinical nerve identification. Lasers Surg. Med. 50:253-261, 2018. © 2017 Wiley Periodicals, Inc.

Nerve detection with optical spectroscopy for regional anesthesia procedures.

BACKGROUND: Regional anesthesia has several advantages over general anesthesia but requires accurate needle placement to be effective. To achieve accurate placement, a needle equipped with optical fibers that allows tissue discrimination at the needle tip based on optical spectroscopy is proposed. This study investigates the sensitivity and specificity with which this optical needle can discriminate nerves from the surrounding tissues making use of different classification methods. METHODS: Diffuse reflectance spectra were acquired from 1563 different locations from 19 human cadavers in the wavelength range of 400-1710 nm; measured tissue types included fascicular tissue of the nerve, muscle, sliding fat and subcutaneous fat. Physiological parameters of the tissues were derived from the measured spectra and part of the data was directly compared to histology. Various classification methods were then applied to the derived parameter dataset to determine the accuracy with which fascicular tissue of the nerve can be discriminated from the surrounding tissues. RESULTS: From the parameters determined from the measured spectra of the various tissues surrounding the nerve, fat content, blood content, beta-carotene content and scattering were most distinctive when comparing fascicular and non-fascicular tissue. Support Vector Machine classification with a combination of feature selections performed best in discriminating fascicular nerve tissue from the surrounding tissues with a sensitivity and specificity around 90 %. CONCLUSIONS: This study showed that spectral tissue sensing, based on diffuse reflectance spectroscopy at the needle tip, is a promising technique to discriminate fascicular tissue of the nerve from the surrounding tissues. The technique may therefore improve accurate needle placement near the nerve which is necessary for effective nerve blocks in regional anesthesia.

Diffuse reflectance spectroscopy: towards clinical application in breast cancer.

Diffuse reflectance spectroscopy (DRS) is a promising new technique for breast cancer diagnosis. However, inter-patient variation due to breast tissue heterogeneity may interfere with the accuracy of this technique. To tackle this issue, we aim to determine the diagnostic accuracy of DRS in individual patients. With this approach, DRS measurements of normal breast tissue in every individual patient are directly compared with measurements of the suspected malignant tissue. Breast tissue from 47 female patients was analysed ex vivo by DRS. A total of 1,073 optical spectra were collected. These spectra were analyzed for each patient individually as well as for all patients collectively and results were compared to the pathology analyses. Collective patient data analysis for discrimination between normal and malignant breast tissue resulted in a sensitivity of 90 %, a specificity of 88 %, and an overall accuracy of 89 %. In the individual analyses all measurements per patient were categorized as either benign or malignant. The discriminative accuracy of these individual analyses was nearly 100 %. The diagnosis was classified as uncertain in only one patient. Based on the results presented in this study, we conclude that the analysis of optical characteristics of different tissue classes within the breast of a single patient is superior to an analysis using the results of a cohort data analysis. When integrated into a biopsy device, our results demonstrate that DRS may have the potential to improve the diagnostic workflow in breast cancer.

Clot composition characterization using diffuse reflectance spectroscopy in acute ischemic stroke.

Acute ischemic stroke caused by large vessel occlusion is treated with endovascular thrombectomy, but treatment failure may occur when clot composition and thrombectomy technique mismatch. In this proof-of-concept study, diffuse reflectance spectroscopy (DRS) is evaluated for identification of clot composition ex vivo. DRS spectra and histology were acquired from 45 clot units retrieved from 29 stroke patients. DRS spectra correlated to clot RBC content, R= 81, p < .001, and could discriminate between RBC-rich and fibrin-rich clots, p < 0.001. Sensitivity and specificity for detection of RBC-rich clots were 0.722 and 0.846 respectively. Applied in an intravascular device, DRS could potentially provide intraprocedural information on clot composition that could increase endovascular thrombectomy efficiency.

Identifying clot composition using intravascular diffuse reflectance spectroscopy in a porcine model of endovascular thrombectomy.

BACKGROUND: Endovascular thrombectomy has revolutionized the management of acute ischemic stroke and proven superior to stand-alone intravenous thrombolysis for large vessel occlusions. However, failed or delayed revascularization may occur as a result of a mismatch between removal technique and clot composition. Determination of clot composition before thrombectomy provides the possibility to adapt the technique to improve clot removal efficacy. We evaluated the application of diffuse reflectance spectroscopy (DRS) for intravascular determination of clot composition in vivo. METHODS: Three clot types, enriched in red blood cells or fibrin or with a mixed content, were prepared from porcine blood and injected into the external carotids of a domestic pig. A guidewire-like DRS probe was used to investigate the optical spectra of clots, blood and vessel wall. Measurement positions were confirmed with angiography. Spectra were analyzed by fitting an optical model to derive physiological parameters. To evaluate the method's accuracy, photon scattering and blood and methemoglobin contents were included in a decision tree model and a random forest classification. RESULTS: DRS could differentiate between the three different clot types, blood and vessel wall in vivo (p<0.0001). The sensitivity and specificity for detection was 73.8% and 98.8% for red blood cell clots, 80.6% and 97.8% for fibrin clots, and 100% and 100% for mixed clots, respectively. CONCLUSION: Intravascular DRS applied via a custom guidewire can be used for reliable determination of clot composition in vivo. This novel approach has the potential to increase efficacy of thrombectomy procedures in ischemic stroke.

Spectral tissue sensing to identify intra- and extravascular needle placement - A randomized single-blind controlled trial.

Safe vascular access is a prerequisite for intravenous drug admission. Discrimination between intra- and extravascular needle position is essential for procedure safety. Spectral tissue sensing (STS), based on optical spectroscopy, can provide tissue information directly from the needle tip. The primary objective of the trial was to investigate if STS can reliably discriminate intra-vascular (venous) from non-vascular punctures. In 20 healthy volunteers, a needle with an STS stylet was inserted, and measurements were performed for two intended locations: the first was subcutaneous, while the second location was randomly selected as either subcutaneous or intravenous. The needle position was assessed using ultrasound (US) and aspiration. The operators who collected the data from the spectral device were blinded to the insertion and ultrasonographic visualization procedure and the physician was blinded to the spectral data. Following offline spectral analysis, a prediction of intravascular or subcutaneous needle placement was made and compared with the "true" needle tip position as indicated by US and aspiration. Data for 19 volunteers were included in the analysis. Six out of 8 intended vascular needle placements were defined as intravascular according to US and aspiration. The remaining two intended vascular needle placements were negative for aspiration. For the other 11 final needle locations, the needle was clearly subcutaneous according to US examination and no blood was aspirated. The Mann-Whitney U test yielded a p-value of 0.012 for the between-group comparison. The differences between extra- and intravascular were in the within-group comparison computed with the Wilcoxon signed-rank test was a p-value of 0.022. In conclusion, STS is a promising method for discriminating between intravascular and extravascular needle placement. The information provided by this method may complement current methods for detecting an intravascular needle position.

The Role of Spectral Tissue Sensing During Lumbar Transforaminal Epidural Injection.

Spectral tissue sensing (STS) exploits the scattering and absorption of light by tissue. The main objective of the present study was to determine whether STS can discriminate between correct and incorrect placement of the needle tip during lumbar transforaminal epidural injection. This was a single-blind prospective observational study in 30 patients with lumbar radicular pain scheduled for lumbar transforaminal epidural injection. Spectral tissue sensing data from the needle tip were acquired along the needle trajectory at 4 predefined measurement points and compared with ultrasound, fluoroscopy, and digital subtraction angiography images. Spectral tissue sensing data contained the full spectra. The lipid and hemoglobin content at the different measurement points was also calculated, and partial least-squares discriminant analysis was used to estimate the sensitivity and specificity of STS. Spectral tissue sensing identified correct needle placement with a sensitivity of 57% and a specificity of 82%, and intraforaminal versus extraforaminal locations were identified with a sensitivity of 80% and a specificity of 71%.

Real-time In Vivo Tissue Characterization with Diffuse Reflectance Spectroscopy during Transthoracic Lung Biopsy: A Clinical Feasibility Study.

PURPOSE: This study presents the first in vivo real-time tissue characterization during image-guided percutaneous lung biopsies using diffuse reflectance spectroscopy (DRS) sensing at the tip of a biopsy needle with integrated optical fibers. EXPERIMENTAL DESIGN: Tissues from 21 consented patients undergoing lung cancer surgery were measured intraoperatively using the fiber-optic platform capable of assessing various physical tissue properties highly correlated to tissue architecture and composition. In addition, the method was tested for clinical use by performing DRS tissue sensing during 11 routine biopsy procedures in patients with suspected lung cancer. RESULTS: We found that water content and scattering amplitude are the primary discriminators for the transition from healthy lung tissue to tumor tissue and that the reliability of these parameters is not affected by the amount of blood at the needle tip. In the 21 patients measured intraoperatively, the water-to-scattering ratio yielded a 56% to 81% contrast difference between tumor and surrounding tissue. Analysis of the 11 image-guided lung biopsy procedures showed that the tissue diagnosis derived from DRS was diagnostically discriminant in each clinical case. CONCLUSIONS: DRS tissue sensing integrated into a biopsy needle may be a powerful new tool for biopsy guidance that can be readily used in routine diagnostic lung biopsy procedures. This approach may not only help to increase the successful biopsy yield for histopathologic analysis, but may also allow specific sampling of vital tumor tissue for genetic profiling.

A library based fitting method for visual reflectance spectroscopy of human skin.

The diffuse reflectance spectrum of human skin in the visible region (400-800 nm) contains information on the concentrations of chromophores such as melanin and haemoglobin. This information may be extracted by fitting the reflectance spectrum with an optical diffusion based analytical expression applied to a layered skin model. With the use of the analytical expression, it is assumed that light transport is dominated by scattering. For port wine stain (PWS) and highly pigmented human skin, however, this assumption may not be valid resulting in a potentially large error in visual reflectance spectroscopy (VRS). Monte Carlo based techniques can overcome this problem but are currently too computationally intensive to be combined with previously used fitting procedures. The fitting procedure presented herein is based on a library search which enables the use of accurate reflectance spectra based on forward Monte Carlo simulations or diffusion theory. This allows for accurate VRS to characterize chromophore concentrations in PWS and highly pigmented human skin. The method is demonstrated using both simulated and measured reflectance spectra. An additional advantage of the method is that the fitting procedure is very fast.

Characterization of age-related effects in human skin: A comparative study that applies confocal laser scanning microscopy and optical coherence tomography.

Skin structure and age-related changes in human skin were characterized in vivo by applying confocal laser scanning microscopy (CLSM) and optical coherence tomography (OCT). The overall effect of aging skin, derived from studies of volunteers belonging to two age groups, was found to be a significant decrease in the maximum thickness of the epidermis and flattening of the dermo-epidermal junction. At a certain depth in the dermis, well below the basal layer, a reflecting layer of fibrous structure is observed in CLSM images. The location of this layer strongly depends on age and is situated much deeper below the skin surface in younger than in older skin. In addition, large structural changes were observed with age. The OCT images show two bright reflecting layers. The first one is due to scattering at the skin surface. The second band appears to be caused by a layer of fibrous structure in the dermis. Direct comparison of CLSM and OCT suggests that the same fibrous layer is imaged by the two techniques. This layer might be due to the transition between the papillary and reticular dermis. A comparison of CLSM and OCT enables a better understanding of the images.

Improved identification of peripheral lung tumors by using diffuse reflectance and fluorescence spectroscopy.

INTRODUCTION: A significant number of transthoracic diagnostic biopsy procedures for lung lesions show indeterminate results. Such failures are potentially due to inadequate recognition of vital tumor tissue. The objective of this study was to evaluate whether optical spectroscopy at the tip of a biopsy needle device can improve the accuracy of transthoracic lung biopsies. METHODS: Ex vivo optical measurements were performed on lung tissue from 13 patients who underwent either lobectomy or segmental resection for primary non-small cell lung cancer or pulmonary metastases from various origins. From Diffuse Reflectance Spectroscopy (DRS) and Fluorescence Spectroscopy (FS) measurements, different parameters were derived such as tissue composition as well as physiological and metabolic characteristics. Subsequently, a classification and regression trees (CART) algorithm was used to classify the type of tissue based on the derived parameters. Histology analysis was used as gold standard to report sensitivity and specificity of the tissue classification based on the present optical method. RESULTS: Collective analysis of all DRS measurements showed an overall discrimination between lung parenchyma and tumor tissue with a sensitivity and specificity of 98 and 86%, respectively. When the data were analyzed per individual patient, eliminating inter-patient variation, 100% sensitivity and specificity was achieved. Furthermore, based on FS parameters, necrotic and non-necrotic tumor tissue could be distinguished with 91% sensitivity and specificity. CONCLUSION: This study demonstrates that DRS provides accurate diagnosis of malignant lung lesions, whereas FS enables identification of necrotic tissue. When both optical techniques are combined within a biopsy device, the diagnostic performance and the quality of transthoracic biopsies could significantly be enhanced.

Optical detection of vascular penetration during nerve blocks: an in vivo human study.

BACKGROUND AND OBJECTIVES: Complications resulting from vascular penetration during nerve blocks are rare but potentially devastating events that can occur despite meticulous technique. In this in vivo human pilot study, we investigated the potential for detecting vascular penetration with optical reflectance spectroscopy during blocks of the sympathetic chain and the communicating ramus at lumbar levels. METHODS: A custom-designed needle stylet with integrated optical fibers was used in combination with a commercial needle shaft. The needle stylet was connected to a console that delivered broadband light to tissue and spectrally resolved light that was scattered near the stylet tip. A total of 18 insertions were performed on 10 patients; testing for vascular penetration at the nerve target region was performed with aspiration and with radio-opaque contrast injections, visualized fluoroscopically. Optical absorption by hemoglobin was quantified with a blood parameter that was calculated from each spectrum. The blood parameter provided a measure of the difference between spectra acquired from the nerve target region and reference spectra acquired from blood extracted from a volunteer. RESULTS: In 2 insertions, vascular penetration was detected. Pronounced optical absorption by hemoglobin was observed to be associated with both of these events and absent in all other cases. The difference between the blood parameters obtained when vascular penetration was detected, and all other blood parameters were statistically significant (P = 0.006), with a diagnostic odds ratio of 35.4 (confidence interval, 2.21 to ∞). CONCLUSIONS: The results from this study suggest that optical spectroscopy has the potential to detect intravascular needle placement, which may in turn increase the safety of nerve blocks.

Diffuse reflectance spectroscopy: a new guidance tool for improvement of biopsy procedures in lung malignancies.

BACKGROUND: A significant number of percutaneous intrathoracic biopsy procedures result in indeterminate cytologic or histologic diagnosis in clinical practice. Diffuse reflectance spectroscopy (DRS) is an optical technique that can distinguish different tissue types on a microscopic level. DRS may improve needle localization accuracy during biopsy procedures. The objective of this study was to assess the ability of DRS to enhance diagnosis of malignant disease in human lung tissue. METHODS: Ex vivo analysis with a DRS system was performed on lung tissue from 10 patients after pulmonary resection for malignant disease. Tissue spectra measured from 500 to 1600 nm were analyzed using 2 analysis methods; a model-based analysis that derives clinical and optical properties from the measurements and a partial least-squares discriminant analysis (PLS-DA) that classifies measured spectra with respect to the histologic nature of the measured tissue. RESULTS: Sensitivity and specificity for discrimination of tumor from normal lung tissue were 89% and 79%, respectively, based on the model-based analysis. Overall accuracy was 84%. The PLS-DA analysis yielded a sensitivity of 78%, a specificity of 86%, and an overall accuracy of 81%. CONCLUSIONS: The presented results demonstrate that DRS has the potential to enhance diagnostic accuracy in minimally invasive biopsy procedures in the lungs in combination with conventional imaging techniques.

Optical detection of peripheral nerves: an in vivo human study.

BACKGROUND AND OBJECTIVES: A critical challenge encountered in interventional pain medicine procedures is to accurately and efficiently identify transitions to peripheral nerve targets. Current methods, which include ultrasound guidance and nerve stimulation, are not perfect. In this pilot study, we investigated the feasibility of identifying tissue transitions encountered during insertions toward peripheral nerve targets using optical spectroscopy. METHODS: Using a custom needle stylet with integrated optical fibers, ultrasound-guided insertions toward peripheral nerves were performed in 20 patients, with the stylet positioned in the cannula of a 20-gauge stimulation needle. Six different peripheral nerves were represented in the study, with 1 insertion per patient. During each insertion, optical reflectance spectra were acquired with the needle tip in subcutaneous fat, skeletal muscle, and at the nerve target region. Differences in the spectra were quantified with 2 parameters that provide contrast for lipid and hemoglobin, respectively. RESULTS: The transition of the needle tip from subcutaneous fat to muscle was associated with lower lipid parameter values (P = 0.003) and higher hemoglobin parameter values (P = 0.023). The transition of the needle tip from the muscle to the nerve target region was associated with higher lipid parameter values (P = 0.008). CONCLUSIONS: The results indicate that the spectroscopic information provided by the needle stylet could potentially allow for reliable identification of transitions from subcutaneous fat to skeletal muscle and from the muscle to the nerve target region during peripheral nerve blocks.

Needle stylet with integrated optical fibers for spectroscopic contrast during peripheral nerve blocks.

The effectiveness of peripheral nerve blocks is highly dependent on the accuracy at which the needle tip is navigated to the target injection site. Even when electrical stimulation is utilized in combination with ultrasound guidance, determining the proximity of the needle tip to the target region close to the nerve can be challenging. Optical reflectance spectroscopy could provide additional information about tissues that is complementary to these navigation methods. We demonstrate a novel needle stylet for acquiring spectra from tissue at the tip of a commercial 20-gauge needle. The stylet has integrated optical fibers that deliver broadband light to tissue and receive scattered light. Two spectrometers resolve the light that is received from tissue across the wavelength range of 500-1600 nm. In our pilot study, measurements are acquired from a postmortem dissection of the brachial plexus of a swine. Clear differences are observed between spectra acquired from nerves and those acquired from adjacent tissue structures. We conclude that spectra acquired with the stylet have the potential to increase the accuracy with which peripheral nerve blocks are performed.

Effect of bile absorption coefficients on the estimation of liver tissue optical properties and related implications in discriminating healthy and tumorous samples.

We investigated differences between healthy tissue and metastatic tumor from ex vivo human partial liver resections using diffuse optical spectroscopy with a fiber optic probe. We extracted various physiological and morphological parameters from the spectra. During evaluation of the residual between the measurements and a fit model based on diffusion theory, we found that bile is an additional chromophore absorbing in the visible wavelength range that was missing in our model. Consistency of the residual with the absorption spectrum of bile was noticed. An accurate measurement of the absorption coefficient of bile from various human bile samples was performed and implemented into the fit model. Having the absorption coefficient of bile as a priori knowledge in the model showed a clear improvement in terms of reducing the fitting discrepancies. The addition of this chromophore yields significantly different estimates of the amount of blood. Furthermore, the estimated bile volume fraction and reduced scattering amplitude turned out to be two main relevant discriminators between normal and metastatic liver tissues.

High-resolution resonant and nonresonant fiber-scanning confocal microscope.

We present a novel, hand-held microscope probe for acquiring confocal images of biological tissue. This probe generates images by scanning a fiber-lens combination with a miniature electromagnetic actuator, which allows it to be operated in resonant and nonresonant scanning modes. In the resonant scanning mode, a circular field of view with a diameter of 190 µm and an angular frequency of 127 Hz can be achieved. In the nonresonant scanning mode, a maximum field of view with a width of 69 µm can be achieved. The measured transverse and axial resolutions are 0.60 and 7.4 µm, respectively. Images of biological tissue acquired in the resonant mode are presented, which demonstrate its potential for real-time tissue differentiation. With an outer diameter of 3 mm, the microscope probe could be utilized to visualize cellular microstructures in vivo across a broad range of minimally-invasive procedures.

Diagnosis of breast cancer using diffuse optical spectroscopy from 500 to 1600 nm: comparison of classification methods.

We report on the use of diffuse optical spectroscopy analysis of breast spectra acquired in the wavelength range from 500 to 1600 nm with a fiber optic probe. A total of 102 ex vivo samples of five different breast tissue types, namely adipose, glandular, fibroadenoma, invasive carcinoma, and ductal carcinoma in situ from 52 patients were measured. A model deriving from the diffusion theory was applied to the measured spectra in order to extract clinically relevant parameters such as blood, water, lipid, and collagen volume fractions, ß-carotene concentration, average vessels radius, reduced scattering amplitude, Mie slope, and Mie-to-total scattering fraction. Based on a classification and regression tree algorithm applied to the derived parameters, a sensitivity-specificity of 98%-99%, 84%-95%, 81%-98%, 91%-95%, and 83%-99% were obtained for discrimination of adipose, glandular, fibroadenoma, invasive carcinoma, and ductal carcinoma in situ, respectively; and a multiple classes overall diagnostic performance of 94%. Sensitivity-specificity values obtained for discriminating malignant from nonmalignant tissue were compared to existing reported studies by applying the different classification methods that were used in each of these studies. Furthermore, in these reported studies, either lipid or ß-carotene was considered as adipose tissue precursors. We estimate both chromophore concentrations and demonstrate that lipid is a better discriminator for adipose tissue than ß-carotene.

Vasoconstrictive effect of topical applied corticosteroids measured by laser doppler imaging and reflectance spectroscopy.

Topical application of corticosteroids induces blanching of the skin, based on changes of the underlying microcirculation of the skin. Usually the intensity of blanching after topical application of corticosteroids is measured subjectively by a trained observer using a visual score. In order to obtain an objective determination of the blanching effect and to assess the underlying effect of the skin perfusion, it is necessary to use noninvasive bioengineering techniques. The aim of this study was to compare changes in the vascular plexus during 72 h after topical application of corticosteroids of different potencies with control sites by two noninvasive techniques: laser Doppler imaging (LDI) and diffuse reflectance spectroscopy (DRS). We used the most potent vasoconstrictor, Clobetasol-di-propionate. After 8 h (1.49 Rm (mean reflectance) +/- 0.6 SEM) and after 30 h (0.52 Rm +/- 0.36) DRS showed significant changes in blood flow (during blanching and reactive hyperemia). LDI showed a slight change after 8 h (-0.04 aU (arbitrary units) +/- 0.02 blanching) and a second, significant reaction after 30 h (LDI: 0.18 aU +/- 0.04 reactive hyperemia). In LDI after 30 h higher values were found in men than in women (clobetasol-17-propionate under occlusion Deltat(30)-t(0) men: 0.47 aU +/- 0.18; n = 7; Deltat(30)-t(0) women: 0.14 aU +/- 0.02; n = 10; P = 0.025). This leads to the conclusion that DRS is of more value for the detection of blanching than LDI, which has its sensitivity in the hyperperfused skin. Measurement with both devices showed clear differences in men and women, which means that sex differences should be taken into account.