Numerous autoimmune, drug-induced, genetic, and inflammatory skin diseases and even scars can benefit from such assessment. Herein we will discuss two examples: patch test quantification used in the diagnosis of contact dermatitis, and monitoring the efficacy of vascular lesion treatments. In medical practice, blood flow measurement can be applied to patch testing, which is used to diagnose contact allergy. Indeed this in vivo test aims to mimic allergic contact dermatitis by reproducing the triggering step of the reaction to a contact allergen 9.
The methodology is simple and consists in applying allergens under occlusion on the skin under standardized conditions. However it requires adequate training for the results to be correctly interpreted and used, especially when a too weakly positive reaction appears. In this case, an objective and user-independent assessment of the test reaction can be obtained using blood flow measurement by either laser Doppler or speckle imaging.
Laser doppler imaging of blood flow in a patch test. Printed with permission from Fullerton et al.
The perfusion image can be analysed by an integrated system software. The relative colour scale extends from the smallest and the largest perfusion value from green to red. For cosmetic procedures, laser Doppler and speckle imaging can also be used to evaluate the performance of skin treatment by laser therapy, with the aim to improve its efficacy 2.
One factor is that the procedure relies on the subjective impression and overall experience of the clinician. The Speckle Flow Index SFI , obtained with laser speckle imaging instrumentation by converting raw speckle reflectance images to speckle contrast images, is a numerical value proportional to the degree of scatterer motion and is higher in feeding vessel regions Fig.
This indicator of microvasculature provides real-time, quantitative feedback during laser surgery, enabling the clinician to go back to the persistent perfusion areas until complete blanching is reached. Both laser Doppler and speckle imaging are innovative and individualized methods that could reduce the number of laser treatment sessions, hence optimizing results and diminishing the cost and potential risks associated with general anaesthesia for this intervention. Printed with permission from Huang Y.
Colour range indicates the level of blood flow in this area. Overall, these approaches are low cost technologies and offer a non-contact method of mapping? Meanwhile they present two main limitations: a low spatial resolution and a relative measurement of the blood flow only at a top surface view. Another potential limitation of laser speckle imaging is that the SFI values also are dependent on tissue optical properties.
Laser Doppler imaging is on the market and has been for some time, whereas laser speckle contrast imaging is still used mostly in the research setting.
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It may be worth further developing laser speckle technique for commercialization, because of 3 main advantages over laser Doppler imaging: lower cost, truly real-time operation enabling movies of perfusion changes 8 and potential ease of integration into current laser systems In clinical dermatology research, it is important to evaluate the efficiency of topical therapeutic interventions and decipher the mechanism underlying their effect, how they distribute and at which concentration in the skin.
For this purpose, it is necessary to quantify and follow the mapping of chemicals or biological compounds in the outermost layers of skin. Raman spectroscopy by contrast can identify skin constituents and provide spatially resolved molecular information under in vivo conditions in a non-invasive and rapid manner.
It is based on depth-resolved vibrational spectra of molecules at optical wavelengths and can monitor conformational changes in lipids and proteins of the skin. Thus, Raman is accepted as a reliable method to quickly and noninvasively measure skin hydration, retinol, lactate and many other molecules 12, Natural moisturising factor NMF is a breakdown product of filaggrin encoded by the gene FLG consisting mainly of a range of hydroscopic amino acids These mutations have a clear permissive effect in the early inflammatory phenomena that characterize eczema and affect both priming of disease and chronicity.
The early follow-up of NMF levels might therefore allow timely prophylactic treatment and appropriate surveillance. Raman spectra can provide specific signatures of NMF levels that predict FLG mutation status, overcoming the need for the more technically demanding genotyping or invasive investigation. Raman spectroscopy could also be applied to give fast and quantitative information before and after emollient application. A wide range of research applications for in vivo Raman spectroscopy is now available However, unlike other techniques that produce images, Raman is at present mainly used for single point measurement.
One significant limitation is that the weak Raman effect gives insufficient signal strength to quickly acquire an image. This drawback can be overcome in the future through nonlinear implementations.
In particular, multiplex stimulated Raman scattering microscopy may provide rapid dynamic imaging at video rate to monitor delivery and diffusion of topical agents, such as sunscreens, moisturizers, tretinoin and metronidazole, through skin tissue in vivo As most chemicals of interest have known Raman spectra, nonlinear Raman technology should enable real-time ascertainment of their distribution without labelling and at the cellular scale in the skin. Multiphoton microscopy MPM is a femtosecond laser scanning microscopy technique based on nonlinear light-matter interactions to produce 3-dimensional 3D images with submicron resolution The most important signals are two-photon excited autofluorescence AF and second harmonic generation SHG.
By this way, images of endogenous biomolecules within tissue can be obtained without using specific fluorescent labels. Indeed, autofluorescence resulting from the distribution of endogenous fluorophores in tissue yields structural and biochemical information without fixation or staining procedures. The main compounds present in skin with two-photon autofluorescence are reduced nicotinamide adenine dinucleotide NADH , flavine adenine dinucleotide FAD , keratin, melanin, collagen, and elastin fibres Fig.
Furthermore, SHG is able to visualize collagen fibres in the dermis. Therefore, MPM provides non-invasive in vivo imaging of the epidermis and superficial dermis, providing useful morphological and label-free molecular information In vivo MPM imaging of normal human skin. Right, cross-sectional view x—z scan corresponding to a vertical plane through the horizontal sections on the left.
Early detection and accurate diagnosis of melanoma is therefore critical for a good prognosis and appropriate treatment. Current standard diagnosis is based on invasive biopsy and histopathologic examination. This observation has highlighted the urgent need to find more consistent skin tumour staging parameters to improve the accuracy of diagnosis decisions by dermatologists.
A few groups are exploring the ability of MPM to provide qualitative and quantitative information for diagnosis of skin lesions. The authors managed to derive a numerical multiphoton melanoma index MMI , combining 3 main criteria, the melanocyte dendrite density, SHG signal strength from collagen and the autofluorescence, which was able to distinguish benign from atypical naevi or melanoma.
Studies in larger patient populations are still necessary to validate the diagnostic performance of MPM for both melanocytic and non-melanocytic tumours Current MPM are unfortunately not suitable for wide-spread clinical use due to several limitations. Secondly, scan times are several orders of magnitude larger than for reflectance confocal microscopy, which provides similar resolution but no compositional information due to lack of discrimination of autofluorescence.
The penetration depth is non-inferior to confocal microscopy and much less of a concern in practice than the tiny sampled area accommodated by the fraction of a mm 2 field of view. Indeed, since skin lesions are often non-uniform, presenting focal dysplasia, skin areas in excess of a couple mm often have to be examined microscopically in order to avoid false-negative diagnoses. The scanning field can be increased by either acquiring mosaic images i. However MPM is unlikely in the foreseeable future to be able in a matter of minutes to capture entire lesions on the skin that are several mm 2 , which by contrast is the case for confocal imaging.
Therefore, MPM will need to undergo substantial advances before it can be used clinically for cancer diagnosis. Multiphoton microscopy is increasingly used in applied dermatological research, in the fields of skin aging, nanoparticle imaging, tissue engineering, and in situ screening of pharmaceutical and cosmetic products. It is particularly useful in skin aging clinical studies to obtain quantitative information on extracellular matrix components under physiological conditions, by measuring both the two-photon autofluorescence of elastin and the SHG of collagen.
This index is well correlated with skin photo-aging in vivo , and is a valuable tool, e. Photo-acoustic tomography PAT , also referred to as opto-acoustic tomography, is an emerging imaging technique with significant promise for biomedical applications.
In this technology, light is absorbed by biological tissue and converted to transient heating, which subsequently creates an ultrasonic wave by thermo-elastic expansion. Ultrasound can then be detected by broadband ultrasonic transducers, and converted into tomographic images.
Photo-acoustic imaging can be performed either by i relying on intrinsic tissue contrast alone e. This technology has the unique combined ability to make use of endogenous contrast alone to provide real-time images, at clinically relevant depths, with relatively high spatial resolution, all without the use of ionizing radiation.
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Laser Physics Letters ; 9 8 : The effect of local corticosteroid therapy and tacrolimus on morphological indices of different skin phototypes. Journal of Dermatology ; Summary: Aim: working out the methods of visualization of information obtained during optical coherent tomography in normal skin and in series of inflammatory disorders.
Keywords: optical coherent tomography , skin diseases diagnostics. All articles of the authors: Alonova M.
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