Triple Spectral Line Imaging of Whole-Body Human Skin: Equipment, Image Processing, and Clinical Data.

Multispectral imaging can provide objective quantitative data on various clinical pathologies, e.g., abnormal content of bio-substances in human skin.

Hyperspectral imaging to accurately segment skin erythema and hyperpigmentation in cutaneous chronic graft-versus-host disease.

In 51 lesions from 15 patients with the inflammatory skin condition chronic graft-versus-host-disease, hyperspectral imaging accurately delineated active erythema and post-inflammatory hyperpigmentation. The method was validated by dermatologist-approved confident delineations of only definitely affected and definitely unaffected areas in photographs. A prototype hyperspectral imaging system acquired a 2.

Three-dimensional representation of triple spectral line imaging data as an option for noncontact skin diagnostics.

Significance: Skin malformations in dermatology are mostly evaluated subjectively, based on a doctor's experience and visual perception; an option for objective quantitative skin assessment is camera-based spectrally selective diagnostics. Multispectral imaging is a technique capable to provide information about concentrations of the absorbing chromophores and their distribution over the malformation in a noncontact way. Conversion of spectral images into distribution maps of chromophores can be performed by means of the modified Beer-Lambert law.

Skin chromophore mapping by smartphone RGB camera under spectral band and spectral line illumination.

Significance: Multispectral imaging enables mapping of chromophore content changes in skin neoplasms, which helps to diagnose a pathology. Different types of light sources can be used for the imaging. Design of laser-based illuminators is more complicated and, consequently, they are more expensive than LED-based illuminators.

Beer-Lambert law for optical tissue diagnostics: current state of the art and the main limitations.

Significance: Beer-Lambert law (BLL) is a widely used tool for contact and remote determination of absorber concentration in various media, including living tissues. Originally proposed in the 18th century as a simple exponential expression, it has survived numerous modifications and updates. The basic assumptions of this law may not be fulfilled in real measurement conditions.

Remitted photon path lengths in human skin: measurement data.

The remitted photon path lengths in human skin can be estimated by modelling; however, there are very few experimental data available to validate the simulations. This study exploited the photon time of flight method where picosecond laser pulses at seven wavelength bands in the spectral range 560-800 nm were launched into forearm skin of 10 volunteers via an optical fiber. The pulses of back-scattered light were detected via another optical fiber placed at variable distance (1, 8, 12, 16 or 20 mm) from the input fiber, with subsequent analysis of their shapes for all 35 spectral-spatial combinations.

Autofluorescence imaging for recurrence detection in skin cancer postoperative scars.

This clinical study is a first attempt to use autofluorescence for recurrence diagnosis of skin cancer in postoperative scars. The proposed diagnostic parameter is based on a reduction in scar autofluorescence, evaluated in the green spectral channel. The validity of the method has been tested on 110 postoperative scars from 56 patients suspected of non-melanoma skin cancer, with eight patients (13 scars) available for the repeated examination.

Photoplethysmography in dogs and cats: a selection of alternative measurement sites for a pet monitor.

Objective: Photoplethysmography (PPG) is an increasingly popular health and well-being tool for monitoring heart rate and oxygen saturation. Due to the pigmentation and hairiness of dogs and cats, a pulse oximeter is routinely placed solely on the tongue. As this approach is feasible only for pet monitor use during surgical procedures, we investigate PPG signal quality on several other measurement sites that would be better tolerated by conscious animals.

Differentiation of seborrheic keratosis from basal cell carcinoma, nevi and melanoma by RGB autofluorescence imaging.

A clinical trial on the autofluorescence imaging of skin lesions comprising 16 dermatologically confirmed pigmented nevi, 15 seborrheic keratosis, 2 dysplastic nevi, histologically confirmed 17 basal cell carcinomas and 1 melanoma was performed. The autofluorescence spatial properties of the skin lesions were acquired by smartphone RGB camera under 405 nm LED excitation. The diagnostic criterion is based on the calculation of the mean autofluorescence intensity of the examined lesion in the spectral range of 515 nm-700 nm.

Multispectral, Fluorescent and Photoplethysmographic Imaging for Remote Skin Assessment.

Optical tissue imaging has several advantages over the routine clinical imaging methods, including non-invasiveness (it does not change the structure of tissues), remote operation (it avoids infections) and the ability to quantify the tissue condition by means of specific image parameters. Dermatologists and other skin experts need compact (preferably pocket-size), self-sustaining and easy-to-use imaging devices. The operational principles and designs of ten portable in-vivo skin imaging prototypes developed at the Biophotonics Laboratory of Institute of Atomic Physics and Spectroscopy, University of Latvia during the recent five years are presented in this paper.

Smartphone snapshot mapping of skin chromophores under triple-wavelength laser illumination.

Chromophore distribution maps are useful tools for skin malformation severity assessment and for monitoring of skin recovery after burns, surgeries, and other interactions. The chromophore maps can be obtained by processing several spectral images of skin, e.g.

Comparison of single-spot technique and RGB imaging for erythema index estimation.

A commercially available point measurement device, the Mexameter(®), and an experimental RGB imaging prototype device were used for erythema index estimation of 50 rosacea patients by analysing the level of skin redness on the forehead, both cheeks and both sides of a nose. Results are compared with Clinician's Erythema Assessment (CEA) values given by two dermatologists. The Mexameter uses 568 nm and 660 nm LEDs and a photodetector for estimation of erythema index, while the used prototype device acquired RGB images at 460 nm, 530 nm and 665 nm LED illumination.

Autofluorescence imaging of basal cell carcinoma by smartphone RGB camera.

The feasibility of smartphones for in vivo skin autofluorescence imaging has been investigated. Filtered autofluorescence images from the same tissue area were periodically captured by a smartphone RGB camera with subsequent detection of fluorescence intensity decreasing at each image pixel for further imaging the planar distribution of those values. The proposed methodology was tested clinically with 13 basal cell carcinoma and 1 atypical nevus.

Study of smartphone suitability for mapping of skin chromophores.

RGB (red-green-blue) technique for mapping skin chromophores by smartphones is proposed and studied. Three smartphones of different manufacturers were tested on skin phantoms and in vivo on benign skin lesions using a specially designed light source for illumination. Hemoglobin and melanin indices obtained by these smartphones showed differences in both tests.

Snapshot RGB mapping of skin melanin and hemoglobin.

The concept of snapshot red-green-blue (RGB) multispectral imaging was applied for skin chromophore mapping. Three monochromatic spectral images have been extracted from a single RGB image dataset at simultaneous illumination of skin by 473-, 532-, and 659-nm laser lines. The spectral images were further transformed into distribution maps of skin melanin, oxyhemoglobin, and deoxyhemoglobin, related to pigmented and vascular skin malformations.

Photobleaching effects on in vivo skin autofluorescence lifetime.

The autofluorescence lifetime of healthy human skin was measured using excitation provided by a picosecond diode laser operating at a wavelength of 405 nm and with fluorescence emission collected at 475 and 560 nm. In addition, spectral and temporal responses of healthy human skin and intradermal nevus in the spectral range 460 to 610 nm were studied before and after photobleaching. A decrease in the autofluorescences lifetimes changes was observed after photobleaching of human skin.

Noncontact monitoring of vascular lesion phototherapy efficiency by RGB multispectral imaging.

A prototype low-cost RGB imaging system consisting of a commercial RGB CMOS sensor, RGB light-emitting diode ring light illuminator, and a set of polarizers was designed and tested for mapping the skin erythema index, in order to monitor skin recovery after phototherapy of vascular lesions, such as hemangiomas and telangiectasias. The contrast of erythema index (CEI) was proposed as a parameter for quantitative characterization of vascular lesions. Skin recovery was characterized as a decrease of the CEI value relative to the value before the treatment.

Clinical evaluation of melanomas and common nevi by spectral imaging.

A clinical trial on multi-spectral imaging of malignant and non-malignant skin pathologies comprising 17 melanomas and 65 pigmented common nevi was performed. Optical density data of skin pathologies were obtained in the spectral range 450-950 nm using the multispectral camera Nuance EX. An image parameter and maps capable of distinguishing melanoma from pigmented nevi were proposed.

Towards noncontact skin melanoma selection by multispectral imaging analysis.

A clinical trial comprising 334 pigmented and vascular lesions has been performed in three Riga clinics by means of multispectral imaging analysis. The imaging system Nuance 2.4 (CRi) and self-developed software for mapping of the main skin chromophores were used.

Contact and contactless diffuse reflectance spectroscopy: potential for recovery monitoring of vascular lesions after intense pulsed light treatment.

Optical fiber contact probe diffuse reflectance spectroscopy and remote multispectral imaging methods in the spectral range of 400 to 1100 nm were used for skin vascular malformation assessment and recovery tracing after treatment by intense pulsed light. The results confirmed that oxy-hemoglobin relative changes and the optical density difference between lesion and healthy skin in the spectral region 500 to 600 nm may be successfully used for objective appraisal of the therapy effect. Color redness parameter a* = 2 is suggested as a diagnostic border to distinguish healthy skin and vascular lesions, and as the indicator of phototreatment efficiency.

2-D mapping of skin chromophores in the spectral range 500 - 700 nm.

The multi-spectral imaging technique has been used for distant mapping of in-vivo skin chromophores by analyzing spectral data at each reflected image pixel and constructing 2-D maps of the relative concentrations of oxy-/deoxy-haemoglobin and melanin. Instead of using a broad visible-NIR spectral range, this study focuses on narrowed spectral band 500-700 nm, speeding-up the signal processing procedure. Regression analysis confirmed that superposition of three Gaussians is optimal analytic approximation for the oxy-haemoglobin absorption tabular spectrum in this spectral band, while superposition of two Gaussians fits well for deoxy-haemoglobin absorption and exponential function - for melanin absorption.

Imaging of laser-excited tissue autofluorescence bleaching rates.

Experimental methodology for imaging of laser-excited tissue autofluorescence bleaching rates has been developed and clinically tested. The fluorescence images were periodically captured from the same tissue area over a certain time, with subsequent detection of the fluorescence intensity decrease rate at each image pixel and further imaging the planar distribution of those values. Spectral features at each image pixel were analyzed with a hyperspectral imaging camera.

Multilaser photoplethysmography technique.

New technique for parallel recording of reflection photoplethysmography signals in broad spectral band (violet to NIR) has been developed based on fiber-coupled laser irradiation and time-resolved spectrometric detection. Differences in photoplethysmography waveforms that were recorded simultaneously at different wavelengths confirmed the depth variety of the skin blood pulsation dynamics, thus the proposed methodology has a potential for application in skin microcirculation studies.

Simultaneous recording of skin blood pulsations at different vascular depths by multiwavelength photoplethysmography.

A new technique for parallel recording of reflection photoplethysmography (PPG) signals in a broad spectral band (violet to near-infrared) has been developed, and its potential for assessment of blood microcirculation at various depths from the skin surface is discussed. PPG signals have been simultaneously detected at cw laser wavelength sets comprising 405, 532, 645, 807, and 1064 nm. Various signal baseline responses to breath holding and different shapes of the PPG pulses originated from the same heartbeat but recorded at different wavelengths have been observed, indicating a depth variety of the skin blood pulsation dynamics.