Contactless SpO with an RGB camera: experimental proof of calibrated SpO.

Camera-based blood oxygen saturation (SpO) monitoring allows reliable measurements without touching the skin and is therefore very attractive when there is a risk of cross-infection, in case of fragile skin, and/or to improve the clinical workflow. Despite promising results, productization of the technology is hampered by the unavailability of adequate hardware, especially a camera, which can capture the optimal wavelengths for SpO measurements in the red near-infrared region. A regular color (RGB) camera is attractive because of its availability, but also poses several risks and challenges which affect the accuracy of the measurement.

Reducing the effects of parallax in camera-based pulse-oximetry.

Camera-based pulse-oximetry enables contactless estimation of peripheral oxygen saturation (SpO). Because of the lack of readily available and affordable single-optics multi-spectral cameras, custom-made multi-camera setups with different optical filters are currently mostly used. The introduced parallax by these cameras could however jeopardise the SpO algorithm assumptions, especially during subject movement.

Pulse oximetry based on photoplethysmography imaging with red and green light : Calibratability and challenges.

Remotely measuring the arterial blood oxygen saturation (SpO) in visible light (Vis) involves different probing depths, which may compromise calibratibility. This paper assesses the feasibility of calibrating camera-based SpO (SpO) using red and green light. Camera-based photoplethysmographic (PPG) signals were measured at 46 healthy adults at center wavelengths of 580 nm (green), 675 nm (red), and 840 nm (near-infrared; NIR).

A Model for Waveform Dissimilarities in Dual-Depth Reflectance-PPG.

The pressure wave is attenuated as it travels through the vascular bed of tissue. Consequently, reflectance photoplethysmography (PPG) waveforms probed using dual-penetrating wavelengths, such as green (G) and red R; the deepest) are dissimilar. To unravel the dual-depth aspect of PPG, we modeled the wavelength-dependency of the shape of reflection-PPG signals in G (520-580 nm) and R (625-720nm).

Calibration of Contactless Pulse Oximetry.

Background: Contactless, camera-based photoplethysmography (PPG) interrogates shallower skin layers than conventional contact probes, either transmissive or reflective. This raises questions on the calibratability of camera-based pulse oximetry.

Methods: We made video recordings of the foreheads of 41 healthy adults at 660 and 840 nm, and remote PPG signals were extracted.

What is sensitive skin? A systematic literature review of objective measurements.

Despite sensitive skin being highly prevalent, no consensus on the definition and pathomechanism of sensitive skin exists. Here we report the results of a systematic literature review of diagnostic methods for sensitive skin at clinical, histological and biophysical levels. A systematic search revealed 27 out of 1,701 articles which we appraised in detail.

Non-contact heart rate monitoring utilizing camera photoplethysmography in the neonatal intensive care unit - a pilot study.

Background: Presently the heart rate is monitored in the Neonatal Intensive Care Unit with contact sensors: electrocardiogram or pulse oximetry. These techniques can cause injuries and infections, particularly in very premature infants with fragile skin. Camera based plethysmography was recently demonstrated in adults as a contactless method to determine heart rate.

Remittance at a single wavelength of 390 nm to quantify epidermal melanin concentration.

Objective quantification of epidermal melanin concentration (EMC) should be useful in laser dermatology to determine the individual maximum safe radiant exposure (IMSRE). We propose a single-wavelength remittance measurement at 390 nm as an alternative optical method to determine EMC and IMSRE. Remittance spectra (360 to 740 nm), melanin index (MI) measurements and the transient radiometric temperature increase, DeltaT(t), upon skin irradiation with an Alexandrite laser (755 nm, 3-ms pulse duration, 6 Jcm(2)) were measured on 749 skin spots (arm and calf) on 23 volunteers (skin phototypes I to IV).

Remote plethysmographic imaging using ambient light.

Plethysmographic signals were measured remotely (> 1m) using ambient light and a simple consumer level digital camera in movie mode. Heart and respiration rates could be quantified up to several harmonics. Although the green channel featuring the strongest plethysmographic signal, corresponding to an absorption peak by (oxy-) hemoglobin, the red and blue channels also contained plethysmographic information.

Thermal depth profiling of vascular lesions: automated regularization of reconstruction algorithms.

Pulsed photo-thermal radiometry (PPTR) is a non-invasive, non-contact diagnostic technique used to locate cutaneous chromophores such as melanin (epidermis) and hemoglobin (vascular structures). Clinical utility of PPTR is limited because it typically requires trained user intervention to regularize the inversion solution. Herein, the feasibility of automated regularization was studied.

Infrared measurement of human skin temperature to predict the individual maximum safe radiant exposure (IMSRE).

Background And Objectives: Radiant exposure (RE) is a critical treatment parameter to be optimized for laser hair removal (LHR). An objective and quantitative method to assess the individual maximum safe radiant exposure (IMSRE) would help clinicians optimize LHR while at the same time providing the safest possible laser therapy.

Study Design: Pulsed photo-thermal radiometry (PPTR) measurements were on a total of 403 spots on 13 volunteers.

Diffuse-reflectance spectroscopy from 500 to 1060 nm by correction for inhomogeneously distributed absorbers.

Diffuse-reflectance spectroscopy for measurement of the absorption and scattering coefficients of biological tissue produces reliable results for wavelengths from 650 to 1050 nm. Implicitly, this approach assumes homogeneously distributed absorbers. A correction factor is introduced for inhomogeneous distribution of blood concentrated in discrete cylindrical vessels.

Improvement of port wine stain laser therapy by skin preheating prior to cryogen spray cooling: a numerical simulation.

Background And Objectives: Although cryogen spray cooling (CSC) in conjunction with laser therapy has become the clinical standard for treatment of port wine stain (PWS) birthmarks, the current approach does not produce complete lesion blanching in the vast majority of patients. The objectives of this study are to: (1) experimentally determine the dynamic CSC heat flux when a skin phantom is preheated, and (2) numerically study the feasibility of using skin preheating prior to CSC to improve PWS laser therapeutic outcome.

Study Design/materials And Methods: A fast-response thin-foil thermocouple was used to measure the surface temperature and thus heat flux of an epoxy skin phantom during CSC.

Comparison of diffusion approximation and Monte Carlo based finite element models for simulating thermal responses to laser irradiation in discrete vessels.

Both diffusion approximation (DA) and Monte Carlo (MC) models have been used to simulate light distribution in multilayered human skin with or without discrete blood vessels. However, no detailed comparison of the light distribution, heat generation and induced thermal damage between these two models has been done for discrete vessels. Three models were constructed: (1) MC-based finite element method (FEM) model, referred to as MC-FEM; (2) DA-based FEM with simple scaling factors according to chromophore concentrations (SFCC) in the epidermis and vessels, referred to as DA-FEM-SFCC; and (3) DA-FEM with improved scaling factors (ISF) obtained by equalizing the total light energy depositions that are solved from the DA and MC models in the epidermis and vessels, respectively, referred to as DA-FEM-ISF.

Determination of an optimized conversion matrix for device independent skin color image analysis.

Background And Objective: A cross-polarized diffuse reflectance (CDR) color imaging system was developed for quantitative evaluation of port wine stain (PWS) response to laser therapy. To obtain calibrated Commission International de l'Eclairage (CIE) color space images from RGB (red, green, and blue) images, it was necessary to derive an optimized conversion matrix specific to our imaging system.

Study Design/materials And Methods: A chromameter (CR-200, Minolta) and CDR imaging system were used to acquire CIELAB (CIE L*, a*, and b*) tristimulus values and RGB image values, respectively.

Determination of human skin optical properties from spectrophotometric measurements based on optimization by genetic algorithms.

We present an initial study on applying genetic algorithms (GA) to retrieve human skin optical properties using visual reflectance spectroscopy (VRS). A three-layered skin model consisting of 13 parameters is first used to simulate skin and, through an analytical model based on optical diffusion theory, we study their independent effects on the reflectance spectra. Based on a preliminary analysis, nine skin parameters are chosen to be fitted by GA.

Novel algorithm for tomographic reconstruction of atmospheric chemicals with sparse sampling.

Numerical studies were performed to evaluate a new air monitoring method for reconstructing chemical exposures and source emissions, based upon optical remote sensing (ORS) and computed tomography (CT). With an ORS-CT system, two-dimensional maps of chemical concentrations can be created that have good spatial and temporal resolution. The mathematical algorithm used to compute the distribution is critical for accurate and useable reconstructions of the concentrations.

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.

Spectral variation of the infrared absorption coefficient in pulsed photothermal profiling of biological samples.

Pulsed photothermal radiometry can be used for non-invasive depth profiling of optically scattering samples, including biological tissues such as human skin. Computational reconstruction of the laser-induced temperature profile from recorded radiometric signals is sensitive to the value of the tissue absorption coefficient in the infrared detection band (muIR). While assumed constant in reported reconstruction algorithms, muIR of human skin varies by two orders of magnitude in the commonly used 3-5 microm detection band.

Cryogen spray cooling in laser dermatology: effects of ambient humidity and frost formation.

Background And Objective: Dynamics of cryogen spray deposition, water condensation and frost formation is studied in relationship to cooling rate and efficiency of cryogen spray cooling (CSC) in combination with laser dermatologic surgery.

Study Design/materials And Methods: A high-speed video camera was used to image the surface of human skin during and after CSC using a commercial device. The influence of ambient humidity on heat extraction dynamics was measured in an atmosphere-controlled chamber using an epoxy block with embedded thermocouples.

Laser pulse impact on rat mesenteric blood vessels in relation to laser treatment of port wine stain.

Background And Objective: To study the impact of laser pulses on animal microvasculature as a model for laser treatment of port wine stains.

Study Design/materials And Methods: Rat mesenteric blood vessels were irradiated with a laser pulse (585 nm, 0.2-0.