Abstract. Acquiring near infrared spectra in vivo usually requires a fiber-optic probe to be pressed against the tissue. The applied pressure can significantly affect the optical properties of the underlying tissue, and thereby the acquired spectra. The existing studies consider these effects to be distortions. In contrast, we hypothesize that the pressureinduced spectral response is site-and tissue-specific, providing additional information for the tissue classification. For the purpose of this study, a custom system was designed for dynamic pressure control and rapid acquisition of spectra. The pressure-induced spectral response was studied at three proximate skin sites of the human hand. The diffuse reflectance and scattering were found to decrease with the applied contact pressure. In contrast, the concentrations of chromophores, and consequently the absorption, increased with the applied contact pressure. The pressure-induced changes in the tissue optical properties were found to be site-specific and were modeled as a polynomial function of the applied contact pressure. A quadratic discriminant analysis classification of the tissue spectra acquired at the three proximate skin sites, based on the proposed pressure-induced spectral response model, resulted in a high (90%) average classification sensitivity and specificity, clearly supporting the working hypothesis.

Abstract. Review of the existing studies on the contact pressure-induced changes in the optical properties of biological tissues showed that the reported changes in transmittance, reflectance, absorption, and scattering coefficient are vastly inconsistent. In order to gain more insight into the contact pressure-induced changes observed in biomedical applications involving common probe-spectrometer diffuse reflectance measurement setups and provide a set of practical guidelines minimizing the influence of the changes on the analysis of acquired spectra, we conducted a series of in vivo measurements, where the contact pressure was precisely controlled, and the spectral and contact pressure information were acquired simultaneously. Classification of three measurement sites on a human hand, representing the natural variability in the perfusion and structure of the underlying tissue, was assessed by training and evaluating classifiers at different contact pressure levels and for different probe operators. Based on the results, three practical guidelines have been proposed to avoid classification performance degradation. First, the most suitable pressure level should be identified. Second, the pressure level should be kept in a narrow range during the acquisition of spectra. Third, applications utilizing probes equipped with a calibrated spring can use several classifiers trained at different contact pressure levels to improve classification performance.

Background To estimate the extent and severity of atopic dermatitis (AD)‐related skin lesions, clinical trials enrolling dogs with AD often use categorical scales such as the Canine Atopic Dermatitis Extent and Severity Index, 4th iteration (CADESI‐04) and Canine Atopic Dermatitis Lesion Index (CADLI). Despite recent progress in the standardization of these AD‐grading scales, the evaluation of the severity of skin lesions (including erythema) remains subjective. Objectives To validate an optical set‐up with a smartphone and a dermatoscope for the objective estimation of skin erythema severity in atopic dogs. Animals Forty‐three dogs with AD. Methods and materials An erythema index (EI) was calculated from calibrated skin images and compared to the dermatologist’s erythema severity estimate using the erythema grading scale used in the CADESI‐04, as well as an ad hoc Visual Analog Scale (VAS) with a continuous palette of red shades. Results We found a strong correlation based on the Spearman rank correlation coefficient between all erythema valuations: CADESI‐04 and VAS: 0.93 [95% CI: (0.85, 0.96)]; CADESI‐04 and EI: 0.85 (0.72, 0.92); VAS and EI: 0.82 (0.67, 0.91). There was a good agreement between the objective EI and CADESI‐04‐based estimates because 71% of samples were classified in the same erythema severity category. When comparing the EI and the VAS, the standard deviation of misestimates was 12% (maximum 100%). Conclusions and clinical relevance The proposed optical set‐up has the potential to make erythema severity estimation objective, thus leading to more reliable AD severity scales for the use in experimental canine AD models or in clinical trials enrolling atopic dogs.

Quality smartphone cameras and affordable dermatoscopes have enabled teledermoscopy to become a popular medical and veterinary tool for analyzing skin lesions such as melanoma and erythema. However, smartphones acquire images in an unknown RGB color space, which prevents a standardized colorimetric skin analysis. In this work, we supplemented a typical veterinary teledermoscopy system with a conventional color calibration procedure, and we studied two mid-priced smartphones in evaluating native and erythematous canine skin color. In a laboratory setting with the ColorChecker, the teledermoscopy system reached CIELAB-based color differences ΔE of 1.8–6.6 (CIE76) and 1.1–4.5 (CIE94). Intra- and inter-smartphone variability resulted in the color differences (CIE76) of 0.1, and 2.0–3.9, depending on the selected color range. Preliminary clinical measurements showed that canine skin is less red and yellow (lower a* and b* for ΔE of 10.7) than standard Caucasian human skin. Estimating the severity of skin erythema with an erythema index led to errors between 0.5–3%. After constructing a color calibration model for each smartphone, we expedited clinical measurements without losing colorimetric accuracy by introducing a simple image normalization on a white standard. To conclude, the calibrated teledermoscopy system is fast and accurate enough for various colorimetric applications in veterinary dermatology.

Highlights Dogs poorly tolerate rectal temperature measurements with a contact thermometer. Existing alternative approaches used uncalibrated infrared thermometers. Gum and inguinal temperature are correlated moderately to rectal temperature. Hyperthermia was detected with sensitivity and specificity up to 90.0% and 78.6%. Future studies should include a calibrated thermometer and control external factors.

Measuring pulse rate (PR) and blood oxygenation (also peripheral oxygen saturation, SpO2) is a common monitoring procedure in veterinary medicine which gives important information about the patient's cardiovascular and respiratory systems. It can be performed as a part of physical examination (ASAVA 2013), surgical procedure (Bednarski et al 2011) or intensive care treatment (Humm and Kellett-Gregory 2016). In addition to veterinary professionals, pet owners are also becoming interested in painless and stress-free monitoring of their animals. This trend is reflected in the pet market, where gadget devices for monitoring the canine or feline location and activity are on the rise (Weiss et al 2013).Measuring PR and SpO2 can be done by the same optical probe, which is based on a pulse oximetry sensor comprising continuously emitting light sources. The probe first emits and then, by the form of design, receives either the transmitted (e.g. on finger, tongue) or the reflected (e.g. on tail) red and infrared (IR) light (Allen 2007). If the acquired data is evaluated in time from a single spectral band, the technique is generally called photoplethysmography (PPG). In this way, pulse oximetry is based on comparing red and IR PPG signal baselines. The acquired PPG signal consists of non-pulsatile (DC) and pulsatile (AC) components. A baseline of PPG signal (i.e. non-pulsatile DC) reflects the collective light absorption due to blood and other tissues while the pulsatile PPG component (AC) is a consequence of local blood volume changes in accordance with the cardiac cycle.In humans, PPG is one of the most popular monitoring tools (Orphanidou 2018) since the device is small, reliable and low cost. In addition to PR and SpO2, PPG is also used to monitor blood pressure, cardiac output, and respiration rate, to detect various vascular diseases (Erts et al 2005, Karlen et al 2012, Bartels and Thiele 2015 and to assess regional anesthesia efficiency (Nijboer and Dorlas 1985, Rubins et al 2010). PPG probes are normally placed on the fingertip for direct bedside monitoring. Recently, imaging PPG (iPPG) has become increasingly valuable since the PPG signals can be obtained from a camera or a mobile phone video (Huelsbusch and Blazek 2002, Jonathan and Leahy 2010, Remer and Bilenca 2015. It was shown that the PPG pulse varies significantly among measurement sites such as fingertips, toes, and ears (Spigulis 2005, Allen 2007). This phenomenon probably occurs due to differences in the cutaneous blood supply of the different anatomic regions (Maeda et al

In this study, the severity of canine skin erythema was assessed objectively for the first time. Atopic dermatitis (AD) is a common canine inflammatory and pruritic skin disease associated with an allergic reaction to exogenous allergens. The monitoring of skin erythema over time with lesion severity scales like the CADESI-4 is an essential diagnostic and research tool, especially for clinical trials. Currently, the erythema assessment is subjective due to visual estimation. In our study, we calculated the erythema index (EI) in 14 atopic dogs based on the analysis of multispectral skin images taken with the Skimager device. The relationship between the EI and a visual erythema estimation was modeled by linear regression with the first-order polynomial. The coefficient of determination (r squared) reached 0.81. Based on such high correlation, we conclude that optical measurements could replace the visual estimation of erythema in atopic dogs and, thus, improve the validity of skin lesion severity scales in dogs.

The recent spread of cheap dermatoscopes for smartphones can empower patients to acquire images of skin lesions on their own and send them to dermatologists. Since images are acquired by different smartphone cameras under unique illumination conditions, the variability in colors is expected. Therefore, the mobile dermatoscopic systems should be calibrated in order to ensure the color constancy in skin images. In this study, we have tested a dermatoscope DermLite DL1 basic, attached to Samsung Galaxy S4 smartphone. Under the controlled conditions, jpeg images of standard color patches were acquired and a model between an unknown device-dependent RGB and a deviceindependent Lab color space has been built. Results showed that median and the best color error was 7.77 and 3.94, respectively. Results are in the range of a human eye detection capability (color error ≈ 4) and video and printing industry standards (color error is expected to be between 5 and 6). It can be concluded that a calibrated smartphone dermatoscope can provide sufficient color constancy and can serve as an interesting opportunity to bring dermatologists closer to the patients.