Noninvasive Monitoring of Dynamical Processes in Bruised Human Skin Using Diffuse Reflectance Spectroscopy and Pulsed Photothermal Radiometry

Optimizing the detection and characterization of bruises using multispectral imaging

The detection and visualization of sub-dermal hematoma (bruises) plays a key role in suspected physical abuse cases, as it aids in the evaluation of both victim and suspect statements. Current methods rely on visual inspection, frequently aided by alternate light sources (ALS). Ideally, ALS increase visual contrast by exploiting differences in light absorption (due to the formation and clearance of chromophores within the bruise). However, in practice the achievable contrast is often limited by light-scattering: the short-wavelength region of the spectrum (comprising most of the chromophore-specific absorption peaks), is also strongly scattered by the dermal tissue. This, in turn, limits achievable penetration depths, effectively obscuring deep-lying bruises. ALS-based contrast enhancement is further complicated by bruise healing; diffusion and enzymatic activity alter the chromophore concentrations as well as their 3D-distribution within the tissue. To overcome these critical limitations, we employ a multi-spectral camera (8 wavelengths simultaneously) in conjunction with both observer-based scoring and a contrast-quantification algorithm to determine the optimal wavelength for the detection and characterization of bruises over time. We show that (i) bruise contrast significantly increases at 480 nm, 620 nm and 850 nm and (ii) the wavelength achieving optimal contrast gradually changes from 850 nm to 578 nm-480 nm as the bruise heals.

Laser speckle contrast imaging of perfusion in oncological clinical applications: a literature review

BACKGROUND

Laser speckle coherence imaging (LSCI) is an emerging imaging modality that enables noninvasive visualization and assessment of tissue perfusion and microcirculation. In this article, we evaluated LSCI in imaging perfusion in clinical oncology through a systematic review of the literature.

METHODS

The inclusion criterion for the literature search in PubMed, Web of Science and Scopus electronic databases was the use of LSCI in clinical oncology, meaning that all animal, phantom, ex vivo, experimental, research and development, and purely methodological studies were excluded.

RESULTS

Thirty-six articles met the inclusion criteria. The anatomic locations of the neoplasms in the selected articles were brain (5 articles), breasts (2 articles), endocrine glands (4 articles), skin (12 articles), and the gastrointestinal tract (13 articles).

CONCLUSIONS

While LSCI is emerging as an appealing imaging modality, it is crucial for more clinical sites to initiate clinical trials. A lack of standardized protocols and interpretation guidelines are posing the most significant challenge.

Correlations of light scattering properties in human skin with the person's age assessed using a non-invasive technique

We analyze the influence of a person's age on the thicknesses and reduced scattering coefficients of the epidermis and dermis in visible part of the spectrum. Their values were assessed using a non-invasive technique which combines pulsed photothermal radiometry and diffuse reflectance spectroscopy with Monte Carlo modeling of light transport in a four-layer model of skin. The analysis is affected by the strong influences of the melanin content on the reduced scattering coefficient of the epidermis, a epi, and blood content in the case of dermis (a der). Separating their contributions reveals a significant decrease of a der with the person's age at an average rate of -0.25 mm-1 per decade, while the contribution of blood in the papillary dermis amounts to 1.0 mm-1%-1. Meanwhile, no influence of the person's age was found on a epi and the thicknesses of the epidermis or dermis.

Objective monitoring of laser tattoo removal in human volunteers using an innovative optical technique: A proof of principle

OBJECTIVES

Assess the suitability of the technique for objective monitoring of laser tattoo removal by an extended treatment protocol.

MATERIALS AND METHODS

One half of the tattoo in the first volunteer was treated with nanosecond and the other half with picosecond laser pulses at 1064 nm. In the second subject, four test areas were treated repeatedly using different radiant exposures from 1.5 to 6 J/cm2 . Measurements of diffuse reflectance spectra and photothermal radiometric transients were performed 4-20 weeks after each treatment session. Inverse Monte Carlo analysis based on a three-layer model of tattooed skin was applied to assess the tattoo characteristics and analyze their changes.

RESULTS

The results clearly indicate a gradual reduction of the ink content and an increase of the subsurface depth of the tattoo layer with all treatments at a radiant exposure of 3 J/cm2 or higher. The observed dependences on laser pulse duration, radiant exposure, and a number of treatments are in excellent agreement with visual fading of the tattoo.

CONCLUSIONS

The presented methodology enables noninvasive characterization of tattoos in human skin and objective monitoring of the laser removal treatment.

Pulsed Photothermal Radiometric Depth Profiling of Bruises by 532 nm and 1064 nm Lasers

Optical techniques are often inadequate in estimating bruise age since they are not sensitive to the depth of chromophores at the location of the bruise. To address this shortcoming, we used pulsed photothermal radiometry (PPTR) for depth profiling of bruises with two wavelengths, 532 nm (KTP laser) and 1064 nm (Nd:YAG laser). Six volunteers with eight bruises of exactly known and documented times of injury were enrolled in the study. A homogeneous part of the bruise was irradiated first with a 5 ms pulse at 532 nm and then with a 5 ms pulse at 1064 nm. The resulting transient surface temperature change was collected with a fast IR camera. The initial temperature-depth profiles were reconstructed by solving the ill-posed inverse problem using a custom reconstruction algorithm. The PPTR signals and reconstructed initial temperature profiles showed that the 532 nm wavelength probed the shallow skin layers revealing moderate changes during bruise development, while the 1064 nm wavelength provided additional information for severe bruises, in which swelling was present. Our two-wavelength approach has the potential for an improved estimation of the bruise age, especially if combined with modeling of bruise dynamics.