Lioudmila Tchvialeva

Polarization speckle imaging as a potential technique for in vivo skin cancer detection

Abstract. Skin cancer is the most common cancer in the Western world. In order to accurately detect the disease, especially malignant melanoma—the most fatal form of skin cancer—at an early stage when the prognosis is excellent, there is an urgent need to develop noninvasive early detection methods. We believe that polarization speckle patterns, defined as a spatial distribution of depolarization ratio of traditional speckle patterns, can be an important tool for skin cancer detection. To demonstrate our technique, we conduct a large in vivo clinical study of 214 skin lesions, and show that statistical moments of the polarization speckle pattern could differentiate different types of skin lesions, including three common types of skin cancers, malignant melanoma, squamous cell carcinoma, basal cell carcinoma, and two benign lesions, melanocytic nevus and seborrheic keratoses. In particular, the fourth order moment achieves better or similar sensitivity and specificity than many well-known and accepted optical techniques used to differentiate melanoma and seborrheic keratosis.

Influence of geometry on polychromatic speckle contrast

Understanding speckle behavior is very important in speckle metrology application. The contrast of a polychromatic speckle depends not only on surface roughness and the coherence length of a light source, as shown in previous works, but also on optical geometry. We applied the Fresnel approach of diffraction theory for the free-space geometry and derived a simple analytical relationship between contrast, coherence length, size of illuminated spot, and distances between source, object, and observation plane. The effect of contrast reduction is found to be significant for low-coherence light sources.

Using a zone model to incorporate the influence of geometry on polychromatic speckle contrast

A simple physical zone model was developed to explain the formation of polychromatic speckle patterns within the Fresnel region. This model represents a reasonable compromise between complex theoretical formulation and simple estimations for practical needs, and allows the speckle contrast to be calculated as a function of geometric parameters for the optics and coherence length of the light source. The model was experimentally verified, and the results are consistent with our previous rigorous theoretical formulation.

Durable rough skin phantoms for optical modeling

Skin phantoms are often used to study and model light propagation. However, existing skin phantoms overlook the important effect of surface roughness on light propagation patterns. This paper reports the construction of durable phantoms with controllable surface roughness and bulk optical properties. With silica microspheres as the scattering particles, we theoretically model the scatterer density required to achieve the desired phantom optical properties before fabrication. The surface roughness and the attenuation coefficients of the constructed phantoms were validated using optical profilometry and ballistic spatial filter photometry. These rough skin phantoms were originally developed for laser speckle studies, but could also be used for studying optical phenomena where light experiences surface and bulk scattering at the same time.

Laser speckle and skin cancer: skin roughness assessment

Incidence of skin cancer has been increasing rapidly since the last few decades. Non-invasive optical diagnostic tools may improve the diagnostic accuracy. In this paper, skin structure, skin cancer statistics and subtypes of skin cancer are briefly reviewed. Among the subtypes, malignant melanoma is the most aggressive and dangerous; early detection dramatically improves the prognosis. Therefore, a non-invasive diagnostic tool for malignant melanoma is especially needed. In addition, in order for the diagnostic tool to be useful, it must be able to differentiate melanoma from common skin conditions such as seborrheic keratosis, a benign skin disease that resembles melanoma according to the well known clinical-assessment ABCD rule. The key diagnostic feature between these two diseases is surface roughness. Based on laser speckle contrast, our research team has recently developed a portable, optical, non-invasive, in-vivo diagnostic device for quantifying skin surface roughness. The methodology of our technique is described in details. Examining the preliminary data collected in a pilot clinical study for the prototype, we found that there was a difference in roughness between melanoma and seborrheic keratosis. In fact, there was a perfect cutoff value for the two diseases based on our initial data.

Eliminating the effect of bulk scattering when measuring skin surface roughness using speckle contrast: a skin phantom study

We have been investigating the quantification of skin surface roughness by polychromatic speckle contrast. Speckle contrast, being a measure of light coherence, decreases as coherence decays when low coherent light is reflected from a rough surface. The main constraint of applying the technique to skin is the presence of bulk scattering along with surface reflection. Bulk scattering also decays coherence and is a source of noise. To examine the effect of bulk contribution, we studied speckle patterns generated by silicone phantoms with controllable roughness and optical parameters in the range of human skin. We discovered that using the theoretical curve plotting speckle contrast vs. surface roughness as a calibration curve overestimates the phantom surface roughness. We propose to use the effective calibration curve for the proper skin roughness measurements. The effective calibration curve was obtained experimentally taking the advantage of its weak dependence on phantoms attenuation coefficients.

Optical discrimination of surface reflection from volume backscattering in speckle contrast for skin roughness measurements

Background: The intermixing of light reflected from tissue surface and scattered from tissue volume complicates skin surface roughness assessment by laser speckle technique, a non-invasive optical method based on the analysis of the contrast of a speckle pattern. Objective: In this study we investigated optical discrimination methods to separate the two contributions in a speckle pattern. Methods: Three discrimination methods, spatial, polarization and spectral filtering, were implemented to suppress light from skin internal volume in a laser speckle device. In order to determine the effectiveness of the discrimination methods, speckle patterns were obtained from healthy volunteers, and polychromatic speckle contrast was computed before and after each filtering procedure. Results: Speckle contrast increased after discrimination filtering. A simple formula was derived to calculate the speckle contrast associated with light scattered from the skin surface. This corrected speckle contrast was proposed to be used for skin roughness assessment.

Backscattering of linearly polarized light from turbid tissue-like scattering medium with rough surface.

Abstract. In the framework of further development of a unified computational tool for the needs of biomedical optics, we introduce an electric field Monte Carlo (MC) model for simulation of backscattering of coherent linearly polarized light from a turbid tissue-like scattering medium with a rough surface. We consider the laser speckle patterns formation and the role of surface roughness in the depolarization of linearly polarized light backscattered from the medium. The mutual phase shifts due to the photons’ pathlength difference within the medium and due to reflection/refraction on the rough surface of the medium are taken into account. The validation of the model includes the creation of the phantoms of various roughness and optical properties, measurements of co- and cross-polarized components of the backscattered/reflected light, its analysis and extensive computer modeling accelerated by parallel computing on the NVIDIA graphics processing units using compute unified device architecture (CUDA). The analysis of the spatial intensity distribution is based on second-order statistics that shows a strong correlation with the surface roughness, both with the results of modeling and experiment. The results of modeling show a good agreement with the results of experimental measurements on phantoms mimicking human skin. The developed MC approach can be used for the direct simulation of light scattered by the turbid scattering medium with various roughness of the surface.

Applying laser speckle images to skin science: skin lesion differentiation by polarization

Skin cancer is a worldwide health problem. It is the most common cancer in the countries with a large white population; furthermore, the incidence of malignant melanoma, the most dangerous form of skin cancer, has been increasing steadily over the last three decades. There is an urgent need to develop in-vivo, noninvasive diagnostic tools for the disease. This paper attempts to response to the challenge by introducing a simple and fast method based on polarization and laser speckle. The degree of maintaining polarization estimates the fraction of linearly maintaining polarization in the backscattered speckle field. Clinical experiments of 214 skin lesions including malignant melanomas, squamous cell carcinomas, basal cell carcinomas, nevi, and seborrheic keratoses demonstrated that such a parameter can potentially diagnose different skin lesion types. ROC analyses showed that malignant melanoma and seborrheic keratosis could be differentiated by both the blue and red lasers with the area under the curve (AUC) = 0.8 and 0.7, respectively. Also malignant melanoma and squamous cell carcinoma could be separated by the blue laser (AUC = 0.9), while nevus and seborrheic keratosis could be identified using the red laser (AUC = 0.7). These experiments demonstrated that polarization could be a potential in-vivo diagnostic indicator for skin diseases.

Polarization Speckles and Skin Applications

Interference and polarization techniques provide the highest sensitivity and precision in optical metrology. The recently introduced polarization speckle method, incorporating both techniques, is a promising biomedical tool. In this chapter we demonstrate how the method could be used in dermatology. Measuring the polarization properties of coherent backscattered light, we obtain the skin surface roughness, which is an important diagnostic parameter in the clinical recognition of some skin cancers, such as melanoma and their differential diagnosis from common benign lesions, such as pigmented seborrheic keratoses. The principle of the technique has been validated in two clinical studies, and the theory between skin surface roughness and depolarization was investigated using electric field Monte Carlo simulations. The goal of this research is to enhance the capacity of portable devices in the hands of primary care providers to enhance the accuracy of cancer diagnoses in a cost-effective manner.