Feb 05, 2020

Skin Parameter Maps: Multispectral dermoscopy reveals more clinical details

Medical Imaging & workflows 6 min read

In today’s dermatology practice, dermoscopy is well established. The technology allows to see more detail of skin lesions and has proven its value in the diagnosis of skin cancer.

On top of that, Barco’s digital skin imaging platform Demetra can reveal even more details of skin lesions: based on multispectral dermoscopic images, we can clearly visualize specific skin structures such as pigment distribution and blood vessels (vasculature).

These visualizations are called Skin Parameter Maps1 (SPMs), and can provide better insight in the inner structures of lesions. Based on a traditional white light dermoscopic image, it can be a challenge to clearly analyze these clinically relevant, individual structures. Skin Parameter Maps, driven by multispectral imaging technology, decompose the dermoscopic image into individual maps that primarily show pigment and vascular structures.

Inspecting the Skin Parameter Maps can thus support your decision on the management strategy, diagnosis, treatment and follow-up of those skin lesions.

 
Dr. Marc Boone, MD, PhD. discussing the added value and clinical applications of SPMs

Types of SPM2

Barco Demetra can generate three types of Skin Parameter Maps:

  • The Pigment Contrast Map clearly visualizes the pigment in the skin by highlighting areas with a higher relative concentration of pigment, such as melanin.
  • The Blood Contrast Map reveals the presence of blood vessels in skin lesions and their morphology by highlighting areas with a higher relative concentration of blood.
  • The Scatter Contrast Map shows the light scattering properties of the skin, allowing to visualize the surface of the skin.

More background information about these maps can be found further in this article, in the 'Theoretical Background' chapter.

Example

Below you can see a traditional dermoscopic image of a lesion, based on polarized white light illumination:

Skin Parameter Maps example

Based on this white light image only, it is difficult to recognize specific structures such as blood vessels. In cases like this, the Skin Parameter Maps, leveraging the multispectral imaging technology, can help by visualizing these structures, which can support an accurate diagnosis.

Below you can find the three Skin Parameter Maps of this lesion, as well as a zoomed in image of the zone in the yellow rectangle:

Skin Parameter Maps example 2

Blood Contrast Map

Skin Parameter Maps example 3

The Blood Contrast Map improves the visualization of the vasculature of the lesion and reveals blood vessels in different orientations and with different morphologies, which are less noticeable in the traditional white light dermoscopic image due to the superposition of pigment and blood structures.

Pigment Contrast Map

Skin Parameter Maps example 4

The Pigment Contrast Map clearly highlights the areas with higher relative concentration of pigment.

Scatter Contrast Map

Skin Parameter Maps example 5

The Scatter Contrast Map is unique in revealing the surface texture of the lesion by using single scattering rather than optical absorption effects, which are typically used by the other Skin Parameter Maps (e.g. Pigment or Blood Contrast Maps). An example of such a surface texture is presented in the above image with a wrinkle network, which is less visible in a traditional polarized white light dermoscopic image. In this example the wrinkle network appears normal around the lesion and inside the lesion it appears to be disrupted.

Conclusion

The histopathologic diagnosis for the lesion in this example is pigmented Basal Cell Carcinoma (BCC). The additional insights provided by the Skin Parameter Maps may support a medical professional in diagnosing lesions such as the one in this example.

Theoretical background2

While a traditional dermatoscope illuminates the skin with white light only, the Demetra skin imaging solution additionally captures a complete set of multispectral images in one go. Those multispectral images are acquired with a set of light sources with different wavelengths. The main skin chromophores, such as pigment or blood, absorb each of those wavelengths in a different way, which is referred to as their “spectral signature”. Based on the known spectral signature of the main skin chromophores, the relative concentration of those substances can be shown in the resulting maps. 

Pigment Contrast Map

Skin Parameter Maps example 6As mentioned, the Pigment Contrast Map shows the relative location of pigment, such as melanin. 

Melanin is a natural pigment normally found in the epidermis of the skin, and produced by the melanocytes. It is inserted in membranous particles called melanosomes, which are subsequently transferred to other cells of the epidermis. Small scale melanocytic structures may be found in non-melanocytic lesions, which in many cases can be correlated to specific pathologies.

Melanin in melanocytic lesions can occupy large regions; it often proliferates inside the epidermis, and, in some cases, such as in melanoma, can escape to the dermis.

Blood Contrast Map

Skin Parameter Maps example 7The Blood Contrast Map shows the relative location of blood. It enhances the contrast of hemoglobin absorption. Hemoglobin is found in the blood vessels, which are located in the dermis and hypodermis. As a result of the contrast enhancement, the presence of blood vessels and their morphology in the papillary dermis of skin lesions is revealed.

Scatter Contrast Map

Skin Parameter Maps The Scatter Contrast Map shows light scattering properties. It enhances the contrast of single scattered photons, and in this way visualizes the surface structure of the skin.

When light is directed to the skin, part of the incident light is first reflected on the surface of the skin, the stratum corneum.

 Scattering inside the epidermis is mainly in the forward direction. A fraction of light can be back-scattered by cell membranes, cell organelles, densely-packed keratin fibers, and melanosomes, especially when their concentration exceeds the normal values, as in the case of a nevus or a melanoma. 

Below the epidermis lies the dermis which is constituted mainly of a dense network of collagen fibers. Collagen is birefringent and a potent scatterer. Light inside the dermis is scattered multiple times, and it is either propagated to an adjacent skin layer, or absorbed.

In this map, dark structures correspond to reduced scattering properties compared to adjacent skin regions. These could have less defined borders opposed to some superficial scattering structures which exhibit well defined borders, such as the skin wrinkle network. These may correspond to regions of epidermal proliferation inside the dermis.

Alternatively, bright spots, which correspond to increased single scattering, could for example correspond to Milia-like cysts.

About Barco Demetra

Barco Demetra® is a revolutionary skin imaging platform co-developed with leading dermatologists. It combines the best of analog and digital skin imaging in a flexible, wireless handheld device. It allows dermatologists to take any kind of picture and makes mapping, follow-up and comparison of skin images smoother and smarter. Demetra is a platform that will evolve over time. We are continuously working on new groundbreaking capabilities, including deep learning algorithms, all developed to improve the quality of skin diagnoses.

Find out more at barco.com/Demetra.

[1] Skin Parameter Maps are part of Demetra’s Analytics Toolkit and can be ordered as an optional add-on subscription to the Demetra platform. More info see barco.com/Demetra

[2] Kapsokalyvas, Dimitrios & Bruscino, Nicola & Alfieri, Domenico & De Giorgi, Vincenzo & Cannarozzo, Giovanni & Cicchi, Riccardo & Massi, Daniela & Pimpinelli, Nicola & Pavone, Francesco. (2013). Spectral morphological analysis of skin lesions with a polarization multispectral dermoscope. Optics express. 21. 4826-4840. 10.1364/OE.21.004826.

 

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