What it does…

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When a physician observes a skin lesion, the light reaching his or her eye is composed of three components, specular, deep dermal and superficial scatter. These collectively account for about 50% of the incident light while the remaining 50% is absorbed in the body.

Specular reflectance or glare from the air/skin surface. This comprises about 5% of the incident light. Specular reflectance has no significant interaction with skin and consequently contains no information and acts as a confounder.

Specular reflectance retains the polarization of the incident light and is rejected in most modern dermatoscopes by using cross polarization limiting the returned light to superficial and deep dermal scattered light.

Deep dermal scatter. This is light that has entered the deeper dermal layers of skin and accounts for about 40% of incident light. Deep dermal scatter is multiply scattered light and consequently has poor geometric contrast. Deep dermal scatter also depolarizes incident light due to the multiple scattering events. A doctors perception of a lesion, either with the naked eye or using available dermatoscopes, is informed primarily by the modulation of this light from variations in melanin, cellular infiltration of collagen and changes in blood perfusion all of which are important markers of cancer.

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However, given the poor geometric contrast and the magnitude of this light, finer structures that are indicative of cancer cannot be visualized from this light.

Superficial scatter. This is light that has entered and is returned from superficial layers: the dermal epidermal junction and the papillary dermis. This light accounts for about 2 -8% of incident light and due to limited scattering, retains the incident polarization. Almost all skin cancers originate in this superficial layer. This papillary dermis is characterized by a rich fabric like pattern or texture formed by the collection of papillae that protrude from the papillary dermis into the epidermal layer. This rich texture is altered when cellular growth due to neoplasia displaces the papillary pattern. Cellular growth presents a more uniform and simple pattern. Superficial scattered light is modulated by this change and offers a powerful contrast mechanism for detection of skin cancer.

For physicians, skin cancer arising in the epidermis is difficult to visualize by naked eye or with existing dermatoscopes because most of the light come from the deeper dermis which confounds and reduces the image contrast needed for detecting early cancer in the superficial layers. Our PSI technology allows the selective imaging of this layer by restricting the imaged light to superficial scatter and excluding both the specular and deep dermal scatter.

How it works…

To see a video explaining how PSI works in a research device named the PolCam that appeared on KOIN Local 6 TV in Portland. Click here to play a movie.

Sclerosing Basal Cell Carcinoma

Conventional Mode

PSI Mode

PSI Mode With Margins