Research and diagnosis in dermatology deals with a large range of diseases and related molecules and tissue transfomations (e.g., color, erythema, pigmentation, etc.). Working with an industrial partner, Photon etc. has developed a software plug-in rendering oxygen, hemoglobin, deoxyhemoglobin and melanin maps intended for use in dermatological clinical studies.
The acquisition of a hyperspectral data cube from 400 to 1000 nm was done using a 2 nm bandwidth (FWHM) filter with images being taken every 1 nm. At this resolution, the acquisition time is approximately five minutes, although this may be lowered by reducing the size of the imaged area or increasing the wavelength spacing of the acquired images. This imaging time is comparable to that of other spectral imaging techniques (e.g., XY or line scans), but Photon etc’s patented non-scanning technology provides images with an unmatched combined spectral/spatial resolution. Moreover, since the system takes complete images one at a time, the inevitable small movements of a subject during data acquisition can be easily compensated for, unlike with other techniques.
The relative presence of oxyhemoglobin (HbO2) and deoxyhemoglobin (Hb) is often of significant interest in the study of skin conditions. The molecular extinction coefficient spectra of both are shown together below. The differences between these spectra allow for their localization and quantification within a hyperspectral image of a subject.
Figure 1 shows a mapping of oxy/deoxyhemoglobin in the fingertip of a subject. This simplified example demonstrates how relative concentrations of oxyhemoglobin may be localized in an image of a subject using the spectral information collected.
A spectral map may be generated to show a distribution of molecules in the skin using the spectral signatures of the substances of interest. Such maps can be analyzed to show evidence of abnormal tissue or to monitor the effect of medication in dermatological clinical studies. A map of melanin concentration in the face of an individual is shown in figure 3 as an example.
The color scale used corresponds to intensity at a key melanin absorption wavelength.