Introduction to DRS

Figure 1. The DRS system consists of a white light source, a probe and a spectrometer.

Diffuse Reflectance Spectroscopy (DRS), sometimes known as Elastic Scattering Spectroscopy, is a non-invasive technique that measures the characteristic reflectance spectrum produced as light passed through a medium. The primary mechanisms are absorption and scattering, both of which vary with wavelength to produce the reflectance spectrum that is recorded. This spectrum contains information about the optical properties and structure of the medium being measured.

OBEL focuses on the use of fibre based instruments measuring the spectra of human skin and lesions. Our clinical DRS system uses a white light source coupled into optical fibres which deliver light to a probe held against the skin. Collection fibres carry the reflected light back to a CCD-based spectrometer. This is illustrated in Figure 1.

Spectra measured from skin can vary greatly between people and even at different body locations on the same individual. Figure 2 illustrates the spectra from skin and a normal mole from two Caucasian subjects, one tanned and the other with pale skin.

Some features of underlying skin that influence the spectra can be quite easily extracted but a lot of information can only be inferred by much more complex processing. In the pictured spectra, the regions of high absorption by hemoglobin around 550nm are clearly visible in the pale skin, but tanned skin has a lower-intensity spectrum because of the absorption at lower wavelengths by superficial melanin. This melanin also masks the signature of structures deeper in the skin.

Figure 2. Sample spectra from light and dark skin and moles point to the complexity of lesion diagnosis.