Applications of optical coherence tomography in dermatology

Histology represents the gold standard for morphological investigation of the skin, though biopsy may alter the original morphology, is non-repeatable on the same site and always requires an iatrogenic trauma. In the past decade, advances in optics, fibre as well as laser technology have enabled the development of a novel non-invasive optical biomedical imaging technique, optical coherence tomography (OCT). The latter is based on a classic optical measurement method known as low-coherence interferometry that enables non-invasive, high resolution, two- or three-dimensional, cross-sectional imaging of microstructural morphology in biological tissue in situ. Using conventional OCT with a lateral resolution of 10-15 μm, the stratum corneum of glabrous skin (palmoplantar), the epidermis and the upper dermis can usually be identified, as well as skin appendages and blood vessels. For example, non-invasive monitoring of cutaneous inflammation, hyperkeratotic conditions and photoadaptive processes is possible by means of OCT. Furthermore, the development of high-output broadband light sources, e.g. femtosecond Ti:sapphire laser, might soon enable ultrahigh image resolutions of about 1 μm in order to investigate skin tissue on the cellular level, which could potentially allow the differentiation between benign and malignant tissues. Beyond a high resolution morphology in OCT images, tissue characterization by additional local physical parameters, such as the scattering coefficient and refractive index may be of great value, in particular in cosmetics and the pharmaceutical industry. Functional OCT imaging based on spectroscopy, tissue birefringence, elastography and Doppler flow reveals further information on tissue properties and represents an important progress of OCT technique in the field of dermatology. Therefore, the advanced versions of OCT technique might not only lead to significant new insights in skin physiology and pathology, but also in diagnosis and therapeutic control of cutaneous disorders with respect to non-invasive diagnosis of conditions and monitoring of disease activity in addition to treatment effects over time.