In vivo optical coherence tomography imaging of human skin: norm and pathology

Background/aims: Since the majority of skin diseases are known to be accomp anied by structural alterations, research efforts are focused on the develo pment of various novel diagnostic techniques capable of providing in vivo i nformation on the skin structure. An essential parameter here is spatial re solution. In this paper we demonstrate the capabilities of optical coherenc e tomography (OCT) in detecting in vivo specific features of thin and thick skin. A particular focus is made on the identification of OCT patterns typ ical of certain pathological processes in skin, by performing parallel hist ological and tomographical studies. Methods: To obtain images of the skin, we used a compact fiber OCT system d eveloped at the Institute of Applied Physics of the Russian Academy of Scie nces. A low coherence source (superluminescent diode) operated at a wavelen gth of 1280 nm; the output power was 0.5-2 mW. This power is low enough to conform to the ANSI safety standards for light exposure. The in-depth resol ution limited by the spectral bandwidth (40-50 nm) of the probing light was similar to 20 mu m. The lateral resolution determined by the probe light f ocusing ranged from 15 to 30 mu m. In this series of experiments the maximu m depth of imaging did not extend beyond 1.5 mm. Obtaining images of skin r egions 2-6 mm long took 2-4 s. OCT capabilities for imaging normal skin of different localization and some skin diseases were studied in 12 healthy vo lunteers and 24 patients. Results: OCT imaging of the skin can detect in vivo such general pathologic al reactions of the human body as active inflammation and necrosis. OCT is useful for in vivo diagnosis of some specific processes in the skin, includ ing hyperkeratosis, parakeratosis and formation of intradermal cavities. OC T imaging is noninvasive and therefore allows frequent multifocal examinati on of skin without any adverse effects. OCT can perform monitoring of disea se progress and recovery in the course of therapy. Morphometric studies, me asurements of the depth and extension of skin pathology within the human bo dy can be easily performed by OCT. Conclusions: OCT allows imaging of subsurface soft tissues with the spatial resolution of 15-20 mu m, a resolution one order of magnitude higher than that provided by other clinically available noninvasive diagnostic techniqu es. An imaging depth of up to 1.5-2 mm, given by current OCT technology, is sufficient to examine the skin. Real time OCT imaging can provide informat ion not only on the structure, but also on some specific features in the fu nctional state, of tissues. OCT imaging is a noninvasive technique, i.e., O CT does not cause trauma and has no side effects since it utilizes radiatio n in the near infrared wavelength range at a power as low as 1 mW.