Nail thickness measurements using optical coherence tomography and 20-MHz ultrasonography

Background Nail diseases are often troubling to the patient and may present a diagnostic challenge to the dermatologist. Biopsies from the nail may be required although often perceived uncomfortable by the patient and potentially scarring. Noninvasive technologies are therefore of particular interest in the study of nails. Optical coherence tomography (OCT) is an optical imaging modality which may provide improved data. Objectives This study evaluates nail morphology and thickness in OCT images in comparison with high-frequency ultrasound (HFUS) imaging of the nail. Methods Ten healthy volunteers were recruited for imaging and nail measurements; OCT and HFUS images were compared qualitatively. Nail thickness measurements with four different techniques were compared: ultrasound, OCT, polarization-sensitive (PS) OCT and callipers. The OCT system was developed at Risoe National Laboratory, Denmark. A commercially available 20-MHz ultrasound system (Dermascan; Cortex Technology, Hadsund, Denmark) was used. Results In standard OCT the nail plate appeared as a layered structure containing a varying number of horizontal homogeneous bands of varying intensity and thickness. PS-OCT images of the nail plate also showed a layered structure. The refractive index of the nail was 1.47 +/- 0.09. OCT and PS-OCT had low coefficients of variation, 6.31 and 6.53, respectively, compared with other methods: HFUS 12.70 and callipers 14.03. Conclusions PS-OCT has to our knowledge not been applied to OCT analysis of the nail, and offers some advantages in separation of the nail bed from the nail plate.