2.1.4　Non-invasive techniques in skin imaging

Dermatological diagnosis has often strongly relied on the observation of naked eyes and clinical experience，therefore the visual perception is of outstanding significance.The development of histological inspection of tissue，immunohistochemistry or electron microscopy have further increased the diagnostic validity thereby gaining new insights into potential pathological mechanisms.The routine histology remains the gold standard for the majority of skin diseases，but the excision biopsy of tissue for evaluation is inherently invasive and procedures are associated with pain，the risk of skin infection and scar formation.

With the fast development of dermoscope，reflectance confocal microscope（RCM），high-frequency ultrasound（HFUS）and optical coherence tomography（OCT），non-invasive skin imaging techniques are now widely applied for the diagnosis and monitoring of skin diseases，such as skin tumors，inflammatory dermatosis，infectious dermatosis，diseases of hair and nails.The non-invasive skin imaging techniques are popular among dermatologists and patients，because they are non-invasive，repeatability and real-time，to avoid unnecessary biopsies.(https://www.daowen.com)