Handheld Multiphoton and Pinhole-free Reflectance Confocal Microscopy Enables Noninvasive, Real-time Cross-sectional Imaging in Skin

Biopsy-based histology has been the foundation of disease diagnosis and management for over a century. A long-sought goal in dermatology is the development of an imaging modality with sufficient resolution and compositional detail to noninvasively interrogate skin histology in vivo. Here, we describe a system that achieves this goal using cross-sectionally scanned, multimodal microscopy (cross-modal). Cross-modal combines multiphoton and reflectance confocal microscopy into one compact system with coordinated three-axis scanning that preserves optical resolution in cross-section. A custom pinhole-free mechanism employing finite-infinite conjugates further simplifies and stabilizes confocal alignment. Evaluated in participants ages 9-81 and Fitzpatrick skin types (FST) 1-5, cross-modal images revealed histological details analogous to those obtained from traditional biopsied tissue. We observed dermal elastosis in sun-damaged skin, elevated melanin in pigmented skin, basaloid nests in basal cell carcinoma, and elongated rete ridges in seborrheic keratosis, supporting cross-modal's potential to deliver histological insights noninvasively.