Multimodal imaging system with ultrasound, photoacoustics, and optical coherence tomography for optical biopsy of melanoma

The rate of skin cancer incidence including melanoma has been steadily increasing in the last decades. While melanoma often show little to no symptoms in the early stages, they can spread to the lymph nodes and drastically reduce survival chances in the later stages. The current gold standard for diagnosis is visual examination, excision, and histological examination of the sample tissue, which is an invasive, costly and time-consuming process. As an alternative to this procedure, we introduce a novel multimodal optical system that integrates ultrasound (US), photoacoustic tomography (PAT), and optical coherence tomography (OCT) with Raman spectroscopy (RS). The setup allows quick and non-invasive skin lesion diagnosis and the determination of 3D lesion depth, helping the dermatologists make a decision on the excision margins. The OCT delivers structural and depth information of thin skin lesions, while the US and PAT measure the penetration depth of thicker lesions and the RS analyzes the chemical composition that can be used to distinguish between benign and malignant skin lesions. In our setup, the RS and OCT share the optical path and the scanning elements, which allows colocalized measurements. The US and PAT are integrated with an acoustical reflector, which enables B-mode measurements at the same position as OCT and RS without switching the scanning head. We demonstrate the imaging capabilities of the multimodal setup on custom made agar phantoms and present first measurements on ex vivo mouse and in vivo human skin samples. We compare the results with the corresponding histological images.