Objective. Sentinel node biopsy in patients with cutaneous melanoma improves staging, provides prognostic information, and leads\nto an increased survival in node-positive patients.However, frozen section analysis of the sentinel node is not reliable and definitive\nhistopathology evaluation requires days, preventing intraoperative decision-making and immediate therapy. Photoacoustic imaging\ncan evaluate intact lymph nodes, but specificity can be hampered by other absorbers such as hemoglobin. Near infrared\nmultispectral photoacoustic imaging is a new approach that has the potential to selectively detect melanin. The purpose of the\npresent study is to examine the potential ofmultispectral photoacoustic imaging to identify melanoma metastasis in human lymph\nnodes. Methods.Three metastatic and nine benign lymph nodes from eight melanoma patients were scanned ex vivo using a Vevo\nLAZR�© multispectral photoacoustic imager and were spectrally analyzed per pixel. The results were compared to histopathology\nas gold standard. Results. The nodal volume could be scanned within 20 minutes. An unmixing procedure was proposed to\nidentify melanoma metastases with multispectral photoacoustic imaging. Ultrasound overlay enabled anatomical correlation. The\npenetration depth of the photoacoustic signal was up to 2 cm. Conclusion.Multispectral three-dimensional photoacoustic imaging\nallowed for selective identification of melanoma metastases in human lymph nodes.
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