Initial results of imaging melanoma metastasis in resected human lymph nodes using photoacoustic computed tomography

The pathological status of the sentinel lymph node is important for accurate melanoma staging, ascertaining prognosis and planning treatment. The standard procedure involves biopsy of the node and histopathological assessment of its status. Drawbacks of this examination include a finite sampling of the node with the likelihood of missing metastases, and a significant time-lag before histopathological results are available to the surgeon. We studied the applicability of photoacoustic computed tomographic imaging as an intraoperative modality for examining the status of resected human sentinel lymph nodes. We first applied the technique to image ex vivo pig lymph nodes carrying metastases-simulating melanoma cells using multiple wavelengths. The experience gained was applied to image a suspect human lymph node. We validated the photoacoustic imaging results by comparing a reconstructed slice with a histopathological section through the node. Our results suggest that photoacoustics has the potential to develop into an intraoperative imaging method to detect melanoma metastases in sentinel lymph nodes.