The Use of Near Infrared Fluorescence Imaging for Sentinel Lymph Node Mapping in Dogs
Locoregional lymph node evaluation is a crucial process for staging many solitary cancers. Identifying and localizing the primary draining lymph node can be challenging, particularly in anatomically complex regions, such as the head and neck. The first lymph node(s) that receive lymphatic drainage from a primary tumour is termed the sentinel lymph node (SLN) and can be predicative of metastatic disease. Several SLN mapping techniques have been described to identify and locate the SLN. Near infrared fluorescence imaging (NIRF) is one technique that has been used successfully in human medicine, and requires a fluorescent contrast agent, commonly, indocyanine green (ICG). However, NIRF has not been extensively investigated in veterinary medicine. Furthermore, a combination of preoperative and intraoperative SLN mapping modalities has been suggested to improve the accuracy of SLN detection. The purpose of this research was to evaluate the use of NIRF for SLN mapping in dogs. The objective of the first study was to determine the agreement between preoperative computed tomography lymphography (CTL) using iohexol and intraoperative NIRF lymphography for SLN detection in dogs with oral tumours. A fair agreement between preoperative and intraoperative SLN mapping modalities was identified. Near infrared fluorescence imaging was effective in localizing SLNs intraoperatively resulting in a high SLN detection rate. In addition, the combination of preoperative and intraoperative modalities resulted in high SLN detection rates. A novel dual-modality imaging contrast agent, Nanotrast-CF800, incorporates both iohexol and ICG within a liposomal nanoparticle for the use of preoperative CTL and intraoperative NIRF for SLN mapping. The feasibility of CF800 and the development of potential associated local and systemic adverse events were assessed in a healthy canine population following local administration within the oral cavity and following intravenous administration in two separate studies. Prolonged retention of the contrast agent within SLNs identified on CT images and/or NIRF were observed. No significant local or systemic adverse events were observed following local and intravenous administration of CF800. The administration of CF800 is safe to use in healthy dogs with prolonged retention within targeted tissues.