Study raises caution on methylene blue with ICG node mapping

A new exploratory study in Animals suggests methylene blue can interfere with indocyanine green, or ICG, during near-infrared fluorescence imaging, a technique increasingly used for sentinel lymph node mapping in canine and feline oncology. The authors, Elisa Maria Gariboldi, Luigi Auletta, and Roberta Ferrari, evaluated methylene blue–ICG mixtures across three near-infrared imaging modalities and reported evidence consistent with fluorescence quenching, meaning the blue dye may dampen the fluorescent signal clinicians are trying to detect. That matters because combined visible dyes and fluorescent tracers are often used together in surgical oncology workflows, and veterinary literature has increasingly framed ICG-based mapping as a promising way to improve real-time lymphatic visualization and node detection. (pmc.ncbi.nlm.nih.gov)

Why it matters: For veterinary teams using or considering fluorescence-guided sentinel lymph node mapping, the study is a reminder that tracer combinations aren't necessarily neutral. Prior veterinary reviews have highlighted the value of methylene blue for intraoperative visualization, while also noting practical drawbacks in some tumor settings, and broader surgical literature has already raised concerns that methylene blue can have concentration-dependent fluorescence limitations and possible quenching effects. At the same time, a separate 2026 JAVMA pilot study in six dogs suggests 10% fluorescein sodium may offer a lower-cost, accessible intraoperative mapping option, with lymphatic tracts visualized in 5 of 6 dogs and sentinel lymph nodes identified in all 6, though that work is preliminary. (pmc.ncbi.nlm.nih.gov)

What to watch: Expect follow-up work on tracer selection, dosing, and sequencing, especially studies that test whether avoiding methylene blue–ICG overlap can improve signal reliability in clinical veterinary oncology cases. (researchgate.net)