Effect of volume and methylene blue on fluorescence intensity and transit of indocyanine green for sentinel lymph node mapping in a simulated feline tumor model

Abstract

OBJECTIVE To compare the effect of volume and solution on transit time and fluorescence intensity (FI) using near-infrared fluorescence imaging (NIRF) in a simulated tumor model in cats. Secondarily, to describe SLN mapping with indocyanine green (ICG) NIRF and report any adverse effects of intradermally injected ICG in cats. ANIMALS 7 healthy purpose-bred domestic shorthaired male cats. METHODS Cats were randomly divided into 2 groups (ICG or ICG + methylene blue [MB]). Transit time and FI were determined for 1 or 2 mL solutions injected intradermally in 4 quadrants around a simulated tumor. Following massage, fluorescence intensity was quantified by calculating the corrected total ROI fluorescence using ImageJ software. Cats were monitored for adverse effects up to 4 weeks post-injection. RESULTS A larger solution volume had decreased transit times to the SLN (P = .001). There was no significant difference in transit times between ICG and ICG-MB. ICG demonstrated a greater FI (P = .001) in the SLN compared to ICG-MB. Methylene blue did not percutaneously fluoresce under NIRF. The volume of the solution did not significantly affect FI. No adverse reactions were reported. CLINICAL RELEVANCE Increased volume of ICG may aid in rapid percutaneous lymphatic tracking from tumor to SLN. Indocyanine green alone may be preferred over ICG-MB for greater visualization of the SLN. Intradermal injections of ICG and ICG-MB were well-tolerated in healthy cats with no significant complications. Clinical evaluation of this technique in an impaired lymphatic system, as seen in cancer patients, should be assessed in future research.

Comparative aspects of targeted sentinel lymph node mapping in veterinary and human medicine: opportunities for future research

“…Indocyanine green also has an excellent safety profile and has been demonstrated to have no significant side effects in companion animals ( 49 ). Applications have included SLN mapping of the oral, head and neck region, caudal abdomen and limbs in healthy and diseased dogs and head and neck region, trunk, perineum, and limbs in healthy and diseased cats ( Figure 3 ) ( 22 , 29 , 41 , 46 , 47 , 50 ). As a result, this technique is gaining popularity in the veterinary field; however, limitations include the accessibility of NIRF equipment and a lack of protocol standardization.…”

“…Methylene blue (MB) is a commonly reported blue dye as it is widely available and cost-effective; however, the use of MB alone heavily relies on the knowledge of the location of the SLN with respect to the tumor as blue staining is not easily visible percutaneously (42)(43)(44). Given that the success of SLN detection using MB alone is highly variable, recent literature has recommended either a shift from using MB entirely, combining MB with ICG-NIRF, or combining preoperative indirect lymphography using CT with intraoperative MB-ICG/NIRF to maximize SLN detection rates (22,45,46). Compared to MB alone, ICG-NIRF has a higher SLN detection rate, greater tissue penetration, and better visualization of the afferent lymphatic tracts (22,41,47).…”