Indocyanine green near-infrared fluorescence imaging shows promise for intraoperative fluorescence of parathyroid tissue in dogs.

Abstract

Objective: To evaluate IV indocyanine green (ICG) near-infrared fluorescence (NIRF) imaging to identify normal canine parathyroid tissue.

Methods: A cumulative effect study followed by a dose evaluation study with 8 purpose-bred dogs was performed from February through April 2023. Dogs were randomized to receive IV ICG at 0.2, 0.3, or 0.4 mg/kg after the thyroid and parathyroid glands were exposed. A NIRF endoscope positioned 8 cm above the thyroid-parathyroid complex obtained images. Subjective and objective measures of fluorescence were recorded and compared for the thyroid gland, external parathyroid gland, and internal parathyroid gland.

Results: Repeated ICG administration did not affect time to peak fluorescence but increased peak parathyroid gland fluorescence. Subjective fluorescence scores of the parathyroid glands were significantly higher in monochromatic modality compared to other ICG-NIRF modalities. Initial fluorescence was immediate for all glands. Mean time to peak objective fluorescence was 0.2 to 1.9 minutes. Higher ICG doses generally had higher peak fluorescence than lower ICG doses. Indocyanine green-NIRF did not consistently distinguish normal parathyroid glands from thyroid tissue.

Conclusions: ICG-NIRF at 0.2 to 0.4 mg/kg effectively fluoresces normal parathyroid glands in dogs, although the subjective fluorescence achieved in the parathyroid glands is similar to fluorescence in the adjacent thyroid glands. Parathyroid fluorescence varied substantially between ICG-NIRF modality, with the highest fluorescence observed in the monochromatic modality.

Clinical relevance: ICG-NIRF may aid in intraoperative localization of parathyroid glands, particularly the identification of ectopic parathyroid tissue. Further evaluation of ICG-NIRF for the identification of pathologic parathyroid tissue in clinical patients is indicated.