Vascularity Assessment of Parathyroid Glands Using Low-Dose ICG and Probe-Based Fluorescence Detection

Indocyanine green (ICG) angiography is used to assess parathyroid gland perfusion after thyroidectomy to reduce rates of hypocalcemia. This study was conducted to evaluate the efficacy of probe-based fluorescence detection of parathyroid glands with ICG for quantitative perfusion assessment.

Patients undergoing endocrine neck surgery were recruited for a prospective study. Parathyroid glands were identified intraoperatively using near infrared autofluorescence (NIRAF) with a probe-based system. A 0.25 mg dose of ICG was administered to patients before surgical closure, and the fluorescence from the parathyroid gland was measured 3 min after injection and compared with pre-ICG NIRAF. Images from ICG angiography were collected and scored by three surgeons to analyze inter-rater variability. Probe-measured ICG ratios were compared with ICG image scores to determine the utility of probe-based ICG perfusion quantification in parathyroid glands.

This study analyzed 25 patients. Analysis of ICG image scores showed moderate agreement (κ = 0.48-0.58). However, there was significant disagreement when glands with poor blood flow, validating the need for a quantitative approach in ICG angiography. A metric of probe-measured fluorescence change after ICG was developed to classify ligated and untouched glands from parathyroidectomies. A ≤ 1.0-fold increase in fluorescence corresponded with devascularized glands, whereas a ≥ 4.5.-fold increase identified well-vascularized glands. Fluorescence between $1.0$ - and $4.5$ -fold identified glands with poor flow.

Scoring of ICG angiography is highly subjective and varies significantly among surgeons. However, probe-based fluorescence measurements after low-dose ICG administration can quantitatively predict the vascularity status of parathyroid glands.