Fluorescence and autofluorescence is, no doubt, the hot-topic in thyroid surgery.
Fluorescence is a physical phenomenon where a substance absorbs light or electromagnetic radiation at one wavelength and then re-emits it at a longer wavelength. When a material absorbs photons, electrons in the material’s atoms or molecules are elevated from their ground state to an excited state. After a very short period of time (nanoseconds), the excited electrons return to a lower energy state and as they do, they release the excess energy as light of a longer wavelength, which is visible as fluorescence.
Flourescence has been used for many years for medical purposes. For example, fluorescent dyes are employed to highlight tissues or cells in diagnostic imaging and surgery. A well known substance is fluorescein. Fluorescein is a synthetic organic compound that fluoresces bright green under ultraviolet (UV) or blue light, making it highly visible even in small quantities. A typical use is to identify CSF (cerebroespinal fluid) leaks in the skull base, introducing it intrathecally (into the subarachnoid space) via a lumbar puncture and looking into the nasal cavity.
Indocyanine Green (ICG) is another fluorescent dye widely used in medical imaging, particularly in surgery. It has a high affinity for plasma proteins and emits near-infrared fluorescence (NIRF), making it highly effective for visualizing vascular structures, lymphatic systems, and specific tissues in real-time during surgery. It has an absorption peak at 780–805 nm (in blood or aqueous solution) and an emission peak al 800–830 nm, and a short half-life (3–4 minutes, with a rapid clearance by the liver). ICG’s fluorescence is activated by near-infrared light, so it is invisible to the naked human eye. It requires specialized imaging systems.
ICG fluorescence is integrated into the da Vinci Surgical System, which includes specialized NIR imaging capabilities. ICG is injected intravenously, typically 10–15 minutes before imaging, at a dose of 0.2–0.5 mg/kg. The robotic system switches to NIR mode to visualize the fluorescent signal. NIR cameras detect and display the fluorescence in real time on the surgeon’s console so that the surgeon observes the highlighted structures on a high-resolution monitor, enhancing precision during complex dissections, or for some other surgical manoeuvrers, like checking the vascular supply to the parathyroid glands after thyroidectomy.
Autofluorescence refers to the natural emission of light by biological tissues when they absorb light, typically in the ultraviolet (UV) or visible spectrum. It occurs without the need for exogenous fluorescent dyes. This phenomenon is due to the presence of intrinsic fluorophores in the tissue.
Parathyroid glands exhibit strong natural autofluorescence when excited by near-infrared light (750–800 nm). This unique property makes autofluorescence a powerful tool for identification, viability assessment (ischemic or damaged tissue shows reduced fluorescence), and therefore, surgical guidance. As it does not require to inject anything (it is just “playing with the light“), autofluorescence is a promising tool.
Is autofluorescence helpful in contributing to protect the parathyroid glands when performing a thyroidectomy? See the last review by Pardal & Pardal: Autofluorescence of the parathyroid glands during total thyroidectomy. Review of systematic reviews. “Near-infrared autofluorescence (NIRAF) is a useful tool for identifying and preserving parathyroid glands during total thyroidectomy, and its use is associated with a reduced risk of postoperative hypocalcemia. The current evidence supports the use of NIRAF, although the strength of the recommendation is weak because of heterogeneity, risk of bias, and inconsistent results among the studies. More well-designed studies are needed to confirm these findings and establish NIRAF as a standard“.
Working on it.
J Granell. Dec 26, 2024.