Intraoperative Mapping of Parathyroid Glands Using Fluorescence Lifetime Imaging

The research progress of label-free optical imaging technology in intraoperative real-time navigation of parathyroid glands

Intraoperative misidentification or vascular injury to the parathyroid glands can lead to hypoparathyroidism and hypocalcemia, resulting in serious postoperative complications. Therefore, functional localization of the parathyroid glands during thyroid (parathyroid) surgery is a key focus and challenge in thyroid surgery. The current clinical prospects of various optical imaging technologies for intraoperative localization, identification, and protection of parathyroid glands varies. However, "Label-free optical imaging technology" is increasingly favored by surgeons due to its simplicity, efficiency, safety, real-time capability, and non-invasiveness. This manuscript focuses on the relatively well-researched near-infrared autofluorescence (NIRAF) and NIRAF-combined studies including those integrating laser speckle imaging, artificial intelligence(AI) optimization, hardware integration, and optical path improvements. It also briefly introduces promising technologies, including Laser-Induced Fluorescence (LIF), Hyperspectral Imaging (HSI), Fluorescence Lifetime Imaging (FLIm), Laser-Induced Breakdown Spectroscopy (LIBS), Optical Coherence Tomography (OCT), and Dynamic Optical Contrast Imaging (DOCI). While these technologies are still in early stages with limited clinical application and standardization, current research highlights their potential for improving intraoperative parathyroid identification. Future studies should focus on refining these methods for broader clinical use.

Defining the Zone of Acute Peripheral Nerve Injury Using Fluorescence Lifetime Imaging in a Crush Injury Sheep Model

PURPOSE

Current technologies to define the zone of acute peripheral nerve injury intraoperatively are limited by surgical experience, time, cumbersome electrodiagnostic equipment, and interpreter reliability. In this pilot study, we evaluated a real-time, label-free optical technique for intraoperative nerve injury imaging. We hypothesize that fluorescence lifetime imaging (FLIm) will detect a difference between the time-resolved fluorescence signatures for acute crush injuries versus uninjured segments of peripheral nerves in sheep.

METHODS

Label-free FLIm uses ultraviolet laser pulses to excite endogenous tissue fluorophores and detect their fluorescent decay over time, generating real-time tissue-specific signatures. A crush injury was produced in eight peripheral nerves of two sheep. A hand-held FLIm instrument captured the time-resolved fluorescence signatures of injured and uninjured nerve segments across three spectral emission channels (390/40 nm, 470/28 nm, and 540/50 nm). The average FLIm parameters (ie, lifetime and intensity ratios) for injured and uninjured nerve segments were compared. We used linear discriminant analysis to differentiate between crushed and uninjured nerve segments.

RESULTS

A total of 23,692 point measurements were collected from eight crushed peripheral nerves of two sheep. Histology confirmed the zone of injury. Average lifetime at 470 nm and 540 nm were significantly different between crushed and uninjured sheep nerve segments. The linear discriminant analysis differentiated between crushed and uninjured areas of eight nerve segments with 92% sensitivity, 85% specificity, and 88% accuracy.

CONCLUSIONS

In this pilot study, FLIm detected differing average lifetime values for crushed versus uninjured sheep peripheral nerves with high sensitivity, specificity, and accuracy.

CLINICAL RELEVANCE

With further investigation, FLIm may guide the peripheral nerve surgeon to the precise zone of injury for reconstruction.

Applications of machine learning in time-domain fluorescence lifetime imaging: a review

Many medical imaging modalities have benefited from recent advances in Machine Learning (ML), specifically in deep learning, such as neural networks. Computers can be trained to investigate and enhance medical imaging methods without using valuable human resources. In recent years, Fluorescence Lifetime Imaging (FLIm) has received increasing attention from the ML community. FLIm goes beyond conventional spectral imaging, providing additional lifetime information, and could lead to optical histopathology supporting real-time diagnostics. However, most current studies do not use the full potential of machine/deep learning models. As a developing image modality, FLIm data are not easily obtainable, which, coupled with an absence of standardisation, is pushing back the research to develop models which could advance automated diagnosis and help promote FLIm. In this paper, we describe recent developments that improve FLIm image quality, specifically time-domain systems, and we summarise sensing, signal-to-noise analysis and the advances in registration and low-level tracking. We review the two main applications of ML for FLIm: lifetime estimation and image analysis through classification and segmentation. We suggest a course of action to improve the quality of ML studies applied to FLIm. Our final goal is to promote FLIm and attract more ML practitioners to explore the potential of lifetime imaging.

John MA, Stafsudd O. Ex vivo hypercellular parathyroid gland differentiation using dynamic optical contrast imaging (DOCI)

Primary hyperparathyroidism, often caused by a single adenoma (80-85%) or four-gland hyperplasia (10-15%), can lead to elevated parathyroid hormone (PTH) levels and resultant hypercalcemia. Surgical excision of offending lesions is the standard of care, as the removal of pathologic adenomas reduces PTH and calcium values to baseline. The small size, variable location, and indistinct external features of parathyroid glands can make their identification quite challenging intraoperatively. Our group has developed the dynamic optical contrast imaging (DOCI) technique, a novel realization of dynamic temporally dependent measurements of tissue autofluorescence. In this study, we evaluated the efficacy of using the DOCI technique and normalized steady-state fluorescence intensity data for differentiating types of human parathyroid and thyroid tissues. We demonstrate that the DOCI technique has the capability to distinguish normal parathyroid tissue from diseased parathyroid glands as well as from adjacent healthy thyroid and adipose tissue across 8 different spectral channels between 405nm-600nm (p<0.05). Patient tissue DOCI data was further analyzed with a logistic regression classifier trained across the 8 spectral channels. After computer training, the computer-aided identification was able to accurately locate hypercellular parathyroid tissue with 100% sensitivity and 98.8% specificity within the captured DOCI image.

Thyroidectomy for Cancer: The Surgeon and the Parathyroid Glands Sparing

BACKGROUND

The diagnosis of thyroid cancer is continuously increasing and consequently the amount of thyroidectomy. Notwithstanding the actual surgical skill, postoperative hypoparathyroidism still represents its most frequent complication. The aims of the present study are to analyze the rate of postoperative hypoparathyroidism after thyroidectomy, performed for cancer by a single first operator, without any technological aid, and to compare the data to those obtained adopting the most recent technological adjuncts developed to reduce the postoperative hypoparathyroidism.

METHODS

During the period 1997-2020 at the Endocrine Surgery Unit of the Department of Clinical and Experimental Medicine of the University of Florence, 1648 consecutive extracapsular thyroidectomies for cancer (401 with central compartment node dissection) were performed. The percentage of hypoparathyroidism, temporary or permanent, was recorded both in the first period (Group A) and in the second, most recent period (Group B). Total thyroidectomies were compared either with those with central compartment dissection and lobectomies. Minimally invasive procedures (MIT, MIVAT, some transoral) were also compared with conventional. Fisher's exact and Chi-square tests were used for comparison of categorical variables. p < 0.01 was considered statistically significant. Furthermore, a literature research from PubMed® has been performed, considering the most available tools to better identify parathyroid glands during thyroidectomy, in order to reduce the postoperative hypoparathyroidism. We grouped and analyzed them by technological affinity.

RESULTS

On the 1648 thyroidectomies enrolled for the study, the histotype was differentiated in 93.93 % of cases, medullary in 4% and poorly differentiated in the remaining 2.06%. Total extracapsular thyroidectomy and lobectomy were performed respectively in 95.45% and 4.55%. We recorded a total of 318 (19.29%) cases of hypocalcemia, with permanent hypoparathyroidism in 11 (0.66%). In regard to the literature, four categories of tools to facilitate the identification of the parathyroids were identified: (a) vital dye; (b) optical devices; (c) autofluorescence of parathyroids; and (d) autofluorescence enhanced by contrast media. Postoperative hypoparathyroidism had a variable range in the different groups.

CONCLUSIONS

Our data confirm that the incidence of post-surgical hypoparathyroidism is extremely low in the high volume centers. Its potential reduction adopting technological adjuncts is difficult to estimate, and their cost, together with complexity of application, do not allow immediate routine use. The trend towards increasingly unilateral surgery in thyroid carcinoma, as confirmed by our results in case of lobectomy, is expected to really contribute to a further reduction of postsurgical hypoparathyroidism.