Mechanisms of delayed indocyanine green fluorescence and applications to clinical disease processes

BACKGROUND

Delayed indocyanine green fluorescence imaging is under investigation in various clinical disease processes. Understanding the mechanisms of indocyanine green accumulation and retention is essential to correctly interpreting and analyzing imaging data. The purpose of this scoping review was to synthesize what is known about the mechanism of indocyanine green retention at the cellular level to better understand the clinical nuances of delayed indocyanine green imaging and identify critical gaps in our knowledge to guide future studies.

METHODS

We performed a scoping review of 7,087 citations after performing database searches of PubMed, Scopus, the Cochrane Library, and the Web of Science Core Collection electronic databases. Studies were eligible for inclusion if they were peer-reviewed original research discussing the mechanism of indocyanine green retention in the results section in disease processes involving inflammation and/or necrosis, including cancer, and were available in English. Data were extracted using Covidence software.

RESULTS

Eighty-nine studies were included in the final analysis. Several features of indocyanine green retention were identified.

CONCLUSION

We identified several mechanistic features involved in indocyanine green accumulation in diseased tissue that overall had distinct mechanisms of indocyanine green retention in tumors, nontumor inflammation, and necrosis. Our study also reveals new insights on how inflammatory infiltrate influences indocyanine green fluorescence imaging. These findings are noteworthy because they add to our understanding of how fluorescence-guided surgery may be optimized based on the pathology of interest via specific indocyanine green dosing and timing of image acquisition.

Tumor Segmentation in Intraoperative Fluorescence Images Based on Transfer Learning and Convolutional Neural Networks

OBJECTIVE

To propose a transfer learning based method of tumor segmentation in intraoperative fluorescence images, which will assist surgeons to efficiently and accurately identify the boundary of tumors of interest.

METHODS

We employed transfer learning and deep convolutional neural networks (DCNNs) for tumor segmentation. Specifically, we first pre-trained four networks on the ImageNet dataset to extract low-level features. Subsequently, we fine-tuned these networks on two fluorescence image datasets (ABFM and DTHP) separately to enhance the segmentation performance of fluorescence images. Finally, we tested the trained models on the DTHL dataset. The performance of this approach was compared and evaluated against DCNNs trained end-to-end and the traditional level-set method.

RESULTS

The transfer learning-based UNet++ model achieved high segmentation accuracies of 82.17% on the ABFM dataset, 95.61% on the DTHP dataset, and 85.49% on the DTHL test set. For the DTHP dataset, the pre-trained Deeplab v3 + network performed exceptionally well, with a segmentation accuracy of 96.48%. Furthermore, all models achieved segmentation accuracies of over 90% when dealing with the DTHP dataset.

CONCLUSION

To the best of our knowledge, this study explores tumor segmentation on intraoperative fluorescent images for the first time. The results show that compared to traditional methods, deep learning has significant advantages in improving segmentation performance. Transfer learning enables deep learning models to perform better on small-sample fluorescence image data compared to end-to-end training. This discovery provides strong support for surgeons to obtain more reliable and accurate image segmentation results during surgery.

Indocyanine Green Fluorescence Navigation in Liver Surgery: A Systematic Review on Dose and Timing of Administration

BACKGROUND

Indocyanine green (ICG) fluorescence has proven to be a high potential navigation tool during liver surgery; however, its optimal usage is still far from being standardized.

METHODS

A systematic review was conducted on MEDLINE/PubMed for English articles that contained the information of dose and timing of ICG administration until February 2021. Successful rates of tumor detection and liver segmentation, as well as tumor/patient background and imaging settings were also reviewed. The quality assessment of the articles was performed in accordance with the Scottish Intercollegiate Guidelines Network (SIGN).

RESULTS

Out of initial 311 articles, a total of 72 manuscripts were obtained. The quality assessment of the included studies revealed usually low; only 9 articles got qualified as high quality. Forty articles (55%) focused on open resections, whereas 32 articles (45%) on laparoscopic and robotic liver resections. Thirty-four articles (47%) described tumor detection ability, and 25 articles (35%) did liver segmentation ability, and the others (18%) did both abilities. Negative staining was reported (42%) more than positive staining (32%). For tumor detection, majority used the dose of 0.5 mg/kg within 14 days before the operation day, and an additional administration (0.02-0.5 mg/kg) in case of longer preoperative interval. Tumor detection rate was reported to be 87.4% (range, 43%-100%) with false positive rate reported to be 10.5% (range, 0%-31.3%). For negative staining method, the majority used 2.5 mg/body, ranging from 0.025 to 25 mg/body. For positive staining method, the majority used 0.25 mg/body, ranging from 0.025 to 12.5 mg/body. Successful segmentation rate was 88.0% (range, 53%-100%).

CONCLUSION

The time point and dose of ICG administration strongly needs to be tailored case by case in daily practice, due to various tumor/patient backgrounds and imaging settings.

Determination of surgical margins in laparoscopic parenchyma-sparing hepatectomy of neuroendocrine tumors liver metastases using indocyanine green fluorescence imaging

BACKGROUND

Neuroendocrine tumors (NETs) are a group of heterogenous tumors originating from neuroendocrine system. Approximately, 40 percent will go through liver metastases, and liver-directed therapy was proved to improve the survival outcome. Parenchyma-sparing hepatectomy is advocated for the resection of NETs liver metastases while the possible relatively low negative margin rate is concerned. Indocyanine green (ICG) fluorescence imaging provides a real-time navigation on determination of surgical margins in colorectal cancer liver metastases. However, there was no previous study that reported the applications of ICG fluorescence imaging in NETs liver metastases. The present study aimed to evaluate the feasibility and security of using ICG fluorescence imaging to determine surgical margins of NETs liver metastases during operation.

METHODS

A retrospective two-arm cohort study was performed on 25 consecutive patients with NETs liver metastases who underwent laparoscopic parenchyma-sparing hepatectomy (LPSH). Patients were divided into two groups according to whether or not the ICG fluorescence imaging was used. Data on sociodemographic characteristics, laboratory parameters, pathology results, and surgical outcomes were collected.

RESULTS

A total of 145 tumors pathologically diagnosed with NETs liver metastases were resected from 25 patients. The pathological results indicated negative margins in all tumors (102/102) in LPSH with ICG fluorescence imaging group. The negative margin rate was significantly higher in LPSH using the ICG fluorescence imaging (100% v.s 88.4%, p = 0.002). Surgical outcomes, including operation time, estimated blood loss, intraoperative transfusion rate, and postoperative morbidity, were comparable between LPSH with and without ICG fluorescence imaging groups.

CONCLUSION

ICG fluorescence imaging showed the potential to identify tumor boundaries and determine surgical margins. This technique may serve as a valuable intraoperative navigation in patients with NETs liver metastases.

Fluorescence-guided hepatobiliary surgery with long and short wavelength fluorophores

Importance

Fluorescence-guided surgery (FGS) is a potentially powerful tool for hepatobiliary (HPB) surgery. The high sensitivity of fluorescence navigation is especially useful in settings where tactile feedback is limited.

Objective

The present narrative review evaluates literature on the use of FDA-approved fluorophores such as methylene blue (MB), 5-aminolevulinic acid (5-ALA), and indocyanine green (ICG) for clinical intra-operative image-guidance during HPB surgery.

Evidence Review

Approaches such as dosing, timing, imaging devices and comparative endpoints are summarized. The feasibility and safety of fluorophores in visualizing the biliary tree, identify biliary leaks, outline anatomic hepatic segments, identify tumors, and evaluate perfusion and graft function in liver transplants are discussed.

Findings

Tumor-specific probes are a promising advancement in FGS with a greater degree of specificity. The current status of tumor-specific probes being evaluated in clinical trials are summarized.

Conclusions and Relevance for Reviews

Relevant discussion of promising tumor-specific probes in pre-clinical development are discussed. Fluorescence-guidance in HPB surgery is relatively new, but current literature shows that the dyes are reliably able to outline desired structures with a variety of dosing, timing, and imaging devices to provide real-time intra-operative anatomic information to surgeons. Development of tumor-specific probes will further advance the field of HPB surgery especially during oncologic resections.

[Indocyanine green fluorescence staining in liver surgery]

BACKGROUND

Indocyanine green (ICG) opens up numerous possibilities for applications in hepatobiliary surgery, due to its exclusive hepatic excretion and its fluorescence properties in the near infrared (NIR) spectrum.

OBJECTIVE

Systematic review of the literature on the application of ICG imaging in open and laparoscopic liver surgery.

MATERIAL AND METHODS

Literature review and summary of the recent scientific original articles and reviews.

RESULTS

The ICG fluorescence imaging is increasingly being used in liver surgery. It allows real-time display of the segmental anatomy of the liver. Moreover, depending on the tumor entity, direct or indirect visualization of liver tumors and metastases is also possible. The detection of bile leaks might also be facilitated. Recent experiences in liver surgery have shown that ICG imaging enables a more sensitive intraoperative detection of additional foci and probably also a higher R0 resection rate; however, the application is mainly helpful for superficial lesions, since the depth of penetration of NIR is only 8-10 mm.

CONCLUSION

Fluorescence staining using ICG is a valuable supplementary tool in modern liver surgery. It is particularly helpful in laparoscopic surgery where tactile control is eliminated and three-dimensional orientation is difficult. These disadvantages can be partially compensated by additional real-time imaging using ICG.

Indocyanine Green Fluorescence Imaging-Guided Surgery in Primary and Metastatic Liver Tumors

BACKGROUND

After surgery for liver tumors, recurrence rates remain high because of residual positive margins or undiagnosed lesions. It has been suggested that detection of hepatic tumors can be obtained with near-infrared fluorescence imaging (FI). Indocyanine green (ICG) has been used with contrasting results. The aims of this study were to explore ICG-FI-guided surgery methodology and to assess its potential applications.

MATERIALS AND METHODS

Out of 14 patients with liver tumors, 5 were not operated on, and 9 patients (3 primary and 6 metastatic tumors) underwent surgery. ICG (0.5 mg/kg) was injected intravenously 24 hours before surgery. Fluorescence was investigated prior to resection to detect liver lesions, during hepatic transection to guide surgery, on both cross-section and benchtop to assess surgical margins, and for pathological evaluation.

RESULTS

All operations were successful and had a short duration. ICG-FI detected all already known lesions (n = 10), and identified 2 additional small tumors (1 hepatocarcinoma and 1 metastasis, diagnostic improvement = 20%). Two hepatocarcinomas were hyperfluorescent; the remaining one, with a central hypofluorescent area and a hyperfluorescent ring, was indeed a mixed cholangiohepatocarcinoma. All metastatic nodules were hypofluorescent with a hyperfluorescent rim. In all cases, in vivo and ex vivo fluorescence revealed clear liver margins. Postoperative pathological examination greatly benefited of liver fluorescence to assess radicality.

CONCLUSION

ICG-FI-guided surgery was shown to be an effective tool to improve both intraoperative staging and radicality in the surgical treatment of primary and metastatic liver tumors.

Long-term follow-up after near-infrared fluorescence-guided resection of colorectal liver metastases: A retrospective multicenter analysis

BACKGROUND

Several studies demonstrated that intraoperative near-infrared fluorescence (NIRF) imaging using indocyanine green (ICG) identifies (sub)capsular colorectal liver metastases (CRLM) missed by other techniques. It is unclear if this results in any survival benefit. This study evaluates long-term follow-up after NIRF-guided resection of CRLM using ICG.

METHODS

First, patients undergoing resection of CRLM with or without NIRF imaging were analyzed retrospectively. Perioperative details, liver-specific recurrence-free interval and overall survival were compared. Second, the prognosis of patients in whom additional metastases were identified solely by NIRF was studied.

RESULTS

Eighty-six patients underwent resection with NIRF imaging and 87 without. In significantly more patients of the NIRF imaging cohort additional metastases were identified during surgery (25% vs. 13%, p = 0.04). Tumors identified solely by NIRF imaging were significantly smaller compared to additional metastases identified also by inspection, palpation or intraoperative ultrasound (3.2 ± 1.8 mm vs. 7.4 ± 2.6 mm, p < 0.001). Liver-specific recurrence-free survival at 4 years was 47% with NIRF imaging and 39% without (hazard ratio at multivariate analysis 0.73, 95% CI 0.42-1.28, p = 0.28). Overall survival at 4 years was 62% and 59%, respectively (p = 0.79). No liver recurrences occurred within 3 years follow-up in 52% of patients in whom additional metastases were resected based on only NIRF imaging.

CONCLUSIONS

This study suggests that NIRF imaging identifies significantly more and smaller tumors during resection of CRLM, preventing recurrences in a subset of patients. Given its safety profile and low expense, routine use can be considered until tumor targeting fluorescent tracers are clinically available.