The clinical use of indocyanine green as a near-infrared fluorescent contrast agent for image-guided oncologic surgery

Dose optimization for near-infrared fluorescence sentinel lymph node mapping in patients with melanoma

BACKGROUND

Regional lymph node involvement is the most important prognostic factor in cutaneous melanoma. As only 20% of patients with melanoma have occult nodal disease and would benefit from a regional lymphadenectomy, the sentinel lymph node (SLN) biopsy was introduced. Near-infrared (NIR) fluorescence has been hypothesized to improve SLN mapping.

OBJECTIVES

  To assess the potential of intraoperative NIR fluorescence imaging to improve SLN mapping in patients with melanoma and to examine the optimal dose of indocyanine green adsorbed to human serum albumin (ICG:HSA).

METHODS

  Fifteen consecutive patients with cutaneous melanoma underwent the standard SLN procedure using (99m) technetium-nancolloid and patent blue. In addition, intraoperative NIR fluorescence imaging was performed after injection of 1·6 mL of 600, 800, 1000 or 1200 μmolL(-1) of ICG: HSA in four quadrants around the primary excision scar.

RESULTS

  NIR fluorescence SLN mapping was successful in 93% of patients. In one patient, no SLN could be identified using either conventional methods or NIR fluorescence. A total of 30 SLNs (average 2·0, range 1-7) were detected, 30 radioactive (100%), 27 blue (73%) and 30 NIR fluorescent (100%). With regard to the effect of concentration on signal-to-background ratios a trend (P=0·066) was found favouring the 600, 800 and 1000 μmol L(-1) groups over the 1200 μmol L(-1) group.

CONCLUSION

 This study demonstrates feasibility and accuracy of SLN mapping using ICG: HSA. Considering safety, cost and pharmacological characteristics, an ICG: HSA concentration of 600 μmolL(-1) appears optimal for SLN mapping in cutaneous melanoma, although lower doses need to be assessed.

Real-time near-infrared (NIR) fluorescent cholangiography in single-site robotic cholecystectomy (SSRC): a single-institutional prospective study

BACKGROUND

Bile duct injury is a rare but serious complication of laparoscopic cholecystectomy and the primary cause is misinterpretation of biliary anatomy. This may occur more frequently with a single-incision approach due to difficulties in exposing and visualizing the triangle of Calot. Intraoperative cholangiography was proposed to overcome this problem, but due to multiple issues, it is not used routinely. Indocyanine green (ICG) near-infrared (NIR) fluorescent cholangiography is non invasive and provides real-time biliary images during surgery, which may improve the safety of single-incision cholecystectomy. This study aims to evaluate the efficacy and safety of this technique during single-site robotic cholecystectomy (SSRC).

METHODS

Patients presenting with symptomatic biliary gallstones without suspicion of common bile duct stones underwent SSRC with ICG-NIR fluorescent cholangiography using the da Vinci Fluorescence Imaging Vision System. During patient preparation, 2.5 mg of ICG was injected intravenously. During surgery, the biliary anatomy was imaged in real time, which guided dissection of Calot's triangle. Perioperative outcomes included biliary tree visualizations, operative time, conversion and complications rates, and length of hospital stay.

RESULTS

There were 45 cases between July 2011 and January 2012. All procedures were completed successfully; there were no conversions and at least one structure was visualized in each patient. The rates of visualization were 93 % for the cystic duct, 88 % for the common hepatic duct, and 91 % for the common bile duct prior to Calot's dissection; after Calot's dissection, the rates were 97 % for all three ducts. Mean hospital stay was 1.1 days and there were no bile duct injuries or any other major complications.

CONCLUSION

Real-time high-resolution fluorescent imaging to identify the biliary tree anatomy during SSRC using the da Vinci Fluorescence Imaging Vision System was safe and effective.

An experimental study to evaluate the Fluobeam 800 imaging system for fluorescence-guided lymphatic imaging and sentinel node biopsy

BACKGROUND

Visualization of the lymphatic system is challenging. Lymphatic imaging is a crucial diagnostic tool for benign and malignant lymphatic pathologies. Fluorescence-guided imaging allows selective lymphatic mapping and sentinel lymph node (SLN) identification. There are a few fluorescence systems, but some drawbacks remain due to technical and ergonomic aspects. The aim of this study was to evaluate the feasibility of the new Fluobeam 800 imaging system.

METHODS

After approval by the ethics committee, the system was evaluated for lymphography and SLN biopsy in an animal model. Five pigs each with 4 lymph node (LN) stations (n = 20 LN stations) were subjected to lymphatic imaging using indocyanine green (ICG). Additionally, the use of ICG was compared with ICG adsorbed to human serum albumin (ICG-HSA). Lymphatic vessels and SLN identification rates were measured.

RESULTS

After injection, a clear fluorescence signal of the lymphatic vessels was visualized leading to the LN station. Overall, ICG fluorescence imaging identified a mean of 2.0 lymphatic vessels and 1.1 (range = 1-2) SLN in 20 of 20 LN stations. Reverse lymphography was feasible. A clinical difference in resolution was not detected between use of ICG-HSA and ICG.

CONCLUSION

This is the first study analyzing the feasibility of the Fluobeam 800 imaging system allowing transcutaneous real-time imaging. It enables detection of the SLN by fluorescence retention with increased detection depth and resolution. After fixation to the ceiling, the ergonomics advanced for simultaneous field navigation and dissection. The new system can be applied for lymphatic imaging for lympatico-reconstructive surgery and SLN biopsy.

Near infrared fluorescence for image-guided surgery

Near infrared (NIR) image-guided surgery holds great promise for improved surgical outcomes. A number of NIR image-guided surgical systems are currently in preclinical and clinical development with a few approved for limited clinical use. In order to wield the full power of NIR image-guided surgery, clinically available tissue and disease specific NIR fluorophores with high signal to background ratio are necessary. In the current review, the status of NIR image-guided surgery is discussed along with the desired chemical and biological properties of NIR fluorophores. Lastly, tissue and disease targeting strategies for NIR fluorophores are reviewed.

Molecular cytogenetic evaluation of the efficacy of photodynamic therapy by indocyanine green in breast adenocarcinoma MCF-7 cells

BACKGROUND

Photodynamic therapy (PDT) is used for the treatment of many types of predominantly epithelial cancers. Photosensitizer is taken up by fast growing tumor cells more actively than by other body cells and is activated by light, generating reactive oxygen species that cause cell death by necrosis or apoptosis. This study aimed to evaluate the efficacy of PDT with indocyanine green (ICG) through the investigation of TP53, HER-2 and TOP2A genes signals as breast cancer gene markers by interphase fluorescence in situ hybridization (nuc-FISH).

METHODS

The photosynthetizer ICG (200 μM) was applied to breast cancer cell line MCF-7 cells (adenocarcinoma) in combination with laser irradiation (807 nm) exposure for 20 min and then incubated for 12, 24 and 48 h. Cell viability was evaluated using trypan blue. The signals for nuc-FISH was investigated and counted for probes specific for the genes TP53 (17p13), HER-2 (17q11.2-q12), and TOP2A (17q21-q22), and BAC-probes RP11-746M1 in 17p11.2 and RP11-403E9 in 17q11.2.

RESULTS

The cell viability of MCF-7 did not reduced significantly when the cells were treated with ICG (200 μM) or exposed to laser irradiation for 20 min followed by incubation for 24 h. ICG/PDT treatment with laser irradiation exposure for 20 min reduced the cell viability after incubating cells for 12, 24 and 48 h highly significantly in a time dependent manner. For nuc-FISH analysis, TP53, HER-2, TOP2A, RP11-746M1 and RP11-403E9 signals did not reduce or increase in a significant manner when the cells were treated with ICG or exposed to laser irradiation for 20 min then incubated for 24h. PDT enhanced amplification of TP53 signals from nuc ish 17p13(TP53×2) to nuc ish 17p13(TP53×3) or nuc ish 17p13(TP53×4). However, the signals of HER-2 gene, TOP2A gene and BAC probes were reduced highly significantly when MCF-7 cells were treated with PDT with all time intervals.

CONCLUSION

ICG/PDT and laser induced cytotoxic effect in MCF-7 cells. Also, PDT enhanced TP53 gene amplification, and reduced HER-2, TOP2A, and BAC probes RP11-746M1 and RP11-403E9 signals. Therefore ICG/PDT can be used for breast cancer treatment. It has the potential to induce apoptotic effect and reduce HER-2 and TOP2A genes propagation. Further in vivo studies are needed to evaluate ICG/PDT as a promising therapeutic approach for breast cancer.

Synthesis and biological evaluation of low molecular weight fluorescent imaging agents for the prostate-specific membrane antigen

Targeted near-infrared (NIR) optical imaging can be used in vivo to detect specific tissues, including malignant cells. A series of NIR fluorescent ligands targeting the prostate-specific membrane antigen (PSMA) was synthesized and each compound was tested for its ability to image PSMA+ tissues in experimental models of prostate cancer. The agents were prepared by conjugating commercially available active esters of NIR dyes, including IRDye800CW, IRDye800RS, Cy5.5, Cy7, or a derivative of indocyanine green (ICG) to the terminal amine group of (S)-2-(3-((S)-5-amino-1-carboxypentyl)ureido)pentanedioic acid 1, (14S,18S)-1-amino-8,16-dioxo-3,6-dioxa-9,15,17-triazaicosane-14,18,20-tricarboxylic acid 2 and (3S,7S)-26-amino-5,13,20-trioxo-4,6,12,21-tetraazahexacosane-1,3,7,22-tetracarboxylic acid 3. The K(i) values for the dye-inhibitor conjugates ranged from 1 to 700 pM. All compounds proved capable of imaging PSMA+ tumors selectively to varying degrees depending on the choice of fluorophore and linker. The highest tumor uptake was observed with IRDye800CW employing a poly(ethylene glycol) or lysine-suberate linker, as in 800CW-2 and 800CW-3, while the highest tumor to nontarget tissue ratios were obtained for Cy7 with these same linkers, as in Cy7-2 and Cy7-3. Compounds 2 and 3 provide useful scaffolds for targeting of PSMA+ tissues in vivo and should be useful for preparing NIR dye conjugates designed specifically for clinical intraoperative optical imaging devices.

Near-infrared optical guided surgery of highly infiltrative fibrosarcomas in cats using an anti-αvß3 integrin molecular probe

We investigated how near-infrared imaging could improve highly infiltrative spontaneous fibrosarcoma surgery in 12 cats in a clinical veterinary phase. We used an RGD-based nanoprobe at different doses and times before surgery and a portable clinical grade imaging system. All tumours were labelled by the tracer and had an overall tumour-to-healthy tissue ratio of 14±1 during surgery. No false negatives were found, and the percentage of tumour cells was linearly correlated with the fluorescence intensity. All cats recovered well and were submitted to long-term follow-up that is currently on-going 1year after the beginning of the study.

Preclinical study of near-infrared-guided sentinel lymph node mapping of the porcine lung

BACKGROUND

The presence of lymph node metastasis is the most important prognostic factor in early non-small cell lung cancer. Our objective was to develop a rapid, simple, and reliable method for thoracic sentinel lymph node (SLN) identification using near-infrared fluorescence imaging and clinically available contrast agents.

METHODS

Indocyanine green (ICG) reconstituted in saline, human serum albumin, human fresh frozen plasma, and autologous porcine plasma was evaluated for optimal formulation and dosing for SLN within porcine lungs. Animals were imaged using the fluorescence-assisted resection and exploration for surgery imaging system. The SLN identification rate, time to identification and fluorescence intensity of the SLN, bronchus, and background were measured.

RESULTS

The SLN identification rates varied widely, ranging from 33% to 100% as a function of the carrier used for ICG reconstitution. No significant difference was noted in SLN fluorescence intensity; however, bronchial intensity was significantly higher with ICG: albumin, which resulted in the lowest rate of SLN identification. Subsequent evaluation with 125 μM and 250 μM ICG:porcine plasma resulted in identification of strongly fluorescent SLNs, with identification rates of 93% and 100% and median signal-to-background ratios of 8.5 and 12.15, respectively, in less than 2 minutes in situ.

CONCLUSIONS

Near-infrared fluorescence imaging with ICG is a reliable method for SLN mapping in the lung with high sensitivity. Mixing of ICG with plasma resulted in strong SLN fluorescence signal with reliable identification rates.

Translational optical imaging

OBJECTIVE

Optical imaging is experiencing significant technologic advances. Simultaneously, an array of specific optical imaging agents has brought new capabilities to biomedical research and is edging toward clinical use. We review progress in the translation of macroscopic optical imaging-including fluorescence-guided surgery and endoscopy, intravascular fluorescence imaging, diffuse fluorescence and optical tomography, and multispectral optoacoustics (photoacoustics)-for applications ranging from tumor resection and assessment of atherosclerotic plaques to dermatologic and breast examinations.

CONCLUSION

Optical imaging could play a major role in the move from imaging of structure and morphology to the visualization of the individual biologic processes underlying disease and could, therefore, contribute to more accurate diagnostics and improved treatment efficacy.

A novel method to quantify IRDye800CW fluorescent antibody probes ex vivo in tissue distribution studies

Background

We describe a new method for biodistribution studies with IRDye800CW fluorescent antibody probes. This method allows the quantification of the IRDye800CW fluorescent tracer in percentage of injected dose per gram of tissue (% ID/g), and it is herein compared to the generally used reference method that makes use of radioactivity.

Methods

Cetuximab was conjugated to both the near-infrared fluorophore IRDye800CW and/or the positron emitter 89-zirconium, which was injected in nude mice bearing A431 human tumor xenografts. Positron emission tomography (PET) and optical imaging were performed 24 h post-injection (p.i.). For the biodistribution study, organs and tumors were collected 24 h p.i., and each of these was halved. One half was used for the determination of probe uptake by radioactivity measurement. The other half was homogenized, and the content of the fluorescent probe was determined by extrapolation from a calibration curve made with the injected probe.

Results

Tumors were clearly visualized with both modalities, and the calculated tumor-to-normal tissue ratios were very similar for optical and PET imaging: 3.31 ± 1.09 and 3.15 ± 0.99, respectively. Although some variations were observed in ex vivo analyses, tumor uptake was within the same range for IRDye800CW and gamma ray quantification: 15.07 ± 3.66% ID/g and 13.92 ± 2.59% ID/g, respectively.

Conclusions

The novel method for quantification of the optical tracer IRDye800CW gives similar results as the reference method of gamma ray quantification. This new method is considered very useful in the context of the preclinical development of IRDye800CW fluorescent probes for optical molecular imaging, likely contributing to the selection of lead compounds that are the most promising for clinical translation.

Near-infrared emitting polymer nanogels for efficient sentinel lymph node mapping

Sentinel lymph node (SLN) mapping has been widely used to predict the metastatic spread of primary tumor to regional lymph nodes in clinical practice. In this research, a new near-infrared (NIR)-emitting polymer nanogel (NIR-PNG) having a hydrodynamic diameter of about 30 nm, which is optimal for lymph node uptake, was developed. The NIR-emitting polymer nanoprobes were designed and synthesized by conjugating IRDye800 organic dye to biodegradable pullulan-cholesterol polymer nanogels. The NIR-PNG nanoprobes were found to be photostable compared with the IRDye800-free dye at room temperature. Upon intradermal injection of the NIR-PNG into the front paw of a mouse, the nanoprobes entered the lymphatic system and migrated to the axillary lymph node within 2 min. The NIR fluorescence signal intensity and retention time of NIR-PNG in the lymph node were superior to the corresponding properties of the IRDye800-free dye. A immunohistofluorescence study of the SLN resected under NIR imaging revealed that the NIR-PNG nanoprobes were predominantly co-localized with macrophages and dendritic cells. Intradermal injection of NIR-PNG nanoprobes into the thigh of a pig permitted real-time imaging of the lymphatic flow toward the SLN. The position of the SLN was identified within 1 min with the help of the NIR fluorescence images. Taken together, the experimental results demonstrating the enhanced photostability and retention time of the NIR-PNG provide strong evidence for the potential utility of these polymer probes in cancer surgery such as SLN mapping.

Sentinel lymph nodes fluorescence detection and imaging using Patent Blue V bound to human serum albumin

Patent Blue V (PBV), a dye used clinically for sentinel lymph node detection, was mixed with human serum albumin (HSA). After binding to HSA, the fluorescence quantum yield increased from 5 × 10(-4) to 1.7 × 10(-2), which was enough to allow fluorescence detection and imaging of its distribution. A detection threshold, evaluated in scattering test objects, lower than 2.5 nmol × L(-1) was obtained, using a single-probe setup with a 5-mW incident light power. The detection sensitivity using a fluorescence imaging device was in the µmol × L(-1) range, with a noncooled CCD camera. Preclinical evaluation was performed on a rat model and permitted to observe inflamed nodes on all animals.

Intraoperative near-infrared imaging of surgical wounds after tumor resections can detect residual disease

PURPOSE

Surgical resection remains the most effective therapy for solid tumors worldwide. The most important prognostic indicator for cure following cancer surgery is a complete resection with no residual disease. However, intraoperative detection of retained cancer cells after surgery is challenging, and residual disease continues to be the most common cause of local failure. We hypothesized that visual enhancement of tumors using near-infrared imaging could potentially identify tumor deposits in the wound after resection.

EXPERIMENTAL DESIGN

A small animal model of surgery and retained disease was developed. Residual tumor deposits in the wound were targeted using an U.S. Food and Drug Administration-approved imaging agent, indocyanine green, by the enhanced permeability and retention effect. A novel handheld spectrometer was used to optically visualize retained disease after surgery.

RESULTS

We found residual disease using near-infrared imaging during surgery that was not visible to the naked eye or micro-CT. Furthermore, examination of tumor nodules was remarkably precise in delineating margins from normal surrounding tissues. This approach was most successful for tumors with increased neovasculature.

CONCLUSIONS

The results suggest that near-infrared examination of the surgical wound after curative resection can potentially enable the surgeon to locate residual disease. The data in this study is the basis of an ongoing Phase I/II clinical trial in patients who undergo resection for lung and breast cancer.

Near-infrared fluorescence sentinel lymph node mapping of the oral cavity in head and neck cancer patients

OBJECTIVES

Elective neck dissection is frequently performed during surgery in head and neck cancer patients. The sentinel lymph node (SLN) procedure can prevent the morbidity of a neck dissection and improve lymph node staging by fine pathology. Near-infrared (NIR) fluorescence imaging is a promising technique to identify the sentinel lymph node (SLN) intraoperatively. This feasibility study explored the use of indocyanine green adsorbed to human serum albumin (ICG:HSA) for SLN mapping in head and neck cancer patients.

MATERIALS AND METHODS

A total of 10 consecutive patients with oral cavity or oropharyngeal cancer and a clinical N0 neck were included. After exposure of the neck, 1.6 mL of ICG:HSA (500 μM) was injected at four quadrants around the tumor. During the neck dissection, levels I-IV were measured for fluorescence using the Mini-FLARE imaging system.

RESULTS

In all 10 patients, NIR fluorescence imaging enabled visualization of one or more SLNs. A total of 17 SLNs were identified. The mean contrast between the fluorescent signal of the lymph nodes and of the surrounding tissue was 8.7±6.4. In 3 patients, of which 1 was false-negative, lymph node metastases were found. After administration of ICG:HSA, the average number of fluorescent lymph nodes significantly increased over time (P<0.001).

CONCLUSION

This study demonstrated feasibility to detect draining lymph nodes in head and neck cancer patients using NIR fluorescence imaging. However, the fluorescent tracer quickly migrated beyond the SLN to higher tier nodes.

Near-infrared fluorescence imaging of a solitary fibrous tumor of the pancreas using methylene blue

A 67-year-old female presented with unexplained abdominal pain. A contrast-enhanced computed tomography scan of the abdomen incidentally revealed a mass in the uncinate process of the pancreas. This mass was resected and based on histopathological findings, diagnosed as a solitary fibrous tumor (SFT) of the pancreas. A SFT is an extremely rare benign mesenchymal tumor that in 65% of cases affects the visceral pleura but can also affect extra-pleural sites. The intraoperative demarcation of pancreatic tumors, such as SFTs, can be challenging. In this report, the first clear intraoperative identification of a SFT of the pancreas in a human was shown using near-infrared fluorescence and methylene blue.

Randomized comparison of near-infrared fluorescence lymphatic tracers for sentinel lymph node mapping of cervical cancer

OBJECTIVE

Near-infrared fluorescence imaging using indocyanine green (ICG) has recently been introduced as a novel technique for sentinel lymph node (SLN) mapping in early-stage cervical cancer. Although preclinical research has shown that ICG adsorbed to human serum albumin (ICG:HSA) improves its performance, the need for HSA has not yet been confirmed in cervical cancer patients. The current randomized study aims to determine whether ICG:HSA offers advantages over using ICG alone.

METHODS

Eighteen consecutive early-stage cervical cancer patients scheduled to undergo pelvic lymphadenectomy were included. Prior to surgery, 1.6 mL of 500 μM ICG:HSA or 500 μM ICG alone was injected transvaginally in 4 quadrants around the tumor. The Mini-FLARE imaging system was used for intraoperative NIR fluorescence detection and quantitation.

RESULTS

SLNs were identified intraoperatively in 78% of the patients. Patient and tumor characteristics were equally distributed over both treatment groups. No significant difference in signal-to-background ratio (9.3 vs. 10.1, P=.72) or average number of detected SLNs (2.9 vs 2.7, P=.84) was found between the ICG:HSA group and the ICG alone group, respectively.

CONCLUSIONS

In conclusion, this double-blind, randomized trial showed no advantage of ICG:HSA over ICG alone for the SLN procedure in early-stage cervical cancer. Further optimization is required to improve the intraoperative detection rate.

A receptor-targeted fluorescent radiopharmaceutical for multireporter sentinel lymph node imaging

PURPOSE

To determine the imaging and receptor-binding properties of a multireporter probe designed for sentinel lymph node (SLN) mapping via nuclear and fluorescence detection.

MATERIALS AND METHODS

The animal experiments were approved by the institutional animal care and use committee. A multireporter probe was synthesized by covalently attaching cyanine 7 (Cy7), a near-infrared cyanine dye, to tilmanocept, a radiopharmaceutical that binds to a receptor specific to recticuloendothelial cells. In vitro binding assays of technetium 99m (99mTc)-labeled Cy7 tilmanocept were conducted at 4°C by using receptor-bearing macrophages. Optical SLN imaging after foot pad administration was performed by using two molar doses of Cy7 tilmanocept. Six mice were injected with 0.11 nmol of 99mTc-labeled Cy7 tilmanocept (low-dose group); an additional six mice were injected with 31 nmol of 99mTc-labeled Cy7 tilmanocept (high-dose group) to saturate the receptor sites within the SLN. After 2.5 hours of imaging, the mice were euthanized, and the sentinel and distal lymph nodes were excised and assayed for radioactivity for calculation of SLN percentage of injected dose and extraction. Four mice were used as controls for autofluorescence. Standard optical imaging software was used to plot integrated fluorescence intensity against time for calculation of the SLN uptake rate constant and scaled peak intensity. Significance was calculated by using the Student t test.

RESULTS

In vitro binding assays showed subnanomolar affinity (mean dissociation constant, 0.25 nmol/L±0.10 [standard deviation]). Fluorescence imaging showed a detection sensitivity of 1.6×10(3) counts·sec(-1)·μW(-1) per picomole of Cy7. All four imaging metrics (percentage of injected dose, SLN extraction, SLN uptake rate constant, and expected peak fluorescence intensity) exhibited higher values (P=.005 to P=.042) in the low-dose group than in the high-dose group; this finding was consistent with receptor-mediated image formation.

CONCLUSION

The multireporter probe 99mTc-labeled Cy7 tilmanocept exhibits in vitro and in vivo receptor-binding properties for successful receptor-targeted SLN mapping with nuclear and optical imaging.

Essential parameters to consider for the characterization of optical imaging probes

The Molecular Imaging and Contrast Agents Database (MICAD) was launched in 2005 to promote the development and application of imaging and contrast agents (probes) to advance the field of molecular imaging. As of March 2012, there are approximately 1170 agents available in MICAD. Based on the modality used for imaging, the largest category of probes described in MICAD are those used for PET (41.6%), followed by agents used for single-photon emission computed tomography (30.3%), optical imaging (12.0%), MRI (9.3%), multimodality imaging (3.4%), ultrasound (2.4%) and x-ray/computed tomography (1.0%). This article is intended to be a guideline for new investigators and students who wish to characterize an optical imaging probe that will be used to perform in vivo molecular imaging studies. It is necessary, however, to ensure that these agents meet certain quality control parameters before they are used in various in vitro and in vivo applications.

Intraoperative Near-infrared Fluorescence Imaging with Novel Indocyanine Green-Loaded Nanocarrier for Spinal Metastasis: A Preliminary Animal Study

Marginal resection during resection of a spinal metastasis is frequently difficult because of the presence of important tissues such as the aorta, vena cava, and dura mater, including the spinal cord adjacent to the vertebral body. Thus, there is an urgent need for novel intraoperative imaging modalities with the ability to clearly identify bone metastasis. We have proposed a novel nanocarrier loaded with indocyanine green (ICG) (ICG-lactosome) with tumor selectivity attributable to its enhanced permeation and retention (EPR) effect. We studied its feasibility in intraoperative near-infrared (NIR) fluorescence diagnosis with ICG-lactosome for imaging spinal metastasis. A rat model of subcutaneous mammary tumor and a rat model of spinal metastasis of breast cancer were used. Fluorescence emitted by the subcutaneous tumors and the spinal metastasis were clearly detected for at least 24 h. Moreover, imaging of the dissected spine revealed clear fluorescence emitted by the metastatic lesion in the L6 vertebra while the normal bone lacked fluorescence. This study was the first report on NIR fluorescence imaging of spinal metastasis in vivo. NIR fluorescence imaging with ICG-lactosome could be an effective intraoperative imaging modality for detecting spinal metastasis.

Near infrared dye indocyanine green doped silica nanoparticles for biological imaging

Indocyanine green (ICG) is an FDA-approved near infrared (NIR) fluorescent dye used in clinical imaging. However, its applications remain limited due to its short half-life, nonspecific plasma binding, optical instability, and poor aqueous stability. Dye doped silica nanoparticles provide an effective barrier in keeping the dye away from the surrounding environment, but ICG cannot be encapsulated into silica easily by conventional methods. In this study, ICG molecules ion-paired with a cationic polymer polyethylenimine (PEI) were successfully encapsulated into a silica matrix to form ICG doped silica nanoparticles by using the Stöber method. Pairing with PEI reduced self-quenching of fluorescence by preventing the aggregation of ICG molecules in silica nanoparticles. Dye leakage was also reduced to the level of 3-6% loss in 5 days. NIR fluorescence images of ICG doped silica NPs below a 2.0 cm thick porcine muscle sample illuminated by NIR light were obtained.

Three-dimensional optical coherence tomography for optical biopsy of lymph nodes and assessment of metastatic disease

BACKGROUND

Numerous techniques have been developed for localizing lymph nodes before surgical resection and for their histological assessment. Nondestructive high-resolution transcapsule optical imaging of lymph nodes offers the potential for in situ assessment of metastatic involvement, potentially during surgical procedures.

METHODS

Three-dimensional optical coherence tomography (3-D OCT) was used for imaging and assessing resected popliteal lymph nodes from a preclinical rat metastatic tumor model over a 9-day time-course study after tumor induction. The spectral-domain OCT system utilized a center wavelength of 800 nm, provided axial and transverse resolutions of 3 and 12 μm, respectively, and performed imaging at 10,000 axial scans per second.

RESULTS

OCT is capable of providing high-resolution label-free images of intact lymph node microstructure based on intrinsic optical scattering properties with penetration depths of ~1-2 mm. The results demonstrate that OCT is capable of differentiating normal, reactive, and metastatic lymph nodes based on microstructural changes. The optical scattering and structural changes revealed by OCT from day 3 to day 9 after the injection of tumor cells into the lymphatic system correlate with inflammatory and immunological changes observed in the capsule, precortical regions, follicles, and germination centers found during histopathology.

CONCLUSIONS

We report for the first time a longitudinal study of 3-D transcapsule OCT imaging of intact lymph nodes demonstrating microstructural changes during metastatic infiltration. These results demonstrate the potential of OCT as a technique for intraoperative, real-time in situ 3-D optical biopsy of lymph nodes for the intraoperative staging of cancer.

Dual-labeling strategies for nuclear and fluorescence molecular imaging: a review and analysis

Molecular imaging is used for the detection of biochemical processes through the development of target-specific contrast agents. Separately, modalities such as nuclear and near-infrared fluorescence (NIRF) imaging have been shown to non-invasively monitor disease. More recently, merging of these modalities has shown promise owing to their comparable detection sensitivity and benefited from the development of dual-labeled imaging agents. Dual-labeled agents hold promise for whole-body and intraoperative imaging and could bridge the gap between surgical planning and image-guided resection with a single, molecularly targeted agent. In this review, we summarized the literature for dual-labeled antibodies and peptides that have been developed and have highlighted key considerations for incorporating NIRF dyes into nuclear labeling strategies. We also summarized our findings on several commercially available NIRF dyes and offer perspectives for developing a toolkit to select the optimal NIRF dye and radiometal combination for multimodality imaging.

Intra-operative fluorescent cholangiography using indocyanin green during robotic single site cholecystectomy

BACKGROUND AND STUDY AIMS

Very recently, robotic single site cholecystectomy (RSSC) has been reported feasible and safe for selected cases. While an intra-operative cholangiography can be performed, data is scarce with respect to its use. Indocyanin green (ICG) has been shown to be a viable option to visualize biliary anatomy. Since the introduction of a new near infrared camera integrated to the da Vinci Si System (Intuitive Surgical, Sunnyvale, CA), the surgeon is able to assess the biliary anatomy by a non-invasive and non-ionizing method. This paper presents the first report of ICG imaging during a RSSC.

PATIENTS AND METHODS

Twelve consecutive patients presenting symptomatic cholelithiasis were prospectively enrolled. They underwent RSSC approximately 45 minutes after intravenous administration of ICG (2.5 mg). The biliary anatomy was analyzed using a near infrared camera integrated to the robot before and after the robotic dissection.

RESULTS

Eight women and four men underwent the procedure. There was a port addition in one case and no peri-operative complications. Mean operative time was 85 minutes (range: 57-125). The cystic, common bile and common hepatic ducts were recognized by fluorescence imaging before the dissection in 91.7%, 50%, and 33.3% of patients, respectively. At least one structure was visualized in 100% of patients. After the completion of Calot's triangle dissection, the cystic, common bile, and common hepatic ducts were recognized in 100%, 83.3%, and 66.7% of cases respectively.

CONCLUSIONS

RSSC using ICG for biliary tree fluorescence imaging can be performed safely. Fluorescent cholangiography enabled real-time identification of the extra-hepatic biliary anatomy using a near infrared camera integrated to the robot. Its routine clinical use merits further investigations.

Fluorescence guidance in urologic surgery

PURPOSE OF REVIEW

Fluorescent tracers can provide anatomical and functional information without altering the visual surgical field. Despite the advances that are being made in tracer development, only a few fluorescent tracers are available for urological interventions.

RECENT FINDINGS

Protoporphyrin IX, hypericin, fluorescein, and indocyanine green were shown to facilitate surgical resection in various ways. Hybrid imaging agents, combining radio and fluorescent labels, have shown improved integration between preoperative and intraoperative imaging. With the rise of surgical fluorescence guidance, various camera systems have been developed that are tailored for optimal detection of the fluorochromes of interest.

SUMMARY

In this review, the basics of fluorescence-guided surgery, including tracer and hardware requirements are discussed.

A review of indocyanine green fluorescent imaging in surgery

The purpose of this paper is to give an overview of the recent surgical intraoperational applications of indocyanine green fluorescence imaging methods, the basics of the technology, and instrumentation used. Well over 200 papers describing this technique in clinical setting are reviewed. In addition to the surgical applications, other recent medical applications of ICG are briefly examined.

Concomitant radio- and fluorescence-guided sentinel lymph node biopsy in squamous cell carcinoma of the oral cavity using ICG-(99m)Tc-nanocolloid

PURPOSE

For oral cavity malignancies, sentinel lymph node (SLN) mapping is performed by injecting a radiocolloid around the primary tumour followed by lymphoscintigraphy. Surgically, SLNs can then be localized using a handheld gamma ray detection probe. The aim of this study was to evaluate the added value of intraoperative fluorescence imaging to the conventional radioguided procedure. For this we used indocyanine green (ICG)-(99m)Tc-nanocolloid, a hybrid tracer that is both radioactive and fluorescent.

METHODS

Fourteen patients with oral cavity squamous cell carcinoma were peritumourally injected with ICG-(99m)Tc-nanocolloid. SLNs were preoperatively identified with lymphoscintigraphy followed by single photon emission computed tomography (SPECT)/CT for anatomical localization. During surgery, SLNs were detected with a handheld gamma ray detection probe and a handheld near-infrared fluorescence camera. Pre-incision and post-excision imaging with a portable gamma camera was performed to confirm complete removal of all SLNs.

RESULTS

SLNs were preoperatively identified using the radioactive signature of ICG-(99m)Tc-nanocolloid. Intraoperatively, 43 SLNs could be localized and excised with combined radio- and fluorescence guidance. Additionally, in four patients, an SLN located close to the primary injection site (in three patients this SLN was located in level I) could only be intraoperatively localized using fluorescence imaging. Pathological analysis of the SLNs revealed a metastasis in one patient.

CONCLUSION

Combined preoperative SLN identification and intraoperative radio- and fluorescence guidance during SLN biopsies for oral cavity cancer proved feasible using ICG-(99m)Tc-nanocolloid. The addition of fluorescence imaging was shown to be of particular value when SLNs were located in close proximity to the primary tumour.

Multimodal interventional molecular imaging of tumor margins and distant metastases by targeting αvβ3 integrin

α(v)β(3) integrin is involved in (tumor-induced) angiogenesis and is a promising candidate for the specific visualization of both primary tumors and of their distant metastases. Combination of radioactive and fluorescent imaging labels in a single multimodal, or rather hybrid, RGD-based imaging agent enables integration of pre-, intra-, and postoperative angiogenesis imaging. A hybrid imaging agent targeting the α(v)β(3) integrin--(111)In-MSAP-RGD (MSAP = multifunctional single-attachment-point reagent), which contains a targeting moiety, a pentetic acid (DTPA) chelate, and a cyanine dye--was evaluated for its potential value in combined lesion detection and interventional molecular imaging in a 4T1 mouse breast cancer model. SPECT/CT and fluorescence imaging were used to visualize the tumor in vivo. Tracer distribution was evaluated ex vivo down to the microscopic level. The properties of (111)In-MSAP-RGD were compared with those of (111)In-DTPA-RGD. Biodistribution studies revealed a prolonged retention and increased tumor accumulation of (111)In-MSAP-RGD relative to (111)In-DTPA-RGD. With (111)In-MSAP-RGD, identical features could be visualized preoperatively (SPECT/CT) and intraoperatively (fluorescence imaging). As well as the primary tumor, (111)In-MSAP-RGD also enabled detection and accurate excision of distant metastases in the head and neck region of the mice. Therefore, the hybrid RGD derivative (111)In-MSAP-RGD shows potential in preoperative planning and fluorescence-based surgical intervention.

Near-Infrared Fluorescent Nanoprobes for in Vivo Optical Imaging

Near-infrared (NIR) fluorescent probes offer advantages of high photon penetration, reduced light scattering and minimal autofluorescence from living tissues, rendering them valuable for noninvasive mapping of molecular events, assessment of therapeutic efficacy, and monitoring of disease progression in animal models. This review provides an overview of the recent development of the design and optical property of the different classes of NIR fluorescent nanoprobes associated with in vivo imaging applications.

Nanocolloidal albumin-IRDye 800CW: a near-infrared fluorescent tracer with optimal retention in the sentinel lymph node

Purpose

At present, the only approved fluorescent tracer for clinical near-infrared fluorescence-guided sentinel node (SN) detection is indocyanine green (ICG), but the use of this tracer is limited due to its poor retention in the SN resulting in the detection of higher tier nodes. We describe the development and characterization of a next-generation fluorescent tracer, nanocolloidal albumin-IRDye 800CW that has optimal properties for clinical SN detection

Methods

The fluorescent dye IRDye 800CW was covalently coupled to colloidal human serum albumin (HSA) particles present in the labelling kit Nanocoll in a manner compliant with current Good Manufacturing Practice. Characterization of nanocolloidal albumin-IRDye 800CW included determination of conjugation efficiency, purity, stability and particle size. Quantum yield was determined in serum and compared to that of ICG. For in vivo evaluation a lymphogenic metastatic tumour model in rabbits was used. Fluorescence imaging was performed directly after peritumoral injection of nanocolloidal albumin-IRDye 800CW or the reference ICG/HSA (i.e. ICG mixed with HSA), and was repeated after 24 h, after which fluorescent lymph nodes were excised.

Results

Conjugation of IRDye 800CW to nanocolloidal albumin was always about 50% efficient and resulted in a stable and pure product without affecting the particle size of the nanocolloidal albumin. The quantum yield of nanocolloidal albumin-IRDye 800CW was similar to that of ICG. In vivo evaluation revealed noninvasive detection of the SN within 5 min of injection of either nanocolloidal albumin-IRDye 800CW or ICG/HSA. No decrease in the fluorescence signal from SN was observed 24 h after injection of the nanocolloidal albumin-IRDye 800CW, while a strong decrease or complete disappearance of the fluorescence signal was seen 24 h after injection of ICG/HSA. Fluorescence-guided SN biopsy was very easy.

Conclusion

Nanocolloidal albumin-IRDye 800CW is a promising fluorescent tracer with optimal kinetic features for SN detection.

Electronic supplementary material

The online version of this article (doi:10.1007/s00259-012-2080-5) contains supplementary material, which is available to authorized users.

Dual-wavelength imaging of tumor progression by activatable and targeting near-infrared fluorescent probes in a bioluminescent breast cancer model

Bioluminescence imaging (BLI) has shown its appeal as a sensitive technique for in vivo whole body optical imaging. However, the development of injectable tumor-specific near-infrared fluorescent (NIRF) probes makes fluorescence imaging (FLI) a promising alternative to BLI in situations where BLI cannot be used or is unwanted (e.g., spontaneous transgenic tumor models, or syngeneic mice to study immune effects).

In this study, we addressed the questions whether it is possible to detect tumor progression using FLI with appropriate sensitivity and how FLI correlates with BLI measurements. In addition, we explored the possibility to simultaneously detect multiple tumor characteristics by dual-wavelength FLI (∼700 and ∼800 nm) in combination with spectral unmixing. Using a luciferase-expressing 4T1-luc2 mouse breast cancer model and combinations of activatable and targeting NIRF probes, we showed that the activatable NIRF probes (ProSense680 and MMPSense680) and the targeting NIRF probes (IRDye 800CW 2-DG and IRDye 800CW EGF) were either activated by or bound to 4T1-luc2 cells. In vivo, we implanted 4T1-luc2 cells orthotopically in nude mice and were able to follow tumor progression longitudinally both by BLI and dual-wavelength FLI. We were able to reveal different probe signals within the tumor, which co-localized with immuno-staining. Moreover, we observed a linear correlation between the internal BLI signals and the FLI signals obtained from the NIRF probes. Finally, we could detect pulmonary metastases both by BLI and FLI and confirmed their presence histologically.

Taken together, these data suggest that dual-wavelength FLI is a feasible approach to simultaneously detect different features of one tumor and to follow tumor progression with appropriate specificity and sensitivity. This study may open up new perspectives for the detection of tumors and metastases in various experimental models and could also have clinical applications, such as image-guided surgery.

Targeted non-covalent self-assembled nanoparticles based on human serum albumin

Human serum albumin (HSA) is a biological nanocarrier that forms non-covalent complexes with a number of synthetic and biomolecules. Previously we demonstrated radiolabeled HSA-based nanoparticles can form non-covalent complexes with fluorescent cyanine dyes yielding imaging agents for surgical guidance towards tumor draining lymph nodes. Here the self-assembly approach enabled rapid clinical translation. Based on this experience we reasoned it would be interesting to expand this non-covalent technology to a targeted approach. Therefore, the ability of HSA to form non-covalent self-assembled complexes with peptides via near-infrared (NIR) cyanine dyes was explored. Föster resonance energy transfer (FRET) quenching interactions between HSA-Cy5 and the non-covalently bound fluorescent molecules indocyanine green (ICG), IR783-CO(2)H and three IR783-labeled targeting peptides were used to monitor complex assembly and disassembly. The host-guest interactions between HSA and IR783-labeled peptides enabled the formation of (bio)nanoparticles that are coated with peptides, which may target α(v)β(3)-integrins, the chemokine receptor 4 (CXCR4), or somatostatin receptors. The potential of CXCR4-targeted (bio)nanoparticles in sentinel lymph node procedures is demonstrated in vivo. By non-covalently binding NIR-dye labeled peptides to an already clinically approved HSA-scaffold, we have readily formed targeted bionanoparticles.

The role of lymphatics in cancer as assessed by near-infrared fluorescence imaging

The lymphatic system is the secondary circulatory system responsible for fluid homeostasis and protein transport in the body. In addition, because the lymphatic system provides a primary pathway for cancer metastasis, lymph node involvement is routinely used as a determinant in cancer staging. Despite their importance, the lymphatics remain poorly understood, in part because of the historic lack of imaging modalities with sufficient spatial and/or temporal resolution to visualize the fine lymphatic structure and subtle contractile function. In recent years, near-infrared fluorescence (NIRF) imaging has emerged as a new imaging modality to non-invasively visualize the lymphatics and assess contractile lymphatic function in humans following administration of microdose amounts of a NIRF contrast agent. In this contribution, we first review NIRF imaging and its clinical application in sentinel lymph node mapping, intraoperative guidance, and assessing the architecture and contractile function of the lymphatics in health and in cancer-related lymphedema. We then present recent NIRF lymphatic imaging for non-invasive assessment of lymphatics both in preclinical melanoma models and in human subjects with melanoma.

Breast cancer sentinel lymph node mapping using near infrared guided indocyanine green and indocyanine green--human serum albumin in comparison with gamma emitting radioactive colloid tracer

AIMS

Recently, a novel method of using near infrared (NIR) guided indocyanine green (ICG) and ICG conjugated with human serum albumin (ICG:HSA) for sentinel lymph node biopsy (SLNB) of breast cancer patients has shown true potential. The aim of this study was to compare the usefulness of NIR guided ICG and ICG:HSA against the gamma emitting radiocolloid (RC).

METHODS

A group of 49 consecutive breast cancer patients underwent SLNB using RC. From this group, the first 28 patients were compared against ICG, while the next 21 patients were compared against ICG:HSA. The number of patients with visible fluorescent path was recorded. Furthermore, the number of SLNs detected by fluorophores percutaneously and total number of intraoperative SLNs detected by fluorophores and/or RC was noted.

RESULTS

NIR guided real time lymphatic flow was observed in 47/49 patients (96%). In all cases except one, SLNs detected by the RC tracer were also detected by their respective fluorophore. Additionally, ICG detected 10 additional SLNs in 8 patients, while 3 additional SLNs were detected by ICG:HSA in 3 patients. Statistical analysis revealed no difference between the number of SLNs detected between ICG versus ICG:HSA and RC versus ICG:HSA. However, a significant statistical difference was observed between RC and ICG (p=0.0117), as well as between the combined NIR guided and RC method (p=0.0033).

CONCLUSIONS

In conclusion, the use of either ICG or ICG:HSA with RC to obtain SLNB seems to be an effective alternative. Compared to RC alone, the use of ICG:HSA, more so than ICG alone, may provide additional benefits.

Photodynamic therapy with indocyanine green injection and near-infrared light irradiation has phototoxic effects and delays paralysis in spinal metastasis

OBJECTIVE

The purpose of this study was to investigate the phototoxic effects of photodynamic therapy (PDT) with indocyanine green (ICG) and near-infrared light irradiation on rat mammary adenocarcinoma cells, and its therapeutic efficacy in a rat model of spinal metastasis.

BACKGROUND DATA

Although PDT has been successfully used as a non-radiation treatment for many malignancies, it has not yet been clinically applied for treating spinal metastasis.

METHODS

For the phototoxicity study, CRL-1666 cells were treated with PDT and cell viability was measured by WST-1 assay. For the efficacy study, 26 female Fischer 344 rats with spinal metastasis in the L6 vertebra were divided into three treatment groups: PDT with local injection of ICG (9 rats), PDT with systemic injection of ICG (10 rats), and no treatment or control (7 rats). Both the PDT groups received near-infrared light irradiation with a total energy of 10 J (1 W for 10 sec). The light was delivered directly through a single silica probe which was set on the left side of the L6 vertebral body. Hindlimb motor function was monitored according to the Basso-Beattie-Bresnahan (BBB) scale. Further, the observation periods were calculated to determine the survival time.

RESULTS

The PDT exerted immediate and persistent phototoxic effects. Furthermore, the PDT with local injection of ICG as well as systemic injection of ICG delayed the deterioration of paralysis and prolonged the observation period.

CONCLUSIONS

PDT with ICG injection and near-infrared light irradiation could be an effective local adjuvant treatment for spinal metastasis.

Translation of near-infrared fluorescence imaging technologies: emerging clinical applications

Technical developments in near-infrared fluorescence (NIRF) imaging and tomography have enabled recent translation into investigational human studies. Noninvasive imaging of the lymphatic vasculature for diagnosis and assessment of function has been uniquely accomplished with NIR using indocyanine green (ICG), a nonspecific dye that has comparatively poor fluorescent properties compared to emerging dyes. Adjunct use of NIRF-ICG for (a) intraoperative sentinel lymph node mapping for cancer staging, (b) video-angiography during surgery, and (c) discrimination of malignant from benign breast lesions detected by mammography and ultrasongraphy also evidences the clinical utility of NIRF. Future NIRF imaging agents that consist of bright fluorescent dyes conjugated to disease-targeting moieties promise molecular imaging and image-guided surgery. In this review, emerging NIRF imaging is described within the context of nuclear imaging technologies that remain the "gold standard" of molecular imaging.

Minimally invasive, longitudinal monitoring of biomaterial-associated inflammation by fluorescence imaging

Implant-associated inflammation is a major cause for the reduced performance/lifetime and failure of numerous medical devices. Therefore, the ability to non-invasively and quantitatively monitor implant-associated inflammation is critically important. Here we show that implant-associated inflammation can be imaged via fluorescence imaging using near-infrared hydrocyanine dyes delivered either locally or intravenously in living mice. This imaging strategy allowed quantitative longitudinal monitoring of inflammation by detecting reactive oxygen species (ROS) released by inflammatory cells in response to implanted poly(ethylene terephthalate) (PET) disks or injected poly (lactic-co-glycolic acid) (PLGA) microparticles, and exhibited a strong correlation to conventional analysis of inflammation. Furthermore, modulation of inflammatory responses via controlled release of the anti-inflammatory agent dexamethasone was detected using this sensitive imaging approach. Thus, hydrocyanine-based fluorescence imaging of ROS could serve as a surrogate measure for monitoring implant-associated inflammation as well as evaluating the efficacy of therapeutic approaches to modulate host responses to implanted medical devices.

Probes for optical imaging: new developments

Recent developments of fluorescent probes beyond approved indocyanine green (ICG) - itself increasingly spreading into new imaging applications like lymphatic mapping, arthritis imaging and tumor surgery - exploit various photophysical and biochemical mechanisms to monitor molecular events with higher specificity and accuracy. Emphasizing nanoparticulate formulations, targeted conjugates, activatable probes, probes with a sensor function and multimodality probes, this review discusses advantages and limitations of each type of probe, thereby critically assessing the desired translation into the clinic.: