Comparison of Near-Infrared Imaging Camera Systems for Intracranial Tumor Detection

Dose optimization of second window indocyanine green in meningioma patients

OBJECTIVE

Surgery remains the first line treatment for meningiomas and can benefit from fluorescence-guided surgical techniques such as second-window indocyanine green (SWIG). In the current study, we compared the use of the standard SWIG dose of 5.0 mg/kg relative to 2.5 mg/kg indocyanine green (ICG) in meningioma patients.

METHODS

Patients were prospectively enrolled in an IRB-approved study of SWIG and received either the standard dose of 5.0 mg/kg or a reduced dose of 2.5 mg/kg of ICG around 24 h prior to their surgery. Intraoperative near-infrared fluorescence imaging was performed with exo- and endoscopic systems. Signal-to-background ratio (SBR) was calculated to quantify fluorescence and was compared between 5.0 mg/kg and 2.5 mg/kg ICG. All patients received pre-operative MRI and, in select cases, the pre-operative MRI was correlated to intraoperative fluorescence imaging.

RESULTS/DISCUSSION

In the current study, we found no significant difference in the SBR of meningiomas in patients that were administered with either 5.0 mg/kg or 2.5 mg/kg ICG. However, in five patients that received the standard-dose SWIG regimen of 5.0 mg/kg ICG we observed dose-related fluorescence quenching - referred to as "inversion" - that interfered with tumor visualization during fluorescence-guided surgery (FGS). When correlated to pre-operative MRI, a similar rim pattern was observed around the primary tumor on T2 FLAIR, which, in retrospect, could be used as a predictor for inversion during FGS in meningioma patients receiving standard-dose ICG.

CONCLUSION

This study demonstrated that a reduced ICG dose was as effective as standard-dose SWIG in meningioma patients. We therefore recommend to adjust the standard ICG dose for meningioma patients to 2.5 mg/kg particularly when rim enhancement is observed on pre-operative T2 FLAIR.

Second window indocyanine green localizes CNS lymphoma in real time in the operating room: report of two cases

Intraoperative distinction of lesional tissue versus normal brain parenchyma can be difficult in neurosurgical oncology procedures. We report the successful, real-time visualization of central nervous system (CNS) lymphoma using the 'Second Window Indocyanine Green' (SWIG) method for two patients who underwent craniotomy for pathology that was determined to be large B cell lymphoma. Indocyanine green (ICG), when administered intravenously the day prior to cranial surgery, is a re-purposed fluorophore that may afford safe, immediate visual confirmation of on-target tissue resection, thereby providing a valuable adjunct to intraoperative navigation and decreasing reliance on frozen pathology analysis. These first reported cases of SWIG for lymphoma in the CNS indicate that further study of fluorophores to improve biopsy targeting and yield is warranted.

Assessment and Comparison of Three Dimensional Exoscopes for Near-Infrared Fluorescence-Guided Surgery using Second-Window Indocyanine-Green

Objective

Compared to microscopes, exoscopes have advantages in field-depth, ergonomics, and educational value. Exoscopes are especially well-poised for adaptation into fluorescence-guided surgery (FGS) due to their excitation source, light path, and image processing capabilities. We evaluated the feasibility of near-infrared FGS using a 3-dimensional (3D), 4 K exoscope with near-infrared fluorescence imaging capability. We then compared it to the most sensitive, commercially-available near-infrared exoscope system (3D and 960 p). In-vitro and intraoperative comparisons were performed.

Methods

Serial dilutions of indocyanine-green (1–2000 μg/mL) were imaged with the 3D, 4 K Olympus Orbeye (system 1) and the 3D, 960 p VisionSense Iridium (system 2). Near-infrared sensitivity was calculated using signal-to-background ratios (SBRs). In addition, three patients with brain tumors were administered indocyanine-green and imaged with system 1, with two also imaged with system 2 for comparison.

Results

Systems 1 and 2 detected near-infrared fluorescence from indocyanine green concentrations of >250 μg/L and >31.3 μg/L, respectively. Intraoperatively, system 1 visualized strong near-infrared fluorescence from two, strongly gadolinium-enhancing meningiomas (SBR=2.4, 1.7). The high-resolution, bright images were sufficient for the surgeon to appreciate the underlying anatomy in the near-infrared mode. However, system 1 was not able to visualize fluorescence from a weakly-enhancing intraparenchymal metastasis. In contrast, system 2 successfully visualized both the meningioma and the metastasis but lacked high resolution stereopsis.

Conclusion

Three-dimensional exoscope systems provide an alternative visualization platform for both standard microsurgery and near-infrared fluorescent guided surgery. However, when tumor fluorescence is weak (i.e., low fluorophore uptake, deep tumors), highly sensitive near-infrared visualization systems may be required.

The Evolution of 5-Aminolevulinic Acid Fluorescence Visualization: Time for a Headlamp/Loupe Combination

BACKGROUND

The use of 5-ALA for intraoperative protoporphyrin IX (PpIX) fluorescent imaging in the resection of malignant gliomas has been demonstrated to improve tumor visualization, increase extent of resection, and extend progression-free survival. The current technique for visualization of 5-ALA consists of excitation and emission filters built into the operating microscope. However, there are notable limitations to this process, including low quantum yield, expense, and masking of surrounding anatomy.

METHODS

We present three cases in which three separate methods were employed for visualizing fluorescence. The devices reported are 1) a low-cost blue light flashlight and 2) a low-cost headlamp, and 3) the first reported case of the new Design for Vision® REVEAL™ FGS (Fluorescence Guided Surgery) 5-ALA fluorescent headlight and loupes. The aim of the study is to provide confirmation that tumor fluorescence can be observed using commercially-available products other than the microscope.

RESULTS

We demonstrate through three intraoperative cases that a variety of devices can produce visible fluorescence of the high-grade tumor and allow for simultaneous real-time visualization of the adjacent brain parenchyma and vasculature. The REVEAL™ FGS system appears to offer increased fluorescence emission compared to all other methods, including the microscope.

CONCLUSIONS

Our study demonstrates the feasibility of using blue/ultraviolet light supplied by a commercially available, inexpensive flashlight or headlamp to visualize 5-ALA fluorescence in high-grade gliomas. We also provide the first documentation of intraoperative use of the new Design for Vision® REVEAL™ FGS 5-ALA fluorescent headlight and loupes and report on the experience. Lack of an operative microscope capable of fluorescent illumination should not be a limiting factor in performing fluorescent-guided glioma resection.

Second window ICG predicts gross-total resection and progression-free survival during brain metastasis surgery

OBJECTIVE

Metastases are the most common intracranial malignancies and complete resection can provide relief of neurological symptoms and reduce recurrence. The authors' prospective pilot study in 2017 demonstrated promising results for the application of high-dose, delayed imaging of indocyanine green (ICG), known as second window ICG (SWIG), in patients undergoing surgery for brain metastases. In this prospective cohort study, the authors evaluated intraoperative imaging and clinical outcomes of treatment using SWIG.

METHODS

Patients were prospectively enrolled in an approved study of high-dose, delayed ICG (SWIG) and received 5 mg/kg (2014-2018) or 2.5 mg/kg (2018-2019) ICG 24 hours preoperatively. Intraoperatively, near-infrared (NIR) imaging was performed using a dedicated NIR exoscope. NIR images were analyzed and the signal-to-background ratio (SBR) was calculated to quantify fluorescence. Residual fluorescence on the postresection NIR view was compared and correlated to the residual gadolinium enhancement on postoperative MRI. Patient survival and predictive factors were analyzed.

RESULTS

In total, 51 intracranial metastases were surgically treated in 47 patients in this cohort. All 51 metastatic tumors demonstrated strong NIR fluorescence (mean SBR 4.9). In tumors ≤ 10 mm from the cortical surface, SWIG with 5 mg/kg ICG produced enhanced transdural tumor visibility (91.3%) compared to 2.5 mg/kg (52.9%; p = 0.0047). Neoplastic margin detection using NIR fluorescence compared to white light improved sensitivity, albeit lowered specificity; however, increasing the SBR cutoff for positive fluorescence significantly improved specificity without sacrificing sensitivity, increasing the overall accuracy from 57.5% to 72.5%. A lack of residual NIR fluorescence after resection was closely correlated with a lack of residual enhancement on postoperative MRI (p = 0.007). Among the 16 patients in whom tumor recurred at the site of surgery, postoperative MRI successfully predicted 8 cases, whereas the postresection NIR view predicted 12 cases. Progression-free survival rate at 12 months was greater for patients without residual NIR fluorescence (38%) than for those without residual enhancement on postoperative MRI (29%).

CONCLUSIONS

The current study demonstrates the clinical benefits of the SWIG technique in surgery for patients with brain metastases. Specifically, this technique allows for dose-dependent, transdural localization of neoplasms and improved sensitivity in neoplastic margin detection. Postresection residual fluorescence can be a powerful tool to evaluate extent of resection in conjunction with MRI, and it may guide decisions on brain metastasis management.

The role of indocyanine green fluorescence in endoscopic endonasal skull base surgery and its imaging correlations

OBJECTIVE

The use of endoscope-integrated indocyanine green (E-ICG) has recently been introduced in skull base surgery. The quantitative correlation between E-ICG and T1-weighted gadolinium-enhanced (T1WGd) images for skull base tumors has not been previously assessed, to the authors' knowledge. In this study, the authors investigated the indications for use and the limitations of E-ICG and sought to correlate the endoscopic fluorescence pattern with MRI contrast enhancement.

METHODS

Following IRB approval, 20 patients undergoing endoscopic endonasal skull base surgery between June 2017 and August 2018 were enrolled in the study. Tumor fluorescence was measured using a blue color value and blood fluorescence as a control. Signal intensities (SIs) of tumor T1WGd images were measured and the internal carotid artery (ICA) SI was used as a control. For pituitary adenoma, the pituitary gland fluorescence was also measured. The relationships between ICG fluorescence and MRI enhancement measurements were analyzed.

RESULTS

Data showed that in pituitary adenoma there was a strong correlation between the ratios of gland/blood fluorescence to gland/ICA SI (n = 8; r = 0.92; p = 0.001) and tumor/blood fluorescence to tumor/ICA SI (n = 9; r = 0.82; p = 0.006). In other pathologies there was a strong correlation between the ratios of tumor/blood fluorescence and tumor/ICA SI (n = 9; r = 0.74; p = 0.022). The ICG fluorescence allowed perfusion assessment of the pituitary gland as well as of the nasoseptal flaps. Visualization of the surrounding vasculature was also feasible.

CONCLUSIONS

Defining the indications and understanding the limitations are critical for the effective use of E-ICG. Tumor fluorescence seems to correlate with preoperative MRI contrast enhancement.

Near-Infrared Imaging with Second-Window Indocyanine Green in Newly Diagnosed High-Grade Gliomas Predicts Gadolinium Enhancement on Postoperative Magnetic Resonance Imaging

PURPOSE

Intraoperative molecular imaging with tumor-targeting fluorophores offers real-time detection of neoplastic tissue. The second window indocyanine green (SWIG) technique relies on passive accumulation of indocyanine green (ICG), a near-infrared fluorophore, in neoplastic tissues. In this study, we explore the ability of SWIG to detect neoplastic tissue and to predict postoperative magnetic resonance imaging (MRI) findings intraoperatively.

PROCEDURES

Retrospective data were collected from 36 patients with primary high-grade gliomas (HGG) enrolled as part of a larger trial between October 2014 and October 2018. Patients received systemic ICG infusions at 2.5-5 mg/kg 24 h preoperatively. Near-infrared fluorescence was recorded throughout the case and from biopsy specimens. The presence/location of residual SWIG signal after resection was compared to the presence/location of residual gadolinium enhancement on postoperative MRI. The extent of resection was not changed based on near-infrared imaging.

RESULTS

All 36 lesions demonstrated strong near-infrared fluorescence (signal-to-background = 6.8 ± 2.2) and 100 % of tumors reaching the cortex were visualized before durotomy. In 78 biopsy specimens, near-infrared imaging demonstrated higher sensitivity and accuracy than white light for diagnosing neoplastic tissue intraoperatively. Furthermore, near-infrared imaging predicted gadolinium enhancement on postoperative MRI with 91 % accuracy, with visualization of residual enhancement as small as 0.3 cm³. Patients with no residual near-infrared signal after resection were significantly more likely to have complete resection on postoperative MRI (p value < 0.0001).

CONCLUSIONS

Intraoperative imaging with SWIG demonstrates highly sensitive detection of HGG tissue in real time. Furthermore, post-resection near-infrared imaging correlates with postoperative MRI. Overall, our findings suggest that SWIG can provide surgeons with MRI-like results in real time, potentially increasing resection rates.

Second-Window Indocyanine Green for Visualization of Hemangioblastoma: A Case Report With Two-Dimensional Operative Video

BACKGROUND AND IMPORTANCE

The proper differentiation of neoplastic tissue from adjacent brain parenchyma can pose a great challenge, especially in eloquent areas of the brain. With the novel technique, "Second-Window Indocyanine Green," injection of a near-infrared fluorophore (ICG) allows for intraoperative visualization of tumors by taking advantage of the compromised vasculature surrounding the tumor. Thus, such a technique may demonstrate utility for hemangioblastomas, which are hypervascular tumors of the central nervous system.

CLINICAL PRESENTATION

Here we present the case of a 39-yr-old male with a demonstrated cystic mass in the left cerebellum, with additional edema spreading towards the vermis. A total of 5 mg/kg of ICG was delivered intravenously 24 h prior to the operation. The tumor was approached via the infratentorial suboccipital approach. We observed strong near-infrared fluorescence through the intact dura, consistent with the tumor location. Surgical pathology confirmed a final diagnosis of cerebellar hemangioblastoma. There was complete resection of the tumor, with the patient discharged uneventfully.

CONCLUSION

We report the first successful case of fluorescence-guided surgery of a cerebellar hemangioblastoma using near-infrared fluorescence imaging with the Second-Window ICG technique. This joins a growing series of publications that demonstrate the efficacy of a novel application of ICG, a near-infrared fluorophore, in accurate intraoperative visualization of neoplastic tissue. While the use of a dedicated near-infrared platform (ie, the VisionSense Iridium [Visionsense, Philadelphia, Pennsylvania]) yields a higher signal-to-background ratio, a neurosurgical microscope (ie, the Leica OH6 [Leica Microsystems, Wetzlar, Germany]) may also provide a suitable option in cases where fluorescence is very strong.

Fluorescence guided surgery for pituitary adenomas

PURPOSE

Resection of pituitary adenomas presents a number of unique challenges in neuro-oncology. The proximity of these lesions to key vascular and endocrine structures as well as the need to interpret neuronavigation in the context of shifting tumor position increases the complexity of the operation. More recently, substantial advances in fluorescence-guided surgery have been demonstrated to facilitate the identification of numerous tumor types and result in increased rates of complete resection and overall survival.

METHODS

A review of the literature was performed, and data regarding the mechanism of the fluorescence agents, their administration, and intraoperative tumor visualization were extracted. Both in vitro and in vivo studies were assessed. The application of these agents to pituitary tumors, their advantages and limitations, as well as future directions are presented here.

RESULTS

Numerous laboratory and clinical studies have described the use of 5-ALA, fluorescein, indocyanine green, and OTL38 in pituitary lesions. All of these drugs have been demonstrated to accumulate in tumor cells. Several studies have reported the successful use of the majority of the agents in inducing intraoperative tumor fluorescence. However, their sensitivity and specificity varies across the literature and between functioning and non-functioning adenomas.

CONCLUSIONS

At present, numerous studies have shown the feasibility and safety of these agents for pituitary adenomas. However, further research is needed to assess the applicability of fluorescence-guided surgery across different tumor subtypes as well as explore the relationship between their use and postoperative clinical outcomes.

Applications of indocyanine green in brain tumor surgery: review of clinical evidence and emerging technologies

Indocyanine green (ICG) is a water-soluble dye that was approved by the FDA for biomedical purposes in 1956. Initially used to measure cardiocirculatory and hepatic functions, ICG's fluorescent properties in the near-infrared (NIR) spectrum soon led to its application in ophthalmic angiography. In the early 2000s, ICG was formally introduced in neurosurgery as an angiographic tool. In 2016, the authors' group pioneered a novel technique with ICG named second-window ICG (SWIG), which involves infusion of a high dose of ICG (5.0 mg/kg) in patients 24 hours prior to surgery. To date, applications of SWIG have been reported in patients with high-grade gliomas, meningiomas, brain metastases, pituitary adenomas, craniopharyngiomas, chordomas, and pinealomas.The applications of ICG have clearly expanded rapidly across different specialties since its initial development. As an NIR fluorophore, ICG has advantages over other FDA-approved fluorophores, all of which are currently in the visible-light spectrum, because of NIR fluorescence's increased tissue penetration and decreased autofluorescence. Recently, interest in the latest applications of ICG in brain tumor surgery has grown beyond its role as an NIR fluorophore, extending into shortwave infrared imaging and integration into nanotechnology. This review aims to summarize reported clinical studies on ICG fluorescence-guided surgery of intracranial tumors, as well as to provide an overview of the literature on emerging technologies related to the utility of ICG in neuro-oncological surgeries, including the following aspects: 1) ICG fluorescence in the NIR-II window; 2) ICG for photoacoustic imaging; and 3) ICG nanoparticles for combined diagnostic imaging and therapy (theranostic) applications.

Dual-agent fluorescent labeling of soft-tissue sarcomas improves the contrast based upon targeting both interstitial and cellular components of the tumor milieu

BACKGROUND

Current practices for fluorescence-guided cancer surgery utilize a single fluorescent agent, but homogeneous distribution throughout the tumor is difficult to achieve. We hypothesize that administering a perfusion and a molecular-targeted agent at their optimal administration-to-imaging time will improve whole-tumor contrast.

EXPERIMENTAL DESIGN

Mice bearing subcutaneous xenograft human synovial sarcomas were administered indocyanine green (ICG) (3 mg/kg) or ABY-029 (48.7 μg/kg)-an epidermal growth factor receptor-targeted Affibody molecule-alone or in combination. Fluorescence contrast and signal distribution were compared between treatment groups. Two commercial fluorescence imaging systems were tested for simultaneous imaging of ICG and ABY-029.

RESULTS

ABY-029 has a moderate positive correlation with viable tumor (ρ = 0.2 ± 0.4), while ICG demonstrated a strong negative correlation (ρ = -0.6 ± 0.1). The contrast-to-variance ratio was highest in the ABY-029 +ICG (2.5 ± 0.8), compared to animals that received ABY-029 (2.3 ± 0.8) or ICG (2.0 ± 0.5) alone. Moreover, the combination of ABY-029 + ICG minimizes the correlation between viable tumor and fluorescence intensity (ρ = -0.1 ± 0.2) indicating the fluorescence signal distribution is more homogeneous throughout the tumor milieu.

CONCLUSION

Dual-agent imaging utilizing a single channel in a commercial fluorescence-guided imaging system tailored for IRDye 800CW is a promising method to increase tumor contrast in a clinical setting.

Evaluation of Diagnostic Accuracy Following the Coadministration of Delta-Aminolevulinic Acid and Second Window Indocyanine Green in Rodent and Human Glioblastomas

PURPOSE

Fluorescence-guided-surgery offers intraoperative visualization of neoplastic tissue. Delta-aminolevulinic acid (5-ALA), which targets enzymatic abnormality in neoplastic cells, is the only approved agent for fluorescence-guided neurosurgery. More recently, we described Second Window Indocyanine Green (SWIG) which targets neoplastic tissue through enhanced vascular permeability. We hypothesized that SWIG would demonstrate similar clinical utility in identification of high-grade gliomas compared with 5-ALA.

PROCEDURES

Female C57/BL6 and nude/athymic mice underwent intracranial implantation of 300,000 GL261 and U87 cells, respectively. Tumor-bearing mice were euthanized after administration of 5-ALA (200 mg/kg intraperitoneal) and SWIG (5 mg/kg intravenous). Brain sections were imaged for protoporphyrin-IX and ICG fluorescence. Fluorescence and H&E images were registered using semi-automatic scripts for analysis. Human subjects with HGG were administered SWIG (2.5 mg/kg intravenous) and 5-ALA (20 mg/kg oral). Intraoperatively, tumors were imaged for ICG and protoporphyrin-IX fluorescence.

RESULTS

In non-necrotic tumors, 5-ALA and SWIG demonstrated 90.2 % and 89.2 % tumor accuracy (p value = 0.52) in U87 tumors and 88.1 % and 87.7 % accuracy (p value = 0.83) in GL261 tumors. The most distinct difference between 5-ALA and SWIG distribution was seen in areas of tumor-associated necrosis, which often showed weak/no protoporphyrin-IX fluorescence, but strong SWIG fluorescence. In twenty biopsy specimens from four subjects with HGG, SWIG demonstrated 100 % accuracy, while 5-ALA demonstrated 75-85 % accuracy; there was 90 % concordance between SWIG and 5-ALA fluorescence.

CONCLUSION

Our results provide the first direct comparison of the diagnostic utility of SWIG vs 5-ALA in both rodent and human HGG. Given the broader clinical utility of SWIG compared with 5-ALA, our data supports the use of SWIG in tumor surgery to improve the extent of safe resections.

CLINICAL TRIAL

NCT02710240 (US National Library of Medicine Registry; https://www.clinicaltrials.gov/ct2/show/NCT02710240?id=NCT02710240&draw=2&rank=1 ).

Folate Receptor Near-Infrared Optical Imaging Provides Sensitive and Specific Intraoperative Visualization of Nonfunctional Pituitary Adenomas

BACKGROUND

Surgical resection is the primary treatment for nonfunctional (NF) pituitary adenomas, but gross-total resection is difficult to achieve in all cases. NF adenomas overexpress folate receptor alpha (FRα).

OBJECTIVE

To test the hypothesis that we could target FRα for highly sensitive and specific intraoperative detection of NF adenomas using near-infrared (NIR) imaging.

METHODS

Fourteen patients with NF pituitary adenoma were infused with the folate analog NIR dye OTL38 preoperatively. NIR fluorescence signal-to-background ratio (SBR) was recorded for each tumor during resection of the adenomas. Extent of surgery was not modified based on the presence or absence of fluorescence. Immunohistochemistry was performed to assess FRα expression in all specimens. Magnetic resonance imaging (MRI) was performed postoperatively to assess residual neoplasm.

RESULTS

Nine adenomas overexpressed FRα and fluoresced with a NIR SBR of 3.2 ± 0.52, whereas the 5 non-FRα-overexpressing adenomas fluoresced with an SBR of 1.5 ± 0.21. Linear regression demonstrated a significant correlation between intraoperative SBR and the FRα expression (P-value < .001). Analysis of 14 margin samples revealed that the surgeon's impression of the tissue had 83% sensitivity, 100% specificity, 100% positive predictive value, and 89% negative predictive value, while NIR fluorescence had 100% for all values. NIR fluorescence accurately predicted postoperative MRI results in 78% of FRα-overexpressing patients.

CONCLUSION

Preoperative injection of folate-tagged NIR dye provides strong signal and visualization of NF pituitary adenomas. It is 100% sensitive and specific for detecting margin neoplasm and can predict postoperative MRI findings. Our results suggest that NIR fluorescence may be superior to white-light visualization alone and may improve resection rates in NF pituitary adenomas.

Surface-Registration Frameless Stereotactic Navigation Is Less Accurate During Prone Surgeries: Intraoperative Near-Infrared Visualization Using Second Window Indocyanine Green Offers an Adjunct

BACKGROUND

Frameless neuronavigation allows neurosurgeons to visualize and relate the position of surgical instruments to intracranial pathologies based on preoperative tomographic imaging. However, neuronavigation can often be inaccurate. Multiple factors have been proposed as potential causes, and new technologies are needed to overcome these challenges.

OBJECTIVE

To evaluate the accuracy of neuronavigation systems compared to near-infrared (NIR) fluorescence imaging using Second Window Indocyanine Green, a novel technique, and to determine factors that lead to neuronavigation errors.

METHODS

A retrospective analysis was conducted on 56 patients who underwent primary resections of intracranial tumors. Patients received 5 mg/kg ICG approximately 24 h preoperatively. Intraoperatively, neuronavigation was used to plan craniotomies to place the tumors in the center. After craniotomy, NIR imaging visualized tumor-specific NIR signals. The accuracy of neuronavigation and NIR fluorescence imaging for delineating the tumor boundary prior to durotomy was compared.

RESULTS

The neuronavigation centers and NIR centers were 23.0 ± 7.7 % and 2.6 ± 1.1 % deviated from the tumor centers, respectively, relative to the craniotomy sizes. In 12 cases, significant changes were made to the planned durotomy based on NIR imaging. Patient position was a significant predictor of neuronavigation inaccuracy on both univariate and multivariate analysis, with the prone position having significantly higher inaccuracy (29.2 ± 8.1 %) compared to the supine (16.2 ± 8.1 %, p value < 0.001) or the lateral (17.9 ± 5.1 %, p value = 0.003) positions.

CONCLUSION

Patient position significantly affects neuronavigation accuracy. Intraoperative NIR fluorescence imaging before durotomy offers an opportunity to readjust the neuronavigation image space to better align with the patient space.

Near-Infrared Fluorescence with Second-Window Indocyanine Green as an Adjunct to Localize the Pituitary Stalk During Skull Base Surgery

A potential application of near-infrared (NIR) fluorescence imaging using second-window indocyanine green (SWIG) is demonstrated. We hypothesized that because the pituitary lacks a blood-brain barrier, we might visualize the pituitary stalk using SWIG. A 52-year-old, right-handed man presented to our clinic for evaluation of progressive loss of vision. Physical examination was significant for loss of right peripheral vision and near-complete loss of left field vision. Prolactin was high-normal at 16.2 mg/dL. Brain magnetic resonance imaging demonstrated a 36-mm sellar mass extending superiorly and laterally crossing the intracranial left internal carotid artery, consistent with a nonfunctional pituitary macroadenoma. We elected to pursue left pterional craniotomy for resection. The patient was eligible for our SWIG clinical trial and consented to the study. SWIG is a novel, investigational technique using Food and Drug Administration-approved indocyanine green to enhance visualization of neoplastic tissue intraoperatively.^1-7 The patient received 2.5 mg/kg of indocyanine green intravenously approximately 24 hours preoperatively. Intraoperatively, under white-light microscopy, the tumor was easily identified and distinguished from the optic nerves and internal carotid artery. After debulking of the gross tumor, NIR visualization using a laser-equipped endoscope⁸ demonstrated strong NIR fluorescence in the pituitary stalk. Despite the distorted anatomy, this technique enabled us to confidently identify and preserve the pituitary stalk. Postoperatively, the patient had persistently high urine output that normalized in 24 hours without desmopressin (sodium 139-140 mmol/L); after uneventful recovery, he was discharged with mild improvement in visual function. This case demonstrated a potential use of our SWIG protocol. As the stalk demonstrates strong NIR fluorescence after high-dose indocyanine green administration, surgeons may be able to better localize and preserve the stalk even in complex skull base tumor cases where the anatomy may be significantly distorted.

Intraoperative near-infrared imaging with receptor-specific versus passive delivery of fluorescent agents in pituitary adenomas

OBJECTIVE

Intraoperative molecular imaging with tumor-targeted fluorescent dyes can enhance resection rates. In contrast to visible-light fluorophores (e.g., 5-aminolevulinic-acid), near-infrared (NIR) fluorophores have increased photon tissue penetration and less contamination from tissue autofluorescence. The second-window ICG (SWIG) technique relies on passive accumulation of indocyanine green (ICG) in neoplastic tissues. OTL38, conversely, targets folate receptor overexpression in nonfunctioning pituitary adenomas. In this study, we compare the properties of these 2 modalities for NIR imaging of pituitary adenomas to better understand the potential for NIR imaging in neurosurgery.

METHODS

A total of 39 patients with pituitary adenomas were enrolled between June 2015 and January 2018 in 2, sequential, IRB-approved studies. Sixteen patients received systemic ICG infusions 24 hours prior to surgery, and another 23 patients received OTL38 infusions 2-3 hours prior to surgery. NIR fluorescence signal-to-background ratio (SBR) was recorded during and after resection. Immunohistochemistry was performed on the 23 adenomas resected from patients who received OTL38 to assess expression of folate receptor-alpha (FRα).

RESULTS

All 16 adenomas operated on after ICG administration demonstrated strong NIR fluorescence (mean SBR 4.1 ± 0.69 [SD]). There was no statistically significant difference between the 9 functioning and 7 nonfunctioning adenomas (p = 0.9). After administration of OTL38, the mean SBR was 1.7 ± 0.47 for functioning adenomas, 2.6 ± 0.91 for all nonfunctioning adenomas, and 3.2 ± 0.53 for the subset of FRα-overexpressing adenomas. Tissue identification with white light alone for all adenomas demonstrated 88% sensitivity and 90% specificity. SWIG demonstrated 100% sensitivity but only 29% specificity for both functioning and nonfunctioning adenomas. OTL38 was 75% sensitive and 100% specific for all nonfunctioning adenomas, but when assessment was limited to the 9 FRα-overexpressing adenomas, the sensitivity and specificity of OTL38 were both 100%.

CONCLUSIONS

Intraoperative imaging with NIR fluorophores demonstrates highly sensitive detection of pituitary adenomas. OTL38, a folate-receptor-targeted fluorophore, is highly specific for nonfunctioning adenomas but has no utility in functioning adenomas. SWIG, which relies on passive diffusion into neoplastic tissue, is applicable to both functioning and nonfunctioning pituitary adenomas, but it is less specific than targeted fluorophores. Thus, targeted and nontargeted NIR fluorophores play important, yet distinct, roles in intraoperative imaging. Selectively and intelligently using either agent has the potential to greatly improve resection rates and outcomes for patients with intracranial tumors.

Second Window Indocyanine Green (SWIG) Near Infrared Fluorescent Transventricular Biopsy of Pineal Tumor

BACKGROUND

Second Window Indocyanine Green (SWIG) is a novel technique for real-time, intraoperative tumor visualization using a high-dose infusion of indocyanine green (ICG) 24 hours before surgery. Due to pathologic diversity found in the pineal region, tissue diagnosis in patients with pineal region mass is essential to optimize further clinical management.

CASE DESCRIPTION

We present the case of a 75-year-old woman with known pineal region mass for 18 years, who presented with progressive classic signs and symptoms of obstructive hydrocephalus over the past 6 months. Preoperative imaging confirmed a contrast-enhancing pineal region tumor, which appeared to be obstructing the aqueduct of Sylvius, causing proximal obstructive hydrocephalus. We delivered 5 mg/kg of ICG intravenously 24 hours before the surgery. The patient underwent an endoscopic third ventriculostomy and a biopsy of the pineal lesion. The tumor demonstrated clear near-infrared fluorescence, which was distinct from surrounding third ventricle floor and ependyma. The signal-to-background ratio was 2.9. The final pathology report revealed a World Health Organization grade I pineocytoma.

CONCLUSIONS

We report on a novel application of near-infrared fluorescence for tumor identification of pineal region tumors, using the "SWIG technique."

Near-infrared intraoperative molecular imaging with conventional neurosurgical microscope can be improved with narrow band "boost" excitation

BACKGROUND

Intraoperative visualization of brain tumors with near-infrared (NIR)-fluorescent dyes is an emerging method for tumor margin approximation but are limited by existing fluorescence detection platforms. We previously showed that a dedicated NIR imaging platform outperformed a state-of-the-art neurosurgical microscope in fluorescence signal characteristics. This study examined whether conventional neurosurgical microscope NIR signal could be improved with the addition of a narrow wavelength excitation source.

METHODS

Imaging was conducted with a broad-spectrum neurosurgical microscope and commercial near-infrared module. Addition of an 805-nm laser was used to "boost" NIR excitation of indocyanine green (ICG). In vitro quantification was performed on serial dilutions of ICG. Patients underwent tumor resection with delayed 24-h imaging of ICG infusion. NIR fluorescence of dura, cortex, or tumor was quantified from images prior to (pre-boost) and following added excitation with the laser (post-boost). Signal to background ratio (SBR) of pre- and post-boost was calculated as a readout of image enhancement.

RESULTS

In vitro, excitation boost effected a 29% increase in mean SBR in six serial dilutions of ICG. Intraoperative boost was performed in 11 patients including meningioma, glioblastoma multiforme, and metastases. Increase in tumor fluorescence was pronounced under direct tumor visualization. Across all patients, boost excitation resulted in 35% mean improvement from pre-boost SBR (p < 0.001).

CONCLUSION

Neurosurgical microscopes remain the preferred method of visualizing tumor during intracranial surgery. However, current modalities for NIR signal detection are suboptimal. We demonstrate that augmentation of a fluorescence microscope module with a focused excitation source is a simple mechanism of improving NIR tumor visualization.

CLINICAL TRIAL REGISTRATION

NCT03262636.

Near-Infrared Optical Contrast of Skull Base Tumors During Endoscopic Endonasal Surgery

BACKGROUND

Near-infrared (NIR) tumor contrast is achieved through the "second-window ICG" technique, which relies on passive accumulation of high doses of indocyanine green (ICG) in neoplasms via the enhanced permeability and retention effect.

OBJECTIVE

To report early results and potential challenges associated with the application of second-window ICG technique in endonasal endoscopic, ventral skull-base surgery, and to determine potential predictors of NIR signal-to-background ratio (SBR) using endoscopic techniques.

METHODS

Pituitary adenoma (n = 8), craniopharyngioma (n = 3), and chordoma (n = 4) patients received systemic infusions of ICG (5 mg/kg) approximately 24 h before surgery. Dual-channel endoscopy with visible light and NIR overlay were photodocumented and analyzed post hoc.

RESULTS

All tumors (adenoma, craniopharyngioma, chordoma) demonstrated NIR positivity and fluoresced with an average SBR of 3.9 ± 0.8, 4.1 ± 1.7, and 2.1 ± 0.6, respectively. Contrast-enhanced T1 signal intensity proved to be the single best predictor of observed SBR (P = .0003). For pituitary adenomas, the sensitivity, specificity, positive predictive value, and negative predictive value of NIR-guided identification of tumor was 100%, 20%, 71%, and 100%, respectively.

CONCLUSION

In this preliminary study of a small set of patients, we demonstrate that second-window ICG can provide NIR optical tumor contrast in 3 types of ventral skull-base tumors. Chordomas demonstrated the weakest NIR signal, suggesting limited utility in those patients. Both nonfunctional and functional pituitary adenomas appear to accumulate ICG, but utility for margin detection for the adenomas is limited by low specificity. Craniopharyngiomas with third ventricular extension appear to be a particularly promising target given the clean brain parenchyma background and strong SBR.

Indocyanine-Green for Fluorescence-Guided Surgery of Brain Tumors: Evidence, Techniques, and Practical Experience

The primary treatment for brain tumors often involves surgical resection for diagnosis, relief of mass effect, and prolonged survival. In neurosurgery, it is of utmost importance to achieve maximal safe resection while minimizing iatrogenic neurologic deficit. Thus, neurosurgeons often rely on extra tools in the operating room, such as neuronavigation, intraoperative magnetic resonance imaging, and/or intraoperative rapid pathology. However, these tools can be expensive, not readily available, time-consuming, and/or inaccurate. Recently, fluorescence-guided surgery has emerged as a cost-effective method to accurately visualize neoplastic areas in real-time to guide resection. Currently, 5-aminolevulinic-acid (5-ALA) remains the only fluorophore that has been approved specifically for fluorescence-guided tumor resection. Its use has demonstrated improved resection rates and prolonged progression-free survival. However, protoporphyrin-IX, the metabolic product of 5-ALA that accumulates in neoplastic cells, fluoresces in the visible-light range, which suffers from limited tissue penetration and significant auto-fluorescence. Near-infrared fluorescence, on the other hand, overcomes these problems with ease. Since 2012, researchers at our institution have developed a novel technique using indocyanine-green, which is a well-known near-infrared fluorophore used traditionally for angiography. This Second-Window-ICG (SWIG) technique takes advantage of the increased endothelial permeability in peritumoral tissue, which allows indocyanine-green to accumulate in these areas for intraoperative visualization of the tumor. SWIG has demonstrated utility in gliomas, meningiomas, metastases, pituitary adenomas, chordomas, and craniopharyngiomas. The main benefits of SWIG stem from its highly sensitive detection of neoplastic tissue in a wide variety of intracranial pathologies in real-time, which can help neurosurgeons both during surgical resections and in stereotactic biopsies. In this review of this novel technique, we summarize the development and mechanism of action of SWIG, provide evidence for its benefits, and discuss its limitations. Finally, for those interested in near-infrared fluorescence-guided surgery, we provide suggestions for maximizing the benefits while minimizing the limitations of SWIG based on our own experience thus far.

Imaging Gliomas with Nanoparticle-Labeled Stem Cells

Objective:

Gliomas are the most common neoplasm of the central nervous system (CNS); however, traditional imaging techniques do not show the boundaries of tumors well. Some researchers have found a new therapeutic mode to combine nanoparticles, which are nanosized particles with various properties for specific therapeutic purposes, and stem cells for tracing gliomas. This review provides an introduction of the basic understanding and clinical applications of the combination of stem cells and nanoparticles as a contrast agent for glioma imaging.

Data Sources:

Studies published in English up to and including 2017 were extracted from the PubMed database with the selected key words of “stem cell,” “glioma,” “nanoparticles,” “MRI,” “nuclear imaging,” and “Fluorescence imaging.”

Study Selection:

The selection of studies focused on both preclinical studies and basic studies of tracking glioma with nanoparticle-labeled stem cells.

Results:

Studies have demonstrated successful labeling of stem cells with multiple types of nanoparticles. These labeled stem cells efficiently migrated to gliomas of varies models and produced signals sensitively captured by different imaging modalities.

Conclusion:

The use of nanoparticle-labeled stem cells is a promising imaging platform for the tracking and treatment of gliomas.