Abstract
Establishing blood vessel patency in neurovascular surgery is an essential component in treating cerebrovascular disorders. Given the difficulty in confirming complete obliteration of the aneurysm sac, ICG videoangiography has emerged as an intraoperative tool that provides neurosurgeons immediate feedback on the status of vessel flow, allowing for surgical modifications to be made without delay. ICG initially emerged as a tool for assessing hepatic, cardiac, and retinovascular function. It is an inert compound with a high affinity for plasma proteins and fluorescence properties making it the ideal candidate for assessment of vessel patency in neurovascular procedures. Requiring only a bolus peripheral vein injection and integration of a near-infrared imaging device into the surgical microscope, ICG can be visualized without disrupting operating room workflow or the surgical field. Quick response time, high-spatial resolution, and low complication rates are features of ICG videoangiography that prove advantageous when compared to the gold standard intra- and postoperative digital subtraction angiography (DSA). Despite this, ICG is not without limitations, specifically in the setting of atherosclerotic vessels, giant, and complex aneurysms. Additionally, there are instances where DSA may prove superior in detecting vessel stenosis and outflow obstruction, prompting the recommendation of ICG as an adjunct to, rather than complete replacement of DSA. In this article, the authors provide a brief overview of the biochemical properties and historical origins of ICG viedoangiography in addition to discussing its current application in aneurysm surgery.
Introduction
Indocyanine green (ICG) is a fluorescent compound that has been utilized for decades in a variety of medical applications. Originally approved by the Food and Drug Administration in 1956, ICG was initially used to evaluate cardiac and hepatic function and later gained extensive use in ophthalmology where it was used to enable angiography (, ). More recently, it has been used to enhance tissue visualization in oncology, plastic surgery, neurosurgery, and other fields ().
Given that the physical properties of ICG may be utilized to facilitate vascular imaging, the utility of ICG angiography in cerebrovascular surgery has become quite apparent.
The first description of ICG angiography for aneurysm surgery was in 2003, where Raabe et al. assessed the feasibility and quality of ICG videoangiography in assessing patency of arterial and venous vessels and exclusion of aneurysm sacs (). In their study, the ability to visually inspect vessel patency with intraoperative ICG angiography allowed for real-time surgical changes that significantly altered the surgical course in a number of cases. Given the importance of maintaining tissue perfusion in neurovascular surgery and the difficulty associated with ensuring complete obliteration of an aneurysm, a number of studies have since explored and championed the utility of ICG angiography in aneurysm surgery (, –) as well as in other neurosurgical settings, such as resection of AVMs and AVFs (–), vascular bypass surgery (), and tumor resection (). With regards to aneurysm surgery, ICG angiography is often contrasted with other intraoperative monitoring techniques such as digital subtraction angiography (DSA) (), intraoperative computed tomography (), and microvascular doppler sonography (), with these studies concluding that ICG angiography should complement rather than replace these alternative imaging methods. In this review, the authors discuss the biochemical properties of ICG dye, provide a brief history of its use in the medical setting, as well as discuss methodology and current applications in aneurysm surgery while considering both the advantages and limitations of this technique.
Biochemical Profile and Properties
Indocyanine green (Figure 1) is a water-soluble, odorless or near odorless tricarbocyanine dye with a strong affinity for plasma proteins (primarily albumin and α- and β-lipoproteins) (, , ). Once administered, ICG remains 98% bound to plasma proteins; this intravascular sequestration of the dye allows blood vessels to be easily visualized using fluorescence imaging techniques. ICG molecules have a spectral absorption range of 750–800 nm, with a peak emission occurring at approximately 832 nm (, , ). The range of light wavelengths where biological tissue absorption and scattering are minimum is between 650 and 900 nm, otherwise known as the biological “optical window” (, ). As a result, light has maximal tissue penetration at this range of wavelengths. As both the excitation and fluorescence wavelengths of ICG lie within the tissue optical window, the dye may be seen beneath several layers of tissue (, ). Furthermore, due to minimal light absorption at this wavelength, tissues have a low degree of near infra-red (NIR) autofluorescence in comparison with ICG, resulting in stark contrast of the dye.
Figure 1
ICG is a relatively safe, nontoxic compound with a lethal dosage (LD50) of 50–80 mg/kg. With a typical ICG angiography dose of 0.2–0.5 mg/kg (
Historical Context
Originally introduced for NIR photography by Kodak research laboratories in 1955, ICG was approved for clinical use by the FDA just a year later in 1956 (23). ICG was initially utilized for quantitative measurements in assessing liver function, in the field of cardiology for determining cardiac output in valvular and septal defects (24), and eventually in the field of ophthalmology beginning in the 1970s (
The first description of NIR videoangiography using ICG dye for intraoperative visualization in aneurysm surgery was described in 2003. Raabe et al. (
Figure 2

Middle cerebral artery aneurysm with the neck dissected and clear view of the parent vessel, and its two branches (A), after retraction showing the neck of the clipped MCA aneurysm (B), and intraoperative ICG videoangiography showing the patency of the branches of the MCA and complete exclusion of the aneurysm from the circulation (C).
Technique
Dosage
The recommended dose of ICG injected peripherally for angiography is between 0.2 and 0.5 mg/kg, not to exceed a maximum dose of 5 mg/kg. The standard dose is injected into a peripheral vein as a bolus of 25 mg dissolved in 5 ml of water (
Microscopy
The technical integration of ICG videoangiography into the optical path of the surgical microscope was first described by Raabe et al. (
Current Applications
The neurosurgeon's goal for aneurysm surgery is complete exclusion of the aneurysm from the circulation while preserving the parent, perforating, and branching vessels. To achieve this, many intraoperative monitoring techniques, such as microvascular Doppler, monitoring of somatosensory and motor evoked potentials, DSA, and more recently ICG videoangiography, may be utilized. Since the publication of Raabe et al. (
In a prospective two-center trial published in 2005, Raabe et al. (
One major utility of ICG is its ability to confirm microsurgical anatomy in a variety of aneurysm cases. de Oliveira et al. (31) have described their experience with 93 ICG videoangiography studies for monitoring the flow in perforating arteries (Figure 3) during intracranial aneurysm surgery. They concluded that ICG videoangiography was able to visualize, during the surgical procedure, the small perforating arteries that cannot be detected by intraoperative DSA (31). In addition, Nagai et al. (32) reported a rare case of a ruptured dissecting aneurysm in the A1 segment. Using ICG, the lateral and medial groups of the basal perforating arteries of the anterior communicating artery complex of the ACA were identified prior to clipping, thereby minimizing the risk of complications related to occluding perforator vessels. Other series have been published that further corroborate these findings (
Figure 3

This basilar tip aneurysm was exposed using a modified orbitozygomatic approach. The perforators arising from the posterior aspect of the basilar apex and P1 can be visualized (A). These perforators are dissected from the aneurysm dome and excluded from the clip construct (B). Post clip ICG demonstrates preservation of the perforators (C).
Advantages and Limitations
In concordance with the benefits stated earlier, Sharma et al. (
Limitations of ICG videoangiography include trouble visualizing aneurysm residuals after clipping when compared with DSA, inability to visualize areas outside the field of the microscope, and difficulty visualizing of arteries at the depth of the surgical field and residual neck in calcified and thrombosed aneurysms. While Raabe et al. (
Future Directions
Given the advantages and ease of use of ICG videoangiography, the dearth of studies examining its utility in other neurovascular procedures suggests that it may be underutilized for these procedures. Examples of these surgeries include ablation of arteriovenous malformations and fistulas along with manipulation and resection of highly vascularized tumors and lesions. The scarcity of data examining ICG videoangiography for these procedures may be a result of their infrequent incidence. Nonetheless, reports on the nuances of employing ICG videoangiography in these procedures may help to further define its specific roles and situational uses. We encourage groups to publish their techniques and experiences with ICG videoangiography in these areas.
One limitation of ICG videaoangiography is its inability to provide information on unexposed vessels. In order to bypass this limitation, several groups have interfaced the indocyanine NIR imaging technology to neuroendoscopes (
In addition to extending ICG videoangiography to lesions and vessels not readily exposed, the robotic system has other benefits which could improve aneurysm surgery. The computer of the robotic console allows additional information to be integrated and simultaneously displayed intraoperatively (44), and the increased precision of movements and ability to navigate narrow anatomical cavities may allow access to deep seated lesions while minimizing brain retraction and dissection. Thus, the expansion of robotics into neurosurgery may be a novel method to incorporate NIR imaging technology and use ICG videoangiography to examine vasculature that is not immediately exposed.
A known drawback to ICG videoangiography is its poor ability to visualize thrombosed, calcified, and buried vessels and aneurysms. This may be in part due to the relatively modest tissue penetration by light at these wavelengths in comparison to other wavelengths. Contrast between ICG and surrounding tissue indeed stems from the fluorescent wavelengths of ICG lying within the tissue optical window. However, Smith et al. (45) discuss the existence of a second optical window, with the first window spanning from 650 to 950 nm and the second from 1,000–1,350 nm. They further state that the first window may not be optimal due to tissue autofluorescence producing substantial background noise and the tissue penetration depth being limited to between 1 and 2 cm. Indocyanine green fluorescing in this first window may significantly detract from the visual quality of ICG angiography. Image acuity may therefore be optimized by utilizing compounds that fluoresce in second optical window. Smith et al. (45) cite simulations and modeling studies suggesting that improvement of signal-to-noise ratios by over 100-fold is possible by using quantum dot fluorophores that emit light at 1,320 nm as opposed to 850 nm. However, currently tested compounds that fluoresce at this range are limited due to safety and toxicity as well as technical challenges associated with imaging technology. Nonetheless, the development of both effective and biologically compatible fluorescent substances that operate within the second optical window may have the potential to greatly enhance fluorescent imaging.
Many of the advantages of ICGVA derive from its safety, convenience and cost effectiveness; preservation of these qualities is necessary for a contrast agent to function optimally. Currently, ICG is the only FDA approved near-infrared dye (
Conclusion
In this article, the authors review the mechanism of action of ICG angiography and examine the evolution of its applications over time, nuances in technique, and clinical implementation. The reviewed data demonstrates that ICG angiography is indeed quite helpful in vascular mapping for cerebral aneurysm surgery and may certainly alter intraoperative decision making. However, its exact role depends on anatomic features of the particular lesion being treated and the technology is ultimately limited by lower accuracy compared to the gold-standard of digital subtraction angiography. Based on these findings, the highest degree of imaging accuracy may be achieved by employing multiple imaging technologies, and we encourage surgeons to use multimodal imaging when possible during aneurysm clipping surgery.
Statements
Author contributions
MK, PN, and SS: conception and design. PN, SS, and ME: acquisition of data and drafting the article. All authors critically revising the article. All authors reviewed submitted version of manuscript. MK approved the final version of the manuscript on behalf of all authors.
Conflict of interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
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Summary
Keywords
cerebral aneurysm, indocyanin green, digital subtraction angiogram, surgical microscope, near infra-red
Citation
Norat P, Soldozy S, Elsarrag M, Sokolowski J, Yaǧmurlu K, Park MS, Tvrdik P and Kalani MYS (2019) Application of Indocyanine Green Videoangiography in Aneurysm Surgery: Evidence, Techniques, Practical Tips. Front. Surg. 6:34. doi: 10.3389/fsurg.2019.00034
Received
11 February 2019
Accepted
22 May 2019
Published
20 June 2019
Volume
6 - 2019
Edited by
Eberval Figueiredo, University of São Paulo, Brazil
Reviewed by
Jorge Marcelo Mura, Instituto de Neurocirugía, Chile; Hiroki Toda, Fukui Red Cross Hospital, Japan
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Copyright
© 2019 Norat, Soldozy, Elsarrag, Sokolowski, Yaǧmurlu, Park, Tvrdik and Kalani.
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: M. Yashar S. Kalani kalani@virginia.edu
This article was submitted to Neurosurgery, a section of the journal Frontiers in Surgery
†These authors have contributed equally to this work
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