Quantitative cerebral perfusion assessment using microscope-integrated analysis of intraoperative indocyanine green fluorescence angiography versus positron emission tomography in superficial temporal artery to middle cerebral artery anastomosis

Correlation between Indocyanine Green Fluorescence Angiography and Laser Speckle Contrast Imaging in a Flap Model

Background

Indocyanine green fluorescence angiography (ICG-FA) is used to assess tissue intraoperatively in reconstructive surgery. This requires an intra-venous dye injection for each assessment. This is not necessary in laser speckle contrast imaging (LSCI); therefore, this method may be better suited for tissue evaluation. To determine this, we compared the two methods in a porcine flap model.

Methods

One random and one pedicled flap were raised on each buttock of six animals. They were assessed with LSCI at baseline, when raised (T0), at 30 minutes (T30) and with ICG-FA at T0 and T30. Regions of interest (ROI) were chosen along the flap axis. Perfusion, measured as perfusion units (PU) in the LSCI assessment and pixel-intensity for the ICG-FA video uptake, was calculated in the ROI. Correlation was calculated between PU and pixel-intensity measured as time to peak (TTP) and area under curve for 60 seconds (AUC60).

Results

Correlation between LSCI and AUC60 for the ICG-FA in corresponding ROI could be seen in all flaps at all time points. The correlation was higher for T0 (r=0.7 for random flap and r=0.6 for pedicled flap) than for T30 (r=0.57 for random flap and r=0.59 for pedicled flap). Even higher correlation could be seen PU and TTP (T0: random flap r=-0.8 and pedicled flap r=0.76. T30: random flap r=-0.8 and pedicled flap r=0.71).

Conclusion

There is a correlation between PU from LSCI and TTP and AUC60 for ICG-FA, indicating that LSCI could be considered for intraoperative tissue assessment.

Quantitative perfusion assessment using indocyanine green during surgery - current applications and recommendations for future use

PURPOSE

Incorrect assessment of tissue perfusion carries a significant risk of complications in surgery. The use of near-infrared (NIR) fluorescence imaging with Indocyanine Green (ICG) presents a possible solution. However, only through quantification of the fluorescence signal can an objective and reproducible evaluation of tissue perfusion be obtained. This narrative review aims to provide an overview of the available quantification methods for perfusion assessment using ICG NIR fluorescence imaging and to present an overview of current clinically utilized software implementations.

METHODS

PubMed was searched for clinical studies on the quantification of ICG NIR fluorescence imaging to assess tissue perfusion. Data on the utilized camera systems and performed methods of quantification were collected.

RESULTS

Eleven software programs for quantifying tissue perfusion using ICG NIR fluorescence imaging were identified. Five of the 11 programs have been described in three or more clinical studies, including Flow® 800, ROIs Software, IC Calc, SPY-Q™, and the Quest Research Framework®. In addition, applying normalization to fluorescence intensity analysis was described for two software programs.

CONCLUSION

Several systems or software solutions provide a quantification of ICG fluorescence; however, intraoperative applications are scarce and quantification methods vary abundantly. In the widespread search for reliable quantification of perfusion with ICG NIR fluorescence imaging, standardization of quantification methods and data acquisition is essential.

Complementary Tools in Cerebral Bypass Surgery

Cerebral revascularization surgery has been advanced by the refinement of several adjunctive tools. These tools include perioperative blood thinners, intraoperative spasmolytic agents, electrophysiological monitoring, and methods for assessing bypass patency or marking arteriotomies. Despite the array of options, the proper usage and comparative advantages of different complements in cerebral bypass have not been well-cataloged elsewhere. In this literature review, we describe the appropriate usage, benefits, and limitations of various bypass adjuncts. Understanding these adjuncts can help surgeons ensure that they receive reliable intraoperative information about bypass function and minimize the risk of serious complications. Overall, this review provides a succinct reference for neurosurgeons on various cerebrovascular bypass adjuncts.

Perfusion Parameters in Near-Infrared Fluorescence Imaging with Indocyanine Green: A Systematic Review of the Literature

(1) Background: Near-infrared fluorescence imaging is a technique capable of assessing tissue perfusion and has been adopted in various fields including plastic surgery, vascular surgery, coronary arterial disease, and gastrointestinal surgery. While the usefulness of this technique has been broadly explored, there is a large variety in the calculation of perfusion parameters. In this systematic review, we aim to provide a detailed overview of current perfusion parameters, and determine the perfusion parameters with the most potential for application in near-infrared fluorescence imaging. (2) Methods: A comprehensive search of the literature was performed in Pubmed, Embase, Medline, and Cochrane Review. We included all clinical studies referencing near-infrared perfusion parameters. (3) Results: A total of 1511 articles were found, of which, 113 were suitable for review, with a final selection of 59 articles. Near-infrared fluorescence imaging parameters are heterogeneous in their correlation to perfusion. Time-related parameters appear superior to absolute intensity parameters in a clinical setting. (4) Conclusions: This literature review demonstrates the variety of parameters selected for the quantification of perfusion in near-infrared fluorescence imaging.

Intraoperative Assessment of Cortical Perfusion After Intracranial-To-Intracranial and Extracranial-To-Intracranial Bypass for Complex Cerebral Aneurysms Using Flow 800

BACKGROUND

Revascularization strategies for complex cerebral aneurysms are largely based on subjective interpretation of flow demands, or indirect measures of perfusion in at-risk territories. Indocyanine Green -based flow analyses ((ICG-BFA); Flow 800, Carl Zeiss, Oberkochen, Germany) provide a real-time, semiquantitative measure of intraoperative cortical perfusion during cerebral bypass surgery for complex aneurysms.

OBJECTIVE

To determine the utility of intraoperative ICG-BFA for assessing cortical perfusion in at-risk territories during cerebral bypass for complex aneurysms requiring vessel sacrifice.

METHODS

Retrospective analysis of consecutive patients from a prospective, single-institution open cerebrovascular database.

RESULTS

Intraoperative ICG-BFA confirmed adequate cortical perfusion in 2 patients with fusiform posterior circulation aneurysms, treated with a posterior inferior cerebellar artery (PICA)-PICA and occipital artery (OA)-to-third segment of the posterior cerebral artery (P3) bypass with proximal vessel sacrifice, respectively. ICG-BFA was used in a third patient that underwent clip reconstruction/ intracranial-to-intracranial bypass for a large middle cerebral artery (MCA) bifurcation aneurysm requiring sacrifice of the temporal M2 branch. In this case, a frontal M3 to temporal M3 side-to-side anastomosis was created to arborize the MCA tree and allow filling of both M2 territories through a single M2 branch. After aneurysm reconstruction, ICG-BFA identified an inadvertent occlusion of the frontal M2 that left the entire MCA distribution reliant on collateral flow but did not cause a neuromonitoring change. Repeat ICG-BFA after clip re-arrangement demonstrated aneurysm occlusion and equal flow in both frontal and temporal MCA cortical distributions from the arborization.

CONCLUSION

ICG-BFA is a useful adjunct for intraoperative cortical flow assessment during cerebral revascularization for complex aneurysms requiring vessel sacrifice.

Whole-Field Indocyanine Green Intensity Analysis to Intraoperatively Predict Cerebral Hyperperfusion Syndrome Following Superficial Temporal Artery-Middle Cerebral Artery Bypass: A Retrospective Case-Control Study in 7-Year Experience With 112 Cases

BACKGROUND

Intraoperative prediction of postoperative cerebral hyperperfusion syndrome (CHS) after cerebrovascular bypass surgery is challenging.

OBJECTIVE

To conduct a retrospective case-control study with indocyanine green (ICG) intensity analysis of the superficial temporal artery-middle cerebral artery (STA-MCA) bypass and investigate whether its washout pattern might be a marker for intraoperative prediction of CHS.

METHODS

Between 2012 and 2018, 6 of 112 patients (5.4%) that underwent STA-MCA bypass exhibited CHS. We selected 5 patients with CHS (3 with atherosclerotic cerebrovascular disease [ASCVD] and 2 with moyamoya) and 15 patients without CHS (60% ASCVD and 40% moyamoya) as a matched control group. During prebypass and postbypass, washout times (WTs) for the first 10%, 25%, 50%, and 75% of maximum ICG intensity measured in the whole-camera field were compared between groups. The changes in WT (ΔWT) from prebypass to postbypass for each ICG intensity level were compared between groups. The cutoff ΔWTs, sensitivities, and specificities were also calculated.

RESULTS

Postbypass WTs were significantly longer in the CHS group than the control group at all ICG intensities (P < .05). ΔWT was significantly greater in the CHS group than the control group for the first 10%, 25%, and 50% ICG intensities (P < .001). A cutoff ΔWT of ≥2.66 s for the first 50% ICG intensity showed a sensitivity of 100% and specificity of 100%.

CONCLUSION

We found that a ΔWT ≥2.66 s for the first 50% ICG intensity could be an intraoperative predictive factor for CHS.

Assessment of ischemic risk following intracranial-to-intracranial and extracranial-to-intracranial bypass for complex aneurysms using intraoperative Indocyanine Green-based flow analysis

Cerebral bypass is often needed for complex aneurysms requiring vessel sacrifice, yet intraoperative predictors of ischemic risk in bypass-dependent territories are limited. Indocyanine Green (ICG)-based flow analyses (ICG-BFAs; Flow 800, Carl Zeiss, Oberkochen, Germany) semi-quantitatively assess cortical perfusion, and in this work we determine the efficacy of ICG-BFA for assessing post-operative ischemic risk during cerebral bypass surgery for complex aneurysms. Retrospective clinical and pre/post-bypass intra-operative ICG-BFA data (delay and blood flow index [BFI]) on ten patients undergoing cerebral bypass for complex cerebral aneurysms requiring vessel sacrifice were collected from a single-institution prospective database and analyzed via non-parametric testing and logistic regression. Mean age was 55.9 ± 14.8 years. Pre/post-bypass delay (median 35.6 [5.1-51.3] vs. 26.0 [17.1-59.9]; p = 0.2) and BFI (median 56.1 [8.1-120.4] vs. 32.2 [3.0-147.4]; p = 0.2) did not significantly differ. Two patients (20%) developed post-operative ischemia in bypass dependent territories. Delay ratio did not differ between patients with and without post-operative ischemia (median 1.15 [0.67-1.64] vs. 0.83 [0.36-3.56]; p = 0.6), nor predict stroke risk (odds ratio = 1.1, p = 0.9). Conversely, BFI ratio was significantly lower for patients experiencing post-operative ischemia than those without ischemia (median 0.11 [0.06-0.17] vs. 0.99 [0.28-1.42]; p = 0.03). A BFI ratio <0.21 predicted the occurrence of post-operative ischemia (odds ratio = 0.02, p = 0.05). These data suggest that intraoperative ICG-BFA may help assess post-operative ischemic risk during cerebral bypass surgery for complex aneurysms requiring vessel sacrifice.

Intraoperative evaluation of local cerebral hemodynamic change by indocyanine green videoangiography: prediction of incidence and duration of postoperative transient neurological events in patients with moyamoya disease

OBJECTIVE

Transient neurological events (TNEs) occur frequently in the acute phase after direct bypass surgery for moyamoya disease (MMD), but there is currently no way to predict them. FlowInsight is a specialized software for analyzing indocyanine green (ICG) videoangiography taken with a surgical microscope. The purpose of this study was to investigate whether intraoperative evaluation of local hemodynamic changes around anastomotic sites using FlowInsight could predict the incidence and duration of TNEs.

METHODS

From patients who were diagnosed with MMD in our hospital between August 2014 and March 2017 and who underwent superficial temporal artery-middle cerebral artery bypass surgery, we investigated 25 hemispheres (in 22 patients) in which intraoperative ICG analysis was performed using FlowInsight. To evaluate the local cerebral hemodynamics before and after anastomosis, regions of interest were set at 3 locations on the brain surface around the anastomotic site, and the mean cerebral blood flow (CBF), mean gradation (Grad), mean transit time (MTT), and mean time to peak (TTP) were calculated from the 3 regions of interest. Furthermore, the change rate in CBF (ΔCBF [%]) was calculated using the formula (postanastomosis mean CBF - preanastomosis mean CBF)/preanastomosis mean CBF. ΔGrad (%), ΔMTT (%), and ΔTTP (%) were similarly calculated.

RESULTS

Postoperative stroke without TNE occurred in 2 of the 25 hemispheres. These 2 hemispheres (in 2 patients) were excluded from the study, and data from the remaining 23 hemispheres (in 20 patients) were analyzed. For each parameter (ΔCBF, ΔGrad, ΔMTT, and ΔTTP) calculated by FlowInsight, the difference between the groups with and without TNEs was significant. The median values for ΔCBF and ΔGrad were significantly higher in the TNE group than in the no-TNE group (ΔCBF 30.13 vs 3.54, p = 0.0106; ΔGrad 62.05 vs 10.78, p = 0.00435), whereas the median values for ΔMTT and ΔTTP were significantly lower in the TNE group (ΔMTT -16.90 vs -7.393, p = 0.023; ΔTTP -29.07 vs -7.02, p = 0.00342). Comparison of the area under the curve (AUC) for each parameter showed that ΔTTP had the highest AUC and was the parameter with the highest diagnostic accuracy (AUC 0.857). The Youden index revealed that the optimal cutoff value of ΔTTP was -11.61 (sensitivity 77.8%, specificity 71.4%) as a predictor of TNEs. In addition, Spearman's rank correlation coefficients were calculated, and ΔCBF, ΔGrad, ΔMTT, and ΔTTP each showed a strong correlation with the duration of TNEs. The larger the change in each parameter, the longer the TNEs persisted.

CONCLUSIONS

Intraoperative ICG videoangiography findings were correlated with the occurrence and duration of TNEs after direct bypass surgery for MMD. Screening for cases at high risk of TNEs can be achieved by ICG analysis using FlowInsight.

Assessment of Hemodynamic Changes and Hyperperfusion Risk After Extracranial-to-Intracranial Bypass Surgery Using Intraoperative Indocyanine Green-Based Flow Analysis

BACKGROUND

Intraoperative blood flow assessments during cerebral bypass would ideally assess vessel patency, downstream perfusion, and risk of postoperative hyperperfusion syndrome (HPS). Previous studies using indocyanine green-based flow analyses (ICG-BFA) have identified multiple parameters that can intraoperatively track bypass-related changes in cerebral perfusion and potentially predict postoperative risk of HPS. Herein, we determine the most robust parameter and anatomic location for intraoperative ICG-BFA assessment of bypass-related perfusion changes and prediction of postoperative risk of HPS.

METHODS

Retrospective analysis of an institutional review board-approved prospective database identified patients undergoing superficial temporal artery-to-middle cerebral artery bypass. Demographic and clinical information, as well as manually calculated and automated pre- and postbypass intraoperative ICG-BFA data from cortical, arterial, and venous regions of interest were recorded and analyzed.

RESULTS

Seven patients underwent superficial temporal artery-to-middle cerebral artery bypass (4 Moyamoya, 3 carotid occlusions). Average age was 48.2 ± 13.9 years (3 female, 4 male). Although all parameters measured showed trends toward improvement postbypass, only changes in arterial and venous automated ICG-BFA slope (also known as blood flow index [maximum intensity/rise time]) reached significance. None of the patients experienced symptomatic HPS, despite 5 of 7 (71.4%) having an increased HPS risk based on previously published ICG-BFA data.

CONCLUSIONS

ICG-BFA has utility for the intraoperative assessment of bypass-related changes in cerebral perfusion, with automated blood flow index being the most robustly affected parameter. Although previously published ICG-BFA indices did not predict the development of symptomatic postoperative HPS, larger-scale studies correlating observed ICG-BFA changes with risk of HPS are warranted.

Bedside assessment of regional cerebral perfusion using near-infrared spectroscopy and indocyanine green in patients with atherosclerotic occlusive disease

This pilot study aimed to investigate the utility of near-infrared spectroscopy/indocyanine green (NIRS/ICG) for examining patients with occlusive cerebrovascular disease. Twenty-nine patients with chronic-stage atherosclerotic occlusive cerebrovascular disease were included. The patients were monitored using NIRS at the bedside. Using ICG time-intensity curves, the affected-to-unaffected side ratios were calculated for several parameters, including the maximum ICG concentration (ΔICGmax), time to peak (TTP), rise time (RT), and blood flow index (BFI = ΔICGmax/RT), and were compared to the affected-to-unaffected side ratios of the regional cerebral blood flow (rCBF) and regional oxygen extraction fraction (rOEF) obtained using positron emission tomography with ¹⁵O-labeled gas. The BFI ratio showed the best correlation with the rCBF ratio among these parameters (r = 0.618; P = 0.0004), and the RT ratio showed the best correlation with the rOEF ratio (r = 0.593; P = 0.0007). The patients were further divided into reduced rCBF or elevated rOEF groups, and the analysis revealed significant related differences. The present results advance the measurement of ICG kinetics using NIRS as a useful tool for the detection of severely impaired perfusion with reduced rCBF or elevated rOEF. This method may be applicable as a monitoring tool for patients with acute ischemic stroke.

Intraoperative FLOW 800 Analysis for Intramedullary Cystic Lesion: A Technical Case Report

BACKGROUND AND IMPORTANCE

During intramedullary lesion surgery, the lesion site and the posterior median sulcus (PMS) should be accurately identified prior to myelotomy to avoid severe injury of the posterior funiculus. However, intramedullary lesions are fundamentally invisible until the myelotomy is performed. Furthermore, the PMS location is frequently unclear due to lesion-induced swelling or distortion of the spinal cord. Intraoperative indocyanine green videoangiography (ICG-VA) followed by FLOW 800 analysis, which shows vascularization of the spinal parenchyma, may provide a solution for these problems in specific cases.

CLINICAL PRESENTATION

A 61-year-old woman suffering from claudication visited our department. Magnetic resonance imaging (MRI) revealed a cystic lesion at the level of Th11. A solid portion was not detected in the T1-weighted images following gadolinium administration. We made a diagnosis of ventriculus terminalis and performed a lesion resection. Prior to opening the PMS, ICG-VA was performed, which revealed an avascular area representing the intramedullary cyst. The PMS was the most avascular area observed in the time-intensity analysis executed using FLOW 800 software (Zeiss, Oberkochen, Germany). Thus, it was helpful in determining the site for myelotomy, which should be performed at the center of the extent of the lesion. The patient was discharged 23 days after the operation, ambulating independently.

CONCLUSION

Intraoperative ICG-VA followed by FLOW 800 analysis was applied to a case of intramedullary cystic lesion. This technique may be helpful in performing safer intramedullary cystic lesion surgery because it enables visualization of the lesion location and confirmation of the PMS.

Near-Infrared Optical Imaging Noninvasively Detects Acutely Damaged Muscle

Muscle damage is currently assessed through methods such as muscle biopsy, serum biomarkers, functional testing, and imaging procedures, each with its own inherent limitations, and a pressing need for a safe, repeatable, inexpensive, and noninvasive modality to assess the state of muscle health remains. Our aim was to develop and assess near-infrared (NIR) optical imaging as a novel noninvasive method of detecting and quantifying muscle damage. An immobilization-reambulation model was used for inducing muscle damage and recovery in the lower hindlimbs in mice. Confirmation of muscle damage was obtained using in vivo indocyanine green-enhanced NIR optical imaging, magnetic resonance imaging, and ex vivo tissue analysis. The soleus of the immobilized-reambulated hindlimb was found to have a greater amount of muscle damage compared to that in the contralateral nonimmobilized limb, confirmed by in vivo indocyanine green-enhanced NIR optical imaging (3.86-fold increase in radiant efficiency), magnetic resonance imaging (1.41-fold increase in T2), and an ex vivo spectrophotometric assay of indocyanine green uptake (1.87-fold increase in normalized absorbance). Contrast-enhanced NIR optical imaging provides a sensitive, rapid, and noninvasive screening method that can be used for imaging and quantifying muscle damage and recovery in vivo.