No Superior Quantitative ICG Parameter Has Been Established as of 2026
As of 2026, no meta-analysis has definitively identified a single superior quantitative ICG perfusion metric among time-based parameters (e.g., time-to-peak), normalized relative ratios, or absolute intensity values. The field remains characterized by significant heterogeneity in measurement protocols and threshold definitions, preventing consensus on optimal quantification methods.
Current State of Quantitative ICG Analysis
The most recent systematic review from 2026 examining quantitative ICG perfusion imaging explicitly highlights this problem 1. While multiple quantitative parameters have been studied—including:
- Time-based parameters: Time-to-peak (TTP), wash-in time, time to maximum intensity
- Intensity-based parameters: Maximum fluorescence intensity (MFI), peak intensity
- Curve-derived parameters: Area under the curve (AUC), inflow/outflow slopes, remaining fluorescence at fixed timepoints
The pooled analysis showed that prolonged TTP (mean difference 4.2 seconds, 95% CI 2.8-5.6) and reduced AUC (mean difference -112.3 arbitrary units, 95% CI -154.1 to -70.5) were both significantly associated with flap compromise 1. However, the study explicitly notes "quantification protocols and threshold definitions were highly heterogeneous (I² > 75%)" 1.
Why No Single Parameter Has Emerged as Superior
Lack of Standardization
The 2018 guidelines on fluorescence imaging reporting emphasize that quantitative analyses should include "raw numeric values and ratios" but do not specify which metrics are superior 2. This reflects the fundamental problem: without standardized injection techniques, imaging times, reconstruction methods, and analyses, direct comparison between different quantitative approaches remains impossible.
Multiple Parameters Show Clinical Utility
Recent 2026 studies demonstrate that different parameter types can all provide clinically useful information:
- Time-based: One study found all four derived perfusion parameters (including TTP and maximum inflow rate) showed significant changes in sigmoid perfusion after aortic reconstruction 3
- Intensity-based: Studies consistently show that decreased peak intensity correlates with tissue necrosis 1
- Combined approaches: Research indicates that combining multiple parameters may be more informative than relying on any single metric 4
Context-Dependent Performance
The optimal parameter appears to depend on the clinical application. For example, time-to-peak may be more relevant for assessing arterial inflow, while remaining fluorescence intensity at fixed timepoints (30 or 60 seconds post-peak) may better reflect venous drainage and tissue retention 3.
Current Best Practice Approach
Given the absence of a definitively superior metric, the pragmatic approach is to:
- Use multiple complementary parameters rather than relying on a single measurement
- Report both time-based and intensity-based metrics to capture different aspects of perfusion 1
- Establish institution-specific thresholds based on local equipment and protocols, as absolute values remain non-standardized
- Prioritize normalized ratios over absolute values when comparing between patients or timepoints, as this reduces inter-device variability 2
Critical Caveat
The 2026 systematic review explicitly states: "Standardization of imaging procedures and diagnostic thresholds is urgently needed to transform these promising techniques into validated, reliable clinical decision-support systems" 1. Until this standardization occurs, no single quantitative parameter can be considered definitively superior across all clinical contexts and imaging systems.
The sensitivity of quantitative ICG-FA for predicting necrosis ranges from 82-94% with specificity of 88-96% 1, but these performance characteristics apply to the technique broadly rather than to any specific quantitative metric.