Quantification of fluorescence angiography: Toward a reliable intraoperative assessment of tissue perfusion - A narrative review

Abstract

Background Accurate intraoperative assessments of tissue perfusion are essential in all forms of surgery. As traditional methods of perfusion assessments are not available during minimally invasive surgery, novel methods are required. Here, fluorescence angiography with indocyanine green has shown promising results. However, to secure objective and reproducible assessments, quantification of the fluorescent signal is essential (Q-ICG). This narrative review aims to provide an overview of the current status and applicability of Q-ICG for intraoperative perfusion assessment. Results Both commercial and custom Q-ICG software solutions are available for intraoperative use; however, most studies on Q-ICG have performed post-operative analyses. Q-ICG can be divided into inflow parameters (ttp, t0, slope, and T 1/2 max) and intensity parameters (Fmax, PI, and DR). The intensity parameters appear unreliable in clinical settings. In comparison, inflow parameters, mainly slope, and T 1/2 max have had superior clinical performance. Conclusion Intraoperative Q-ICG is clinically available; however, only feasibility studies have been performed, rendering an excellent usability score. Q-ICG in a post-operative setting could detect changes in perfusion following a range of interventions and reflect clinical endpoints, but only if based on inflow parameters. Thus, future studies should include the methodology outlined in this review, emphasizing the use of inflow parameters (slope or T 1/2 max), a mass-adjusted ICG dosing, and a fixed camera position.

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

“…The authors described the diversity in perfusion parameters and methodology in the field of gastrointestinal surgery, concluding that the application of ICG-NIRF imaging in this field requires standardization before implementation in a clinical setting. A potential means of achieving standardization is by the process of normalization, a mathematical means of correcting for fluctuations in fluorescence intensity, as yet only described in animal studies with promising results [ 67 , 68 , 69 ].…”

Fluorescence Image-Guided Surgery for Thyroid Cancer: Utility for Preventing Hypoparathyroidism

“…Contrast-enhanced fluorescence imaging with intravenous ICG or fluorescein injection can visualize preserved versus impaired perfusion (e.g., congruent results shown intraoperatively for adrenal perfusion) [9]. However, except for quantitative contrast-enhanced NIR imaging research protocols [74], fluorescent signals and ICG scores are generally assessed subjectively. For ICG injections, the rate at which the fluorescence signal intensity increases, as well as the added signal intensity produced by reinjections, can only be objectively assessed with a quantitative approach, which has not yet been integrated into commercially available NIR imaging systems.…”

Novel Intraoperative Imaging of Gastric Tube Perfusion during Oncologic Esophagectomy—A Pilot Study Comparing Hyperspectral Imaging (HSI) and Fluorescence Imaging (FI) with Indocyanine Green (ICG)

“…Nevertheless, the patient cohort is too small to make further conclusions. Lütken et al evaluated different ways for quantification of FI-ICG and concluded that a combination of timing and inflow intensity reflect clinical outcomes at best [ 34 ]. To date, there is no consensus on the best quantification method for FI-ICG, because it is highly complex, results are conflicting, and no cut-off values have been established yet [ 34 ].…”

“…Lütken et al evaluated different ways for quantification of FI-ICG and concluded that a combination of timing and inflow intensity reflect clinical outcomes at best [ 34 ]. To date, there is no consensus on the best quantification method for FI-ICG, because it is highly complex, results are conflicting, and no cut-off values have been established yet [ 34 ]. During the last years, our group has clearly demonstrated the impact of using HSI in evaluating the perfusion of the gastric tube during esophagectomy [ 17 , 22 ].…”