Advancing Fluorescence Angiography

Introduction: Intravenously injected Indocyanine green (ICG) can be visualised using surgical near infrared (NIR) cameras as it permeates tissues and vasculature. ICG fluorescence angiography (ICGFA) is used intraoperatively to address malperfusion related complications in colorectal and reconstructive surgery. However, ICGFA technique, interpretation, and equipment is unstandardised and is impacted by patient physiology. This research seeks to analyse current ICGFA practices and equipment. Subsequently, this work aims to investigate and develop quantitative ICGFA (QICGFA) methodologies, with a view to advancing contemporary applications and also developing new uses. Methods: Commercially available NIR systems were assessed for fluorescence variations relating to target positioning using stereotactic sensors. Regarding operator ICGFA interpretation, recordings were integrated into a digital interactive platform to evaluate decision-making and test the impact of proposed protocols on interpretation consistency. Post hoc quantification from diagnostic and therapeutic colorectal ICGFA recordings as well as from reconstructive procedures were analysed for associations to tissue status and postoperative outcomes. Subsequently, novel computational and clinical workflows were developed that could deliver surgical guidance and complication prediction based on comparing the target tissue perfusion to similar regions or the same tissue at earlier time points. Results: The presented NIR signal varied by system, setup (e.g. camera-scope angle configuration), and target positioning. While expert users unconsciously appreciated fluorescence fluctuations, proposed protocols which controlled for spatial variables did not improve user interpretation. The developed methodologies demonstrated feasible QICGFA perfusion pattern assessment and presentation for autologous and implant-based breast reconstructions, with these profiles being used to train complication-predicting artificial intelligence methods for the latter. Colorectal mucosa QICGFA curve patterns were associated with polyp pathology. Regarding post resection anastomotic guidance, the proposed clinical and algorithmic workflow comparing bowel ICGFA to an earlier time point demonstrated recommendations which were concordant with expert level judgements. Conclusions: Supported by an understanding of the underlying science, QICGFA perfusion patterns can be determined in a manner that potentially supports surgical decision-making for optimal healing outcomes and pathological diagnosis. Technical and clinical considerations associated with current practice need careful consideration for best use of these capabilities.