COLOFLOW: Laser Speckle Contrast Imaging Versus Near-infrared Fluorescence Imaging With Indocyanine Green

Study Title: COLOFLOW: Quantified ICG Fluorescence versus Laser Speckle Contrast Imaging (LSCI) for Perfusion Assessment in Colorectal Surgery.

Background Anastomotic leakage is a serious complication after colorectal surgery, occurring in approximately 10-15% of patients and contributing substantially to postoperative morbidity and mortality. Surgeons increasingly use indocyanine green (ICG) fluorescence imaging to assess bowel perfusion during surgery, but interpretation remains largely subjective and the technique has limitations, including dye dependency and difficulties with repeated measurements. Laser Speckle Contrast Imaging (LSCI) is a dye-free, real-time imaging technique that provides objective perfusion maps and may overcome several of these limitations.

Aim The primary aim of the study is to determine how well subjective intraoperative ICG fluorescence assessment agrees with LSCI perfusion imaging when evaluating bowel perfusion at the planned anastomotic site during colorectal surgery.

Secondary aims are:

To evaluate the spatial agreement between postoperative quantitative ICG analysis and LSCI perfusion boundaries.

To assess the feasibility of using the PerfusiX-IGS LSCI system during open colorectal surgery.

To record clinical outcomes, including anastomotic leakage rates.

Study Design COLOFLOW is a prospective, single-centre, observational study conducted at the Leiden University Medical Centre (LUMC). No randomization, blinding, or intervention is performed. LSCI measurements are recorded for research purposes only and do not influence surgical decision-making.

Participants The study includes approximately 30 adult patients undergoing elective colon or rectal resection with creation of a primary anastomosis. This population corresponds to patients enrolled in the ongoing QUANTICOLON study.

Inclusion Criteria

Age ≥18 years. Elective colorectal resection with primary anastomosis. Ability to provide informed consent.

Exclusion Criteria

Palliative surgery. Poor intraoperative visualization. Conditions that substantially interfere with perfusion assessment.

Methods

During surgery:

The surgeon identifies the planned bowel transection site under white light. The bowel is exteriorized for imaging. The PerfusiX-IGS LSCI system records a perfusion map. Standard-of-care ICG fluorescence imaging is then performed and interpreted subjectively by the surgeon.

After surgery, ICG recordings are quantitatively analysed using dedicated software to derive perfusion parameters such as:

Time to fluorescence onset (T0) Time to peak intensity (Tmax) Maximum intensity (Imax) Maximum normalized slope Outflow area-under-the-curve measurements

A custom Python-based analysis is used to compare the location of perfusion boundaries identified by both imaging techniques.

Outcomes Primary Endpoint

Agreement between subjective ICG interpretation and LSCI perfusion mapping, assessed by:

Categorical agreement (adequate vs. inadequate perfusion). Spatial agreement between perfusion boundaries identified by both modalities.

Secondary Endpoints

Distance between quantitative ICG and LSCI perfusion boundaries. Feasibility and usability of the PerfusiX-IGS system. Success rate of obtaining calibrated image documentation. Thirty-day postoperative outcomes, including complications and anastomotic leakage.

Statistical Analysis Categorical agreement will be evaluated using Cohen's kappa coefficient, while spatial agreement will be assessed with Bland-Altman analysis. Secondary analyses will explore whether quantitative ICG measurements provide better agreement with LSCI than subjective assessment alone.

Ethical Considerations The study is classified as non-WMO (non-Medical Research Involving Human Subjects Act) because it introduces no intervention beyond standard care. LSCI is non-contact, non-invasive, and does not influence treatment decisions. Risks to participants are minimal and primarily related to the storage and handling of anonymized imaging data.

Conclusion COLOFLOW investigates whether objective, dye-free LSCI can serve as a reliable reference method for bowel perfusion assessment during colorectal surgery and whether postoperative quantitative analysis of ICG fluorescence can improve upon the current subjective interpretation of ICG imaging. The study aims to support the development of more standardized and objective perfusion assessment strategies that may ultimately help reduce anastomotic leakage.