## 4 Discussion
The quantitative parameter for OCT did not significantly differ between Loc1 and Loc4, nor in the case of anastomotic leakage. This observation might be explained by the method of analysis that assessed only one transection of 2.5 mm depth for quantification, indicating that limited field of view techniques might be prone to sampling errors. SDF and LSCI show perfusion restriction towards the fundus, but both show non-significant higher values at Loc4 in the case of anastomotic leakage. As mentioned above, the SDF and LSCI trends might be comparable due to focus on the same perfusion units and might be higher in the case of anastomotic leakage due to venous outflow obstruction. FA visualises the spatial distribution of ICG that is bound to plasma proteins, and thus assesses the patency of vessels and shows vascular confines. FA parameters were able to indicate perfusion restriction towards the fundus as well as in patients with anastomotic leakage. In the case of venous congestion, FA parameters might show resistance in the vasculature, which leads to prolonged time values and a reduced rate in the increase in fluorescence intensity. Furthermore, FA time values might show what degree of arterial diffusion (instead of direct arterial flow) or venous outflow obstruction might lead to anastomotic leakage. Although FA use is dependent on ICG injection, ICG is a safe dye and can be applied at low dosages. Moreover, FA imaging systems are available for laparoscopy, which is clinically beneficial. Therefore, and on the basis of this study, FA quantitative parameters are most promising for future research. T\({}_{1/2}\) and mean slope will be promising quantitative parameters for intraoperative clinical decision-making if a threshold can be derived for patient outcomes, including anastomotic leakage. According to the threshold, change in management can include the administration of medication, to shorten the gastric conduit at the maximum extent, or no anastomotic reconstruction and oesophagealomy. The latter option is a very radical solution with a decreased quality of life and need for surgery in the future to make a new reconstruction. Most surgeons would probably choose to make an extra effort to shorten the gastric conduit and make an anastomosis at increased risk instead of choosing no reconstruction as an option. Furthermore, the threshold can be used to identify high-risk patients for anastomotic leakage. The quantitative parameters for FA may be biased by the duration of imaging, as this might not have been long enough to reach the peak value (F\({}_{\text{max}}\)). This study was further limited by a relatively small number of patients with a low absolute number of anastomotic leakages, and particularly measurements at Loc4 were infrequent. However, this pilot study can guide future studies, by for example serving as a base for sample size calculations. Furthermore, the exact anastomotic site was not recorded, but the anastomosis was constructed between Loc3 and Loc4. At Loc3, no differences were observed for any quantitative parameter, however at Loc4 differences were found. The site of anastomotic reconstruction may have led to bias in the observations. In addition, the system used for SDF measurements involves an older model and older software, and possibly new models (e.g., Cytocam) allow higher resolution, and new software (AVA 5, MicroVision Medical, Amsterdam, The Netherlands) might perform better. However, the SDF technique is still employed, and sampling error and increased values in the case of anastomotic leakage can still be expected. In addition, the parameters were not assessed in relation to patient risk factors. Co-morbidities such as diabetes mellitus and cardiovascular disease affect the (micro) circulation [26; 27], and might therefore influence the read-out of the parameters. Furthermore, diabetes mellitus and chronic obstructive pulmonary disease are known risk factors for anastomotic leakage [28]. Owing to the small sample size, correction for co-morbidities was not performed.