Surgeons are nowadays unable to visualize and quantitatively evaluate microvascularisation in real-time during surgery. Complications due to vascular compromise are a major problem, especially in reconstructive surgery. Poor blood perfusion leads to ischemia and even tissue necrosis. If, however, perfusion and ischemia could be monitored during surgery, then surgeons could change their reconstructive design and the anaesthesiologists could improve perfusion with fluids, inotropes or vasopressors, if necessary. Surgeons therefore need a tool that is able to image in high resolution (microvascularisation), direct, intra-operative, in 3D (to image thrombosis, luminal narrowing or distinct overlaying vessels) and that produces quantitative data to objectify image interpretation.

Optical techniques, based on the interaction of light with tissue, are able to image tissue at high resolution and in real-time. These techniques are FDA-approved and have emerged as powerful diagnostic tools in different departments of medicine, such as ophthalmology for visualizing retina vascularisation and dermatology for skin diagnostics.

In this study, investigators hypothesize that four novel optical technologies: Fluorescence Imaging, Laser Speckle Contrast Imaging, Optical Coherence Tomography and Sidestream Darkfield Microscopy are able to quantitatively image perfusion in real-time during surgery.

Primary objective - Perfusion will be measured with all the techniques focussed on 4 areas; from 'good' to 'decreased' perfusion (biologically)

Fluorescence Imaging (FI): Time to intensity measurements at four sides Laser Speckle Contrast Imaging (LSCI): Perfusion Units Optical Coherence Tomography (OCT): Vessel density & decorrelation time Sidestream Darkfield Microscopy (SDF): Total vessel density, proportion of perfused vessels, perfused vessel density, max flow index, De Backer score, perfusion in mm/sec.

Differences in parameters between the four sites will be statistically be compared.

Secondary objectives

- Relation of parameters to patient outcome in terms of adverse events.

Inclusion Criteria:

• Age ≥ 18 years - Scheduled for reconstructive surgery with free flap reconstruction or laparoscopic transhiatal and 3-stage transthoracic gastric tube surgery.

Exclusion Criteria:

• Allergic to iodide (indocyanine green)
• Hyper-thyroidism
• Breastfeeding
• No informed consent
• Allergic to ephedrine
• Ischaemic heart disease
• Thyrotoxicosis
• Autonomic thyroid adenomas
• Intraoperative hypertension or tachycardia

Adult patients receiving reconstructive surgical treatment in the Academic Medical Center: 20 patients receiving free flap reconstructive surgery, and 20 patients receiving thoracolaparoscopic esophagectomy with gastric tube reconstruction. Patients will be selected irrespective of medical history, ethnic background or gender, stated that a physician of the department of Biomedical Engineering and Physics is available at time of surgery.