Monitoring tissue oxygenation is important in clinical applications such as breast surgery, Surgical reconstruction with free flaps is complex: a flap is taken from a healthy area of the body to be transposed into the damaged area. This operation requires microsurgical reconstruction of the vascular network. Tissue alterations may occur if the blood supply of the flap is not normal. This must be rapidly detected in order to avoid irreversible and extremely serious damages.
We developed a Time-Resolved approach to get information in depth and separate the contribution of the upper layer from the lower layer of interest (flap). The TR system is detailed in [1-2]. We designed a specific optical stethoscope probe built from materials compliant with the clinical constraints. Distances between sources and detectors (SD) are 6, 8 and 13mm. We focused on the 750-800 and 850nm wavelengths.
Abdominal flap were collected and buried on the left lateral abdominal muscle of the pig (~1cm deep of skin, fat and highly absorbing muscle) . Either arterial or venous occlusions were performed (20 minutes of rest / 20 minutes of occlusion / 10-20 minutes release). US control of the upper layer and flap thicknesses has been systematically done. The two layers (surface layer and flap) were systematically controlled and monitored by two invasive LICOX (Integra laboratory) that measure the tissue pressure in Oxygen.
We measured and analyzed 16 pigs (32 flaps) with arterial and venous occlusions; clinical control and LICOX were systematically performed. For each acquired data, we compared the results obtained in NIRS (integral of the TR signal) and in Resolved Time.
Our results show that while the detection of occlusion depends on its depth in NIRS, we were able to detect occlusions whatever the sample (from the surface down to 1.23 mm) using the Resolved Time signals. In addition, the Oxy and Deoxy concentrations information provided by TR made it possible to identify the type of occlusion, which LICOX does not always allow.
 Planat-Chrétien A., et al. Diffuse Optical Imaging V, H. Dehghani and P. Taroni, eds., Vol. 9538 of SPIE Proceedings (Optical Society of America, 2015), paper 953806 (2015).
 Planat-Chrétien A., et al., Biomedical Optics Congress 2018, Clinical and Translational, OSA Technical Digest (Optical Society of America, 2018), paper JW3A.27 (2018).
 Lartizien R, et al.,J Stomatol Oral Maxillofac Surg. 2017
Financial support ANR-15-CE19_0010 (Agence Nationale de Recherche, France).