Laser Speckle Contrast Imaging in Reconstructive Surgery

Objectives Reconstructive surgery aims to restore function or normal appearance by reconstructing defective organs after trauma or disease. In patients undergoing reconstructive surgery, previous trauma, surgery or radiotherapy can result in compromised blood supply. This will affect the viability of the tissue and increases the risk for postoperative complications, such as ischemia and infection. It is therefore important to assess the tissue viability, both before, during and after the surgery. This can be done using different techniques that monitor the perfusion of the skin covering the affected area. In this thesis, LSCI have been evaluated for tissue monitoring in reconstructive surgery. The technique allows for a fast and noninvasive assessment of superficial tissue perfusion over a wide field. Based on previous work on the technology, we have seen clear advantages with LSCI compared to other methods, for example laser Doppler flowmetry (LDF). We have evaluated laser speckle contrast imaging (LSCI) as a tool for tissue monitoring in reconstructive surgery in four studies. Methods In study I we used a bench top model and healthy subjects to address methodological concerns subjected to the LSCI technology. We investigated the effect of motion distance and angle on the assessed perfusion value In study II we used a porcine model to compare LSCI and LDF as tools to detect partial and full venous outflow obstruction. We used both methods to assess a flap based on the cranial gluteal artery perforator with partial and complete occlusion of the vein and artery. In study III we used the same porcine model as in study II to investigate the possibility to use LSCI intraoperatively to identify flap areas with compromised circulation and thereby predict areas with a high risk of postoperative necrosis. In study IV we used LSCI for intraoperative evaluation of tissue viability during deep inferior epigastric perforator (DIEP) free flap surgery and to investigate the perfusion distribution according to the Hartrampf zones, as measured with LSCI, in relation to the selected perforator in the deep inferior epigastric perforator free flap. Results In study I we saw that tissue perfusion as measured with LSCI increases with increasing tissue motion, independent of frame rate, number of images, and tissue perfusion. Measured perfusion will decrease when images are acquired at an angle larger than 45° but distances between 15 and 40 cm do not affect the measured perfusion. In study II we observed significant decreases in perfusion during both partial and complete venous occlusion with both LSCI and LDF. However, higher variability seen with LDF, measured as % coefficient of variation. In study III a decrease in perfusion during the first 30 min after raising the flap and a perfusion value below 25 PU after 30 min was a predictor for tissue morbidity 72h after surgery. In study IV the highest perfusion values were found in zone I and higher perfusion in zone II compared to zone III, directly after the flap was raised. No remaining significant difference between zone I, II and III could be seen after anastomosis of the vessels. All flaps with a minimum perfusion <30 PU, measured after the flap was shaped and inserted, later suffered from partial flap necrosis. Conclusion LSCI is a technology that has the potential to contribute to tissue monitoring in reconstructive surgery. It has many advantages over other techniques, such as the fast acquisition time, the spatial resolution and the fact that it is completely non-invasive. However, the current system is still too bulky to be easily introduced into a clinical setting and the technology is also subject to certain drawbacks which limit its usability. It is sensitive to motion artefacts; only superficial tissue is assessed and cannot offer absolute perfusion data. If these disadvantages could be addressed, LSCI could contribute to a more accurate survey of tissue perfusion and thus better outcome in reconstructive surgery