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

The use of laser speckle contrast imaging to predict flap necrosis: An experimental study in a porcine flap model

Background: We evaluated the use of laser speckle contrast imaging (LSCI) in the perioperative planning in reconstructive flap surgery. The aim of the study was to investigate whether LSCI can predict regions with a high risk of developing postoperative necrosis. Our hypothesis was that, perioperatively, such regions have perfusion values below a threshold value and show a negative perfusion trend. Methods: A porcine flap model based on the cranial gluteal artery perforator was used. Images were acquired before surgery, immediately after surgery (t = 0), after 30 min (t =30 min), and after 72h (t = 72 h). Regions of interest (ROIs) were chosen along the central axis of the flap. Clinical evaluation of the flap was made during each time point. Results: At t = 72 h, a demarcation line could be seen at a distance of 15.8 +/- 0.4 cm away from the proximal border of the flaps. At t =0, perfusion decreased gradually from the proximal to the distal ROI. At t =30 min, perfusion was significantly lower in the ROI distal to the final demarcation line than that at t = 0, and in all flaps, these ROIs had a perfusion amp;lt;25 PU. At t= 72 h, perfusion in the ROI proximal to this line returned to baseline levels, whereas perfusion in the distal ROI remained low. Conclusions: In our model, a decrease in perfusion during the first 30 min after surgery and a perfusion amp;lt;25 PU at t = 30 min was a predictor for tissue morbidity 72 h after surgery, which indicates that LSCI is a promising technique for perioperative monitoring in reconstructive flap surgery. (C) 2018 Published by Elsevier Ltd on behalf of British Association of Plastic, Reconstructive and Aesthetic Surgeons.Funding Agencies|County of Ostergotland</p

Stretchable gold nanowire-based cuff electrodes for low-voltage peripheral nerve stimulation

Objective. Electrical stimulation of the peripheral nervous system (PNS) can treat various diseases and disorders, including the healing process after nerve injury. A major challenge when designing electrodes for PNS stimulation is the mechanical mismatch between the nerve and the device, which can lead to non-conformal contact, tissue damage and inefficient stimulation due to current leakage. Soft and stretchable cuff electrodes promise to tackle these challenges but often have limited performance and rely on unconventional materials. The aim of this study is to develop a high performance soft and stretchable cuff electrode based on inert materials for low-voltage nerve stimulation. Approach. We developed 50 mu m thick stretchable cuff electrodes based on silicone rubber, gold nanowire conductors and platinum coated nanowire electrodes. The electrode performance was characterized under strain cycling to assess the durability of the electrodes. The stimulation capability of the cuff electrodes was evaluated in an in vivo sciatic nerve rat model by measuring the electromyography response to various stimulation pulses. Main results. The stretchable cuff electrodes showed excellent stability for 50% strain cycling and one million stimulation pulses. Saturated homogeneous stimulation of the sciatic nerve was achieved at only 200 mV due to the excellent conformability of the electrodes, the low conductor resistance (0.3 Ohm sq(-1)), and the low electrode impedance. Significance. The developed stretchable cuff electrode combines favourable mechanical properties and good electrode performance with inert and stable materials, making it ideal for low power supply applications within bioelectronic medicine.Funding Agencies|Swedish Foundation for Strategic Research, Swedens Innovation Agency (VINNOVA); Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO Mat LiU) [2009 00971]</p

A Soft and Stretchable Multielectrode Cuff for Selective Peripheral Nerve Stimulation

Bioelectronic medicine can treat diseases and disorders in humans by electrically interfacing with peripheral nerves. Multielectrode cuffs can be used for selective stimulation of portions of the nerve, which is advantageous for treatment specificity. The biocompatibility and conformability of cuffs can be improved by reducing the mechanical mismatch between nerve tissue and cuffs, but selective stimulation of nerves has yet to be achieved with soft and stretchable cuff electrodes. Here, this paper reports the development of a soft and stretchable multielectrode cuff (sMEC) for selective nerve stimulation. The device is made of 50 mu m thick silicone with embedded gold nanowire conductors, which renders it functional at 50% strain, and provides superior conformability for wrapping nerves. By using different stimulation protocols, high functional selectivity is achieved with the sMECs eight stimulation electrodes in a porcine sciatic nerve model. Finite element modeling is used to predict the potential distribution within the nerve, which correlate well with the achieved stimulation results. Recent studies are showing that mechanical softness is of outermost importance for reducing foreign body response. It is therefore believed that the soft high-performance sMEC technology is ideal for future selective peripheral nerve interfaces for bioelectronic medicine.Funding Agencies|Swedish Foundation for Strategic Research; Swedish Research Council [2019-04424]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoeping University (Faculty Grant SFO Mat LiU) [2009 00971]; European Research Council, "e-NeuroPharma" ERC-2018-ADG [834677]</p

Monitoring of partial and full venous outflow obstruction in a porcine flap model using laser speckle contrast imaging

Background: In microsurgery, there is a demand for more reliable methods of postoperative monitoring of free flaps, especially with regard to tissue-threatening obstructions of the feeding arteries and draining veins. In this study, we evaluated laser speckle contrast imaging (LSCI) and laser Doppler flowmetry (LDF) to assess their possibilities to detect partial and full venous outflow obstruction, as well as full arterial occlusion, in a porcine flap model. Methods: Cranial gluteal artery perforator flaps (CGAPs) were raised, and arterial and venous blood flow to and from the flaps was monitored using ultrasonic flow probes. The venous flow was altered with an inflatable cuff to simulate partial and full (50% and 100%) venous obstruction, and arterial flow was completely obstructed using clamps. The flap microcirculation was monitored using LSCI and LDF. Results: Both LDF and the LSCI detected significant changes in flap perfusion. After partial (50%) venous occlusion, perfusion decreased from baseline, LSCI: 63.5 +/- 12.9 PU (p = 0.01), LDF 31.3 +/- 15.7 (p = 0.64). After 100% venous occlusion, a further decrease in perfusion was observed: LSCI 54.6 +/- 14.2 PU (p amp;lt; 0.001) and LDF 16.7 +/- 12.8 PU (p amp;lt; 0.001). After release of the venous cuff, LSCI detected a return of the perfusion to a level slightly, but not significantly, below the baseline level 70.1 +/- 11.5 PU (p=0.39), while the LDF signal returned to a level not significant from the baseline 36.1 +/- 17.9 PU (p amp;gt; 0.99). Perfusion during 100% arterial occlusion decreased significantly as measured with both methods, LSCI: 48.3 +/- 7.7 (PU, pamp;lt;0.001) and LDF: 8.5 +/- 4.0 PU (pamp;lt;0.001). During 50% and 100% venous occlusion, LSCI showed a 20% and 26% inter-subject variability (CV%), respectively, compared to 50% and 77% for LDF. Conclusions: LSCI offers sensitive and reproducible measurements of flap microcirculation and seems more reliable in detecting decreases in blood perfusion caused by venous obstruction. It also allows for perfusion measurements in a relatively large area of flap tissue. This may be useful in identifying areas of the flap with compromised microcirculation during and after surgery. (C) 2016 British Association of Plastic, Reconstructive and Aesthetic Surgeons. Published by Elsevier Ltd. All rights reserved.Funding Agencies|county of Ostergotland</p

Methodological concerns with laser speckle contrast imaging in clinical evaluation of microcirculation

Background Laser Speckle Contrast Imaging (LSCI) is a non-invasive and fast technique for measuring microvascular blood flow that recently has found clinical use for burn assessment and evaluation of flaps. Tissue motion caused by for example breathing or patient movements may however affect the measurements in these clinical applications, as may distance between the camera and the skin and tissue curvature. Therefore, the aims of this study were to investigate the effect of frame rate, number of frames/image, movement of the tissue, measuring distance and tissue curvature on the measured perfusion. Methods Methyl nicotinate-induced vasodilation in the forearm skin was measured using LSCI during controlled motion at different speeds, using different combinations of frame rate and number of frames/image, and at varying camera angles and distances. Experiments were made on healthy volunteers and on a cloth soaked in a colloidal suspension of polystyrene microspheres. Results Measured perfusion increased with tissue motion speed. The relation was independent of the absolute perfusion in the skin and of frame rate and number of frames/image. The measured perfusion decreased with increasing angles (16% at 60, p = 0.01). Measured perfusion did not vary significantly between measurement distances from 15 to 40 cm (p = 0.77, %CV 0.9%). Conclusion Tissue motion increases and measurement angles beyond 45 decrease the measured perfusion in LSCI. These findings have to be taken into account when LSCI is used to assess moving or curved tissue surfaces, which is common in clinical applications.Funding Agencies|ALF grants, Region Ostergotland</p

Vascular Occlusion in a Porcine Flap Model : Effects on Blood Cell Concentration and Oxygenation.

Background: Venous congestion in skin flaps is difficult to detect. This study evaluated the ability of tissue viability imaging (TiVi) to measure changes in the concentration of red blood cells (CRBC), oxygenation, and heterogeneity during vascular provocations in a porcine fasciocutaneous flap model. Methods: In 5 pigs, cranial gluteal artery perforator flaps were raised (8 flaps in 5 pigs). The arterial and venous blood flow was monitored with ultrasonic flow probes. CRBC, tissue oxygenation, and heterogeneity in the skin were monitored with TiVi during baseline, 50% and 100% venous occlusion, recovery, 100% arterial occlusion and final recovery, thereby simulating venous and arterial occlusion of a free fasciocutaneous flap. A laser Doppler probe was used as a reference for microvascular perfusion in the flap. Results: During partial and complete venous occlusion, increases in CRBC were seen in different regions of the flap. They were more pronounced in the distal part. During complete arterial occlusion, CRBC decreased in all but the most distal parts of the flap. There were also increases in tissue oxygenation and heterogeneity during venous occlusion. Conclusions: TiVi measures regional changes in CRBC in the skin of the flap during arterial and venous occlusion, as well as an increase in oxygenated hemoglobin during venous occlusion that may be the result of reduced metabolism and impaired delivery of oxygen to the tissue. TiVi may provide a promising method for measuring flap viability because it is hand-held, easy to-use, and provides spatial information on venous congestion

Areas in which different concentrations of methyl nicotinate were applied (1: 40 mM, 2: 10 mM, 3: 2.5 mM) on the volar side of the forearm at different speeds (A: 0 mm/s, B: 25 mm/s, C: 41 mm/s, D: 90 mm/s).

<p>Areas in which different concentrations of methyl nicotinate were applied (1: 40 mM, 2: 10 mM, 3: 2.5 mM) on the volar side of the forearm at different speeds (A: 0 mm/s, B: 25 mm/s, C: 41 mm/s, D: 90 mm/s).</p

Example of images with and without motion artefacts of the hands in 2 burn patients.

<p>Images A and C do not have motion artefacts, while image B and D do. All images were taken of the same patient and injury. Note that measured perfusion is higher in images B and D, as a result of patient motion.</p

System settings used in the investigation of motion in calibration fluid and in the skin of the forearm of 8 healthy subjects.

<p>System settings used in the investigation of motion in calibration fluid and in the skin of the forearm of 8 healthy subjects.</p