Evaluation of Microvascular Anastomosis Using Real-Time, Ultra–High-Resolution, Fourier Domain Doppler Optical Coherence Tomography

BACKGROUND: Evolution and improvements in microsurgical techniques and tools have paved the way for super-microsurgical anastomoses with vessel diameters often approaching below 0.8 mm in the clinical realm and even smaller (0.2–0.3 mm) in murine models. Several imaging and monitoring devices have been introduced for post-operative monitoring but intra-operative guidance, assessment and predictability have remained limited to binocular optical microscope and surgeon’s experience. We present a high-resolution real time 3D imaging modality for intra-operative evaluation of luminal narrowing, thrombus formation and flow alterations. METHODS: An imaging modality that provides immediate, in-depth high resolution 3D structure view and flow information of the anastomosed site called phase resolved Doppler optical coherence tomography (PRDOCT) was developed. 22 mouse femoral artery anastomoses and 17 mouse venous anastomoses were performed and evaluated with PRDOCT. Flow status, vessel inner lumen 3D structure, and early thrombus detection were analyzed based on PRDOCT imaging results. Initial PRDOCT based predictions were correlated with actual long term surgical outcomes. Eventually four cases of mouse orthotopic limb transplantation were carried out and PRDOCT predicted long term patency were confirmed by actual results. RESULTS: PRDOCT was able to provide high-resolution 3D visualization of the vessel flow status and vessel inner lumen. The assessments based on PRDOCT visualization shows a 92% sensitivity and 90% specificity for arterial anastomoses and 90% sensitivity and 86% specificity for venous anastomoses. CONCLUSIONS: PRDOCT is an effective evaluation tool for microvascular anastomosis. It can predict the long term vessel patency with high sensitivity and specificity

Microvascular anastomosis guidance and evaluation using real-time three-dimensional Fourier-domain Doppler optical coherence tomography.

Vascular and microvascular anastomoses are critical components of reconstructive microsurgery, vascular surgery, and transplant surgery. Intraoperative surgical guidance using a surgical imaging modality that provides an in-depth view and three-dimensional (3-D) imaging can potentially improve outcome following both conventional and innovative anastomosis techniques. Objective postoperative imaging of the anastomosed vessel can potentially improve the salvage rate when combined with other clinical assessment tools, such as capillary refill, temperature, blanching, and skin turgor. Compared to other contemporary postoperative monitoring modalities--computed tomography angiograms, magnetic resonance (MR) angiograms, and ultrasound Doppler--optical coherence tomography (OCT) is a noninvasive high-resolution (micron-level), high-speed, 3-D imaging modality that has been adopted widely in biomedical and clinical applications. For the first time, to the best of our knowledge, the feasibility of real-time 3-D phase-resolved Doppler OCT (PRDOCT) as an assisted intra- and postoperative imaging modality for microvascular anastomosis of rodent femoral vessels is demonstrated, which will provide new insights and a potential breakthrough to microvascular and supermicrovascular surgery

Microvascular anastomosis guidance and evaluation using real-time three-dimensional Fourier-domain Doppler optical coherence tomography

Vascular and microvascular anastomoses are critical components of reconstructive microsurgery, vascular surgery, and transplant surgery. Intraoperative surgical guidance using a surgical imaging modality that provides an in-depth view and three-dimensional (3-D) imaging can potentially improve outcome following both conventional and innovative anastomosis techniques. Objective postoperative imaging of the anastomosed vessel can potentially improve the salvage rate when combined with other clinical assessment tools, such as capillary refill, temperature, blanching, and skin turgor. Compared to other contemporary postoperative monitoring modalities—computed tomography angiograms, magnetic resonance (MR) angiograms, and ultrasound Doppler—optical coherence tomography (OCT) is a noninvasive high-resolution (micron-level), high-speed, 3-D imaging modality that has been adopted widely in biomedical and clinical applications. For the first time, to the best of our knowledge, the feasibility of real-time 3-D phase-resolved Doppler OCT (PRDOCT) as an assisted intra- and postoperative imaging modality for microvascular anastomosis of rodent femoral vessels is demonstrated, which will provide new insights and a potential breakthrough to microvascular and supermicrovascular surgery

Evaluation of microvascular anastomosis using real-time, ultra-high-resolution, Fourier domain Doppler optical coherence tomography.

BACKGROUND: Evolution in microsurgical techniques and tools has paved the way for supermicrosurgical anastomoses, with vessel diameters often approaching below 0.8 mm in the clinical realm and even smaller (0.2 to 0.3 mm) in murine models. Several imaging and monitoring devices have been introduced for postoperative monitoring, but intraoperative guidance, assessment, and predictability have remained limited to binocular optical microscopy and the surgeon\u27s experience. The authors present a high-resolution, real-time, three-dimensional imaging modality for intraoperative evaluation of luminal narrowing, thrombus formation, and flow alterations. METHODS: An imaging modality that provides immediate, in-depth, high-resolution, three-dimensional structure view and flow information of the anastomosed site, called phase-resolved Doppler optical coherence tomography, was developed. Twenty-two mouse femoral artery anastomoses and 17 mouse venous anastomoses were performed and evaluated. Flow status, vessel inner lumen three-dimensional structure, and early thrombus detection were analyzed based on imaging results. Predictions formed correlated with actual long-term surgical outcomes. Eventually, four cases of mouse orthotopic limb transplantation were carried out, and predicted long-term patency based on imaging results was confirmed by actual results. RESULTS: The assessments based on high-resolution three-dimensional visualization of the vessel flow status and inner lumen provided by phase-resolved Doppler optical coherence tomography show 92 percent sensitivity and 90 percent specificity for arterial anastomoses and 90 percent sensitivity and 86 percent specificity for venous anastomoses. CONCLUSIONS: Phase-resolved Doppler optical coherence tomography is an effective evaluation tool for microvascular anastomosis. It can predict the long-term vessel patency with high sensitivity and specificity

Unfavorable Geology and Mitigation Measures for Water Inrush Hazard during Subsea Tunnel Construction: A Global Review

Water inrush hazard seriously threatens construction safety of subsea tunnels in unfavorable geological areas. In recent years, a large number of subsea tunnels have been built worldwide, some of which have experienced many water inrush disasters, especially in Japan and Norway. In this paper, a systematic methodology is proposed to rigorously review the current literature about water inrush in subsea tunnels. Emphasis is placed on recorded causes and evolution processes of water inrush, as well as relevant mitigation measures. In particular, the geological conditions that generate such water inrush hazards are initially discussed by counting cases of tunnel water inrush in the past decades (43 cases of water inrush hazards in tunnels (including mountain tunnels)). The process of formation of failure modes of water inrush, and the corresponding research methods (including theoretical, numerical and experimental) are reviewed, and can be used to pave the ways for hazard prevention and future research. This is followed by a summary of the prevention methods and mitigation measures used in practice, and a short discussion of the achievements and limitations of each method. Then combined with the evolution characteristics of the failure area, the water inrush process of different modes is divided into three stages, with a proposed a grouting scheme for each stage. Finally, concluding remarks, current research gaps and future research directions on subsea tunnel water inrush are provided and discussed

MEMS-Based Handheld Fourier Domain Doppler Optical Coherence Tomography for Intraoperative Microvascular Anastomosis Imaging

<div><p>Purpose</p><p>To demonstrate the feasibility of a miniature handheld optical coherence tomography (OCT) imager for real time intraoperative vascular patency evaluation in the setting of super-microsurgical vessel anastomosis.</p><p>Methods</p><p>A novel handheld imager Fourier domain Doppler optical coherence tomography based on a 1.3-µm central wavelength swept source for extravascular imaging was developed. The imager was minimized through the adoption of a 2.4-mm diameter microelectromechanical systems (MEMS) scanning mirror, additionally a 12.7-mm diameter lens system was designed and combined with the MEMS mirror to achieve a small form factor that optimize functionality as a handheld extravascular OCT imager. To evaluate <i>in-vivo</i> applicability, super-microsurgical vessel anastomosis was performed in a mouse femoral vessel cut and repair model employing conventional interrupted suture technique as well as a novel non-suture cuff technique. Vascular anastomosis patency after clinically successful repair was evaluated using the novel handheld OCT imager.</p><p>Results</p><p>With an adjustable lateral image field of view up to 1.5 mm by 1.5 mm, high-resolution simultaneous structural and flow imaging of the blood vessels were successfully acquired for BALB/C mouse after orthotopic hind limb transplantation using a non-suture cuff technique and BALB/C mouse after femoral artery anastomosis using a suture technique. We experimentally quantify the axial and lateral resolution of the OCT to be 12.6 µm in air and 17.5 µm respectively. The OCT has a sensitivity of 84 dB and sensitivity roll-off of 5.7 dB/mm over an imaging range of 5 mm. Imaging with a frame rate of 36 Hz for an image size of 1000(lateral)×512(axial) pixels using a 50,000 A-lines per second swept source was achieved. Quantitative vessel lumen patency, lumen narrowing and thrombosis analysis were performed based on acquired structure and Doppler images.</p><p>Conclusions</p><p>A miniature handheld OCT imager that can be used for intraoperative evaluation of microvascular anastomosis was successfully demonstrated.</p></div

Application of handheld probe in the mouse experiment.

<p>(a) Handheld probe investigating the surgical site of an experimented mouse; (b) Illustration of how the beam scans across the vessel region (red lines indicate that fast B-mode scanning beam, white arrow indicates slow beam scanning direction, yellow circles marks vessel groove to be implemented in our future probe optimization).</p

Handheld probe illustration.

<p>(a) Probe compared to a quarter coin (H: height 37.24 mm, W: width 32.43 mm, L: length 136.7 mm). (b) Optics layout inside the probe. (c) Image of the probe held by hand.</p

Selective frames of simultaneous structure and Doppler imaging of the surgical sites from distal (left) to proximal (right).

<p>White lines represent manually segmented blood vessel inner lumen, red lines represent manually segmented thrombosis, blue lines outline the blood flowing area within the vessel inner lumen. (a) Mouse 1 artery (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114215#pone.0114215.s002" target="_blank">Video S1</a>); (b) Mouse 1 vein (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114215#pone.0114215.s003" target="_blank">Video S2</a>) and (c) Mouse 2 artery (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114215#pone.0114215.s004" target="_blank">Video S3</a>). Videos were played back at 24 frames per second. Images were cropped to best fit the area of interest (scale bar: 500 µm, Doppler color bar range: −16.3 mm/s to 16.3 mm/s).</p