# Cooperative Three-View Imaging Optical Coherence Tomography for Intraoperative Vascular Evaluation
## 1 Introduction  
Vascular anastomosis is a common surgical procedure that connects two blood vessels in various surgical subspecialties. It is considered as the foundation for reconstructive microsurgery, vascular surgery and transplant surgery [1]. Postoperative evaluation of the surgical outcome requires objective assessment of the vessel lumen patency, flow restoration status and thrombosis morphology of the anastomosed vessel site instead of surgeon's subjective judgement and accumulated experience over the years [2]. Different methods have been developed to provide the objective evaluation of the vessel status, such as skin surface temperature measurement, transcutaneous oxygen measurement, laser Doppler flowmeters, implantable Doppler monitoring, transit-time flow monitoring, and intraoperative angiography [2; 3; 4; 5]. However, these methods lack the direct imaging capability of the anastomosed vessel site. Optical coherence tomography is a noninvasive optical imaging modality that can provide high-speed, high-resolution, three-dimensional images of biological samples [6]. Ever since its invention,it has been widely used for diagnosis, therapy monitoring, and ranging [7; 8; 9; 10; 11; 12; 13]. Combined with Doppler flow sensing principle, phase resolved Doppler OCT (PRDOCT) was developed to get the sample structure and flow information simultaneously [14]. Blood flow restoration, 3D thrombosis morphology and stenosis information thus can thus be acquired objectively and quickly using OCT [15; 16]. A real-time, detailed imaging methodology of the vasculature after anastomosis procedures can significantly affect patient outcomes [17]. In our past work, we have demonstrated the unique advantages and potential of PRDOCT imaging as the intraoperative evaluation method for vascular anastomosis [2; 18; 19]. However, the capability of PRDOCT imaging to visualize large vessels is significantly reduced by the limited penetration depth of light in blood vessels. Although using longer wavelength for imaging such as 1.3 \(\upmu\)m band light can get a larger penetration depth, there are still problems for vessels with inner diameter larger than 0.5 mm due to the strong scattering and absorption of blood within the vessel tunnel [18]. One consequent issue is that OCT images can only show the partial outer area of the vessel, which results in an incomplete cross-sectional view of the vessel under investigation. Various methods have been proposed to increase the effective FOV of OCT images. The multi-angle oblique OCT technique combines OCT images from multiple 3D scan volumes to form one single volume that contains the missing part in each individual volume scanning [20]. However, this method requires multiple 3D volume scans that takes more scanning time and complicated restoration algorithms to form the final volume. Rotational imaging OCT (RI-OCT) was proposed for mouse embryonic study [21]. In RI-OCT, a mouse embryo was placed on a rotational stage. By registering OCT images of the embryo at different controlled angles, a whole embryo cross-sectional image was generated. Sample rotation is required in RI-OCT, which is impossible for intraoperative vessel imaging applications. Recently, a long-range and wide FOV OCT has been developed based on an akinetic programmable swept source [22]. Promising as it is, the limited physical penetration depth of light into blood cannot be solved. In this work, we propose a cooperative three-view imaging optical coherence tomography to increase the effective FOV. Taking advantages of the tubular structure of vessel that are exposed during the surgery, we add two extra left and right views for image scanning compared to conventional OCT one view scanning. The vessel is placed at the middle of the top, left and right imaging views. By dividing the conventional scanning OCT line into three parts and shifting the focal plane of the left and right part via customized waveplate and folding mirror, an extra left and right view are achieved.