# Cooperative Three-View Imaging Optical Coherence Tomography for Intraoperative Vascular Evaluation
## 3 Results
### Rat Femoral Artery Imaging  
We further evaluated our cooperative three-view imaging method for in vivo rat femoral artery inspection. A segment of the femoral artery was exposed and placed on the micro stage for imaging. Figure 10: **(A)**_en-face_ OCT image of a diameter of 1.8 mm tube; (**B–E**) show the results of image registration based the pixel weighted averaging algorithm. Figure 9: Results of horizontal and lateral scale matching for B-mode images of a 1.8 mm outer diameter tube at four different positions (**A–D**). Red dashed rectangles mark the regions that are selected and processed. The top parts of Figure 11A,B show the initial B-mode images of the femoral artery at two different locations. The bottom parts of Figure 11A,B show the vessel after image scale matching and rotation. The average outer diameter of the artery was measured to be 0.9 mm. Due to the strong scattering and absorption effect of blood, it is impossible for any single view to resolve the bottom structure of the vessel. As the diameter of the vessel goes up, the problem becomes more severe. However, with cooperative three-view imaging circumferential structure information of the vessel can be obtained within one fast B-mode scan from outer wall to the center. During intraoperative imaging, the thrombosis structure attached to the inner wall of vessel is important to visualize. Extravascular circumferential imaging can help get as much the thrombosis structure information as possible. Since thrombosis grows on the inner vessel wall, in each single view when the vessel is investigated from outside to inside, the vessel wall and thrombosis structure can be visualized before reaching the limited imaging penetration depth. Although the shadowing effect of blood will cause the bottom vessel wall and thrombosis information to be missing in each individual view, part of the missing information can be resolved in the other two complementary views. Figure 12A shows the _en-face_ image of the vessel imaged. We can clearly see the vessel projections in each view. In addition, utilization of the micro stage for vessel placement during the imaging can effectively remove motion artifacts caused by sample movement in the images. Figure 12B,C show the synthesized whole view cross-sectional image at the blue dashed line and green dashed line, respectively, in Figure 12A. Whole vessel information has been depicted clearly in Figure 12B,C. One thing that needs to be pointed out is that although we tested our method on blood vessel samples, this method holds the potential to be extended to other tubular structures that requires circumferential imaging, such as lymph vessels and nerve fiber tracts when limited penetration depth is an issue. Figure 11: Cross-sectional structure images of rat femoral artery at two different positions (**A**) and (**B**). Figure 12: (**A**) _en-face_ OCT image of the rat femoral artery with a diameter of 0.9 mm; (**B**) Synthetic image of the blue line position in (**A**); (**C**) Synthetic image of the green line position in (**A**). We have demonstrated the structure imaging capability of our proposed cooperative three-view imaging for both phantom tubes and a rat vessel. On the other hand, flowing imaging is also of interest for intraoperative applications. However, to perform the phase-resolved Doppler imaging, the sampling distance between adjacent A-scans needs to be comparably smaller than the system optical lateral resolution. During previous in vivo imaging experiments, the number of A-scans in a single B-mode image was set at 1000 to achieve a fast imaging frame rate, which made the sampling distance in the lateral direction 12 \(\upmu\)m. Since 12 \(\upmu\)m was close to the lateral optical resolution, Doppler flow images were not reliable. We set the number of A-scans in one B-mode image as 4000 to meet the oversampling requirement here to evaluate the Doppler flow imaging capability.