# Cooperative Three-View Imaging Optical Coherence Tomography for Intraoperative Vascular Evaluation
## 3 Results  
### Phantom Imaging  
We first evaluated our system for plastic tube phantom imaging. Before showing the results, it is necessary to show how to interpret the imaging results. Figure 7 illustrates the original B-mode image from cooperative three-view scanning. The red box in the top of Figure 7 is the left view image, the blue box shows the central view imaging while the yellow box shows the right view image. To place the left view image in the correct physical position as in the bottom of Figure 7, the red box should be flipped left to right and rotated 90\({}^{\circ}\) anti-clockwise. To place the right view image in the correct physical position as in the bottom-left of Figure 7, the yellow box should be flipped left to right and rotated 90\({}^{\circ}\) clock-wise. The reason behind these operations is that the left view beam scans from top to bottom and right view beam scans from bottom to top when beams are folded.  
Figure 7: Typical B-mode image from cooperative three-view imaging and its operation to place three individual view into correct physical position. Left, right and central view image are marked out by red, yellow and blue boxes respectively.  
To demonstrate the capability of the system for tube imaging with different sizes, we imaged phantom tubes with outer diameters of 1 mm, 2.0 mm, and 2.5 mm, respectively. The inner wall of the tube was modified by filling certain plastic clay in the tube to mimic a thrombosis structure in blood vessels and the flow was simulated by milk flow pumped at different rates. The results are shown in Figure 8A-C. We can clearly see the left, central, and right view of the sample in each B-mode image. Between the image zones of each individual view, there are mirror holder margins that separate the threeview images.  
From Figure 8 we can see that when the outer diameter of the tube goes beyond 2 mm, it became impossible for each single view to resolve the whole tube cross-sectional structure. Bottom information of the tube for each view was missing due to the limited penetration depth, which will be a problem for conventional single view imaging OCT systems.  
The initial B-mode image needed to be processed to construct the synthetic cross-sectional image of the sample, which included horizontal and lateral scale matching and image registration. Figure 9A-D show the results of image horizontal and lateral scale matching for four selective B-mode images of a 1.8 mm outer diameter tube at different positions within a C-mode imaging. The top row of the figure is the initial B-mode image where the area of interest is marked out by a dashed red rectangular. The bottom row of the figure shows the results after scale matching.  
After image scale matching, images from three views were manually registered. A MATLAB graphics user interface (GUI) was developed to realize the manual registration process based on the weighted average fusion algorithm. First, left, right, and top view images needed to be cropped out from one single B-mode frame. Then, the left and right view images were rotated and scaled to the same scale and coordinates as that of top view image. Then the left and right view images were shifted rigidly for registration. Figure 10A shows the _en-face_ image generated by summing the volume in the axial direction. We can see that the tube structure in the groove under the central view and the projections from left and right views are reflected through the 45\({}^{\circ}\) mirrors. Figure 10B-E are the synthesized whole-view cross-sectional images of the tube based on Figure 9A-D, respectively,  
Figure 8: Cooperative three-view imaging of phantom tubes with different outer diameters (**A**) 1 mm, (**B**) 2 mm, and (**C**) 2.5 mm, respectively.  
corresponding to the dashed line marked in Figure 10A. We can see clearly that the synthesized whole-view image contains all the information from each view and has effectively solved the problem of information missing in each individual view due to limited penetration depth.