# Cooperative Three-View Imaging Optical Coherence Tomography for Intraoperative Vascular Evaluation
## Materials and Methods
### Optical Design of The Sample Arm  
To realize cooperative three-view imaging, optics of the sample arm were designed to meet the following three main performance specifications. First, there should be a synthetic 3 mm \(\times\) 3 mm square shape FOV to accommodate different tube structures within a diameter of 3 mm. The size of the synthetic FOV can be changed depending on the application requirement. Here a 3 mm \(\times\) 3 mm FOV is designed to meet the imaging demand of most of the vessel sizes in clinical reconstructive surgery. Second, the optical scanning segment line for each individual view at its focal plane should lie on the same plane to guarantee cross-sectional imaging for the same sample position. Third, to form the image at the same position relative to the reference beam of OCT, the optical path length (OPL) of each individual view should be the same from the sample arm collimator to its focal plane. The optical setup of the cooperative three-view imaging sample arm is shown in Figure 2A. It was designed and optimized in Zemax (Radiant Zemax LLC, Redmond, WA, USA). Light from the sample arm is transmitted through a single-mode fiber. A laser beam then passes through a collimator (F220 APC, Thorlabs, Newton, NJ, USA), and a two-axis galvanometer scanner (GVSM002, Thorlabs, Newton, NJ, USA) is used to perform beam scanning. The center of the galvanometer scanner is placed at the focal plane of one pair of achromatic doublets (AC254-150-C, \(\Phi\)25.4 mm, Thorlabs, Newton, NJ, USA). Then the scanning beam perpendicularly emerged from the Mirror1 and was split into three parts. A cylindrical WavePlate2 with a diameter of 25.4 mm, thickness of 14 mm and an 8 mm \(\times\) 8 mm square hole in the center was used to shift the focal plane of the side views backward by 6 mm. In this configuration, the sample can be imaged at the ideal imaging position of each view, which is near the focal plane of each view when the reference position is fixed. Eventually, a 3 mm \(\times\) 3 mm rectangular scanning area was constructed by adjusting the position of the Mirror2 and Mirror3. A 22.5 mm long customized wedge WavePlate1 shown in Figure 2B was designed to match the OPL of the three individual imaging paths. The front surface size of waveplate1 is 12 mm \(\times\) 4 mm while the back surface of waveplate1 is 12 mm \(\times\) 6 mm. A customized waveplate shown in Figure 2B,C were manufactured using N-SF6 HT material (C.F. Technology, Beijing, China) working at a bandwidth of 1020 nm-1390 nm. Surfaces of the waveplate were coated with an antireflection coating. Figure 1: The principle of cooperative three-view imaging. The initial lateral scanning range is \(L\), and the synthetic FOV height and width is \(a\) and \(b\) respectively. Two focal planes (FP1 and FP2) are shifted to be \(H\) apart. Two 45\({}^{\circ}\) oriented folding mirrors (M1 and M2) are used to deflect the scanning beam to form the left and right view. Positions of the focused scanning spots at the focal plane for left view, right view, and central view at different slow axis scanning angles based on Zemax simulations are shown in Figure 3. From Figure 3 we can clearly see that the focused scanning spots from three views lie almost on the same line. It will keep cross-sectional images of the sample from different views on the same plane, which is easier for poster image registration. Figure 4 shows the spot diagrams on the image plane for the sample arm. The maximum radial field angle (6.4\({}^{\circ}\) and 1.2\({}^{\circ}\)) of the scanner in XY-directions corresponds a rectangle FOV of \(12\:\mathrm{mm}\times 3\:\mathrm{mm}\) and each scanning area has a 3 mm \(\times\) 3 mm square FOV. The optic design was optimized in Zemax to achieve a near-diffraction limited resolution of 12 \(\upmu\)m. An airy disk is marked out with blue circles on the spot diagrams. Figure 3: Focused spots of the left view (LV), central view (CV) and right view (RV)of the scanning line on the focal plane for different slow-axis scanning angles.