## 4 Experimental Results  
### LR-DOCT with 1% Intralipid Flow  
In order to validate LR-DOCT for moving volume scatterers, Doppler flow experiments are performed by means of a 1% Intralipid emulsion flowing through a glass capillary, as described in Section 3.1. The Doppler angle is 1.7\({}^{\circ}\) and the maximum flow velocity at the capillary center is estimated to be 69 mm/s. Thus, the transverse displacement \(\delta x\) of the flowing oil particles of the Intralipid emulsion amounts to 0.6 for the case of the detected M-scan, which strongly reduces the phase correlation [20; 21; 27]. Figure 6 presents the processed flow-relevant parts of the grayscale structural (a) and the Doppler flow images (b) of the detected M-scan, the forward lateral (FL) and the backward lateral (BL) B-scans differing in the speckle pattern, and the resulting Doppler phase shift. The number of analyzed A-scans is chosen to be 512. As expected, highly correlated speckle appears at the capillary border for the M-scan due to the small flow velocity in this area. For the FL-scan, the \(X\)-galvanometer scanner velocity is set to 69 mm/s, which corresponds to the transverse velocity component of the Intralipid flow at the capillary center. In this case, the correlation at the border area gets lost, whereas a high correlation occurs at a wide range of the capillary lumen identified by the elongated speckle pattern. In contrast, the speckle seems to be uncorrelated for the case of the BL-scan, where the \(X\)-scanner is moved in the opposite direction at 69 mm/s. The visual assessment of the Doppler images in Figure 6b suggests a high noise of the Doppler phase shift at the capillary center in the M-scan, at the capillary border in the FL-scan, and over the entire capillary lumen in the BL-scan, which is caused by the reduced correlation of adjacent A-scans. As predicted in Section 2.2, the phase-sensitive image of the BL-scan visually shows the highest noise of the Doppler phase shift. For the quantification of the phase correlation, the correlation quotient \(CQ\), defined in former research [20; 21], is calculated as a function of \(z\) and is overlaid in color on the structural images, as presented in Figure 6c. \(CQ\) is shown in red for the highest correlation between consecutive A-scans. The results of \(CQ\) prove the suggestions made by the observed speckle patterns in Figure 6a and the estimated phase shift noise in Figure 6b. Additionally, the standard deviation of the mean Doppler phase shift is given in Figure 6d. As described in previous studies [20; 21; 27], the distribution of \(\Delta\varphi\) cannot be worse than isotropic in the original interval of \([-\pi,\pi]\), resulting in an upper limit of \(\pi/\surd 3\), as shown by the red color of the \(\sigma_{\Delta\varphi}\) scale bar. By means of the colored structural information for visualizing \(\Delta\varphi\), \(CQ\), and \(\sigma_{\Delta\varphi}\), the possibility to laterally track the flowing oil particles  
Figure 6: (**a**) Grayscale structural SD-OCT images of the M-scan, the forward (FL-scan) and backward lateral Doppler scan (BL-scan) of the 1% Intralipid flow through a 312 μm glass capillary. (**b**) Corresponding phase-resolved Doppler flow images for the measured Doppler angle \(\vartheta\) of 1.7\({}^{\circ}\). (**c**) Colored correlation images representing the correlation quotient \(CQ\) in accordance to [20; 21]. (**d**) Standard deviation \(\sigma_{\Delta\varphi}\) of the mean Doppler phase shift of 512 single A-scans overlaid to the structural images. with a simultaneous decrease of the phase shift noise for small Doppler angles and high flow velocities, becomes apparent. For quantitative analysis, the averaged phase shift of 512 single measurement points is calculated, as described in Equation (4) and presented in Figure 7a. The measured \(\Delta\varphi\) of the M-scan shown by the blue points does not display a quadratic profile, verified by the fitted power law with an exponent of 2.4.