Liu Wenzhong, Yi Ji, Chen Siyu, Jiao Shuliang, Zhang Hao F
Department of Biomedical Engineering, Northwestern University, Evanston, Illinois 60208.
Department of Biomedical Engineering, Florida International University, Miami, Florida 33174.
Med Phys. 2015 Sep;42(9):5356-62. doi: 10.1118/1.4928597.
Doppler optical coherence tomography (OCT) is widely used for measuring retinal blood flow. Existing Doppler OCT methods require the eyeball axial length, in which empirical values are usually used. However, variations in the axial length can create a bias unaccounted for in the retinal blood flow measurement. The authors plan to develop a Doppler OCT method that can measure the total retinal blood flow rate without requiring the eyeball axial length.
The authors measured the retinal blood flow rate using a dual-ring scanning protocol. The small and large scanning rings entered the eye at different incident angles (small ring: 4°; large ring: 6°), focused on different locations on the retina, and detected the projected velocities/phase shifts along the probing beams. The authors calculated the ratio of the projected velocities between the two rings, and then used this ratio to estimate absolute flow velocity. The authors tested this method in both Intralipid phantoms and in vivo rats.
In the Intralipid flow phantom experiments, the preset and measured flow rates were consistent with the coefficient of determination as 0.97. Linear fitting between preset and measured flow rates determined the fitting slope as 1.07 and the intercept as -0.28. In in vivo rat experiments, the measured average total retinal blood flow was 7.02 ± 0.31 μl/min among four wild-type rats. The authors' measured flow rates were consistent with results in the literature.
By using a dual-ring scanning protocol with carefully controlled incident angle difference between the two scanning rings in Doppler OCT, the authors demonstrated that it is feasible to measure the absolute retinal blood flow without knowing the eyeball axial length.
多普勒光学相干断层扫描（OCT）被广泛用于测量视网膜血流。现有的多普勒OCT方法需要眼球的轴向长度，通常使用的是经验值。然而，轴向长度的变化会在视网膜血流测量中产生未被考虑的偏差。作者计划开发一种无需眼球轴向长度就能测量视网膜总血流率的多普勒OCT方法。
作者使用双环扫描协议测量视网膜血流率。小扫描环和大扫描环以不同的入射角进入眼睛（小环：4°；大环：6°），聚焦在视网膜的不同位置，并检测沿探测光束的投影速度/相移。作者计算了两个环之间投影速度的比值，然后用这个比值来估计绝对流速。作者在脂质乳剂模型和活体大鼠中测试了该方法。
在脂质乳剂血流模型实验中，预设流速和测量流速一致，决定系数为0.97。预设流速和测量流速之间的线性拟合确定拟合斜率为1.07，截距为-0.28。在活体大鼠实验中，四只野生型大鼠的视网膜平均总血流测量值为7.02±0.31μl/min。作者测量的流速与文献中的结果一致。
通过在多普勒OCT中使用双环扫描协议，并仔细控制两个扫描环之间的入射角差异，作者证明了在不知道眼球轴向长度的情况下测量绝对视网膜血流是可行的。
