Velocity Analysis by Using Doppler Fourier Domain Optical Coherence Tomography with Variable Reference Length

The measurement of blood flow is important in studying the pathophysiology and treatment of several diseases of blood vessels, like atherosclerosis. We present a method for flow measurement using resonant Doppler imaging with spectrometer based Fourier Domain Optical Coherence Tomography (FD-OCT). A modified Michelson interferometer, integrated in a 3D scanner head, with a variable reference length is used to determine velocities. Two methods are applied where cross-sectional images (B-scans) are taken while the reference arm for each depth scan (A-scan) has different states. In the 2-state method the reference mirror is moving axial towards respectively backwards in successive A-scans. In the 3-state method the velocity is changed and a third state with a constant reference length is appended. The change in reference length is realized by a piezo actuator. The velocities can be calculated from the phase information as well as from the intensity information of the complex A-scans. It is shown that the ambiguity velocity range depends on the number of used reference arm states. The velocity range in the 3-state method is twice the range of the 2-state method. The system was tested by measuring the velocity of an electrically exited loud speaker membrane with an attached gold mirror. Flow measurements were taken with a 1 % Intralipid emulsion flowing threw a capillary. The results of the two methods where phase and intensity are analyzed are compared to the expected velocity profile. We expect the velocity range of resonant Doppler FD OCT measurements is arbitrary extendable by using more reverence arm states while the algorithm for analyzing phase and intensity information is getting more complicated. With the extended velocity range Doppler FD OCT can be used for more applications.