A concise algorithm for detection of vibration from Fourier domain OCT

Optical interferometry using Fourier domain OCT (FD-OCT) can image structures using vibration as the contrast mechanism. An A-scan measurement of light reflected from a tissue at a position x,y yields an intensity spectrum, I(λ), which is sequentially acquired over a short time period, 88 ms, to yield 1000 spectra at equally spaced time points, I(λ,t), while an audio frequency of sound pressure is imparted to the tissue to induce vibration. Analysis converts I(λ,t) into displacement Δz(z,t) of tissue structures along the z axis. Fourier analysis converts Δz(t) at each z into a vibration spectrum, and the amplitude of vibration at the driving audio frequency is specified. This process is repeated for each x position at a given y, to yield an image of vibration amplitude, A(z,x) [nm]. Hence, vibration amplitude becomes the contrast mechanism. This method is not a new idea, but a derivative of Doppler OCT. This report simply provides a concise algorithm in MATLAB for students wishing to implement vibration measurements using FD-OCT. An example shows the vibration of the ossicles of the middle ear viewed through the intact tympanic membrane.