Optical Coherence Tomography Enables the Depth-Resolved Measurement of Cilia Beat Frequency in Ex Vivo Human...

The movement of cilia in the fallopian tubes (FTs) facilitates important processes involved in fertility, and abnormalities in cilia function are linked with diseases including endometriosis and pelvic inflammatory disease. For the first time, we demonstrate the use of optical coherence tomography (OCT) to create depth-resolved mapping of motile cilia locations and quantify cilia beat frequency (CBF) in human FT samples ex vivo.

Segments of the FT ampulla were acquired from five patients following salpingectomy under an IRB approved protocol. The samples were longitudinally opened to expose the luminal surface for imaging. A sequence of at least 500 OCT images were acquired at 5-10 locations on each sample. To define the location of the motile cilia in the images, pixel-wise Fast Fourier Transform (FFT) analysis of intensity fluctuations with a sliding temporal window was performed on each image sequence. The frequencies corresponding to the physiological range of CBF (2-10 Hz) were selected for mapping, while the part of the FFT spectrum at higher frequencies (> 23 Hz) was used to define the noise threshold. The frequency with the highest FFT amplitude for each supra-threshold pixel was considered the CBF for this pixel and used to create a color-coded CBF map. The CBF map was overlaid with the OCT intensity image sequences to reveal cilia locations. Frequency histograms from the sliding window were examined to assess temporal consistency of the mapping and evaluate movement artifacts.

OCT image sequences clearly showed the structure of FT plicae. The ciliated epithelium was obvious as a "shimmering" (rapidly changing intensity) layer atop plicae. Colored pixels on CBF maps visually aligned to these shimmering regions. Frequency histograms revealed that the image sequence peak CBF could be robustly determined, even in the presence of outliers attributable to table vibrations or bulk sample movement.

OCT can provide depth-resolved maps of CBF in human ex vivo FT tissue. Potentially, this technique can aid in understanding cilia dynamics in the normal human FT over the menstrual cycle and across age, as well as in diseases that affect the FTs. Future work will be directed toward in vivo implementation including miniaturization and robust motion compensation.