Significance: Speckle variation induced by intracellular motion (IM) in the urothelium was observed in optical coherence tomography (OCT) images. IM can be used as a dynamic contrast to segment the urothelium by comparing two sequential OCT images. This method opens the possibility of specifically tracking the distribution of urothelial cancerous cells for identifying the microinvasion of bladder tumors.
Approach: OCT images were acquired ex vivo with fresh porcine bladder tissue. IM was analyzed by tracking speckle variation using autocorrelation function, then quantified with constrained regularization method for inverting data (CONTIN method) to identify the decorrelation time (DT) of the speckle variations. Variance analysis was also conducted to show IM amplitude and distribution in the urothelium. The segmentation of the urothelium was demonstrated with OCT images with a visible urothelial layer and OCT images with an invisible urothelial layer.
Results: Significant speckle variation induced by IM was observed in the urothelium. However, the distribution of the IM is heterogeneous. The DTs are mostly concentrated between 1 and 30 ms. With the IM as a dynamic contrast, the urothelium can be accurately and exclusively segmented, even the urothelial layer is invisible in normal OCT images.
Conclusions: IM can be used as a dynamic contrast to exclusively track urothelial cell distribution. This contrast may provide a new mechanism for OCT to image the invasion depth and pattern of urothelial cancerous cells for accurately substaging of bladder cancer.
Intracellular motion (IM) is originated from the motion of molecules and organelles in the cytoplasm of eukaryotic cells. IM is essential for the proper functioning of cells. Instead of tracking specific molecules, coherent gated methods measure the speckle variation induced by IM. Initially, holographic optical coherence imaging was used to image the IM of tumor spheroids and drugs' responses1,2 . Later on, with optical coherence tomography (OCT), IM has been used as an endogenous contrast to reveal the cellular and subcellular structures with freshly excised tissue. The uniqueness of the coherent gated method is that it can detect IM at different depths without requiring fluorescence tagging. Therefore, the imaged objects can stay at a more natural status.
The bladder urothelium is usually considered as an impermeable barrier to urine, but recent reports pointed that it was not only a passive impermeable membrane but also has some sensory and signaling functions. While aquaporin expression has been found in the urothelium, which implicits water transportation through the urothelium, it has never been observed directly the process of water transportation through the urothelium. We describe here for first time how water is transported through the urothelium through osmosis.
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