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Background: Acute tubular necrosis (ATN) after renal ischemia-reperfusion would cause the loss of functional units in the kidney, that are usually used to characterize the activity of the kidney. Apparently, ATN will lead to uneven distribution of uriniferous tubules. The renal activity could be evaluated by analyzing the uniformity of renal tubular distribution. Methods: Optical coherence tomography (OCT) has been proved to have the ability of imaging the microstructure of kidney in vivo and in real time. Based on the renal ischemia-reperfusion model of Wistar rats described in previous studies, kidneys of three Wistar rats were ischemia for 75 minutes and reperfused for one and a half hour. The normal kidney before ischemia and every 5 minutes after blood reperfusion were imaged using a SDOCT system in 3D mode in vivo. Inhomogeneous distribution of tubules could be clearly observed in the en face OCT images of kidney after blood reperfusion. Box dimension based on fractal theory can be used to evaluate the uniformity of object distribution. This paper applied box dimension to assess the uniformity of renal tubular distribution in OCT images of kidney. The fractal dimension of en face OCT images at the same depth below the renal capsule were calculated using Fractal box count toolbox in ImageJ. Results: The results showed that the box dimensions of OCT kidney images changed a lot at different times of ischemia-reperfusion process. The value was largest for normal kidney, and reached a minimum when ischemia, then gradually increased to a stable value after reperfusion. Therefore, the fractal box dimension value could be applied to assess the status of kidney. Conclusion: The renal tubular uniformity featured by fractal box dimension of OCT images could be used to evaluate the renal ischemia - reperfusion injury.
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