Update 3d_microstructure.md

3d_microstructure.md

 #### Front page image
 
 <div align="center"><a href="homepage.md"><img src="images/result_final_470x940.png" alt="Volume of peripheral nerves with thickness colored."/></a></div>
+<div align="center">Illustration in 470x940 pixels. Image shows volume of peripheral nerves with thickness colored.</div>
 
 <div align="center"><a href="homepage.md"><img src="images/result_final_230x460.png" alt="Volume of peripheral nerves with thickness colored."/></a></div>
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+<div align="center">Illustration in 230x460 pixels. Image shows volume of peripheral nerves with thickness colored.</div>
 
 # Analysis of 3D Microscopy Images
 **3D image analysis is a core research area within the [Visual Computing section](https://lab.compute.dtu.dk/abda/image-section-homepage/-/blob/master/homepage.md) at [DTU Compute](https://www.compute.dtu.dk/). Our research ambition is to investigate and develop new methods for 3D image analysis for fast and accurate quantification of 3D structures. The purpose is to contribute to futher advancing 3D imaging as a reliable tool for measuring microstructure. Our research is in close collaboration with scientists developing and using 3D imaging. Therefore, we focus on methods that can handle large images.**