An image of a mouse kidney, entitled “Kidney Rainbow,” is the winner of the second annual Biomed Central (BMC) “Research in Progress” photo competition. From microscopy images to researchers at work, this year’s competition received more than 350 submissions reflecting the innovative spirit, curiosity, and integrity of researchers around the world. The winning image by Nian Wang at the Center for In Vivo Microscopy, Duke University, was obtained by diffusion tensor imaging, an MRI-based imaging technique. The bright neon colors represent the orientation of different tubules, which collect filtrate from blood passing through the kidney and process it into urine. Higher-order diffusion magnetic resonance imaging (MRI) is a noninvasive imaging technique that makes it possible to estimate the location, orientation, and anisotropy of the tubular tracts in the kidney. With high spatial and angular resolution, the track density image of the kidney is obtained at 10-μm isotropic resolution. The colors stand for the different orientation of the tubules. Courtesy of Nian Wang, Center for In Vivo Microscopy, Duke University. A total of 15 images — the winner, the runner-up, two highly commended, and 11 special mentions — were chosen for their visual appeal, as well as originality, photo quality, creativity, and composition. All images are open access and available under a Creative Commons Attribution 4.0 International license. To view the 15 images, visit the BMC blog.