The Grinding Imaging Reconstruction Instrument (GIRI) at Princeton University enables three-dimensional reconstructions of centimeter-scale samples that cannot be imaged using traditional x-ray computed tomography techniques.

GIRI consists of a computer numerical control surface grinder that has been retrofitted with a high resolution imaging stage. The system automatically removes material from the surface of a sample, takes an image, and repeats until the entire sample is ground away. The resulting image stack – which serves as a digital archive of the sample – is processed using a neural network that can accurately trace objects of interest after being trained by a researcher. Digital models of the isolated objects enable direct measurement of spatial statistics (e.g., porosity permeability, density, curvature, aspect ratio, etc.) without stereological corrections and/or prior assumptions about the underlying three-dimensional structure of a sample.