The following overview is excerpted from: Ketcham, R.A., and Iturrino, G.J. (2005) Nondestructive high-resolution visualization and measurement of anisotropic effective porosity in complex lithologies using high-resolution X-ray computed tomography. Journal of Hydrology, 302, 92-106.
Align3D is a collection of IDL routines that implement a three-dimensional alignment and subtraction of two HRXCT data sets, also known as “subtraction analysis.” If a sample is scanned twice in different states, once dry and once saturated with a fluid, the difference between the two data sets corresponds to the location of fluid in the second scan. This in turn reveals the interconnected, or “effective” porosity of the sample. A uniquely powerful aspect of this analysis is that it provides the porosity in each data voxel as a fractional value (i.e. from 0 to 100%), and provides essentially limitless resolution: even micro-pores far smaller than the resolution of the CT data are reflected in the fractional porosity data. The three-dimensional effective porosity map provided by this analysis can be used to gain insight into the rock and mineral structures behind permeability and flow characteristics. It also opens the possibility of determining the three-dimensional anisotropy of permeability. The HRXCT analysis is essentially non-destructive, as any fluid, including distilled water or groundwater in equilibrium with the sample material, can be employed.
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Papers Utilizing Align3D
Gipps, P., & Gu, K. (1999) Some experience with geospatial imagery and route optimization. Transportation Research Record: Journal of the Transportation Research Board, 143-152.
Ketcham, R.A., and Iturrino, G.J. (2005) Nondestructive high-resolution visualization and measurement of anisotropic effective porosity in complex lithologies using high-resolution X-ray computed tomography. Journal of Hydrology, 302, 92-106. Supplemental material: http://www.ctlab.geo.utexas.edu/pubs/ketcham&iturrino/k&i.htm
Rowe, T. B., Luo, Z. X., Ketcham, R. A., Maisano, J. A., & Colbert, M. W. (2016) X-ray computed tomography datasets for forensic analysis of vertebrate fossils. Scientific data, 3, 160040.