For instance, a number of radiographs reduced to a few hundreds can decrease acquisition down to 50 ms. The time lapse between two image acquisitions is limited by the exposure time and the number of radiographs taken, in relation with the sample composition (highly absorbent materials require a longer exposure time) and the desired quality of the reconstructed volume (a lower number of radiographs increases artifacts).
Dynamic acquisition, e.g., high-frequency time-lapse acquisition, involves continuous imaging of the sample, a technique also called X-ray tomoscopy. In addition, it greatly reduces artifacts inherent to motion of fluids previously encountered. Fast tomography imaging provides direct visualization to rapidly evolving or unstable systems, such as flowing fluids (liquid, gas) or reacting components. Depending on these constraints, imaging is performed either in situ or ex situ using specifically designed setups to control flow, temperature, and pressure (see Section 2).
In the latter case, the time step, ranging from a few seconds to minutes, corresponds to the acquisition duration of the whole set of radiographs. Time-lapse imaging involves imaging at discrete time steps, e.g., hours, days or months, during the process, whereas real-time imaging involves fast and continuous imaging. The sample is imaged repetitively during dynamic processes at discrete time steps that vary according to: (i) the rate of the process, and (ii) the duration necessary to record a set of radiographs. In particular, improvements in optics and detectors, and increasing computational power and data storage have initiated the progressive transition from 3D geometry imaging to 4D time-lapse imaging and 4D real-time imaging, also called dynamic imaging or 4D XMT. Īdvances in 3rd generation synchrotron facilities in the 1990’s and in laboratory systems more recently have opened and increased the access of the technique to various research domains. Specific reviews are dedicated to pore-scale flow, reactive transport, structural geology and rock mechanics, high pressure science and dynamic processes in geologic systems. Useful information about the XMT technique and fields of geosciences explored are reviewed in a fruitful and exhaustive list of articles. Additional information about the sample mineralogy, chemical composition or phase identification can be obtained by coupling XMT to X-ray diffraction imaging, X-ray fluorescence imaging, dual-energy or spectral imaging near the absorption edge, or by using specific XMT imaging setup like phase-contrast, holotomography or grating interferometry. Every voxel in the reconstructed volume represents the linear average X-ray attenuation coefficient ? ¯ T ( E ) of the different phases contained in this volume element.
Spacechem no thanks necessary series#
The development of XMT relies on three-dimensional (3D) reconstruction of the internal and external structure of a sample from a series of two-dimensional (2D) radiographs taken at different rotation angles. The technique is based on the attenuation of X-rays crossing a sample, which depends on the X-ray energy and on the atomic composition and density of the material under investigation. X-ray micro-tomography (XMT) imaging has unraveled the complex structure of many geological materials for 30 years. Here, we review recent advances in 4D X-ray micro-tomography applied to thermo-hydro-mechano-chemical (THMC) sub-surface processes where fluids, porosity, minerals, and rock microstructures evolve together. Image processing allows for tracking the evolution of the fluid–fluid or fluid–mineral interfaces as well as measuring incremental deformations, as rocks deform and react through time under in situ conditions of the sub-surface. The technique is increasingly used to explore dynamic processes in porous and fractured rocks, thanks to synchrotron sources and laboratory XMT scanners, new generations of detectors, and increasing computational power. time, to the three-dimensional spatial visualization of rock and mineral microstructures. X-ray micro-tomography (XMT), as a non-invasive and non-destructive imaging technique, offers an unprecedented opportunity to add the fourth dimension, i.e. From crystal shape to rock microstructure or pore space and fluid distribution, parameters characterizing the rock physico-chemical properties evolve at different time and spatial scales. The dynamic response of rocks to thermal, hydrodynamical, mechanical, and geochemical solicitations is of fundamental interest in several disciplines of geosciences, including geo-engineering, geophysics, rock physics, hydrology, mineralogy, and environmental and soil sciences.