X-ray microtomography

The fan-beam system is based on a one-dimensional (1D) X-ray detector and an electronic X-ray source, creating 2D cross-sections of the object. Typically used in human computed tomography systems.

The cone-beam system is based on a 2D X-ray detector (camera) and an electronic X-ray source, creating projection images that later will be used to reconstruct the image cross-sections.

In an open system, X-rays may escape or leak out, thus the operator must stay behind a shield, have special protective clothing, or operate the scanner from a distance or a different room. Typical examples of these scanners are the human versions, or designed for big objects.

In a closed system, X-ray shielding is put around the scanner so the operator can put the scanner on a desk or special table. Although the scanner is shielded, care must be taken and the operator usually carries a dosimeter, since X-rays have a tendency to be absorbed by metal and then re-emitted like an antenna. Although a typical scanner will produce a relatively harmless volume of X-rays, repeated scannings in a short timeframe could pose a danger. Digital detectors with small pixel pitches and micro-focus x-ray tubes are usually employed to yield in high resolution images.[6]

Closed systems tend to become very heavy because lead is used to shield the X-rays. Therefore, the smaller scanners only have a small space for samples.

Because microtomography scanners offer isotropic, or near isotropic, resolution, display of images does not need to be restricted to the conventional axial images. Instead, it is possible for a software program to build a volume by 'stacking' the individual slices one on top of the other. The program may then display the volume in an alternative manner.[7]

For X-ray microtomography, powerful open source software is available, such as the ASTRA toolbox.[8][9] The ASTRA Toolbox is a MATLAB and python toolbox of high-performance GPU primitives for 2D and 3D tomography, from 2009 to 2014 developed by iMinds-Vision Lab, University of Antwerp and since 2014 jointly developed by iMinds-VisionLab, UAntwerpen and CWI, Amsterdam. The toolbox supports parallel, fan, and cone beam, with highly flexible source/detector positioning. A large number of reconstruction algorithms are available, including FBP, ART, SIRT, SART, CGLS.[10]

For 3D visualization, tomviz is a popular open-source tool for tomography.

Volume rendering is a technique used to display a 2D projection of a 3D discretely sampled data set, as produced by a microtomography scanner. Usually these are acquired in a regular pattern, e.g., one slice every millimeter, and usually have a regular number of image pixels in a regular pattern. This is an example of a regular volumetric grid, with each volume element, or voxel represented by a single value that is obtained by sampling the immediate area surrounding the voxel.

Where different structures have similar threshold density, it can become impossible to separate them simply by adjusting volume rendering parameters. The solution is called segmentation, a manual or automatic procedure that can remove the unwanted structures from the image[11].[12]

• Reconstructing fire-damaged artifacts, such as the En-Gedi Scroll and Herculaneum papyri
• Unpacking cuneiform tablets wrapped in clay envelopes[13] and clay tokens

• Both in vitro and in vivo small animal imaging
• Neurons[14]
• Human skin samples
• Bone samples, including teeth,[15] ranging in size from rodents to human biopsies
• Lung imaging using respiratory gating
• Cardiovascular imaging using cardiac gating
• Imaging of the human eye, ocular microstructures and tumors[16]
• Tumor imaging (may require contrast agents)
• Soft tissue imaging[17]
• Insects[18] – Insect development[19][20]
• Parasitology – migration of parasites,[21] parasite morphology[22][23]
• Tablet consistency checks[24]

Developmental biology

• Tracing the development of the extinct Tasmanian tiger during growth in the pouch[25]
• Model and non-model organisms (elephants,[26] zebrafish,[27] and whales[28])

• Small electronic components. E.g. DRAM IC in plastic case.

• Spray nozzle

• Ceramics and Ceramic–Metal composites.[1] Microstructural analysis and failure investigation
• Composite material with glass fibers 10 to 12 micrometres in diameter

• Plastic foam

• Detecting defects in a diamond and finding the best way to cut it.

• 3-D imaging of foods[29]
• Analysing heat and drought stress on food crops[30]
• Bubble detection in squeaky cheese[31]

• Piece of wood to visualize year periodicity and cell structure

• Concrete after loading

In geology it is used to analyze micro pores in the reservoir rocks[32][33], it can used in microfacies analysis for sequence stratigraphy. In petroleum exploration it is used to model the petroleum flow under micro pores and nano particles.

It can give a resolution up to 1 nm.

• Sandstone
• Porosity and flow studies[34][35]

• Vertebrates
• Invertebrates[36]

X-ray microtomography of a radiolarian, Triplococcus acanthicus

This is a microfossil from the Middle Ordovician with four nested spheres. The innermost sphere is highlighted red. Each segment is shown at the same scale.[37]

• Benthonic foraminifers

• Digitally unfolding letters of correspondence which employed letterlocking.[38][39]

• Locating stardust-like particles in aerogel using X-ray techniques[40]
• Samples returned from asteroid 25143 Itokawa by the Hayabusa mission[41]

• Visualizing with blue and green or blue filters to see depth

• Cigarettes
• Social insect nests[42]