Microtomography

Microtomography, like tomography, uses x-rays to create cross-sections of a 3D-object that later can be used to recreate a virtual model without destroying the original model. The term micro is used to indicate that the pixel sizes of the cross-sections are in the micrometer range. This also means that the machine is much smaller in design compared to the human version and is used to model smaller objects.

These scanners are typically used for small animals (in-vivo scanners), biomedical samples, foods, microfossils, and other studies for which minute detail is desired.

The first X-ray microtomography system was conceived and built by Jim Elliott in the early 1980s. The first published X-ray microtomographic images were reconstructed slices of a small tropical snail, with pixel size about 50 micrometers. (JC Elliott and SD Dover. X-ray microtomography. J. Microscopy 126, 211-213, 1982.)

In 2005, Skyscan, a company that produces scientific instruments, introduced a nano-ct scanner, introducing the concept of Nanotomography. Other companies producing such scanners include Scanco Medical AG (www.scanco.ch).

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Working principle

• Imaging system

Fan beam reconstruction

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

Cone beam reconstruction

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

• Sample holder system

The sample stays still, and the camera and electronic x-ray source rotates.

This is best used for in-vivo animal scans, and other situations where the sample should remain unmoving, but is more expensive.

E.g.SkyScan-1076 or SkyScan-1078 or Scanco VivaCT 40 scanners for sample details.

The sample rotates, and the camera and electronic x-ray source stays still.

Much cheaper to build, since moving the sample requires fewer components than moving the camera and the electronic x-ray source.

• Open/Closed systems

Open x-ray system

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.

E.g. Scanco medical XtremeCT scanner.

Closed x-ray system

In a closed system, x-ray shielding is put around the scanner so the operator can put the scanner on his desk or special table. Although the scanner is shielded, care must be taken and the operator usually carries a dose meter, 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.

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.

E.g. SkyScan-1076 or SkyScan-1078 or Scanco mCT 40 or Scanco mCT 80 scanners.

Typical use

• Biomedical

• Both dead and alive (in vivo) rat and mouse scanning.
• Human skin samples, small tumors, mice bone for osteoporosis research.

See in vivo microCT scanners for scanning examples.

• Electronics

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

• Microdevices

E.g. spray nozzle

• Composite materials and metallic foams

E.g. composite material with glass fibers 10 to 12 micrometres in diameter

• Polymers, plastics

E.g. plastic foam

• Diamonds

E.g. detecting defects in a diamond and finding the best way to cut it.

• Food and seeds

• E.g. piece of chocolate cake, cookies
• 3-D Imaging of Foods Using X-Ray Microtomography [1]

• Wood and paper

E.g. piece of wood to visualize year periodicity and cell structure

• Building materials

E.g. concrete after loading.

• Geology

E.g. sandstone

• Microfossils

E.g. bentonic foraminifers

• Space

E.g. Locating Stardust-like particles in aerogel using x-ray techniques [2]

• Others

E.g. cigarettes

• Stereo images

Visualizing with blue and green or blue filters to see depth

Publications

• Synchrotron and non synchrotron X-ray microtomography threedimensional representation of bone ingrowth in calcium phosphate biomaterials
• Microfocus X-ray Computer Tomography in Materials Research
• Locating Stardust-like particles in aerogel using x-ray techniques
• 3-D Imaging of Foods Using X-Ray Microtomography
• Use of micro CT to study kidney stones