Microtomography like tomography

Tomography

Tomography refers to imaging by sections or sectioning, through the use of any kind of penetrating wave. A device used in tomography is called a tomograph, while the image produced is a tomogram. The method is used in radiology, archaeology, biology, geophysics, oceanography, materials science,...

, uses x-ray

X-ray

X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

s 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. These pixel sizes have also resulted in the terminology micro-computed tomography, micro-ct, micro-computer tomography, high resolution x-ray tomography, and similar terminologies. All of these names generally represent the same class of instruments.

This also means that the machine is much smaller in design compared to the human version and is used to model smaller objects. In general, there are two types of scanner setups. In one setup, the X-ray source and detector are typically stationary during the scan while the sample/animal rotates. The second setup, much more like a clinical CT scanner, is gantry based where the animal/specimen is stationary in space while the X-ray tube and detector rotate around. 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. Many believe that the technology did not really take off until the advent of the cone beam reconstruction algorithm originally authored by Lee Feldkamp.

Working principle

• Imaging system

Fan beam reconstruction

The fan-beam system is based on a 1-dimensional x-ray

X-ray

X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

 detector and an electronic x-ray source, creating 2-dimensional cross-sections

Cross section (geometry)

In geometry, a cross-section is the intersection of a figure in 2-dimensional space with a line, or of a body in 3-dimensional space with a plane, etc...

 of the object. Typically used in human Computed tomography

Computed tomography

X-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...

 systems.

Cone beam reconstruction

Cone beam reconstruction

For microtomography, X-ray scanners typically use two methods for scanning:*Fan beam reconstruction* Cone beam reconstruction.Cone beam reconstruction uses a 2-dimensional approach for obtaining projection data. Instead of utilizing a single row of detectors, as fan beam methods do, a cone beam...

The cone-beam system is based on a 2-dimensional x-ray detector (camera

Camera

A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura , an early mechanism for projecting images...

) and an electronic x-ray source, creating projection images that later will be used to reconstruct the image cross-sections.

• 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.

Closed x-ray system

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 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.

The principle

Because microtomography scanners offer isotropic

Isotropy

Isotropy is uniformity in all orientations; it is derived from the Greek iso and tropos . Precise definitions depend on the subject area. Exceptions, or inequalities, are frequently indicated by the prefix an, hence anisotropy. Anisotropy is also used to describe situations where properties vary...

, 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.

Volume rendering

Volume rendering

Volume rendering

In scientific visualization and computer graphics, volume rendering is a set of techniques used to display a 2D projection of a 3D discretely sampled data set.A typical 3D data set is a group of 2D slice images acquired by aCT, MRI, or MicroCT scanner....

 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.

Image segmentation

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

Segmentation (image processing)

In computer vision, segmentation refers to the process of partitioning a digital image into multiple segments . The goal of segmentation is to simplify and/or change the representation of an image into something that is more meaningful and easier to analyze...

, a manual or automatic procedure that can remove the unwanted structures from the image.

Typical use

• Biomedical
• Both in vitro
  In vitro
  In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...
  
   and in vivo
  In vivo
  In vivo is experimentation using a whole, living organism as opposed to a partial or dead organism, or an in vitro controlled environment. Animal testing and clinical trials are two forms of in vivo research...
  
   small animal imaging
• Human skin samples
• Bone samples, ranging in size from rodents to human biopsies
• Lung imaging using respiratory gating
• Cardiovascular imaging using cardiac gating
• Tumor imaging (may require contrast agents)
• Soft tissue imaging (may require contrast agents)
• Electronics
  Electronics
  Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...
  
  

Small electronic components. E.g. DRAM

Dram

Dram or DRAM may refer to:As a unit of measure:* Dram , an imperial unit of mass and volume* Armenian dram, a monetary unit* Dirham, a unit of currency in several Arab nationsOther uses:...

 IC

Integrated circuit

An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...

 in plastic case.

• Microdevices

E.g. spray nozzle

Spray nozzle

A spray nozzle is a precision device that facilitates dispersion of liquid into a spray. Nozzles are used for three purposes: to distribute a liquid over an area, to increase liquid surface area, and create impact force on a solid surface...

• Composite materials and metallic foams
  Metal foam
  A metal foam is a cellular structure consisting of a solid metal, frequently aluminium, containing a large volume fraction of gas-filled pores. The pores can be sealed , or they can form an interconnected network . The defining characteristic of metal foams is a very high porosity: typically...
  
  

E.g. composite material with glass fibers 10 to 12 micrometre

Micrometre

A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...

s in diameter

• Polymers, plastics

E.g. plastic foam

• Diamond
  Diamond
  In mineralogy, diamond is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions...
  
  s

E.g. detecting defects in a diamond

Diamond

In mineralogy, diamond is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions...

 and finding the best way to cut it.

• Food
  Food
  Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals...
  
   and seeds
  SEEDS
  SEEDS is a voluntary organisation registered under the Societies Act of India....
  
  
• E.g. piece of chocolate cake
  Chocolate cake
  Chocolate cake is a cake flavored with melted chocolate or cocoa powder.-History:Chocolate cake is made with chocolate; it can be made with other ingredients, as well. These ingredients include fudge, vanilla creme, and other sweeteners. The history of chocolate cake goes back to 1764, when Dr...
  
  , cookies
• 3-D Imaging of Foods Using X-Ray Microtomography
• Wood
  Wood
  Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...
  
   and paper
  Paper
  Paper is a thin material mainly used for writing upon, printing upon, drawing or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets....
  
  

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

Cell structure

Cell structure may refer to:* An organelle, or the layout of organelles of the biological cell itself* The structure of a covert cell, often involved in underground resistance, organised crime, terrorism or any group requiring stealth in its operations...

• Building materials

E.g. concrete

Concrete

Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

 after loading.

• Geology
  Geology
  Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
  
  
• E.g. sandstone
  Sandstone
  Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
  
  
• porosity
  Porosity
  Porosity or void fraction is a measure of the void spaces in a material, and is a fraction of the volume of voids over the total volume, between 0–1, or as a percentage between 0–100%...
  
   and flow studies
• Microfossils

E.g. bentonic foraminifers

• Space
  Space
  Space is the boundless, three-dimensional extent in which objects and events occur and have relative position and direction. Physical space is often conceived in three linear dimensions, although modern physicists usually consider it, with time, to be part of a boundless four-dimensional continuum...
  
  

E.g. Locating Stardust

Cosmic dust

Cosmic dust is a type of dust composed of particles in space which are a few molecules to 0.1 µm in size. Cosmic dust can be further distinguished by its astronomical location; for example: intergalactic dust, interstellar dust, interplanetary dust and circumplanetary dust .In our own Solar...

-like particles in aerogel

Aerogel

Aerogel is a synthetic porous material derived from a gel, in which the liquid component of the gel has been replaced with a gas. The result is a solid with extremely low density and thermal conductivity...

 using x-ray techniques

• Others

E.g. cigarettes

• Stereo images
  Stereoscopy
  Stereoscopy refers to a technique for creating or enhancing the illusion of depth in an image by presenting two offset images separately to the left and right eye of the viewer. Both of these 2-D offset images are then combined in the brain to give the perception of 3-D depth...
  
  

Visualizing with blue and green or blue filters to see depth

Publications

• MicroComputed Tomography: Methodology and Applications
• 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
• Application of the Gatan X-ray Ultramicroscope (XuM) to the Investigation of Material and Biological Samples
• 3D Synchrotron X-ray microtomography of paint samples