Tomography

From ArticleWorld

Tomography refers to the process of generating an image showing a slice or section of the internal structure of an object. The resulting image is called a tomogram and the instrument used to produce it is called a tomograph. It is used in both scientific research and industry. The technique is based on the mathematical principle of tomographic reconstruction which was developed by Johann Radon in the early 20th century.

The word ‘tomography’ is derived from two Greek words ‘tomos’ meaning ‘slice’ and ‘graphia’ meaning ‘description’.

Types of tomography

Some of the major types of tomography are described below:

• Atom probe tomography (APT): Developed in 1955, APT allows scientists to determine the positions of atoms in an object with atomic precision using a position sensitive detector.

• Computed tomography (CT): This refers to the modern medical technology that makes use of X-ray imaging and computerized digital image processing to produce three-dimensional images of the internal parts of the human body. Since a series of images is taken about a single axis, this process is also referred to as ‘computed axial tomography’ (CAT). Though the technology is primarily used in healthcare, it also finds important applications in the civil and mechanical engineering fields. Internal cracks, structural/foundational damages and deteriorated machine parts can be pinpointed using this technique.

• Cryo-electron tomography (Cryo-ET): Used in molecular biology, Cryo-Et provides a 3D reconstruction of a sample from tilted 2D images. It is a form of cryo-electron microscopy.

• Electrical impedance tomography (EIT): This method aims at producing cross-sectional images of the distribution of conductivity in human tissues through the use of surface electrical measurements.

• Magnetic resonance imaging (MRI): This method uses powerful magnets to take 2 or 3 dimensional images of the internal structure of objects.

• Optical coherence tomography (OCT): This type of tomography produces very high resolution images of internal structures. It is mostly used in medical research.

• Positron emission tomography (PET): A nuclear medicine tomographic imaging technology, PET uses positron signals emitted from radioactive tracers to produce images of the distribution of tracers in the body in order to diagnose illnesses.

• Quantum state tomography: Also known as quantum tomography, this method is used for studying the quantum properties of light and other sources of quantum systems.

• Single photon emission computed tomography (SPECT): A type of computed tomography (CT), SPECT is used to provide 3D images of the internal structures in the human body.

• Seismic tomography: This technique uses seismographic records to produce a 3D representation of the Earth’s interior. Used since the 1970s, seismic tomography has revolutionized the way scientists study the Earth’s structure.