Information about Hounsfield Scale
The Hounsfield scale is a quantitative scale for describing radiodensity.
, it is defined as
where
is the linear attenuation coefficient of water at the same (effective) energy.
CT machines were the first imaging devices for detailed visualization of the internal three-dimensional anatomy of living creatures, initially only as tomographic reconstructions of slice views or sections. Since the early 1990s, with advances in computer technology and scanners using spiral CT technology, internal three-dimensional anatomy is viewable by three-dimensional software reconstructions, from multiple perspectives, on computer monitors. By comparison, conventional X-Ray images show only compressed two-dimensional images of complex anatomy, i.e. radiodensity shadows.
Definition
The radiodensity of distilled water at standard pressure and temperature (STP) is defined as zero Hounsfield units (HU). The radiodensity of air at STP is defined as -1000 HU. For a material X with linear attenuation coefficient , it is defined as
where
is the linear attenuation coefficient of water at the same (effective) energy.
Rationale
The above standards were chosen as they are universally available references and suited to the key application for which computed axial tomography was developed: imaging the internal anatomy of living creatures based on organized water structures and mostly living in air, e.g. humans.The HU of common substances
| Substance | HU |
|---|---|
| Air | -1000 |
| Fat | -120 |
| Water | 0 |
| Muscle | +40 |
| Bone | +1000 |
History
It was established by Sir Godfrey Newbold Hounsfield, one of the principal engineers and developers of computed axial tomography (CAT, or CT scans).CT machines were the first imaging devices for detailed visualization of the internal three-dimensional anatomy of living creatures, initially only as tomographic reconstructions of slice views or sections. Since the early 1990s, with advances in computer technology and scanners using spiral CT technology, internal three-dimensional anatomy is viewable by three-dimensional software reconstructions, from multiple perspectives, on computer monitors. By comparison, conventional X-Ray images show only compressed two-dimensional images of complex anatomy, i.e. radiodensity shadows.
External links
- Hounsfield Unit - fpnotebook.com
- Introduction to CT physics - elsevierhealth.com
Radiodensity is the property of relative transparency to the passage of X-rays through a material. Radiolucent indicates greater transparency to X-ray photons. Radiodense indicates greater opacity to X-ray photons.
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Radiodensity is the property of relative transparency to the passage of X-rays through a material. Radiolucent indicates greater transparency to X-ray photons. Radiodense indicates greater opacity to X-ray photons.
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Distilled water is water that has virtually all of its impurities removed through distillation. Distillation involves boiling the water and re-condensing the steam into a clean container, leaving most if not all solid contaminants behind.
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Pressure (symbol: p) is the force per unit area applied on a surface in a direction perpendicular to that surface.
Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.
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Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.
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Temperature is a physical property of a system that underlies the common notions of hot and cold; something that is hotter generally has the greater temperature. Temperature is one of the principal parameters of thermodynamics.
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Temperature is a physical property of a system that underlies the common notions of hot and cold; something that is hotter generally has the greater temperature. Temperature is one of the principal parameters of thermodynamics.
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In chemistry and other sciences, STP or standard temperature and pressure is a standard set of conditions for experimental measurements, to enable comparisons to be made between sets of data.
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Air or Earth's atmosphere is a layer of gases surrounding the planet Earth.
Air may also refer to:
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Air may also refer to:
- Air (1977 video game), an air combat based mainframe computer game
- Air (band), a French electronic music duo
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Godfrey Newbold Hounsfield CBE, FRS, (28 August 1919 – 12 August 2004) was an English electrical engineer who shared the 1979 Nobel Prize for Physiology or Medicine with Allan McLeod Cormack for his part in developing the diagnostic technique of X-ray computed tomography (CT).
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engineer is someone who is trained or professionally engaged in a branch of engineering.[1] Engineers use technology, mathematics, and scientific knowledge to solve practical problems.
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Computed tomography (CT), originally known as computed axial tomography (CAT or CT scan) and body section roentgenography, is a medical imaging method employing tomography where digital geometry processing is used to generate a three-dimensional image of the
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Anatomy (from the Greek ἀνατομία anatomia, from ἀνατέμνειν
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Tomography is imaging by sections or sectioning. A device used in tomography is called a tomograph, while the image produced is a tomogram. The method is used in medicine, archaeology, biology, geophysics, oceanography, materials science and other sciences.
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Centuries: 19th century - 20th century - 21st century
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1960s 1970s 1980s - 1990s - 2000s 2010s 2020s
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For the band, see .
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Computed tomography (CT), originally known as computed axial tomography (CAT or CT scan) and body section roentgenography, is a medical imaging method employing tomography where digital geometry processing is used to generate a three-dimensional image of the
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X-rays (or Röntgen rays) are a form of electromagnetic radiation with a wavelength in the range of 10 to 0.01 nanometers, corresponding to frequencies in the range 30 PHz to 30 EHz. X-rays are primarily used for diagnostic radiography and crystallography.
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Radiodensity is the property of relative transparency to the passage of X-rays through a material. Radiolucent indicates greater transparency to X-ray photons. Radiodense indicates greater opacity to X-ray photons.
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A shadow is a region of darkness where light is blocked. It occupies all of the space behind an opaque object with light in front of it. The cross section of a shadow is a two-dimensional silhouette, or reverse projection of the object blocking the light.
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