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Result : Searchterm 'Hounsfield Unit' found in 1 term [] and 4 definitions []
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Hounsfield Unit
 
(HU) [CT scanner display unit] The arbitrary scale is defined by air, which has a CT number of -1000 HU, and water, with a CT number of 0 HU. It is named after Sir Godfrey Hounsfield, who developed the first clinical CT scanner.

See also Hounsfield Scale.
 
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Hounsfield scaleOpen this link in a new window
'The Hounsfield unit (HU) scale is a linear transformation of the original linear attenuation coefficient measurement in one in ...'
by en.wikipedia.org    
Contrast Enhancement of Chest CT imagesOpen this link in a new window
'In modalities such as computed tomography (CT), chest radiography and mammography, images from the acquisition system usually ...'
by hbil.bme.columbia.edu    
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CT Number
 
(Computed tomography number) The CT number is a selectable scan factor based on the Hounsfield scale. Each elemental region of the CT image (pixel) is expressed in terms of Hounsfield units (HU) corresponding to the x-ray attenuation (or tissue density).
CT numbers are displayed as gray-scale pixels on the viewing monitor. White represents pixels with higher CT numbers (bone). Varying shades of gray are assigned to intermediate CT numbers e.g., soft tissues, fluid and fat. Black represents regions with lower CT numbers like lungs and air-filled organs.

• View the NEWS results for 'CT Number' (6).Open this link in a new window. 
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Contrast
 
Contrast is the relative difference of intensities in two adjacent regions of an image. When referring to computed tomography (CT), contrast is defined as a difference in Hounsfield units between structures. The measurement of contrast resolution in CT imaging involves determining how easy it is to differentiate tissues whose CT density is similar to that of their surroundings. An image lacks contrast when there are no sharp differences between black and white. Brightness refers to the overall lightness or darkness of an image.
The contrast between air, soft tissue, and bones in x-ray and CT images is based on their different absorption of x-rays. Differences in tissue density, thickness and changes of the x-ray spectrum have consequences for image contrast, image noise as well as patient dose.
Optimized tube current, collimation, pitch and image reconstruction improves the contrast. Higher image contrast is produced by increased slice thickness, smaller matrix, and large field of view which results in large voxel size; high mAs to reduce noise; low pass filter.
See also Contrast Enhanced Computed Tomography.

• View the NEWS results for 'Contrast' (18).Open this link in a new window. 


  Further Reading:
  Basics:
Contrast enhancement of soft tissues in Computed Tomography images(.pdf)Open this link in a new window
'Even though soft tissues are of primary interest to radiologists, they are represented using only 12.5% of the total number of ...'
by facweb.cti.depaul.edu    
Contrast Enhancement of Chest CT imagesOpen this link in a new window
'In modalities such as computed tomography (CT), chest radiography and mammography, images from the acquisition system usually ...'
by hbil.bme.columbia.edu    
Scattered Radiation and ContrastOpen this link in a new window
'When an x-ray beam enters a patient's body, a large portion of the photons engage in Compton interactions and produce scattered ...'
by www.sprawls.org    
  News & More:
Toshiba Unveils New Low-Contrast X-Ray Imaging Feature at RSNAOpen this link in a new window
'CHICAGO -- Toshiba America Medical Systems, Inc., a leader in diagnostic and medical imaging, will unveil its new low-contrast ...'
Wednesday, 28 November 2007 by findarticles.com    
Optimization of low-contrast detectability in thin-collimated modern multidetector CT using an interactive sliding-thin-slab averaging algorithm.Open this link in a new window
'To analyze the effects of the sliding-thin-slab averaging algorithm on low-contrast performance in MDCT imaging and to find ...'
Tuesday, 5 August 2008 by www.find-health-articles.com    
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Hounsfield Scale
 
(H) The Hounsfield scale displays radiodensity in a linear scale of gray shades expressed in Hounsfield units (HU). The Hounsfield scale is a quantitative transformation of the attenuation coefficient.
The Hounsfield value -1000 is defined as the radiodensity of air, 0 H that of distilled water at standard pressure and temperature, and denser tissues like for example cranial bone can reach 2000 H. The radiation attenuation of dental fillings or artificial implants depends on atomic number of the elements used. Titanium usually has an amount of +1000 HU. Iron steel can have a density greater than the highest range (traditional 3095 H) covered by the standard Hounsfield scale of a CT scanner. Areas with attenuation coefficients that exceed the scale's maximum are white areas in which no detail is visible.
Some CT machines are relatively tolerant, precise representing regions with very high densities. Sometimes, an option is available to select an extended CT number scale.


  Further Reading:
  Basics:
Hounsfield scaleOpen this link in a new window
'The Hounsfield unit (HU) scale is a linear transformation of the original linear attenuation coefficient measurement in one in ...'
by en.wikipedia.org    
Contrast Enhancement of Chest CT imagesOpen this link in a new window
'In modalities such as computed tomography (CT), chest radiography and mammography, images from the acquisition system usually ...'
by hbil.bme.columbia.edu    
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Linearity
 
Linearity is a property of a system, characterized by output that is directly proportional to the input.
In computed tomography (CT), linearity describes the amount to which the CT number of a material is exactly proportional to the density of this material (in Hounsfield units). This accuracy between the linear attenuation coefficient and the CT number is also utilized to describe the performance of a CT scanner.
The linearity of a gamma camera is a measure of the geometrical correctness of the images.
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