Hounsfield unit
From EmergiWiki
Contents |
Background
Hounsfield unit - Sir Godfrey Newbold Hounsfield, 20th century, British research scientist, Nobel prize laureate in medicine/physiology in 1979, devised a system to measure the attenuation coefficient of tissues in computed tomography (CT). Hounsfield units are also termed CT numbers (Table 1). Also see Hounsfield unit (HU).
Sample HU Values
Tissue CT number (HU) Bone 1000 Liver 40 to 60 Brain white matter ~20 to 30 HU Brain grey matter ~37 to 45 HU Blood 40 Muscle 10 to 40 Kidney 30 Cerebrospinal fluid 15 Water 0 Fat -50 to -100 Air -1000
Practical Implications
In accordance with this system, lesions whose attenuation values are close to that of water are consistent with, but not specific for, cysts. Lesions composed solely or predominantly of fat produce negative CT numbers; however, some types of liposarcoma contain great amounts of fat, and some forms of lipoma reveal abundant nonfatty tissue. haematomas characteristically demonstrate inhomogeneous areas with regions of both high attenuation (approximately 50 HU) and low attenuation (approximately 10 HU) in the subacute stage and homogeneous areas of low attenuation (120 HU) in the chronic stage. The measurement of attenuation values of bone lesions may be more difficult, especially in narrow bones in which the contribution of the cortex may prohibit accurate assessment.
The identification of gas in soft tissue or bone by CT is possible owing to its very low attenuation value. Gas within a vertebral body documented by CT, for example, is an important sign of ischemic necrosis of bone. Intraosseous gas is also identified in some cases of osteomyelitis and in subchondral cysts (pneumatocysts), particularly in the ilium and vertebral bod
Notes & References
[1] Hounsfield Unit. Medcyclopaedia. Available online at: http://www.medcyclopaedia.com/library/topics/volume_iii_1/h/hounsfield_unit.aspx
Credits & Notices
Authors-contributors to this page (listed alphabetically, last name, first & middle initial only, no institutional affiliations, no scientific titles):
Stawicki SP
Please make sure you look at the existing references before editing to avoid listing the same citation more than once. The order of references is not important as long as the appropriate reference number in the text points to the correct reference number in the references section.
