Computed Tomography (CT)

What are Hounsfield Units?


"Hounsfield units are a unit of measure that represents the different density levels of tissues and or other substances. The density of pure water was arbitrarily set at 0 HU and that of air at -1000 HU." (Hofer, 2000)

2000 Hoffer, M. CT Teaching Manual, Georg Thieme Verlag, pp.12-13.

What is attenuation?


"The relationship between the CT number of a structure and its physical density is defined by the equation Q = CT + 1000 (Q in mg/cm3, CT in HU (Hounsfield Units)). This equation holds true as long as the effective atomic number of the substance (i.e. its atomic composition) in the displayed voxel is similar to that of water. This applies with reasonable accuracy to fluids, soft tissues, and less to fat but not to iodinated contrast media of calcified structures.

What is CT?

ShareThisWhat is Computed Tomography (CT)?

"Computed tomography (formerly known as computerized axial tomography or CAT scan) measures the weakening, or attenuation, of x-ray beams as they pass through sections of an object from hundreds of different angles. From the evidence of these measurements, a computer is able to reconstruct two and three dimensional images of the objects interior." (Eisenberg, 1992)

1992 Eisenberg, E. L. Radiology. An Illustrated History, A. S. Patterson (ed.), Mosby Year Book, pp. 467-468.

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