Editing CT scan (section)

==== Grayscale ====
[[Pixel]]s in an image obtained by CT scanning are displayed in terms of relative [[radiodensity]]. The pixel itself is displayed according to the mean [[attenuation]] of the tissue(s) that it corresponds to on a scale from +3,071 (most attenuating) to −1,024 (least attenuating) on the [[Hounsfield scale]]. A [[pixel]] is a two dimensional unit based on the matrix size and the field of view. When the CT slice thickness is also factored in, the unit is known as a [[voxel]], which is a three-dimensional unit.<ref>{{Cite book |url=https://books.google.com/books?id=63xxDwAAQBAJ |title=Brant and Helms' fundamentals of diagnostic radiology |date=2018-07-19 |publisher=Lippincott Williams & Wilkins |isbn=978-1-4963-6738-9 |edition=Fifth |pages=1600 |access-date=24 January 2019}}</ref> Water has an attenuation of 0 [[Hounsfield units]] (HU), while air is −1,000&nbsp;HU, cancellous bone is typically +400&nbsp;HU, and cranial bone can reach 2,000&nbsp;HU.<ref>{{Cite book |title=Brain mapping: the methods |date=2002 |publisher=Academic Press |isbn=0-12-693019-8 |editor-last=Arthur W. Toga |edition=2nd |location=Amsterdam |oclc=52594824 |editor-last2=John C. Mazziotta}}</ref> The attenuation of metallic implants depends on the atomic number of the element used: Titanium usually has an amount of +1000&nbsp;HU, iron steel can completely block the X-ray and is, therefore, responsible for well-known line-artifacts in computed tomograms. Artifacts are caused by abrupt transitions between low- and high-density materials, which results in data values that exceed the dynamic range of the processing electronics.<ref name="...">{{Cite book |last1=Jerrold T. Bushberg |title=The essential physics of medical imaging |last2=J. Anthony Seibert |last3=Edwin M. Leidholdt |last4=John M. Boone |date=2002 |publisher=Lippincott Williams & Wilkins |isbn=0-683-30118-7 |edition=2nd |location=Philadelphia, PA |page=358 |oclc=47177732}}</ref>