Editing CT scan (section)

==== {{anchor|3D}} Volume rendering ====
{{Main|Volume rendering}}
[[File:12-06-11-rechtsmedizin-berlin-07.jpg|thumbnail|3D human skull from computed tomography data]]

A threshold value of radiodensity is set by the operator (e.g., a level that corresponds to bone). With the help of [[edge detection]] image processing algorithms a 3D model can be constructed from the initial data and displayed on screen. Various thresholds can be used to get multiple models, each anatomical component such as muscle, bone and cartilage can be differentiated on the basis of different colours given to them. However, this mode of operation cannot show interior structures.<ref>{{Cite journal |last1=Calhoun |first1=Paul S. |last2=Kuszyk |first2=Brian S. |last3=Heath |first3=David G. |last4=Carley |first4=Jennifer C. |last5=Fishman |first5=Elliot K. |date=1999-05-01 |title=Three-dimensional Volume Rendering of Spiral CT Data: Theory and Method |url=https://pubs.rsna.org/doi/full/10.1148/radiographics.19.3.g99ma14745 |journal=RadioGraphics |volume=19 |issue=3 |pages=745–764 |doi=10.1148/radiographics.19.3.g99ma14745 |issn=0271-5333 |pmid=10336201}}</ref>

Surface rendering is limited technique as it displays only the surfaces that meet a particular threshold density, and which are towards the viewer. However, In volume rendering, transparency, colours and [[Phong shading|shading]] are used which makes it easy to present a volume in a single image. For example, Pelvic bones could be displayed as semi-transparent, so that, even viewing at an oblique angle one part of the image does not hide another.<ref>{{Cite journal |last1=van Ooijen |first1=P. M. A. |last2=van Geuns |first2=R. J. M. |last3=Rensing |first3=B. J. W. M. |last4=Bongaerts |first4=A. H. H. |last5=de Feyter |first5=P. J. |last6=Oudkerk |first6=M. |date=January 2003 |title=Noninvasive Coronary Imaging Using Electron Beam CT: Surface Rendering Versus Volume Rendering |url=http://www.ajronline.org/doi/10.2214/ajr.180.1.1800223 |journal=American Journal of Roentgenology |volume=180 |issue=1 |pages=223–226 |doi=10.2214/ajr.180.1.1800223 |issn=0361-803X |pmid=12490509}}</ref>