Editing CT scan (section)

==== Multiplanar reconstruction and projections{{anchor|Multiplanar_reconstruction}} ====
[[File:Ct-workstation-neck.jpg|thumb|Typical screen layout for diagnostic software, showing one volume rendering (VR) and multiplanar view of three thin slices in the [[axial plane|axial]] (upper right), [[sagittal plane|sagittal]] (lower left), and [[coronal plane]]s (lower right)]]
[[File:CT of spondylosis causing radiculopathy.png|thumb|left|Special planes are sometimes useful, such as this oblique longitudinal plane in order to visualize the neuroforamina of the vertebral column, showing narrowing at two levels, causing [[radiculopathy]]. The smaller images are axial plane slices.|148x148px]]
Multiplanar reconstruction (MPR) is the process of converting data from one [[anatomical plane]] (usually [[Transverse plane|transverse]]) to other planes. It can be used for thin slices as well as projections. Multiplanar reconstruction is possible as present CT scanners provide almost [[isotropy|isotropic]] resolution.<ref name="ref3">{{Cite book |last1=Udupa |first1=Jayaram K. |url=https://books.google.com/books?id=aR6PHYluq4oC&q=3D+Imaging+in+Medicine%2C+2nd+Edition |title=3D Imaging in Medicine, Second Edition |last2=Herman |first2=Gabor T. |date=1999-09-28 |publisher=CRC Press |isbn=978-0-8493-3179-4}}</ref>

MPR is used almost in every scan. The spine is frequently examined with it.<ref>{{Cite journal |last1=Krupski |first1=Witold |last2=Kurys-Denis |first2=Ewa |last3=Matuszewski |first3=Łukasz |last4=Plezia |first4=Bogusław |date=2007-06-30 |title=Use of multi-planar reconstruction (MPR) and 3-dimentional &#91;sic&#93; (3D) CT to assess stability criteria in C2 vertebral fractures |url=http://www.jpccr.eu/Use-of-multi-planar-reconstruction-MPR-and-3-dimentional-3D-CT-to-assess-stability,71238,0,2.html |journal=Journal of Pre-Clinical and Clinical Research |volume=1 |issue=1 |pages=80–83 |issn=1898-2395}}</ref> An image of the spine in axial plane can only show one vertebral bone at a time and cannot show its relation with other vertebral bones. By reformatting the data in other planes, visualization of the relative position can be achieved in sagittal and coronal plane.<ref>{{Cite journal |last=Tins |first=Bernhard |date=2010-10-21 |title=Technical aspects of CT imaging of the spine |journal=Insights into Imaging |volume=1 |issue=5–6 |pages=349–359 |doi=10.1007/s13244-010-0047-2 |issn=1869-4101 |pmc=3259341 |pmid=22347928}}</ref>

New software allows the reconstruction of data in non-orthogonal (oblique) planes, which help in the visualization of organs which are not in orthogonal planes.<ref>{{Cite web |title=CT imaging: Where are we going? (Proceedings) |url=https://www.dvm360.com/view/ct-imaging-where-are-we-going-proceedings |access-date=2021-03-21 |website=DVM 360|date=April 2010}}</ref><ref>{{Cite book |last1=Wolfson |first1=Nikolaj |url=https://books.google.com/books?id=8Y5FDAAAQBAJ&q=Modern+software+allows+reconstruction+in+non-orthogonal&pg=PA373 |title=Orthopedics in Disasters: Orthopedic Injuries in Natural Disasters and Mass Casualty Events |last2=Lerner |first2=Alexander |last3=Roshal |first3=Leonid |date=2016-05-30 |publisher=Springer |isbn=978-3-662-48950-5}}</ref> It is better suited for visualization of the anatomical structure of the bronchi as they do not lie orthogonal to the direction of the scan.<ref>{{Cite journal |last1=Laroia |first1=Archana T |last2=Thompson |first2=Brad H |last3=Laroia |first3=Sandeep T |last4=van Beek |first4=Edwin JR |date=2010-07-28 |title=Modern imaging of the tracheo-bronchial tree |journal=World Journal of Radiology |volume=2 |issue=7 |pages=237–248 |doi=10.4329/wjr.v2.i7.237 |issn=1949-8470 |pmc=2998855 |pmid=21160663 |doi-access=free}}</ref>

Curved-plane reconstruction (or curved planar reformation = CPR) is performed mainly for the evaluation of vessels. This type of reconstruction helps to straighten the bends in a vessel, thereby helping to visualize a whole vessel in a single image or in multiple images. After a vessel has been "straightened", measurements such as cross-sectional area and length can be made. This is helpful in preoperative assessment of a surgical procedure.<ref>{{Cite journal |last1=Gong |first1=Jing-Shan |last2=Xu |first2=Jian-Min |date=2004-07-01 |title=Role of curved planar reformations using multidetector spiral CT in diagnosis of pancreatic and peripancreatic diseases |journal=World Journal of Gastroenterology |volume=10 |issue=13 |pages=1943–1947 |doi=10.3748/wjg.v10.i13.1943 |issn=1007-9327 |pmc=4572236 |pmid=15222042 |doi-access=free}}</ref>

For 2D projections used in [[radiation therapy]] for quality assurance and planning of [[external beam radiotherapy]], including digitally reconstructed radiographs, see [[Beam's eye view]].

{| class="wikitable"
|+Examples of different algorithms of thickening multiplanar reconstructions<ref>{{Cite journal |last1=Dalrymple |first1=Neal C. |last2=Prasad |first2=Srinivasa R. |last3=Freckleton |first3=Michael W. |last4=Chintapalli |first4=Kedar N. |date=September 2005 |title=Informatics in radiology (infoRAD): introduction to the language of three-dimensional imaging with multidetector CT |journal=Radiographics |volume=25 |issue=5 |pages=1409–1428 |doi=10.1148/rg.255055044 |issn=1527-1323 |pmid=16160120}}</ref>
!Type of projection
!Schematic illustration
!Examples (10&nbsp;mm slabs)
!Description
!Uses
|-
|Average intensity projection (AIP)
|[[File:Average intensity projection.gif|frameless]]
|[[File:Coronal average intensity projection CT thorax.gif|frameless|118x118px]]
|The average attenuation of each voxel is displayed. The image will get smoother as slice thickness increases. It will look more and more similar to conventional [[projectional radiography]] as slice thickness increases.
|Useful for identifying the internal structures of a solid organ or the walls of hollow structures, such as intestines.
|-
|[[Maximum intensity projection]] (MIP)
|[[File:Maximum intensity projection.gif|frameless]]
|[[File:Coronal maximum intensity projection CT thorax.gif|frameless|118x118px]]
|The voxel with the highest attenuation is displayed. Therefore, high-attenuating structures such as blood vessels filled with contrast media are enhanced.
|Useful for angiographic studies and identification of pulmonary nodules.
|-
|[[Minimum intensity projection]] (MinIP)
|[[File:Minimum intensity projection.gif|frameless]]
|[[File:Coronal minimum intensity projection CT thorax.gif|frameless|117x117px]]
|The voxel with the lowest attenuation is displayed. Therefore, low-attenuating structures such as air spaces are enhanced.
|Useful for assessing the lung parenchyma.
|}