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'''Phase-contrast X-ray imaging''' or '''phase-sensitive X-ray imaging''' is a general term for different technical methods that use information concerning changes in the [[phase (waves)|phase]] of an [[X-ray]] beam that passes through an object in order to create its images. Standard X-ray imaging techniques like [[radiography]] or [[computed tomography|computed tomography (CT)]] rely on a decrease of the X-ray beam's intensity ([[attenuation]]) when traversing the [[sample (material)|sample]], which can be measured directly with the assistance of an [[X-ray detector]]. However, in phase contrast X-ray imaging, the beam's [[phase shift]] caused by the sample is not measured directly, but is transformed into variations in intensity, which then can be recorded by the detector.<ref name=Keyrilainen2010>{{Cite journal | last1 = Keyriläinen | first1 = J. | last2 = Bravin | first2 = A. | last3 = Fernández | first3 = M. | last4 = Tenhunen | first4 = M. | last5 = Virkkunen | first5 = P. | last6 = Suortti | first6 = P. | doi = 10.3109/02841851.2010.504742 | title = Phase-contrast X-ray imaging of breast | journal = Acta Radiologica | volume = 51 | issue = 8 | pages = 866–884 | year = 2010 | pmid = 20799921| s2cid = 19137685 }}</ref>
In addition to producing [[Projectional radiography|projection images]], phase contrast X-ray imaging, like conventional transmission, can be combined with [[tomography|tomographic techniques]] to obtain the 3D distribution of the real part of the [[Refractive index#Complex index of refraction and absorption|refractive index]] of the sample. When applied to samples that consist of atoms with low [[atomic number]] ''Z'', phase contrast X-ray imaging is more sensitive to density variations in the sample than [[Radiography|conventional transmission-based X-ray imaging]]. This leads to images with improved [[soft tissue]] contrast.<ref name=diemoz2012>{{Cite journal | last1 = Diemoz | first1 = P. C. | last2 = Bravin | first2 = A. | last3 = Coan | first3 = P. | doi = 10.1364/OE.20.002789 | title = Theoretical comparison of three X-ray phase-contrast imaging techniques: Propagation-based imaging, analyzer-based imaging and grating interferometry | journal = Optics Express | volume = 20 | issue = 3 | pages = 2789–2805 | year = 2012 | pmid = 22330515| bibcode = 2012OExpr..20.2789D | url = http://discovery.ucl.ac.uk/1345033/ | doi-access = free | hdl = 10281/345410 | hdl-access = free }}</ref>
In the last several years, a variety of phase-contrast X-ray imaging techniques have been developed, all of which are based on the observation of [[Interference (wave propagation)|interference patterns]] between diffracted and undiffracted waves.<ref name=Weon2006>{{cite journal|last=Weon|first=B. M.|author2=Je, J. H. |author3=Margaritondo, G. |title=Phase contrast X-ray imaging|journal=International Journal of Nanotechnology|date=2006|volume=3|issue=2–3|pages=280–297|url=http://inderscience.metapress.com/content/50744rtclhukb8xw/|access-date=11 January 2013|bibcode = 2006IJNT....3..280W |doi = 10.1504/IJNT.2006.009584 |citeseerx=10.1.1.568.1669}}</ref> The most common techniques are crystal interferometry, propagation-based imaging, analyzer-based imaging, edge-illumination and grating-based imaging (see below).
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