Editing Radiodensity

{{short description|Opacity to the radio wave and X-ray portion of the electromagnetic spectrum}}
{{more citations needed|date=August 2010}}
'''Radiodensity''' (or '''radiopacity''') is [[opacity (optics)|opacity]] to the [[radio wave]] and [[X-ray]] portion of the [[electromagnetic spectrum]]: that is, the relative inability of those kinds of [[electromagnetic radiation]] to pass through a particular material. '''Radiolucency''' or '''hypodensity''' indicates greater passage (greater '''transradiancy''') to X-ray [[photon]]s<ref name="squires">Novelline, Robert. ''Squire's Fundamentals of Radiology''. Harvard University Press. 5th edition. 1997. {{ISBN|0-674-83339-2}}.</ref> and is the analogue of [[transparency and translucency]] with [[light|visible light]]. Materials that inhibit the passage of electromagnetic radiation are called '''radiodense''' or '''radiopaque''', while those that allow radiation to pass more freely are referred to as '''radiolucent'''. Radiopaque volumes of material have white appearance on [[radiography|radiographs]], compared with the relatively darker appearance of radiolucent volumes. For example, on typical radiographs, bones look white or light gray (radiopaque), whereas muscle and skin look black or dark gray, being mostly invisible (radiolucent).

Though the term radiodensity is more commonly used in the context of [[Qualitative data|qualitative]] comparison, radiodensity can also be quantified according to the [[Hounsfield scale]], a principle which is central to [[X-ray computed tomography]] (CT scan) applications. On the Hounsfield scale, [[distilled water]] has a value of 0 Hounsfield units (HU), while air is specified as -1000 HU.

In modern medicine, radiodense substances are those that will not allow X-rays or similar radiation to pass. [[Radiography|Radiographic imaging]] has been revolutionized by radiodense [[contrast medium|contrast media]], which can be passed through the bloodstream, the [[gastrointestinal tract]], or into the cerebral spinal fluid and utilized to highlight CT scan or X-ray images. Radiopacity is one of the key considerations in the design of various devices such as guidewires or [[stent]]s that are used during [[radiology|radiological]] intervention. The radiopacity of a given endovascular device is important since it allows the device to be tracked during the interventional procedure.
The two main factors contributing to a material's radiopacity are density and atomic number. Two common radiodense elements used in medical imagery are [[barium]] and [[iodine]].

Medical devices often contain a radiopacifier to enhance visualization during implantation for temporary implantation devices, such as catheters or guidewires, or for monitoring the position of permanently implanted medical devices, such as stents, hip and knee implants, and screws. Metal implants usually have sufficient radiocontrast that additional radiopacifier is not necessary. Polymer-based devices, however, usually incorporate materials with high electron density contrast compared to the surrounding tissue. Examples of radiocontrast materials include titanium, tungsten, barium sulfate,<ref>{{cite journal |last1=Lopresti |first1=Mattia |last2=Alberto |first2=Gabriele |last3=Cantamessa |first3=Simone |last4=Cantino |first4=Giorgio |last5=Conterosito |first5=Eleonora |last6=Palin |first6=Luca |last7=Milanesio |first7=Marco |title=Light Weight, Easy Formable and Non-Toxic Polymer-Based Composites for Hard X-ray Shielding: A Theoretical and Experimental Study |journal=International Journal of Molecular Sciences |date=28 January 2020 |volume=21 |issue=3 |pages=833 |doi=10.3390/ijms21030833|pmid=32012889 |pmc=7037949 |doi-access=free }}</ref> bismuth oxide<ref>{{cite journal |last1=Lopresti |first1=Mattia |last2=Palin |first2=Luca |last3=Alberto |first3=Gabriele |last4=Cantamessa |first4=Simone |last5=Milanesio |first5=Marco |title=Epoxy resins composites for X-ray shielding materials additivated by coated barium sulfate with improved dispersibility |journal=Materials Today Communications |date=20 November 2020 |volume=26 |pages=101888 |doi=10.1016/j.mtcomm.2020.101888|s2cid=229492978 }}</ref> and zirconium oxide. Some solutions involve direct binding of heavy elements, for instance iodine, to polymeric chains in order to obtain a more homogeneous material which has lower interface criticalities.<ref>{{cite journal |last1=Nisha |first1=V. S |last2=Rani Joseph |title=Preparation and properties of iodine-doped radiopaque natural rubber |journal=Journal of Applied Polymer Science |date=15 July 2007 |volume=105 |issue=2 |pages=429–434 |doi=10.1002/app.26040|url=http://dyuthi.cusat.ac.in/purl/818 |url-access=subscription }}</ref> When testing a new medical device for regulatory submission, device manufacturers will usually evaluate the radiocontrast according to [http://www.astm.org/Standards/F640.htm ASTM F640 "Standard Test Methods for Determining Radiopacity for Medical Use."]

==See also==
*[[Hounsfield scale]]

==References==
{{Reflist}}

==External links==
* [http://www.campoly.com/index.php/download_file/view/213/108/ Application note on measuring radiopacity]

{{Medical imaging}}

[[Category:Radiography]]
[[Category:Radiology]]