Radiodensity

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Radiodensity (or radiopacity) is 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 photons^[1] and is the analogue of transparency and translucency with 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 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

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,^[2] bismuth oxide^[3] 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.^[4] When testing a new medical device for regulatory submission, device manufacturers will usually evaluate the radiocontrast according to ASTM F640 "Standard Test Methods for Determining Radiopacity for Medical Use."

See also

• Hounsfield scale

References