Radiodensity (or radiopacity) is
opacity
Opacity or opaque may refer to:
* Impediments to (especially, visible) light:
** Opacities, absorption coefficients
** Opacity (optics), property or degree of blocking the transmission of light
* Metaphors derived from literal optics:
** In lingu ...
to the
radio wave
Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz (GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm (short ...
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
[Novelline, Robert. ''Squire's Fundamentals of Radiology''. Harvard University Press. 5th edition. 1997. .] 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
qualitative
Qualitative descriptions or distinctions are based on some quality or characteristic rather than on some quantity or measured value.
Qualitative may also refer to:
*Qualitative property, a property that can be observed but not measured numericall ...
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.
Radiographic imaging has been revolutionized by radiodense
contrast media, which can be passed through the bloodstream, the
gastrointestinal tract
The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organ (biology), organs of the digestive syste ...
, 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
stents that are used during
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
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element.
Th ...
and
iodine
Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , and boils to a vi ...
.
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, bismuth oxide 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.
When testing a new medical device for regulatory submission, device manufacturers will usually evaluate the radiocontrast according t
ASTM F640 "Standard Test Methods for Determining Radiopacity for Medical Use."
See also
*
Hounsfield scale
References
{{Reflist
External links
Application note on measuring radiopacity
Radiography
Radiology