Radiodensity
Encyclopedia
Radiodensity refers to the relative inability of electromagnetic radiation
, particularly X-rays, to pass through a particular material. Radiolucency indicates greater transparency or "transradiancy" to X-ray photon
s. Materials that inhibit the passage of electromagnetic radiation are called radiodense, while those that allow radiation to pass more freely are referred to as radiolucent. The term refers to the relatively opaque
white appearance of dense meterials or substances on radiographic
imaging studies, compared with the relatively darker appearance of less dense materials.
X-rays are part of the electromagnetic spectrum
, with photon energies above those of visible
(and ultraviolet
) light. X-rays are distinguished from gamma ray
s in that they are produced not by transitions within the atomic nucleus
, but either by deceleration of a charged particle
or by the transition of state of orbital
electron
s. Diagnostic X-rays are produced using X-ray tube
s. The radio waves
portion of the electromagnetic spectrum represents much lower energy/frequency photons than visible light. Thus, referring to the property of X-ray density as radiodensity appears contradictory by current knowledge, but is still used as a historical artifact.
Though the term radiodensity is more commonly used in the context of 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. Radiographic imaging
has been revolutionized by radiodense 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 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
.
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
, particularly X-rays, to pass through a particular material. Radiolucency indicates greater transparency or "transradiancy" to X-ray photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
s. Materials that inhibit the passage of electromagnetic radiation are called radiodense, while those that allow radiation to pass more freely are referred to as radiolucent. The term refers to the relatively opaque
Opacity (optics)
Opacity is the measure of impenetrability to electromagnetic or other kinds of radiation, especially visible light. In radiative transfer, it describes the absorption and scattering of radiation in a medium, such as a plasma, dielectric, shielding material, glass, etc...
white appearance of dense meterials or substances on radiographic
Radiography
Radiography is the use of X-rays to view a non-uniformly composed material such as the human body. By using the physical properties of the ray an image can be developed which displays areas of different density and composition....
imaging studies, compared with the relatively darker appearance of less dense materials.
X-rays are part of the electromagnetic spectrum
Electromagnetic spectrum
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....
, with photon energies above those of visible
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
(and ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
) light. X-rays are distinguished from gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
s in that they are produced not by transitions within the atomic nucleus
Atomic nucleus
The nucleus is the very dense region consisting of protons and neutrons at the center of an atom. It was discovered in 1911, as a result of Ernest Rutherford's interpretation of the famous 1909 Rutherford experiment performed by Hans Geiger and Ernest Marsden, under the direction of Rutherford. The...
, but either by deceleration of a charged particle
Charged particle
In physics, a charged particle is a particle with an electric charge. It may be either a subatomic particle or an ion. A collection of charged particles, or even a gas containing a proportion of charged particles, is called a plasma, which is called the fourth state of matter because its...
or by the transition of state of orbital
Atomic orbital
An atomic orbital is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom. This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus...
electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s. Diagnostic X-rays are produced using X-ray tube
X-ray tube
An X-ray tube is a vacuum tube that produces X-rays. They are used in X-ray machines. X-rays are part of the electromagnetic spectrum, an ionizing radiation with wavelengths shorter than ultraviolet light...
s. The radio waves
Radio waves
Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies from 300 GHz to as low as 3 kHz, and corresponding wavelengths from 1 millimeter to 100 kilometers. Like all other electromagnetic waves,...
portion of the electromagnetic spectrum represents much lower energy/frequency photons than visible light. Thus, referring to the property of X-ray density as radiodensity appears contradictory by current knowledge, but is still used as a historical artifact.
Though the term radiodensity is more commonly used in the context of qualitative comparison, radiodensity can also be quantified according to the Hounsfield scale
Hounsfield scale
The Hounsfield scale, named after Sir Godfrey Newbold Hounsfield, is a quantitative scale for describing radiodensity.-Definition:The Hounsfield unit scale is a linear transformation of the original linear attenuation coefficient measurement into one in which the radiodensity of distilled water at...
, a principle which is central to X-ray computed tomography (CT scan) applications. On the Hounsfield scale, distilled water
Distilled water
Distilled water is water that has many of its impurities removed through distillation. Distillation involves boiling the water and then condensing the steam into a clean container.-History:...
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
Radiography
Radiography is the use of X-rays to view a non-uniformly composed material such as the human body. By using the physical properties of the ray an image can be developed which displays areas of different density and composition....
has been revolutionized by radiodense contrast media
Contrast medium
A medical contrast medium is a substance used to enhance the contrast of structures or fluids within the body in medical imaging...
, which can be passed through the bloodstream, the gastrointestinal tract
Gastrointestinal tract
The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....
, 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
Stent
In the technical vocabulary of medicine, a stent is an artificial 'tube' inserted into a natural passage/conduit in the body to prevent, or counteract, a disease-induced, localized flow constriction. The term may also refer to a tube used to temporarily hold such a natural conduit open to allow...
s that are used during radiological
Radiology
Radiology is a medical specialty that employs the use of imaging to both diagnose and treat disease visualized within the human body. Radiologists use an array of imaging technologies to diagnose or treat diseases...
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
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...
and iodine
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
.