Adverse effects
Abdominal radiograph of a pregnant woman, a procedure that should be performed only after proper assessment of benefit versus risk
Diagnostic X-rays (primarily from CT scans due to the large dose used) increase the risk of developmental problems and cancer in those exposed.[29][30][31] X rays are classified as a carcinogen by both the World Health Organization's International Agency for Research on Cancer and the U.S. government.[24][32] It is estimated that 0.4% of current cancers in the United States are due to computed tomography (CT scans) performed in the past and that this may increase to as high as 1.5-2% with 2007 rates of CT usage.[33]
Experimental and epidemiological data currently do not support the proposition that there is a threshold dose of radiation below which there is no increased risk of cancer.[34] However, this is under increasing doubt.[35] It is estimated that the additional radiation will increase a person's cumulative risk of getting cancer by age 75 by 0.6–1.8%.[36] The amount of absorbed radiation depends upon the type of X-ray test and the body part involved.[37] CT and fluoroscopy entail higher doses of radiation than do plain X-rays.
To place the increased risk in perspective, a plain chest X-ray will expose a person to the same amount from background radiation
that we are exposed to (depending upon location) every day over 10
days, while exposure from a dental X-ray is approximately equivalent to 1
day of environmental background radiation.[38]
Each such X-ray would add less than 1 per 1,000,000 to the lifetime
cancer risk. An abdominal or chest CT would be the equivalent to 2–3
years of background radiation to the whole body, or 4–5 years to the
abdomen or chest, increasing the lifetime cancer risk between 1 per
1,000 to 1 per 10,000.[38] This is compared to the roughly 40% chance of a US citizen developing cancer during their lifetime.[39]
For instance, the effective dose to the torso from a CT scan of the
chest is about 5 mSv, and the absorbed dose is about 14 mGy.[40] A head CT scan (1.5mSv, 64mGy)[41]
that is performed once with and once without contrast agent, would be
equivalent to 40 years of background radiation to the head. Accurate
estimation of effective doses due to CT is difficult with the estimation
uncertainty range of about ±19% to ±32% for adult head scans depending
upon the method used.[42]
The risk of radiation is greater to unborn babies, so in pregnant
patients, the benefits of the investigation (X-ray) should be balanced
with the potential hazards to the unborn fetus.[43][44] In the US, there are an estimated 62 million CT scans performed annually, including more than 4 million on children.[37] Avoiding unnecessary X-rays (especially CT scans) will reduce radiation dose and any associated cancer risk.[45]
Medical X-rays are a significant source of man-made radiation
exposure. In 1987, they accounted for 58% of exposure from man-made
sources in the United States.
Since man-made sources accounted for only 18% of the total radiation
exposure, most of which came from natural sources (82%), medical X-rays
only accounted for 10% of total American radiation exposure; medical procedures as a whole (including nuclear medicine)
accounted for 14% of total radiation exposure. By 2006, however,
medical procedures in the United States were contributing much more
ionizing radiation than was the case in the early 1980s. In 2006,
medical exposure constituted nearly half of the total radiation exposure
of the U.S. population from all sources. The increase is traceable to
the growth in the use of medical imaging procedures, in particular computed tomography (CT), and to the growth in the use of nuclear medicine.[25][46]
Dosage due to dental X-rays varies significantly depending on the
procedure and the technology (film or digital). Depending on the
procedure and the technology, a single dental X-ray of a human results
in an exposure of 0.5 to 4 mrem. A full mouth series may therefore
result in an exposure of up to 6 (digital) to 18 (film) mrem, for a
yearly average of up to 40 mrem.[47][48][49][50][51][52][53]
Other uses
Other notable uses of X-rays include
Each dot, called a reflection, in this diffraction pattern forms from
the constructive interference of scattered X-rays passing through a
crystal. The data can be used to determine the crystalline structure.
- X-ray crystallography in which the pattern produced by the diffraction of X-rays through the closely spaced lattice of atoms in a crystal is recorded and then analysed to reveal the nature of that lattice. A related technique, fiber diffraction, was used by Rosalind Franklin to discover the double helical structure of DNA.[54]
- X-ray astronomy, which is an observational branch of astronomy, which deals with the study of X-ray emission from celestial objects.
- X-ray microscopic analysis, which uses electromagnetic radiation in the soft X-ray band to produce images of very small objects.
- X-ray fluorescence, a technique in which X-rays are generated within a specimen and detected. The outgoing energy of the X-ray can be used to identify the composition of the sample.
- Industrial radiography uses X-rays for inspection of industrial parts, particularly welds.
- Industrial CT (computed tomography) is a process which uses X-ray equipment to produce three-dimensional representations of components both externally and internally. This is accomplished through computer processing of projection images of the scanned object in many directions.
- Paintings are often X-rayed to reveal the underdrawing and pentimenti or alterations in the course of painting, or by later restorers. Many pigments such as lead white show well in X-ray photographs.
- X-ray spectromicroscopy has been used to analyse the reactions of pigments in paintings. For example, in analysing colour degradation in the paintings of van Gogh[55]
- Airport security luggage scanners use X-rays for inspecting the interior of luggage for security threats before loading on aircraft.
- Border control truck scanners use X-rays for inspecting the interior of trucks.
X-ray fine art photography of needlefish by Peter Dazeley
- X-ray art and fine art photography, artistic use of X-rays, for example the works by Stane Jagodič
- X-ray hair removal, a method popular in the 1920s but now banned by the FDA.[56]
- Shoe-fitting fluoroscopes were popularized in the 1920s, banned in the US in the 1960s, banned in the UK in the 1970s, and even later in continental Europe.
- Roentgen stereophotogrammetry is used to track movement of bones based on the implantation of markers
- X-ray photoelectron spectroscopy is a chemical analysis technique relying on the photoelectric effect, usually employed in surface science.
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