X-ray

Hand mit Ringen (Hand with Ring): print of Wilhelm Röntgen's first "medical" X-ray, of his wife's hand, taken on 22 December 1895 and presented to Professor Ludwig Zehnder of the Physik Institut, University of Freiburg, on 1 January 1896. The dark oval on the third finger is a shadow produced by her ring

X-rays are primarily used for diagnostic radiography.

Unit of measure

The rem is the traditional unit of dose equivalent. The SI counterpart is the sievert (Sv).

Exposure

Reported dosage (exposure) due to dental X-rays seems to vary significantly. Depending on the source, a typical dental X-ray of a human results in an exposure of perhaps, 3 mrems (30 to 9,000 μSv).

Hard X-rays

fgdgWhen medical X-rays are being produced, a thin metallic sheet is placed between the emitter and the target, effectively filtering out the lower energy (soft) X-rays. When this is placed close to the window of the X-ray tube, the resultant X-ray is said to be hard.

Details

The frequency of hard X-rays is higher than that of soft X-rays, and the wavelength is shorter. Hard X-rays overlap with the range of "long"-wavelength (lower energy) gamma rays. However the distinction between the two terms in medicine depends on the source of the radiation, not its wavelength.

In medical applications, this is usually tungsten or a more crack-resistant alloy of rhenium (5%) and tungsten (95%), but sometimes molybdenum for more specialized applications, such as when soft X-rays are needed as in mammography.

In crystallography, a copper target is most common, with cobalt often being used when fluorescence from iron content in the sample might otherwise present a problem.

Radiographs obtained using X-rays can be used to identify a wide spectrum of pathologies. Due to their short wavelength, in medical applications, X-rays act more like a particle than a wave. This is in contrast to their application in crystallography, where their wave-like nature is most important.

Cardiovascular system X-ray

To generate an image of the cardiovascular system, including the arteries and veins (angiography) an initial image is taken of the anatomical region of interest. A second image is then taken of the same region after iodinated contrast material has been injected into the blood vessels within this area. These two images are then digitally altered, leaving an image of only the iodinated contrast outlining the blood vessels. The doctor (Radiologist) or surgeon then compares the image obtained to normal anatomical images to determine if there is any damage or blockage of the vessel.

Bones X-ray

To take an X-ray of the bones, short X-ray pulses are shot through a body with radiographic film behind. The bones absorb the most photons by the photoelectric process, because they are more electron-dense. The X-rays that do not get absorbed turn the photographic film from white to black, leaving a white shadow of bones on the film.

Non-medical use

For most modern non-medical applications, X-ray production is achieved in a different way.

Efficiency

The efficiency of X-ray tubes is less than 2%. Most of the energy is used to heat up the anode.