X-ray Imaging

X-ray is an electromagnetic radiation of extremely short wavelength and high frequency between the gamma and the ultraviolet radiation. These are commonly produced by accelerating (or decelerating) charged particles using high-voltage electricity supply at a piece of metal (typically tungsten). What gets reflected beck is X-rays. And X-rays are the oldest sources of EM radiation used for imaging.

figure 1: Producing X-rays

X-rays are roughly classified into two types

1. Soft x-rays

These have different optical properties than visible light and therefore experiments must take place in ultra high vacuum, where the photon beam is manipulated using special mirrors and diffraction gratings.

2. Hard x-rays

These are the highest energy x-rays, while the lower energy x-rays are referred to as soft x-rays. The distinction between hard and soft x-rays is not well defined. Hard x-rays are typically those with energies greater than around 10 keV. More relevant to the distinction are the instruments required to observe them and the physical conditions which the x-rays are produced.

Properties of X-rays

• They have very short wave length.
• They are electrically neutral.
• They cause ionization (adding or removing electrons in atoms).
• They affect photographic film in the same way as the visible light.
• They are absorbed by metal and bone.
• They are transmitted by healthy body tissue.

Domains which are used X-ray imaging

In medical science

X-rays are still best known as a medical tool, used in both diagnosis and treatment. Standard X-ray images easily differentiate between bone and soft tissue; bones are good at absorbing X-rays, whereas soft tissues like skin and muscle allow the rays to pass straight through. That makes X-ray photography extremely useful for all kinds of medical diagnosis; they show up broken bones, tumors and lung conditions such as tuberculosis and emphysema.

Dentist also use X-rays extensively to help them understand what’s happening in parts of your mouth inside your teeth and gums.

The most common methods of X-ray in medical imaging are

• Radiography (Plain X-rays)
• Computed tomography (CT)
• Mammography
• Angiography
• Fluoroscopy

1. Radiography (Plain X-rays)

In radiography, a beam of X-rays produced by an X-ray generator, is transmitted through an object (the part of the body to be scanned). The X-rays are absorbed by the material they pass through in different amounts depending on the density and composition of the material. X-rays that are not absorbed pass through the object and are recorded on X-ray sensitive film.

figure 2: Basic steps for X-ray imaging                    figure 3: A typical X-ray radiography of the chest

2. Computed tomography (CT)

Computer tomography (CT) scanners produce detailed images of the body. Due to their high resolution, these images can provide additional information compared to conventional radiography.

The most prominent part of a CT scanner is the gantry – a circular, rotating frame with an X-ray tube mounted on one side and a detector on the opposite side. A fan shaped beam of X-rays is created as the rotating frame spins the X-ray tube and detector around the patient. As the scanner rotates, several thousand images are taken in one rotation resulting in one complete cross-sectional images of the body. Built on these data, it is possible to create 3D visualization and views from different angles.

                 figure 4: principle of CT scanner                  figure 5: Modern CT scan provides very                                                                                       detailed images (blood vessels, internal                                                                                           organ) 

3. Mammography

This is a special type of X-ray imaging used to create detailed images of the breast and is commonly used in screening for breast cancer.  In digital mammography electronic detectors that convert X-rays into electrical signals are used instead of film. This produce images of the breast that can be viewed on a computer screen or printed on special film similar to conventional mammograms.

        figure 6: In mammography each breast is        figure 7: Normal breast tissue in mammogram

       compressed horizontally   

4. Angiography

This is a special type of X-ray technique for viewing blood vessels and organs, especially the heart, by injecting a contrast agent into the blood that enhances its visibility on the X-ray image.

figure 8: Angiography of a blood vessel in the region of the knee

5. Fluoroscopy

This is a type of medical imaging that produces a continuous live X-ray image of the patient’s internal structure on a monitor.

Figure 9: The colon is clearly seen on the air-contrast barium enema

In security sector

X-rays are useful for checking bags at airport check-ins. X-rays pass straight through soft materials such as leather and plastic but are blocked by the metal in guns, knives and weapons. Typically suitcases and bags travel up through large scanners on conveyor belts, with X-ray images of their contents appearing instantly on computer screen studied by security guards.

Figure 10: X-ray use in the airport

In aeronautical engineering

X-ray help to track down things like cracks and fatigue in metal components. Turbine blades in airplane jet engines are tested in this way to make sure they are not harboring any problems that would cause them to fail suddenly during flight. 

Figure 11: turbine blade

In photography and art industry

Fine art black and white floral photographic prints can be made from X-ray films of flowers. Optimum technique for making the x-ray image would use unscreened fine-grain industrial x-ray film covered by thin light-protective plastic. The film is exposed at low kilo voltage for multiple seconds with floral material laying on the light-protected film in specimen radiographic equipment. The film is hand developed. Once the x-ray image is created, it can be used like any photographic negative to make a print or digital image.

Figure 12: fine art black and white floral photographic print

And also X-ray imaging used in oil paintings in order to prove the artist authenticity.

In scientific research area

X-ray is use in studying the inner structure of materials. If fire beam of X-ray at a crystal, the atoms scatter the beam in a very precise way, casting a kind of shadow of the crystal’s interior pattern from which you can measure the distance between one atom and its neighbors. This is called X-ray diffraction or X-ray crystallography.

Astronomy

X-ray used looking through telescope to see light from distant objects even ones far out into space. Radio telescopes, for example, are more like giant satellite dish antennas that capture radio waves being given off from those distant sources. X-ray also travel through space and we can study them in a similar way with telescope tuned to recognize their particular frequency.

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