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X-Ray Imaging

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X-Ray Imaging

X-rays are high-energy electromagnetic waves with small wavelengths that can pass through many materials. They are used in imaging and medical physics.

What is x-ray imaging?

X-rays are electromagnetic waves that have wavelengths varying between 0.01 and 10 nanometres (nm). This means that the frequency and energy of these waves are high. In fact, they are high enough for x-ray radiation to be a type of ionising radiation.

X-ray Imaging, Electromagnetic spectrum, StudySmarterFigure 1. Electromagnetic spectrum. Rosenfeld Media, Flickr (CC BY-NC-SA 2.0).

X-rays are used in medical physics for x-ray imaging. This imaging technique uses a small amount of controlled radiation to produce images of the human body’s interior.

Because various organs absorb radiation differently, images reveal different areas of our body in either black or white.

The process of producing x-ray images

When a negatively charged electrode is heated, it causes the electrons to be emitted from it, which produces energy. In x-ray imaging, this energy is directed towards a metal plate at high velocity. When the energy collides with the atoms in the plate, x-rays are created.

X-ray imaging, x-ray machine, StudySmarterFigure 2. An x-ray machine. David Jackmanson, Flickr (CC BY-NC-SA 2.0).

The process begins with the patient lying down on or standing up in front of a cassette. This cassette includes a film that is exposed to the x-ray wave. First, the x-ray wave enters the body, passing through organs, muscles, and bones. As the soft tissue cannot absorb the electromagnetic wave, it passes through and leaves the film under or behind the patient exposed, which leads to these areas appearing in black in the final image.

The bones and hard tissues absorb the electromagnetic x-ray wave so it cannot get through to the film as easily, which makes these areas appear in light grey or white in the image.

X-ray imaging, Chest x-ray, StudySmarterFigure 3. A chest x-ray scan. Yale Rosen, Flickr (CC BY-NC-SA 2.0).

What are the applications of X-ray imaging?

X-ray imaging has applications in medical, dental, and industrial fields. Most of these applications are based on the x-ray’s ability to pass through matter. In medical physics, x-ray imaging is used for a variety of purposes, such as getting an image of broken bones, swallowed objects, lung infections, or damage to bones from arthritis. X-rays are also used with CT scanners to help achieve a layer-by-layer image.

In industry, x-ray imaging can help to analyse paintings to reveal their age or underlying brushstroke methods to identify or verify the artist.

Another common use of x-ray imaging is to scan passengers or luggage at airports or malls. When used for luggage, the machine has a detector that detects the x-rays after they pass through the object. The x-rays are then sent through a filter, which filters out the lower-energy x-rays while the high-energy x-rays are detected by a second detector. A computer compares the data yielded by the two detectors to better depict low-energy items, such as most biological compounds.

Since different objects absorb different amounts of x-rays, these differences can be seen on the screen used by the operator. There are three primary categories depending on the spectrum of energy that passes through the object: organic, inorganic, and metal.

X-ray imaging.  StudySmarterFigure 4. X-ray imaging used in an airport luggage scanner. Wayan Vota, Flickr (CC BY-NC-SA 2.0).

Applications of x-rays in materials and chemistry sampling

There are three x-ray imaging techniques used for a variety of purposes. They are: x-ray fluorescence spectrometry, particle-induced x-ray emission (PIXE) spectrometry, and x-ray diffraction.

  • X-ray fluorescence spectrometry is a non-lethal analytical method for identifying elements and their quantities in solid, powdered, and liquid samples.
  • Particle-induced x-ray emission (PIXE) is an analytical approach based on the theory of x-ray emission. Also known as proton-induced x-ray emission, this is a strong, non-destructive analytical method that can identify all elements from sodium to uranium in solids, liquids, thin films, and aerosol filter materials.
  • X-ray diffraction or XRD is a flexible, non-destructive analytical method for identifying and quantifying the many crystalline forms of chemicals found in powdered and solid samples, known as phases.

X-Ray Imaging - Key takeaways

  • X-rays are high-energy electromagnetic waves with short wavelengths that can pass through many materials.
  • The three techniques for x-ray imaging in materials and chemistry sampling are x-ray fluorescence spectrometry, particle-induced x-ray emission (PIXE) spectrometry, and x-ray diffraction (XRD).

  • Some of the common applications of x-ray imaging include scanning the human body for fractured bones, ingested objects, arthritis-related bone deterioration, and lung infections; scanning passengers or luggage at airports or malls; and analysing paintings.

  • In the process of x-ray imaging in medical fields, the x-ray wave enters the body, passing through organs and muscles. As the soft tissue cannot absorb electromagnetic waves, they pass through, leaving the film under or behind the patient exposed, which leads to these areas appearing in black in the image. Bones and hard tissue, which absorb the electromagnetic x-ray wave, by contrast, appear in light grey or white.

Frequently Asked Questions about X-Ray Imaging

X-ray imaging is done in order to create images of the interior of the human body. It is mostly done for the purpose of getting a view of fractured bones, arthritis-related bone deterioration, ingested objects, and lung infections.

First, the x-ray wave enters the body, passing through organs and muscles. As the soft tissue cannot absorb electromagnetic waves, they pass through, leaving the film under or behind the patient exposed, which leads to these areas appearing in black in the final image. The bones and hard tissues, by contrast, absorb the electromagnetic x-ray wave so it cannot get through to the film as easily, which makes these areas appear in light grey or white in the image.

The varying reduction of the x-ray beam inside a patient’s body generates a picture. Increased reduction of objects cast shadows. An object’s picture contrast relies on its x-ray beam reduction.

Final X-Ray Imaging Quiz

Question

Which of the following is the wavelength range of x-ray waves?

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Answer

0.01-10 nm.

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Question

Which of the following are not classified as ionising radiation?

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Answer

 Radio waves.

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Question

In x-ray imaging, if the x-ray wave is not absorbed by an object, in which colour does that section appear in the final image?


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Answer

Black.

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Question

Which of the following is a technique used for x-ray imaging?


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Answer

All of them.

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Which of the following is an application of x-ray imaging?


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Answer

All of them.

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Question

X-ray imaging can be used for analysing paintings. True or false?


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Answer

True.

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Question

When scanning passengers and luggage, what are the three primary categories detected, depending on the spectrum of the energy?

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Answer

Organic, inorganic, and metal.

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X-rays are also used with CT scanners to help achieve a layer-by-layer image. True or false?


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Answer

True.

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Question

Can soft tissue absorb x-ray electromagnetic waves as well as hard tissue?


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Answer

 No, it cannot.

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Question

In medical physics, in order to get an x-ray scan, what kind of object is placed under or behind the patient?

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Answer

A cassette that includes a film.

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Question

When bones absorb the electromagnetic x-ray wave, in which colour do they appear in the film?

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Answer

 Light grey or white.

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Question

Can x-ray imaging be used to visualise metal objects in a patient’s bones?


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Answer

Yes, it can.

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Question

When x-ray imaging is used for scanning passengers or luggage, which x-rays get filtered out?

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Answer

Lower energy x-rays.

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Question

X-ray imaging uses huge amounts of controlled radiation to produce images of the human body’s interior. True or false?


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Answer

False.

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Question

What is the reason that x-ray images reveal different regions of the human body in either black or white?

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Answer

Because various organs absorb radiation differently.

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Question

What are diagnostic X-rays?

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Answer

Diagnostic X-rays or radiography is an examination that is used for medical diagnosis using electromagnetic radiation beams to produce high-resolution images.   

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Why are diagnostic X-rays useful?

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Answer

X-ray imaging allows medical professionals to provide patients with fast and reliable medical diagnoses of the state of their internal organs and bones without the need for an incision. 

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Who took the first X-ray image and how?

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Answer

Wilhelm Conrad Röntgen took the first X-ray image by experimenting with cathode rays and their behaviour around substances. 

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Question

List the different types of X-ray machines.

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Answer

1. Conventional

2. CT (computed tomography)

3. Angiography

4. Mammography

5. Fluoroscopy

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Question

Which of the following is not considered a risk of X-rays machines?

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Answer

Transmission of diseases.

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Question

How do X-ray machines work?

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Answer

X-ray machines use a fixed beam to point x-rays at a single spot. As these rays move through the body, they are absorbed in different amounts depending on the tissue, and they project shadows tracing an image of the internal structures.

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Question

How is a conventional X-ray film processed?

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Answer

A sheet of plastic is covered with a radiation-sensitive chemical contained in an X-ray cassette. The shadows are projected onto the film as a result of the intensity of radiation received by the film.

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What is computed tomography?

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Computed tomography (CT) creates several cross-sectional images to form a 3D image of very high resolution using a computer. 

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What is an angiogram?

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Answer

An angiogram takes images of the bloodstream by injecting a contrasting agent into an artery so that the blood flowing structures of the body are more visible. 

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What is mammography? 

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Answer

Mammography is the process of using low-energy X-rays to examine the human breast for early diagnosis of breast cancer.  

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What is fluoroscopy?

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Answer

Fluoroscopy is an imaging technique that produces real-time images of movement within the body shown on a fluorescent screen.

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Question

Angiograms are not used to diagnose _____?

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Answer

Bone fractures.

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What is mammography used for? 

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Answer

Irregular breast masses.

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Question

What X-ray machine is more suitable to diagnose blocked arteries?

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Answer

Angiogram.

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What is a contrasting agent? 

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Answer

It is an agent injected in the bloodstream or orally to view specific features in more detail.

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Question

Why is X-ray absorption/attenuation a useful phenomenon for medical imaging?

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Answer

Different tissues attenuate X-rays by different amounts, producing variation in the X-ray intensities that reach the detector. This produces contrast in the image and allows us to distinguish tissues.

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How many main X-ray attenuation mechanisms are there?

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Answer

There are four key mechanisms – two absorb the X-ray photons, while two scatter incoming photons.

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Question

List the four attenuation mechanisms in order of minimum required photon energy.


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Answer

1. Simple scatter 

2. Photoelectric effect 

3. Compton scattering 

4. Pair production

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Question

Outline how simple (Rayleigh) scattering attenuates the X-ray beam.

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Answer

The oscillating electric field of the photon interacts with tissue atoms, creating a force acting between the two particles. This force deflects the photon (which has negligible mass compared to the atom) and scatters it within the tissue. This reduces the intensity of the remaining X-ray beam, which passes through the tissue.

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Outline how Compton scattering attenuates the X-ray beam.

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Answer

Photons with energy between 0.5-5.0MeV can transfer sufficient energy to electrons to eject them from their atomic shells. A portion of the photon energy is transferred during electron ejection, and the new lower-energy photon is scattered in a new direction, reducing the intensity of the remaining X-ray beam, which passes through the tissue.

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Question

Outline how the photoelectric effect attenuates the X-ray beam.

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Answer

X-ray photons with energy <100keV can have an energy equal to the shell binding energy of electrons around atoms in the material. The photon can therefore be absorbed by the atom and its energy transferred to an electron, which escapes and ionises the atom. As the atom drops from its ionised state back to ground energy, it emits an X-ray photon. The original photon is destroyed and the emitted photon does not travel coherently with the beam, attenuating its intensity.

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Question

Outline how the pair production effect attenuates the X-ray beam.


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Answer

Photons with energies >1.022MeV are sufficient to be absorbed by the nucleus of an atom and produce an electron-positron antiparticle pair. These antiparticles are quickly annihilated, which produces a pair of 511keV photons travelling in opposite directions from the annihilation point. As the original photon is absorbed and the emitted photons are not coherent with the beam, its intensity is attenuated.

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Question

Simple scattering has an effect on X-ray attenuation with which photon energy range?


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Answer

A photon energy range between 1-20keV.

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Question

The photoelectric effect has an effect on X-ray attenuation with which photon energy range?


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Answer

A photon energy range of < 100keV.

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Question

Compton scattering has an effect on X-ray attenuation with which photon energy range?


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Answer

A photon energy range between 0.5–5.0MeV.

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Question

Simple pair production has an effect on X-ray attenuation with which photon energy range?


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Answer

A photon energy range > 1.022MeV. 

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Question

Why do materials consisting of atoms with larger atomic numbers (Z) attenuate the X-ray beam more during medical scans?


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Answer

Medical X-rays typically operate in the range of 30-100keV, which means the photoelectric effect is the dominant mechanism. As this effect occurs when the photon collides with an electron orbiting an atom, atoms with larger atomic numbers (which also have more electrons) are more likely to produce a collision. This results in a higher rate of X-ray beam attenuation.

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Question

Why does the majority of the X-ray energy deposition dose occur near the skin?


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Answer

Photons with lower energy are more likely to be absorbed by tissue due to the photoelectric effect, as the probability of absorption is proportional to (Z/E)3. This means that the lower-energy photons are absorbed quickly as they penetrate through the skin, while higher-energy photons are more likely to pass all the way through the patient without being absorbed.

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Question

Why may larger patients have a higher risk of sustaining skin injuries from an X-ray?


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Answer

X-ray attenuation is proportional to the thickness of the substance the beam must penetrate, meaning larger patients can require a higher intensity beam to achieve good images.

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Question

How are X-rays transformed into photons?

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Answer

When electrons impact the positive electrode, energy is released and the electron transforms into a highly energised photon or X-ray. 

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Question

What are X-rays?

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Answer

High energy electromagnetic waves that have a short wavelength and high frequency.

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Question

List some applications of X-ray imaging. 

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Answer

Medical (CT scan, angiogram), industrial (security or stress analysis imaging), or research (for material property research).

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Question

What is X-ray attenuation?

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Answer

The reduction of energy due to the absorption of X-rays as they travel through a material.   

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Question

List some image processing algorithms.

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Answer

Low- and high-pass filters, directional or edge detection filters, and linear contrast stretch.

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Question

Which of the following is true? 

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Answer

A low-pass filter allows low spatial frequencies to pass while blocking high spatial frequencies.  

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