Basics of Radiation Physics: X-Ray and Others

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Questions and Answers

What is the source of X-ray production?

X-ray machine (correct)

Patient's body

Radioactive isotopes

External radioactive material

What happens when the filament voltage is increased in an X-ray tube?

Tube current decreases

X-ray beam spectrum changes

Tube current remains constant

Tube current increases (correct)

What is the purpose of the rotating anode in an X-ray tube?

To generate X-rays

To increase tube current

To dissipate heat generated (correct)

To decrease filament voltage

What are the two types of X-ray radiation generated in an X-ray tube?

Characteristic radiation and bremsstrahlung radiation Signup and view all the answers

Why do radiographers change the X-ray machine settings?

To alter the properties of the X-ray beam Signup and view all the answers

What is the role of the filament in an X-ray tube?

To produce high-speed electrons Signup and view all the answers

What is the direction of the X-ray beam in an X-ray machine?

Towards the patient from the X-ray tube Signup and view all the answers

Why are different X-ray beam spectra applied to different body parts?

To optimize the imaging process for each body part Signup and view all the answers

What is the result of a high energy electron colliding with an inner shell electron in a tungsten atom?

The ejection of both electrons from the atom, leaving a hole in the inner layer Signup and view all the answers

What is the approximate percentage of the X-ray beam that consists of bremsstrahlung X-rays?

80% Signup and view all the answers

What is the density of natural tissue that is between soft tissues?

2 - Fat Signup and view all the answers

What is the purpose of adding filters to the X-ray beam?

To select out low energy X-rays Signup and view all the answers

What is the effect of structures being further away from the detector in an X-ray beam?

They appear larger Signup and view all the answers

What is the relationship between wavelength and frequency of X-rays?

λ = c/ѵ Signup and view all the answers

What is the percentage of kinetic energy of electrons converted into X-rays?

Less than 1% Signup and view all the answers

What is the result of an electron passing near the nucleus in bremsstrahlung X-ray generation?

The electron is slowed and deflected Signup and view all the answers

What is the shape of the X-ray beam as it travels from the source?

Diverging Signup and view all the answers

What is the result of the structures that are nearer the detector in an X-ray image?

They are magnified in relation to those that are farther away Signup and view all the answers

What is the intensity of the continuous spectrum at the short wavelength limit?

Zero Signup and view all the answers

What is the equation for measuring the un-attenuated beam intensity?

I = I0 e^-µx Signup and view all the answers

Why would a radiographer want to move the X-ray source further away from the subject?

To reduce the magnification effect Signup and view all the answers

What is the main difference between X-ray attenuation in bone and lung tissue?

X-rays are attenuated more by bone than by lung tissue Signup and view all the answers

Why would a radiographer want to place structures that need to be measured accurately closer to the detector?

To improve the accuracy of measurements Signup and view all the answers

What is a common acute health effect of radiation exposure?

Skin redness Signup and view all the answers

What is the purpose of describing X-ray abnormalities in terms of density?

To identify the tissue involved in the abnormality Signup and view all the answers

What is the purpose of the equation I = I0 e^-µx?

To measure the un-attenuated beam intensity Signup and view all the answers

What is the result of a greater difference in density or thickness of two adjacent structures in an X-ray image?

Greater contrast between the structures Signup and view all the answers

What is the value of Planck's constant?

6.63x10^-34 J s Signup and view all the answers

What is the representation of low density material such as air on a final radiograph?

Black Signup and view all the answers

What is the purpose of moving the X-ray source further away from the subject?

To reduce the magnification of the image Signup and view all the answers

What is the composition of a radiographic image?

A map of X-rays that have either passed freely through the body or have been variably attenuated Signup and view all the answers

How many different densities are useful to determine the nature of an abnormality in an X-ray image?

5 Signup and view all the answers

Study Notes

Basics of X-ray Physics

X-rays are produced by the interaction of accelerated electrons with tungsten nuclei within the tube anode.
Two types of radiation are generated: characteristic radiation and bremsstrahlung (braking) radiation.
Changing the X-ray machine settings alters the properties of the X-ray beam.

X-ray Production

X-rays are produced within the X-ray machine, with no external radioactive material involved.
Radiographers can change the current and voltage settings on the X-ray machine to manipulate the properties of the X-ray beam produced.
Different X-ray beam spectra are applied to different body parts.

The X-ray Tube

A small increase in the filament voltage results in a large increase in tube current, which accelerates high-speed electrons from the very high temperature filament negative cathode within a vacuum, towards a positive tungsten target anode.
The anode rotates to dissipate heat generated.
X-rays are generated within the tungsten anode and an X-ray beam is directed towards the patient.

X-ray Generation

X-rays are generated via interactions of the accelerated electrons with electrons of tungsten nuclei within the tube anode.
There are two types of X-ray generated: characteristic radiation and bremsstrahlung radiation.
Characteristic radiation is generated when a high-energy electron collides with an inner shell electron, both are ejected from the tungsten atom, leaving a 'hole' in the inner layer, which is filled by an outer shell electron with a loss of energy emitted as an X-ray photon.
Bremsstrahlung radiation is generated when an electron passes near the nucleus, it is slowed, and its path is deflected, and energy lost is emitted as a bremsstrahlung X-ray photon.

The X-ray Spectrum

A spectrum of X-ray energy is produced within the X-ray beam as a result of characteristic and bremsstrahlung radiation generation.
The spectrum can be manipulated by changing the X-ray tube current or voltage settings, or by adding filters to select out low energy X-rays.
Radiographers can apply different spectra of X-ray beams to different body parts.

The X-ray Beam

X-rays travel in straight lines and a beam of X-rays diverges from its source.
Structures the beam hits first will be magnified in relation to those that are nearer the detector.
Occasionally, magnification can be helpful in localizing abnormalities.
To reduce magnification, the X-ray source can be moved further away from the subject.
Structures that need to be measured accurately should be placed closer to the detector.

Tissue Densities

An X-ray image is a map of X-ray attenuation.
Attenuation of X-rays is variable depending on density and thickness of tissues.
Describing X-ray abnormalities in terms of density may help in determining the tissue involved.
The denser the tissue, the more X-rays are attenuated.
For example, X-rays are attenuated more by bone than by lung tissue.
There are five different densities that can be useful to determine the nature of an abnormality: low density material (air), very dense material (metal or contrast material), and bodily tissues (varying degrees of grey, depending on density and thickness).

Nature of X-rays

According to the quantum theory, electromagnetic radiation can also be considered as particles called photons.
Each photon has an associated amount of energy.
The relationship between wavelength and frequency is λ = c/ν, where c is the velocity of light.
Most of the kinetic energy of the electrons striking the target is converted into heat, less than 1% being transformed into X-rays.

Properties of the Continuous Spectrum

The continuous spectrum is a smooth, monotonic function of intensity vs wavelength.
The intensity is zero up to a certain wavelength – short wavelength limit (λ SWL).

Acute Health Effects of Radiation Exposure

At very high doses, radiation can impair the functioning of tissues and organs and produce acute effects such as nausea and vomiting, skin redness, hair loss, acute radiation syndrome, local radiation injuries (also known as radiation burns), or even death.

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Description

Learn about the basics of X-ray physics, including how X-rays are produced and the two types of radiation generated. This quiz is based on a lecture by Dr. Ziyad Shihab Ahmed Al-Sarraj from the College of Pharmacy at Ashur University.