X-Ray Spectrum and Absorption

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Questions and Answers

What is the primary mechanism by which characteristic X-ray radiation is produced?

When an electron is emitted from the cathode and travels to the anode

When an electron interacts with an atomic electron within the anode (correct)

When an electron is absorbed by the anode and releases energy

When an electron interacts with an atomic electron within the cathode

What is the purpose of the linear attenuation coefficient (μ) in X-ray attenuation?

To measure the energy of the X-ray beam

To measure the probability of X-ray interaction with the material per unit length (correct)

To measure the density of the material

To measure the intensity of the X-ray beam

What is the effect of increasing the energy of the X-ray beam on the linear attenuation coefficient (μ)?

It increases the linear attenuation coefficient (correct)

It is dependent on the density of the material

It has no effect on the linear attenuation coefficient

It decreases the linear attenuation coefficient

What is the half-value thickness (HVT) of a material?

The thickness of the material that reduces the intensity of the beam of radiation by 50% Signup and view all the answers

What is the most common way of X-ray interaction with matter at diagnostic X-ray range?

Photoelectric effect Signup and view all the answers

What is the characteristic of Bremsstrahlung radiation?

It has a broad energy spectrum Signup and view all the answers

What is the purpose of the equation I = I˳ e –μx in X-ray attenuation?

To calculate the attenuation of an X-ray beam Signup and view all the answers

What is the relationship between the atomic number (Z) and the probability of photoelectric effect?

The probability of photoelectric effect increases with increasing atomic number Signup and view all the answers

What is the primary purpose of increasing the current in the cathode circuit?

To increase the number of electrons Signup and view all the answers

What is the advantage of using a rotating anode X-ray tube?

It helps to prevent overheating of the anode Signup and view all the answers

What is the Bremsstrahlung Spectrum?

A continuous X-ray spectrum resulting from the deceleration of electrons Signup and view all the answers

What is the purpose of using two filaments in an X-ray tube?

To produce X-rays with interchangeable focal spots Signup and view all the answers

What is the benefit of using a high melting point material for the anode?

It prevents overheating of the anode Signup and view all the answers

What is the result of increasing the kV peak?

Increased bremsstrahlung radiation Signup and view all the answers

What is the effect of increasing the focal spot area?

It increases image blurring Signup and view all the answers

What is the line-focus principle?

A technique to reduce image blurring by angulating the anode Signup and view all the answers

What is the primary mechanism of direct radiation interaction with tissue?

Direct transfer of radiation energy to DNA molecules Signup and view all the answers

What is the minimum lag period between irradiation and cancer development for stochastic effects?

5 years Signup and view all the answers

What is the purpose of fluoroscopy in medical imaging?

All of the above Signup and view all the answers

What is the primary component of a CT scanner that collects transmission projection data?

Detector array Signup and view all the answers

What is the term that refers to a picture of a slice of the body?

Tomography Signup and view all the answers

What type of radiation effect follows high radiation doses and results in relatively immediate damage?

Deterministic effect Signup and view all the answers

What is the purpose of the X-ray detector system in fluoroscopy?

Producing images in rapid sequence Signup and view all the answers

What is the result of indirect radiation interaction with tissue?

Formation of free radicals that cause DNA damage Signup and view all the answers

What is the wavelength range of X-rays?

1-0.1 Å Signup and view all the answers

What is the primary factor that determines the energy of X-ray photons?

The frequency of the radiation Signup and view all the answers

What is the main purpose of the high positive potential in an X-ray tube?

To accelerate the negative electrons Signup and view all the answers

What is the effect of increasing the atomic number of the anode on X-ray beam intensity?

Increases the intensity Signup and view all the answers

What is the purpose of the screen in the cassette in film-screen technique?

To convert X-ray photons to visible light photons Signup and view all the answers

What happens to the valence band electrons when the detector is exposed to X-rays in computed radiography?

They move to the conduction band Signup and view all the answers

What is the equation that represents the energy of X-ray photons?

E = h c / λ Signup and view all the answers

What is the main problem involved in obtaining good X-ray images?

Blurring Signup and view all the answers

What is the percentage of accelerated electrons energy converted to heat in an X-ray tube?

99% Signup and view all the answers

What is the term for the blurred edge of an object in the X-ray image?

Penumbra Signup and view all the answers

What is the component of the X-ray tube that controls the number of electrons produced?

Cathode (filament) Signup and view all the answers

What is the term that represents the energy of X-ray photons?

Penetrating power Signup and view all the answers

What is the type of detector used in digital radiography?

Amorphous selenium (a-Se) detector Signup and view all the answers

What is formed when the X-rays are absorbed by the amorphous selenium (a-Se) detector?

Latent image as an electronic signal Signup and view all the answers

What is avoided in digital radiography due to the use of amorphous selenium (a-Se) detectors?

Light scattering problem Signup and view all the answers

What is the function of the photomultiplier system in computed radiography?

To convert blue light to electronic signal Signup and view all the answers

What is the primary mechanism by which X-ray photons are produced in the Bremsstrahlung spectrum?

Electrons decelerated by the positive electric field of the target nucleus Signup and view all the answers

What is the benefit of increasing the area struck by electrons on the anode?

It decreases the heat concentration on the anode Signup and view all the answers

What is the relationship between the atomic number (Z) of the target and the production of Bremsstrahlung radiation?

The production of Bremsstrahlung radiation is directly proportional to Z Signup and view all the answers

What is the effect of increasing the kV peak on the X-ray photons?

It increases the energy of the X-ray photons Signup and view all the answers

What is the purpose of using a rotating anode X-ray tube?

To overcome the overheating problem of the anode Signup and view all the answers

What is the advantage of using a high melting point material for the anode?

It helps to overcome the overheating problem of the anode Signup and view all the answers

What is the effect of increasing the current in the cathode circuit?

It increases the number of electrons Signup and view all the answers

What is the purpose of using two filaments in an X-ray tube?

To allow for interchangeable large or small focal spots Signup and view all the answers

What is the minimum energy required for pair production to occur?

1.02 MeV Signup and view all the answers

At what energy does the Compton Effect become more probable than the Photoelectric Effect in bone?

100 KeV Signup and view all the answers

What is the primary purpose of using high Z materials as X-ray contrast media?

To increase the Photoelectric Effect Signup and view all the answers

What is the atomic number of soft tissue?

7.42 Signup and view all the answers

At what energy does the Compton Effect become more probable than the Photoelectric Effect in water or soft tissue?

30 KeV Signup and view all the answers

What is the result of the conversion of a high-energy photon into two particles in pair production?

An electron and a positron Signup and view all the answers

What is the characteristic of the materials used as X-ray contrast media?

High Z number Signup and view all the answers

What is the relationship between the energy of the X-ray photon and the Compton Effect in materials with low Z number?

The Compton Effect is more probable at low energy Signup and view all the answers

What is the primary factor that affects the linear attenuation coefficient (μ) of a material?

All of the above Signup and view all the answers

What is the effect of increasing the energy of the X-ray beam on the photoelectric effect?

It decreases the probability of photoelectric effect Signup and view all the answers

What is the Half-value Thickness (HVT) of a material?

The thickness that reduces the beam intensity to one-half of its value Signup and view all the answers

What is the formula to calculate the Half-value Thickness (HVT)?

HVT = 0.693 / μ Signup and view all the answers

What is the result of X-ray absorption by tissue?

The X-ray beam is reduced in intensity Signup and view all the answers

What is the purpose of the equation I = I˳ e –μx in X-ray attenuation?

To calculate the transmitted beam intensity Signup and view all the answers

What is the relationship between the atomic number (Z) and the probability of photoelectric effect?

The probability of photoelectric effect increases with increasing atomic number Signup and view all the answers

What is the effect of Compton scattering on X-ray beam intensity?

It decreases the X-ray beam intensity Signup and view all the answers

Study Notes

Bremsstrahlung Spectrum (Continuous X-ray)

A small fraction of accelerated electrons interact with the atomic nucleus, losing kinetic energy and emitting X-ray photons of equal energy (bremsstrahlung radiation)
The amount of bremsstrahlung depends on the target's atomic number (Z) and kV peak

Characteristic X-ray

Emitted when an electron interacts with an atomic electron, ejecting it from its shell
The ejected electron vacancy is filled by an outer shell electron, emitting an X-ray photon with energy equal to the binding energy difference between the two shells

X-ray Absorption by Tissue

X-ray attenuation reduces the beam intensity due to absorption and scattering
Measured using the equation: I = I₀ e^(-μx)
Linear attenuation coefficient (μ) measures the probability of photon interaction per unit length in a material
Depends on X-ray energy, atomic number (Z), and material density (ρ)
Half-value thickness (HVT) is the material thickness that reduces beam intensity by 50%

X-ray Interaction with Matter

Photoelectric effect: low-energy X-ray photons transfer energy to atomic electrons, more common in high-Z materials
Probability of photoelectric effect depends on the material

X-ray Tube Components

Anode material should have a high melting point (e.g., tungsten: 3400°C)
Techniques to overcome overheating:
- Equipping the X-ray tube with two filaments for large or small focal spots
- Increasing the anode area struck by electrons (focal spot area) without increasing image blurring
- Using rotating anode X-ray tubes (3600 rpm)

Types of X-rays

Bremsstrahlung Spectrum (Continuous X-ray)
Characteristic X-ray

Radiation Interactions with Tissue

Direct interaction: radiation energy directly transferred to DNA, causing structural changes
Indirect interaction: radiation energy absorbed by water molecules, forming free radicals that damage DNA molecules

Adverse Health Effects of Radiation

Deterministic effects: high radiation doses causing immediate damage (minutes, hours, days, weeks)
Stochastic effects: low radiation doses potentially leading to cancer development (lag period 5-20 years)

Fluoroscopy

Continuous acquisition of X-ray images over time (real-time X-ray movie)
Used for positioning catheters, visualizing contrast agents, and invasive therapeutic procedures

Computed Tomography (CT Scan)

X-rays pass through the body at multiple angles, collecting transmission projection data
Detector array collects data, which is synthesised by a computer into tomographic images of the patient

Physics of Diagnostic X-Rays

X-rays are electromagnetic radiation with very short wavelengths (λ 1-0.1 A°) and high penetrating power.
The energy carried by each photon depends on the frequency of radiation: E = h υ = h c /λ.

X-Ray Production

X-rays are produced when highly energetic electrons interact with matter, converting some of their kinetic energy into electromagnetic radiation.
The main components of an X-ray tube are:
A source of electrons (cathode, filament)
An evacuated space in which the electrons are accelerated (glass envelope)
A high positive potential to accelerate the negative electrons (kV)
A target which the electrons strike (anode)
Up to 99% of accelerated electrons' energy is converted to heat, and approximately 1% is converted to X-ray photons.

Techniques to Overcome Overheating Problem in the Anode

Using an anode material with a high melting point (e.g., tungsten, 3400°C)
Equipping the X-ray tube with two filaments for large or small focal spots
Increasing the area struck by electrons (focal spot area) without increasing image blurring by angulating the anode (line-focus principle)
Using a rotating anode X-ray tube (3600 rotations per minute)

Types of X-Rays

Bremsstrahlung Spectrum (Continuous X-ray): produced when accelerated electrons are decelerated and change direction, emitting X-ray photons of equal energy
Characteristic X-ray: emitted when an electron interacts with an atomic electron within the anode, ejecting it from its shell and filling the vacancy with an outer shell electron, emitting an X-ray photon

X-Ray Interaction with Matter

X-rays interact with matter through photoelectric effect, Compton scattering, and pair production
Photoelectric effect: low-energy X-ray photon transfers all its energy to an atomic electron, commonly occurring in materials with high atomic number (Z)
Compton scattering: X-ray photon collides with a loosely bound outer shell electron, transferring energy to the electron
Pair production: high-energy photon is converted into an electron-positron pair, rarely occurring at diagnostic energy range

X-Ray Image Formation

Basic requirements for X-ray image production are X-ray source and image receptor
Image receptors:
Film-screen technique: X-ray film and phosphor layer convert X-ray photons to visible light photons
Computed radiography (CR) phosphor detectors: convert X-ray photons to electronic signals
Digital radiography (DR): digital detectors convert X-ray photons to electronic signals

Radiographic Image Quality

Blurring is a major problem in obtaining good X-ray images
Bremsstrahlung Spectrum (Continuous X-ray) is the main cause of blurring
Penumbra: blurred edge of an object in the X-ray image

X-Ray Absorption by Tissue

X-ray attenuation is the reduction of the X-ray beam due to absorption and scattering
Attenuation can be measured using the equation: I = I˳ e –μx
Linear attenuation coefficient (μ) measures the probability of photon interaction per unit length in a specified material
Half-value thickness (HVT) is the thickness of material that reduces the intensity of the beam to half its value

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Description

Explore the characteristics of X-ray radiation, including the continuous Bremsstrahlung spectrum and characteristic X-rays, as well as X-ray absorption by tissue.