X-Ray Spectrum and Absorption
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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?

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

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

    <p>Photoelectric effect</p> Signup and view all the answers

    What is the characteristic of Bremsstrahlung radiation?

    <p>It has a broad energy spectrum</p> Signup and view all the answers

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

    <p>To calculate the attenuation of an X-ray beam</p> Signup and view all the answers

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

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

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

    <p>To increase the number of electrons</p> Signup and view all the answers

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

    <p>It helps to prevent overheating of the anode</p> Signup and view all the answers

    What is the Bremsstrahlung Spectrum?

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

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

    <p>To produce X-rays with interchangeable focal spots</p> Signup and view all the answers

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

    <p>It prevents overheating of the anode</p> Signup and view all the answers

    What is the result of increasing the kV peak?

    <p>Increased bremsstrahlung radiation</p> Signup and view all the answers

    What is the effect of increasing the focal spot area?

    <p>It increases image blurring</p> Signup and view all the answers

    What is the line-focus principle?

    <p>A technique to reduce image blurring by angulating the anode</p> Signup and view all the answers

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

    <p>Direct transfer of radiation energy to DNA molecules</p> Signup and view all the answers

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

    <p>5 years</p> Signup and view all the answers

    What is the purpose of fluoroscopy in medical imaging?

    <p>All of the above</p> Signup and view all the answers

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

    <p>Detector array</p> Signup and view all the answers

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

    <p>Tomography</p> Signup and view all the answers

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

    <p>Deterministic effect</p> Signup and view all the answers

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

    <p>Producing images in rapid sequence</p> Signup and view all the answers

    What is the result of indirect radiation interaction with tissue?

    <p>Formation of free radicals that cause DNA damage</p> Signup and view all the answers

    What is the wavelength range of X-rays?

    <p>1-0.1 Å</p> Signup and view all the answers

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

    <p>The frequency of the radiation</p> Signup and view all the answers

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

    <p>To accelerate the negative electrons</p> Signup and view all the answers

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

    <p>Increases the intensity</p> Signup and view all the answers

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

    <p>To convert X-ray photons to visible light photons</p> Signup and view all the answers

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

    <p>They move to the conduction band</p> Signup and view all the answers

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

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

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

    <p>Blurring</p> Signup and view all the answers

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

    <p>99%</p> Signup and view all the answers

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

    <p>Penumbra</p> Signup and view all the answers

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

    <p>Cathode (filament)</p> Signup and view all the answers

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

    <p>Penetrating power</p> Signup and view all the answers

    What is the type of detector used in digital radiography?

    <p>Amorphous selenium (a-Se) detector</p> Signup and view all the answers

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

    <p>Latent image as an electronic signal</p> Signup and view all the answers

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

    <p>Light scattering problem</p> Signup and view all the answers

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

    <p>To convert blue light to electronic signal</p> Signup and view all the answers

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

    <p>Electrons decelerated by the positive electric field of the target nucleus</p> Signup and view all the answers

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

    <p>It decreases the heat concentration on the anode</p> Signup and view all the answers

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

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

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

    <p>It increases the energy of the X-ray photons</p> Signup and view all the answers

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

    <p>To overcome the overheating problem of the anode</p> Signup and view all the answers

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

    <p>It helps to overcome the overheating problem of the anode</p> Signup and view all the answers

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

    <p>It increases the number of electrons</p> Signup and view all the answers

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

    <p>To allow for interchangeable large or small focal spots</p> Signup and view all the answers

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

    <p>1.02 MeV</p> Signup and view all the answers

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

    <p>100 KeV</p> Signup and view all the answers

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

    <p>To increase the Photoelectric Effect</p> Signup and view all the answers

    What is the atomic number of soft tissue?

    <p>7.42</p> 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?

    <p>30 KeV</p> Signup and view all the answers

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

    <p>An electron and a positron</p> Signup and view all the answers

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

    <p>High Z number</p> 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?

    <p>The Compton Effect is more probable at low energy</p> Signup and view all the answers

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

    <p>All of the above</p> Signup and view all the answers

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

    <p>It decreases the probability of photoelectric effect</p> Signup and view all the answers

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

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

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

    <p>HVT = 0.693 / μ</p> Signup and view all the answers

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

    <p>The X-ray beam is reduced in intensity</p> Signup and view all the answers

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

    <p>To calculate the transmitted beam intensity</p> Signup and view all the answers

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

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

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

    <p>It decreases the X-ray beam intensity</p> 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.

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