X-Ray Generation and Tube Current
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Questions and Answers

What determines the tube current at a given kVp?

  • Number of electrons available from the filament (correct)
  • Type of electromagnetic radiation used
  • Atomic number of the biological system
  • Energy of the incident x-ray

    • What type of interaction between radiation and matter does not cause ionization?

  • Thomson scattering
  • Compton scattering (correct)
  • Photoelectric reaction
  • Low-energy photon absorption

    • What is the energy of the photoelectron determined by?

  • Atomic number of the biological system
  • Difference between the energy of the incident x-ray and the electron binding energy (correct)
  • Energy of the incident x-ray only
  • Type of electromagnetic radiation used

    • What is the characteristic radiation yielded in biological systems?

    <p>Weak characteristic radiation</p> Signup and view all the answers

    What is the range of travel for low-energy electrons emitted in biological systems?

    <p>A few millimeters</p> Signup and view all the answers

    What are the three products of the photoelectric reaction?

    <p>Photoelectron, characteristic radiation, and ionized atom</p> Signup and view all the answers

    What affects the tube current for a given filament current?

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

    What type of electromagnetic radiation is involved in the photoelectric reaction?

    <p>X-ray</p> Signup and view all the answers

    What is the primary purpose of controlling kVp, mA, and grid in X-ray machine operation?

    <p>To enhance image quality</p> Signup and view all the answers

    What is the term for the amount of energy an electron has in each shell?

    <p>Binding energy</p> Signup and view all the answers

    What is the result of an atom or molecule changing its energy state, according to Quantum Theory?

    <p>The emission or absorption of energy</p> Signup and view all the answers

    What is the primary purpose of personnel monitoring devices in radiology?

    <p>To minimize radiation exposure to personnel</p> Signup and view all the answers

    What determines the atomic number (Z) of an atom?

    <p>The number of protons in the nucleus</p> Signup and view all the answers

    What is the term for the distribution of radiation in a room?

    <p>Radiation distribution</p> Signup and view all the answers

    Why is it important for radiologic technologists to know how to position personnel for minimum radiation exposure?

    <p>To minimize radiation exposure to personnel</p> Signup and view all the answers

    What is the term for the number of protons and neutrons in an atomic nucleus?

    <p>Atomic mass</p> Signup and view all the answers

    What is the relationship between the wavelength and frequency of electromagnetic radiation?

    <p>Wavelength is inversely proportional to frequency</p> Signup and view all the answers

    What is the primary mechanism by which X-rays interact with matter?

    <p>Ionization of atoms</p> Signup and view all the answers

    What is the purpose of the control panel in an X-ray machine?

    <p>To monitor the X-ray machine's performance</p> Signup and view all the answers

    What is the primary function of the transformer in an X-ray generator?

    <p>To step up the voltage of the X-ray tube</p> Signup and view all the answers

    What is the effect of ionizing radiation on living cells?

    <p>It disrupts the cell's DNA structure</p> Signup and view all the answers

    What is the relationship between the frequency and energy of electromagnetic radiation?

    <p>Frequency is directly proportional to energy</p> Signup and view all the answers

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

    <p>To heat the tungsten target</p> Signup and view all the answers

    What is the effect of alternating current on the X-ray tube?

    <p>It produces a pulsating X-ray beam</p> Signup and view all the answers

    What is the primary advantage of using a step-up transformer in an X-ray generator?

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

    What is the effect of X-ray radiation on the human body?

    <p>It can cause cancer and genetic damage</p> Signup and view all the answers

    Study Notes

    X-ray Generation

    • X-ray tube current is determined by the number of electrons available from filament heating at a given kVp.
    • kVp affects tube current for a given filament current.

    Interactions with Matter

    • Scattering: interactions with matter that change the direction of radiation without changing its wavelength.
    • Photoelectric Reaction: interaction with matter where x-rays are absorbed and not scattered, resulting in:
      • Ejection of an electron with kinetic energy (KE) equal to the difference between the incident x-ray energy and the binding energy.
      • Weak characteristic radiation in biological systems.
      • Three products: photoelectron, characteristic radiation, and radiologic physics and safety.

    Operator Knowledge

    • Operator must know how to:
      • Operate the x-ray machine and its features.
      • Position the patient properly.
      • Control image quality (kVp, mA, grid, etc.).
      • Minimize radiation levels (colimitation, special dose rate controls).
      • Position personnel for minimum radiation exposure.
      • Use shielding devices and personnel monitoring devices.
    • Operator must know how radiation is distributed in the room and applicable laws and institution policies.

    Atom Structure

    • Atom: the smallest particle of matter that maintains the properties of an element.
    • Consists of a nucleus with surrounding electron shells.
    • Atomic number (Z) = number of protons.
    • Atomic mass (A) = number of protons + neutrons.
    • Quantum Theory: atoms and molecules can only exist in certain energy states, and when they change state, they must emit or absorb energy.

    Electron Orbital Shells

    • Energy of atoms is quantized, with electrons revolving around the nucleus at discrete energy levels.
    • Binding energy: the amount of energy an electron has in each shell.
    • Closer to the nucleus, binding energy increases.
    • Bound electrons have negative total energy.
    • Calculating electrons in a shell: 2(n^2).

    Electromagnetic Waves

    • EM radiation is emitted when electric charges are accelerated.
    • EM radiation has wavelike properties, with properties of absorption and emission in discrete energy bundles (photons).
    • Energy is transferred to any material it interacts with.
    • High-energy EM radiation can ionize matter.

    Ionization

    • Ionization: the process of an atom gaining or losing an electron, resulting in a net charge.
    • Positive charge: cation.
    • Negative charge: anion.
    • X-rays ionize atoms, causing biological effects (short and long-term).

    Electricity

    • Static electricity: electric charge at rest.
    • Current electricity: moving electric charge.
    • Direct current: flow of electrons in one direction.
    • Alternating current: flow of electrons in alternating directions.

    X-ray Machine Components

    • Generator: supplies electric power to the x-ray tube.
    • X-ray tube: produces x-rays.
    • Control panel: controls the machine.

    X-ray Generator

    • Produces smooth, high-voltage direct current from low-voltage AC current.
    • Transforms low-voltage AC to high-voltage AC.
    • Rectifies high-voltage AC current to DC current.
    • Smooths voltage dips with capacitive filters, offset circuitry, or increased frequency.

    Transformers

    • Current in a wire generates a magnetic field.
    • A changing magnetic field produces a transient electric field, and a changing electric field produces a transient magnetic field.
    • Induced EMF's exist only in a coil if the flux through the coil is changing.
    • EMF = -N x change in flux per unit time.

    Laws of Transformers

    • 𝑵𝒑 / 𝑽𝒑 = 𝑵𝒔 / 𝑽𝒔.
    • 𝑽𝒑 ∗ 𝑰𝒑 = 𝑽𝒔 ∗ 𝑰𝒔.

    Current Rectification

    • Uses a diode to alter AC current so that it all enters in the same direction.
    • Full-wave rectification creates a better image than half-wave rectification.

    Smoothing Out

    • Principle disadvantages of full-wave rectification: tube pulsation, varying intensity, and quality of the beam.
    • Capacitor stores energy and releases it when current stops flowing, creating a slower decrease in current.
    • Ripple factor: variation in voltage across the x-ray tube expressed as a percentage of its maximum value.

    X-ray Tube Head

    • Evacuated glass envelope with a CRT (cathode regulated tube).
    • Negatively charged tungsten cathode with a coil filament.
    • Positively charged copper anode with a tungsten target.
    • Window and added filtration.
    • Beam limiting device.

    X-ray Generation

    • Electrons thermionically "boil-off" the filament embedded in the cathode.
    • Electrons are "shot" at the anode target by applying a strong potential difference (kVp).
    • High-energy electrons interact with target atoms to produce photons in the x-ray wavelength.
    • Electrons not absorbed are conducted away, completing the circuit.
    • X-ray beam is polyenergetic, with photons comprising varied energies (spectrum).

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    Harrington Intro Imaging Midterm PDF

    Description

    This quiz covers the principles of x-ray generation, including the relationship between filament heating, tube current, and peak voltage. It also touches on the interactions of radiation with matter.

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