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Questions and Answers
What determines the tube current at a given kVp?
What type of interaction between radiation and matter does not cause ionization?
What is the energy of the photoelectron determined by?
What is the characteristic radiation yielded in biological systems?
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What is the range of travel for low-energy electrons emitted in biological systems?
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What are the three products of the photoelectric reaction?
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What affects the tube current for a given filament current?
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What type of electromagnetic radiation is involved in the photoelectric reaction?
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What is the primary purpose of controlling kVp, mA, and grid in X-ray machine operation?
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What is the term for the amount of energy an electron has in each shell?
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What is the result of an atom or molecule changing its energy state, according to Quantum Theory?
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What is the primary purpose of personnel monitoring devices in radiology?
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What determines the atomic number (Z) of an atom?
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What is the term for the distribution of radiation in a room?
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Why is it important for radiologic technologists to know how to position personnel for minimum radiation exposure?
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What is the term for the number of protons and neutrons in an atomic nucleus?
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What is the relationship between the wavelength and frequency of electromagnetic radiation?
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What is the primary mechanism by which X-rays interact with matter?
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What is the purpose of the control panel in an X-ray machine?
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What is the primary function of the transformer in an X-ray generator?
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What is the effect of ionizing radiation on living cells?
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What is the relationship between the frequency and energy of electromagnetic radiation?
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What is the purpose of the filament in an X-ray tube?
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What is the effect of alternating current on the X-ray tube?
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What is the primary advantage of using a step-up transformer in an X-ray generator?
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What is the effect of X-ray radiation on the human body?
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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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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.
