1 X-ray Production Flashcards
The mass
–The mass of a body is a measure of its resistance to acceleration.
–Mass is measured in kilograms (kg).
Velocity
–Velocity is the speed of a body moving in a given direction.
–Velocity is measured in meters per second (m/s).
Acceleration
–Acceleration is the rate of change of velocity.
–Acceleration is measured in meters per second squared (m/s2).
Force
–A force causes a body to deviate from a state of rest or constant velocity (push or pull).
–Force = mass × acceleration, measured in newtons (N).
–The four physical forces in the universe are gravitational, electrostatic, strong, and weak.
The electrostatic force
–The electrostatic force causes protons and electrons to attract each other.
–Electrostatic forces hold atoms together.
Strong forces
–Strong forces hold the nucleus together.
Weak forces
–Weak forces are involved in beta decay.
Energy
–Energy is the ability to do work.
–Energy is measured in joules (J).
–Energy (joule) = power (watt) × time (second)
Einstein formula
–E = mc2 where E is energy, m is mass, and c is the velocity of light.
Electric charge
–Electric charge of an electron (or proton) is 1.6 × 10–19 coulomb (C).
Electric current
–Electric current, measured in amperes (A), is the flow of electrons through a circuit.
–An ampere is the amount of charge that flows divided by time.
–1 ampere = 1 coulomb per second
Power
–Power is the rate of performing work.
–Power is the energy used divided by time, measured in watts (W).
–1 watt = 1 joule per second
–Power (watt) = current (ampere) × voltage (volt)
A wave
–A wave is an entity that varies in space and time.
–Waves are characterized by a wavelength, frequency, and velocity.
Wavelength (λ)
–Wavelength (λ) is the distance between successive crests of waves.
–Wavelengths are measured in meters (m).
Frequency (f)
–Frequency (f) is the number of wave oscillations per unit of time.
–Frequencies are measured in cycles per second, where one cycle per second is equal
to one hertz (Hz).
The wave period
–The wave period is the time required for one wavelength to pass.
–Wave period is 1/f.
The wave velocity (v)
–The wave velocity (v) is the product of the wavelength and frequency, and measured in
meters per second (m/s).
–Velocity (m/s) = frequency (Hz) × wavelength (m)
Electromagnetic radiation
–Electromagnetic radiation is a wave that is associated with oscillating electric and magnetic fields.
–The product of the wavelength (λ) and frequency (f) of electromagnetic radiation is equal to the speed of light (c = fλ).
X-rays
–X-rays are a form of electromagnetic radiation.
–Low-frequency electromagnetic radiation has a long wavelength.
–High-frequency electromagnetic radiation has a short wavelength.
Photons
–Electromagnetic radiation is quantized, meaning that it exists in discrete quantities called photons.
–Photons may behave as waves or particles but have no mass.
–Photon energy is E = h f = h (c/λ), where h is Plank’s constant.
Generators consist of
–Generators consist of an input power supply, transformer, and rectification circuit.
Single-phase generators used in
–Dental radiography where teeth are relatively thin and longer exposure times are tolerable (no moving parts).
A transformer
–A transformer changes the size of the input voltage and is capable of producing high and low voltages.
–Np/Ns = Vp/Vs,
Rectification
–Rectification changes the AC voltage into a DC voltage across the x-ray tube.
–Rectification is achieved using diodes, which permit current to flow in only one direction.
Full-wave rectification
–Rectification for single-phase power supply normally uses four diodes.
–There are two pulses per cycle of 1/60 second.
–Each pulse ranges from zero volts to a peak (maximum) voltage.
–The maximum voltage is known as the kVp (p stands for peak).
Voltage waveform
–Voltage waveform is a plot of voltage over time.
The voltage waveform ripple
–The voltage waveform ripple is the maximum voltage minus the minimum voltage per cycle expressed as a percentage of the maximum voltage.
–Single-phase systems have 100% ripple.
–Three-phase 6-pulse systems have ∼13% ripple.
–Three-phase 12-pulse systems have ∼4% ripple.
Excitation
–Excitation occurs when atomic electrons are energized to higher energy states.
Ionization
–Ionization occurs when an atomic electron is removed from an atom.
Bremsstrahlung
–Bremsstrahlung x-rays are produced when energetic electrons interact with nuclear electric fields.
–Bremsstrahlung means braking radiation.
–Bremsstrahlung x-ray production increases with increases in both the accelerating voltage (kV) and the atomic number (Z) of the target.
Characteristic radiation
–Characteristic radiation is produced when target electrons are ejected by the incident energetic electrons.
–Only K-shell characteristic x-rays are important in diagnostic radiology.
X-ray intensity increase by
–The number of x-ray photons. – X-ray tube current. – Exposure time. – The tube current (mA) and exposure time (s) is known as the mAs. – The x-ray tube voltage (kV)
The filament
–The filament is the source of electrons that are accelerated toward the anode to produce x-rays.
Space charge
–Electrons emitted from a heated filament form a negative cloud around the filament called a space charge, which prevents further emission of electrons.
The tube current
–The tube current is the flow of electrons from the filament to the target embedded in the anode.
Focal spots
–The area of the target struck by the electrons is determined by the filament size and focusing cup.
–The focal spot is the size of the source of x-rays as viewed by the patient.
The anode angle
–The anode angle is the angle between the target surface and the central beam.
–Typical anode angles range from 7 degrees to 20 degrees.
Anodes
–Electrons striking the target produce heat and x-rays.
–The target is embedded in an anode material, which temporarily stores the heat energy deposited into the target.
