ELECTROMAGNETISM & XRAY IMAGING SYSTEM Flashcards
What is the primary function of an x-ray imaging system?
To convert electric energy into electromagnetic energy.
The study of stationary electric charges.
electrostatics
What are the smallest units of electric charge?
Electrons and protons.
What is the SI unit of electric charge?
Coulomb (C).
How many electron charges are in 1 Coulomb?
6x10^18
What does it mean for an object to be electrified?
It has too few or too many electrons.
How can electrification be created?
By contact, friction, or induction.
What is electric ground?
An object that serves as a reservoir for stray electric charges.
What is Coulomb’s Law?
Electrostatic force is directly proportional to the product of charges and inversely proportional to the square of the distance between them.
What is the SI unit of electric potential?
Volt (V).
What is 1 Volt equivalent to?
1 Joule/Coulomb.
What is electrodynamics?
The study of electric charges in motion.
What is a conductor?
A material through which electrons flow easily.
What is an insulator?
A material that does not allow electron flow.
What is a semiconductor?
A material that behaves as both a conductor and insulator under different conditions.
What is a superconductor?
A material that allows electron flow without resistance.
What does Ohm’s Law state?
Voltage across a circuit is equal to current times resistance:
V=IR.
What is the SI unit of resistance?
Ohm (Ω).
What are the two types of electric circuits?
Series and parallel circuits.
How is total resistance calculated in a series circuit?
RT = R1+R2+R3
How is total resistance calculated in a parallel circuit?
1/RT = 1/R1+1/R2+1/R3
Inhibits electron flow.
RESTRCITOR
What does a battery do in a circuit?
Provides electric potential.
Momentarily stores electric charge
Capacitor
What is direct current (DC)?
Electrons flowing in one direction.
What is alternating current (AC)?
Electrons flowing alternately in opposite directions.
What is magnetite?
An oxide of iron, also called lodestone.
What creates a magnetic field?
Any charged particle in motion.
A magnet with two poles (north and south).
dipolar magnet
An accumulation of aligned atomic magnets.
magnetic domain
What are the four magnetic states of matter?
Nonmagnetic, diamagnetic, paramagnetic, and ferromagnetic.
What is magnetic permeability?
The ability of a material to attract magnetic field lines.
What is magnetic susceptibility?
The degree to which a material can be magnetized.
What is the SI unit of magnetic field strength?
tesla
Developed the voltaic pile, a precursor to the modern battery.
alessandro volta
A coil of wire that creates a magnetic field when carrying current.
solenoid
What is Faraday’s Law?
The magnitude of an induced current depends on magnetic field strength, velocity, angle, and conductor turns.
Converts electric energy into mechanical motion.
electric motor
Converts mechanical motion into electric energy.
electric generator
What is a transformer?
A device that changes the intensity of alternating voltage and current.
What is a step-up transformer?
Increases voltage while decreasing current.
What is a step-down transformer?
Decreases voltage while increasing current.
What is a high-voltage generator?
Increases output voltage for x-ray production.
What does a rectifier do?
Converts AC to DC.
Voltage flows in only one direction, using half the AC cycle.
half-wave rectification
Converts the entire AC cycle into usable current.
full-wave rectification
What is the advantage of a high-frequency generator?
Produces a nearly constant voltage, improving image quality and reducing patient dose.
What is the purpose of a capacitor discharge generator?
Maintains x-ray tube voltage during exposure.
Acts as a rapid switch to stop x-ray emission.
grid-controlled x-ray tube
A measure of variation in voltage during x-ray production.
voltage ripple
What is the voltage ripple percentage for a single-phase system?
100%
What is the voltage ripple percentage for a high-frequency system?
Less than 1%.
What are the three main sections of the x-ray imaging system?
X-ray tube, operating console, and high-voltage generator.
What is the composition of the examination table?
Carbon fiber, for strength and minimal x-ray absorption.
What does the operating console control?
X-ray tube current, voltage, line compensation, and exposure time.
What is radiation quantity?
The number or intensity of x-rays in the beam, measured in mR or mR/mAs.
What is radiation quality?
The penetrability of the x-ray beam, expressed in kVp or HVL.
What is the purpose of the autotransformer?
Supplies a precise voltage to the filament and high-voltage circuits.
Vp meter measure?
Voltage, not directly kVp.
Controlling x-ray tube current by heating the filament.
filament circuit
What is thermionic emission?
The release of electrons from a heated filament.
What is space charge?
A cloud of electrons near the filament.
Difficulty in emitting additional electrons due to electrostatic repulsion.
space charge effect
Automatically adjusts to the highest mA for the shortest exposure time.
falling load generator
Steps down voltage and provides current to heat the filament.
filament transformer
What is the purpose of the guard timer?
Terminates an exposure after 6 seconds.
What is the role of the timer circuit?
Makes and breaks the high voltage across the x-ray tube.
What are the four types of timing circuits?
Synchronous timer, electronic timer, mAs timer, and automatic exposure control (AEC).
A device that drives a shaft at precisely 60 revolutions per second.
synchronous timer
What is an electronic timer?
The most accurate and sophisticated timer, allowing intervals as small as 1 ms.
Monitors mA and exposure time, terminating exposure when the desired mAs is reached.
mAs timer
Automatically terminates exposure when the image receptor receives sufficient radiation.
automatic exposure control (AEC)
What does a solid-state detector measure?
Timer accuracy as short as 1 ms.
What is the turns ratio in a high-voltage transformer?
Ratio of secondary windings to primary windings, e.g., 500:1.
Ensures current flows in one direction, converting AC to DC.
rectification
What is a solid-state rectifier made of?
silicon
Contact point between p-type and n-type semiconductors, allowing current to flow in one direction.
p-n junction
What is the purpose of inverter circuits in high-frequency generators?
Converts DC into square pulses.
What is the typical frequency range of high-frequency generators?
10–100 kHz.
What is a single-phase power disadvantage?
Produces x-rays with low energy due to high voltage ripple.
What is the advantage of three-phase power?
Produces nearly constant voltage across the x-ray tube.
What is a shell-type transformer?
A transformer with primary and secondary windings wrapped around a central core for greater efficiency.
A transformer with one winding used to control kVp.
autotransformer
What is line compensation?
Adjustment of incoming voltage to a consistent level.
Increases voltage from the autotransformer to kVp levels needed for x-ray production.
high-voltage generator
What is the role of a capacitor in the x-ray imaging system?
Stores electric charge temporarily.
What are the components of a high-voltage generator?
High-voltage transformer, filament transformer, and rectifiers.
Acts as a variable resistor to control current.
rheostat
What is the voltage range for diagnostic x-rays?
25–150 kVp.
What is the purpose of a diode?
Allows current to flow in only one direction.
What are the three main parts of the x-ray imaging system?
X-ray tube, operating console, and high-voltage generator.
side of the x-ray tube where x-rays are produced.
anode
side of the x-ray tube that emits electrons.
cathode
What is the principle of electromagnetic induction?
A changing magnetic field induces an electric current.
Retention of magnetization in materials even after the magnetic field is removed.
hysteresis
A region in a material where magnetic dipoles align.
magnetic domain
A material’s ability to support magnetic field formation.
magnetic permeability
What are ferromagnetic materials?
Strongly magnetized materials like iron and cobalt.
What are paramagnetic materials?
Weakly attracted materials like gadolinium.
What are diamagnetic materials?
Materials weakly repelled by a magnetic field, e.g., water.
What does a magnetic dipole create?
A small magnet.
What does an electromagnet consist of?
A current-carrying coil of wire around an iron core.
Powers the rotating anode of the x-ray tube.
induction motor
Reduces energy loss and increases efficiency.
transformer core
What is eddy current loss in transformers?
Energy loss due to induced currents in the core.
A semiconductor device used in high-frequency generators.
thyristor
What is the energy range for x-ray photons in diagnostic imaging?
30–150 keV.
What are the two types of x-ray tubes?
Radiographic and fluoroscopic.
Supports the patient and allows tilting for fluoroscopic procedures.
fluoroscopic table
Switches current direction in an electric motor.
commutator ring
What are the three primary regions of the x-ray spectrum?
Bremsstrahlung radiation, characteristic radiation, and continuous spectrum.
What is the main purpose of the x-ray tube housing?
Protects against leakage radiation and supports the tube.
What material is commonly used for x-ray tube housing?
Lead-lined material to reduce leakage radiation.
What is the function of the filament in the x-ray tube?
Emits electrons through thermionic emission.
What is the typical range of filament current?
3–6 amperes.
Focuses the electron beam onto the target area of the anode.
focusing cup
What material is commonly used as the anode target?
Tungsten, due to its high melting point and atomic number.
What is the maximum tilt angle of a fluoroscopic table?
90 degrees to the foot side and 30 degrees to the head side.
What is the typical rotation speed of a standard anode?
3,000–10,000 revolutions per minute (rpm).
What is the purpose of oil in the x-ray tube housing?
Provides insulation and cooling.
Transmits electrical energy from the generator to the x-ray tube.
high-voltage cable
The x-ray beam that exits the x-ray tube and is directed at the patient.
primary beam
What is the purpose of a grid in radiology?
Reduces scatter radiation reaching the image receptor, improving image contrast.
What is the common grid ratio in diagnostic imaging?
8:1 or 12:1.
Holds the grid and image receptor in place.
a bucky system
What is the function of an image intensifier in fluoroscopy?
Converts x-rays into a visible light image, enhancing brightness.
What is the output phosphor in an image intensifier?
Converts electrons into a visible light image.
What is automatic brightness control (ABC) in fluoroscopy?
Maintains consistent image brightness by adjusting exposure factors.
What is a photomultiplier tube used for in imaging?
Amplifies light signals for processing.
What is the role of a flat-panel detector in digital imaging?
Captures x-ray photons and converts them into electrical signals.
used for storing and managing digital images.
PACS
a standard for storing and transmitting medical images.
DICOM
What is the difference between CR and DR systems?
CR uses cassettes with photostimulable plates, while DR uses flat-panel detectors.
What is beam filtration?
The removal of low-energy x-rays from the beam to reduce patient dose.
What is the minimum total filtration required for diagnostic x-ray tubes?
2.5 mm aluminum equivalent for x-ray tubes operating above 70 kVp
