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Radiology I

Physics of Radiology

QuestionAnswer
Alternating Current An electric current that reverses its direction many times per second
Amperage The strength of an electric current, measured in amperes
Anode An electrode with a positive charge
Anode heel effect Because of the angle of the anode target, the x-ray beam has greater intensity on the cathode side of the tube, with the intensity diminishing toward the anode side
Bremsstrahlung radiation Strong electrostatic force of the nucleus causes the electron to 'slow down' As it loses energy, it changes direction, loses energy, and reappears as an x-ray photon.
Cathode A negatively charged electrode within the x-ray tube. It comprises a filament and a focusing cup.
Characteristic Radiation A projectile electron interacts with an electron in an inner (K) shell of the tungsten atom. The K-shell electron is ejected from its orbit; an outer shell electron drops into the open position and creates an energy difference: emitted as an x-ray photon.
Circuit A course or pathway through which an electrical current passes.
Current A flow of electrons along a conductor in a closed circuit.
Direct Current An electric current flowing in one direction only.
Exposure Switch The switch that generates the power to the x-ray tube. A remote-control device that permits current to flow through the circuit.
Filament A coiled tungsten wire that is the source of electrons during x-ray production.
Focal Spot The physical area of the target that is bombarded by electrons during x-ray production
Focal spot bloom When the anode is bombarded with radiation, it becomes very hot. This can expand the size of the anode and therefore decrease sharpness.
Generator Device that converts some form of mechanical energy into electrical energy.
Ground A protective measure to neutralize an electrical charge by connecting the electrical device to the earth via a conductor
Heat bloom Same as focal spot bloom.
heat dissipation Process of becoming cooler, temperature reduction.
Hertz The SI unit of frequency equal to one cycle per second.
High frequency The range of electromagnetic waves between 3 and 30 MHz.
Line focus principle The relationship between the actual and effective focal spots in the x-ray tube. By angling the face of the anode the actual focal spot can remain relatively large, while the effective focal spot is reduced in size.
Line voltage compensator A device that monitors electric power for medical devices such as x-ray equipment and adjusts for voltage fluctuations.
Off-focus radiation X-rays produced in the anode but not at the focal spot.
Photons A small, discrete bundle of energy; a particle of visible or invisible light.
Potential difference The difference of electrical potential between two points
Power The product of Volts times Time. It is expressed in Watts and describes the function of a generator. Current X Volts = Watts (I x V = W)
Pulses (timer) A single vibration or short burst of sound, electric current or light
Rectifier Electronic device that allows current flow in only one direction.
Resistance That property of an element in a circuit that resists or impedes the flow of electricity.
Rotating anode A method of dissipating heat in general purpose x-ray tubes because the tube must be capable of producing high intensity x-ray beams in a short time.
Rotor Causes the target to rotate rapidly during x-ray production.
Space charge effect The restriction of the anode which restricts the number of electrons boiled off the filament.
Stationary anode A fixed anode (non-rotating) in the x-ray tube.
Target A metal that abruptly decelerates and stops electrons in the tube current, thereby allowing the production of x-rays.
Thermionic emission The boiling off of electrons from the filament.
Transformer A device used to increase or decrease voltage (or current) through electromagnetic induction.
Unsharpness Loss of spatial resolution in a radiographic image.
Voltage An electromotive force or potential difference expressed in volts.
Watt One ampere of current that flows through an electric potential of one volt.
Waveform Graphic representation of a wave.
X-ray tube An energy converter. It receives electrical energy and converts it into two other forms: x-radiation and heat.
An example of electromagnetic radiation is x-rays. Another example of electromagnetic radiation is visible light
Properties of x-rays include: they act like both waves and particles
A mechanism for cooling the x-ray tube is rotating anode
Why should a minimum of two views of the patient be taken with each x-ray study? "cone down" or collimate the aperture of the x-ray beam
The rectifier converts: alternating current (AC) to direct current (DC)
Due to the Heel Effect, the thickest area in the field of view should be on the cathode side of the primary beam
List some parts in an x-ray tube. Electrons; Photons; Anode; Cathode; Grid; Cassette; Collimator; Bucky, Vacuum Tube
Describe what a grid is and why it is needed in radiology. Grids are placed between the patient and the x-ray film to reduce the scattered radiation which improves image contrast.
Four recommendations for the Care of the X-ray Machine discussed in class: Don,t drop/hit x-ray tube (especially portable units, fragile), Don't leave x-ray machine on continuously (longevity), Don't hold down rotor necessarily long, Don't take too many high energy exposures in rapid succession (overheating tube)
Created by: Raevyn1