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What is the electromagnetic spectrum?
the range of wavelengths or frequencies over which electromagnetic radiation extends
what is a photon?
the smallest quantity of any type of electromagnetic energy
what is radiation?
energy that comes from a source and travels through some material or through space
what is ionizing radiation?
radiation that has enough energy to eject electrons from electrically neutral atoms, leaving behind charged atoms
what are the four types of ionizing radiation?
alpha particles, beta particles, X-Rays, gamma rays
what gives off the highest percent of man made radiation
medical x rays
what are the 6 characteristics of X-ray photons?
have no mass
obey inverse square law
always travel at the speed of light
have variable wavelength and frequencies
energy and frequency are directly proportional
are electrically neutral
what are the units for x ray exposure?
roentgen (R) and Air krema (Gya)
what is the conversion of roentgen to air krema?
100R = 1 Gya
what are the units for absorbed dose of radiation?
rad and gray (Gyt)
what is the conversion of rad to gray?
100rad = 1 Gyt
what are the units for equivalent does of X rays?
rem and sievert (Sv)
what is the conversion of rem to sievert?
100rem = 1Sv
what does roentegen measure?
x-ray ability to ionize air
what does rad measure?
amount of radiation deposited/mass
varies for tissue type and energy
what does Gya and Gyt refer to?
radiation does in air and tissue respectively
1Gya = 1Gyt
what does rem measure?
used to express the amount of radiation received by radiation workers and populations
what units are the common units?
roentgen, rad, rem
what units are SI units?
air krema, Gray, Sievert
how do we convert from common to SI units?
divide by 100
how do we convert from SI to common units?
multiply by 100 or move decimal 2 to the left
how do we convert from milli to non-milli?
divide by 1000 or move decimal 3 to the left
how do we convert from non-milli to milli
multiply by 1000 or move decimal 3 to the right
what is the Curie (Ci)?
the unit of quantity of radioactive material, not the radiation emitted by that material
what is the SI unit for Curie?
Becquerel (Bq)
1 Ci = 3.7 x 10^10 Bq
what is a wave?
an entity that varies in space and time
what are the 3 defining characteristics of a wave?
wavelength, frequency, velocity
what is wavelength?
the distance over which the wave's shape repeats, usually between successive crests or valleys
what is frequency?
number of waves per unit of time
what is velocity?
the product of wavelength and frequency
do xrays travel at a constant speed?
yes, the speed of light
what is true of wave physics?
the shorter the wavelength the higher the frequency
what is the inverse square law?
the intensity of x-rays is inversely proportional to the square of the distance traveled
what is the inverse square law equation?
intensity = 1/d^2
what does inverse square law tell us?
as distance from radiation source increases, the intensity of the beam decreases
I1/I2 = (d2/d1)^2
what are the 4 basic components of an X-Ray suite?
the high voltage generator, operating console, x-ray tube, image receptor
when x-rays are produced, how are the eitted?
isotropically, with equal intensity in all directions
what x-rays do we use?
only the beams that are emitted through the window of the tube, useful or primary beam
what is leakage radiation?
x-rays that escape through the protective housing
what is the protective housing?
steel housing with lead lining to prevent leakage radiation and electric shock
leakage radiation must not exceed...
100 mR/hour at 1 meter
where are x-rays created?
x-ray tube
what is the x-ray tube?
an electronic vacuum tube with components contained in a glass or metal enclosure
what are the basic internal components of the x-ray tube?
cathode and anode
what does the vacuum component of x-ray tube allow for?
more efficient x-ray production
what does the glass enclosure of the x-ray tube do?
reduces electron flow from cathode to anode
what is the most common cause of tube failure?
tungsten vaporization
what is the anode?
site of x ray production
what occurs in the cathode?
thermionic emission
is the cathode positively or negatively charged?
negatively charged
where are the filaments located in the cathode?
in a focusing cups
What is thermionic emission?
an electric circuit sends electrons to the filaments, which heats up to the point of boiling off a cloud of electrons
what is the filament made of?
thoriated tungsten
Why is tungsten the best metal for the x-ray source?
has higher thermionic emission
how do the electrons interact with the anode?
the electrons are expelled by the cathode and the kinetic energy of the projective electrons is transferred to the target of the anode
what are the two main products of the transfer of kinetic energy?
heat and electromagnetic energy (how x rays are made)
what does the focusing cup do?
used to direct the negatively charged electrons into a smaller area
Is the focusing cup positively or negatively charged?
negatively charged
what is the purpose of the small focal point filament?
used when better spatial resolution is required -- fine details need higher resolution
what is the purpose of the large focal spot?
used when large body parts are imaged
Is the anode positively or negatively charged?
positively charged
Why is the anode positively charged?
so it can draw the electrons from the cathode towards it
how are x-rays created?
created when electrons are shot over from the cathode and slam into the anode
what are the two types of anodes?
stationary and rotating
when are stationary anodes used?
used in x-ray units in which high tube current and power are not required
what are rotating anodes able to produce?
higher energy x-rays and shorter exposure times as a result of more surface area and more heat dissipation
what does the induction motor do?
rotates the anode
what makes up the induction motor?
stator and rotor
what is the stator?
outside the enclosure, consists of a series of electromagnets equally spaced around the neck of the tube
what is the rotor?
part inside the enclosure
consists of a copper/iron shaft
what are the three main functions of the anode?
electrical conductor
thermal dissipator
provides mechanical support for the target
what is the target?
Area of the anode struck by the electrons from the cathode
where is the target in a stationary anode?
embedded in the anode
where is the target in a rotating anode?
the target is the rotating disc
what are the 3 reasons that the target of the anode is made of tungsten?
atomic number
high melting point
thermal conductivity
what must happen in order to produce X-Rays?
a very high voltage potential has to be reached and the current must be direct
what is required to produce a high enough voltage to produce x-rays?
high voltage transformer
voltage rectifier
what does a voltage rectifier do?
allows current to flow in only one direction
converts alternating current to (AC) to direct current (DC)
what percent of energy used is converted to x-rays?
~1% is converted
what happens to the remainder of the energy that is not converted to x-rays?
~99% is wasted as heat energy. this is often the limitng factor of how many x-rays can be made in a single exposure
what is the most common type of generator used for x-rays?
high frequency <1% ripple
what percent ripple does an alternating current have?
100%
what percent ripple does a single phase half rectified and single phase full rectified generator has?
100%
what percent ripple does a triple phase full rectified generator have?
~14%
what is true about the impact of the generator type with making x-rays?
the lower the voltage % ripple the greater the x-ray quantity and energy
as the voltage ripple decreases what happens to x-rays?
the ability to produce higher energy and higher energy quantity x-rays increase
what voltage power are most x-ray imaging systems operating consoles?
220 v
what does the line compensator do?
measures the voltage provided to the x-ray machine and adjusts that voltage to be exactly 220v
what does radiation quantity refer to?
the number of x-rays or intensity of the x-ray beam
what impacts the number of x-rays that reach the image receptor?
related to both the x-ray tube current (mA) and the time that the tube is energized
what does the radiation energy refer to?
the penetrability of the x-ray beam
expressed in kilovolt peak (kVp)
what is radiation quantity?
mAs, equivalent to how many x-rays are made
what is radiation energy?
kVp, equivalent to the x-rays ability to penetrate matter
can the technologist cintril the characteristics of the electron beam?
yes, by changing mAs and kVp
what piece of equipment allows the operator to control mAs and kVp?
on the operating console
what does automatic exporsure control do?
measured the quantity of radiation that reaches the image receptor, automatically terminates the exposure when the receptor receives the required intensity
what is the actual focal spot?
the area of the anode from which x-ray photons are emitted
what is the effective focal spot?
the are that is projected onto the patient
what determines the focal spot size?
the target angle
what happens when the target is angled?
the effective are of the target becomes much smaller than the focal spot
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