X ray physics exam 1

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