Physics Flashcards
source of rad in XR tube
focal spot
bc of line focus principle, the effective focal spot size decreases w decreasing?
target angle
high capacity tube rotors revolve at?
10,000 rpm
XR intensity (I) is lower on the anode side of the tube bc of the
heel effect
cathode side of tube should be towards the _______ part of pt
thicker
formula for heat units (HU) for a 3-phase, 6-pulse XR machine?
1.35 x kVp x mA x s
tube failure can occur from?
long exposure T’s
a dual focus tube has 2?
filaments
ea tube has it’s own tube rating chart to show?
max exposure T’s
the _______ is/are outside the glass envelope?
stators
heel effect is caused by the?
anode angle
the effective focal spot size is ________ the actual focal spot size.
smaller than
projectile e-‘s travel from?
cathode to anode
during an exposure most of the ______ energy of the projectile e-‘s is converted to _____
kinetic; heat
the efficiency of XR production increases as _____ increases
kVp
approx. ___ of the kinetic energy of the projectile e-‘s is converted to XRs at the target
1%
e- interactions @ the inner shell of target atoms produce ________ rad
characteristic
most of the heat generated at the target is due to?
outer-shell excitation
production of heat @ anode is directly proportional to?
tube current
useful characteristic XRs from tungsten targets are ______ XRs
K-shell
characteristic K-shell XRs have an effective energy of _____ keV
69
most XRs produced at the target are ________
bremsstrahlung
at 55 kVp ______ of the XRs produced are bremsstrahlung
100%
bremsstrahlung XRs are produced by _____ at the target
slowing e-‘s
characteristic XRs are produced by
released binding energy
quantity of bremsstrahlung rad increases proportionately w increased _____
mAs
an exposure taken at 100 kVp would have a continuous emission spectrum w a max energy of _____ keV
100
the ____ of an XR beam is higher when the peak of the emission spectrum is further to the ______
quality; right
an increase in mAs would _____ the ________ of the emission spectrum
increase; amplitude only
an increase in kVp would ______ the ________ of the emission spectrum
increase; amplitude & pos.
changes in ________ result in directly proportional changes in the amplitude of the emission spectrum
mA & T
the discrete portion of the XR emission spectrum would change pos. w a change in?
target material
amplitude of emission spectrum is _______ w a ________ generator than/as w a 3-phase generator
lower; single-phase
a 15% increase in kVp is = to
doubling mAs
how does added filtration affect the emission spectrum?
reduced amplitude and shift to R
Roentgens (or grays) is the measurement for XR?
quantity, exposure, & Intensity
of useful XRs in the beam defines the XR
quantity
standard XR machines produce about ____ mR/mAs at 70 kVp measured at 100cm SID
5
XR quantity increases in direct proportion to increases in?
mAs
if the distance from the source to the img (SID) is reduced by 1/2, how is the XR intensity at the img affected?
increased 4x’s
if filter thickness is _____, then XR intensity is _____
increased, reduced; or reduced, increased (inversely proportional)
a 10% increase in kVp has _____ effect on XR intensity than/as a 10% increase in mAs
much greater
if XR quantity is doubled, the optical density (OD) on the finished radiograph will be?
increased by a factor of 2
if a tech changes the technique from 70 kVp @ 200 mAs to 70 kVp @ 400 mAs, the the XR intensity will _______ and optical density (OD) will _______
double, double
the inverse square law has the same effect on optical density (OD) and XR __________
intensity, exposure, & quantity
an increase of 15% in kVp is = to increasing mAs _________
100%
if the intensity of a 70 kVp exposure at 20 mAs is 100 mR, what would it be at 5 mAs?
25 mR
if an exposure is 50 mR at an SID of 40”, what would the exposure be at an SID of 60”?
22.2 mR
XR intensity is proportional to?
kVp^2
penetrability of an XR beam is called XR _______
quality
an XR beam that should pass through dense tissue would have high?
penetrability & quality
a low quality beam would also have low?
penetrability
beam quality is affected by?
kVp & filtration
the half value layer (HVL) of XR beam is a measurement of beam?
quantity
img contrast is affected by?
beam quality & kVp
the HVL is lowered by a decrease in?
kVp
XR beam quality is improved by
increased filtration
main purpose os added filtration is to reduce
pt dose
added filtration will _____ beam quality and ______ beam quantity
increase, decrease
a compensating filter is used to create _____ optical density (OD) w a body part of ______ thickness
uniform; non-uniform
2 primary forms of XR interaction in the diagnostic range are
Compton scattering & photoelectric absorption
an incident XR interacts w an atom without ionization during __________
coherent scattering
an outer-shell e- is ejected & the atom is ionized w?
Compton interactions
which XR interaction involves the ejection of the K-shell e-?
photoelectric absorption
the scattered XR from a Compton interaction usually retains _____ of the energy of the indecent photon
most
Compton scatter is directed at (a) _______ angle from the incident beam
any
as kVp _____, the probability of photoelectric absorption ________
increases, decreases
there is complete absorption of the incident XR photon w
photoelectric effect
_________ only occurs at the very high energies used in rad therapy and in nuclear med PET imaging.
pair production
only at energies above 10 MeV can _______ take place
photodisintegration
when the mass density of the absorber is ______, it results in ______ Compton scatter
increased, increased; OR decreased, decreased (direct relationship)
K-shell binding energy increases w increasing ______
atomic #
what has the greatest mass density?
bone
img fog is caused by?
Compton scatter/interactions
bc of differential absorption, about ____ of the incident beam from the XR tube contributes to the finished img
0.5%
differential absorption is dependent on?
the kVp of exposure, atomic number (Z) of absorber, & mass density of absorber
attenuation is caused by?
absorption & scattering
Ba is a good contrast agent bc of it’s
high Z
the use of contrast agents increases the amount of?
differential absorption, Compton Scatter, photoelectric absorption
a neg. contrast agent is?
air
XR transmitted without interaction contribute to
the radiographic img
Compton interactions, photoelectric absorption, & transmitted XRs ALL contribute to?
differential absorption
high kVp techniques reduce
pt dose
if 5% of an incident beam is transmitted through a body part, then 95% of that beam was
attenuated
smallest quantity of any type of electromagnetic rad
photon
velocity of all electromagnetic rad?
3 x 10^8 m/s
rate of rise and fall of a sine wave is called its
frequency
a hertz (Hz) is = to
1 cycle per sec
electromagnetic wave equation?
c=f⋋
the _____ of electromagnetic rad is constant
velocity
if the wavelength of a beam of electromagnetic rad increases by a factor of 2, then its frequency must
decrease by 1/2
the intensity of rad _____ in _____ proportion to the square of the distance of the object from the source
decreases, inverse
the reduction of rad intensity due to scattering & absorption is called ______
attenuation
velocity of light?
c = 3 x 10^8 m/s
max # of e-‘s that can exist in an electron shell is calculated w?
2n^2
the shell # of an atom is called the
principal quantum #
the unit of measure of rad in the air is the
roentgen
the ______ is the unit used to describe the dose of ionizing rad received by a pt
rad
what unit is used to measure occupational dose?
rem
a measure od 10^-3 rads is a?
millirad
quantity of matter as described by its energy equivalence
mass
what has form/shape & occupies space
matter
energy of motion
kinetic
ability to do work
energy
rate of doing work
power
standard unit of mass in SI system?
kg
atoms & molecules are the fundamental building blocks of
matter
radio waves, light, & XRs are all ex’s of ________ energy
electromagnetic
removal of an e- from an atom
ionization
ionizing rad is capable of removing ________ from atoms as it passes through matter
e-‘s
biggest source of manmade ionizing rad exposure to the public
diagnostic XRs
Wilhelm Roentgen discovered XRs while experimenting w?
Crookes tube
radioactive material measured in
curies
which of the following is ionizing electromagnetic rad? (beta rays, gamma rays, radio waves, alpha rays)
gamma rays
Newton’s 2nd law is written mathematically as?
F=MA
who invented fluoroscopic machine?
Thomas Edison
term “atom” was first used by the
Greeks
smallest particle that has all the properties of an element is a(n) ______
atom
periodic table of elements was developed by _______ in the late 19th century
Mendeleev
a pos. charged nucleus surrounded by neg. charged e-‘s in well-defined orbits is the _______ model of the atom
Bohr
fundamental particles of an atom?
proton, e-, neutron
chem element is determined by the # of ____ in the atom
protons
an atom in a normal state has an electric charge of
zero
the binding energies or energy levels of e-‘s are represented by their?
shells
when an atom has the same # of protons, but diff # of neutrons, its called an
isotope
when atoms of various elements combine, they form
molecules
an atom that loses/gains 1+ e- is an ____
ion
neutral atom has the same # of ______ & e-s
protons
innermost e- shell is
K-shell
atomic # symbolized w
Z
Aluminum has a Z of 13. how many protons does it have?
13
atomic # of molybdenum is 42 and the atomic mass # is 98. how many neutrons does it have?
56
only diff btw XRs & gamma rays is
their origin
the _______ is the least penetrating form of ionizing rad
alpha particle
gamma rays are produced in the _______ of the atom
nucleus
the T required for a quantity of radioactivity to be reduced to 1/2 of its original value
1/2 life
examples of particulate rad?
alpha & beta particles
what’s common amongst all electromagnetic rad’s?
their velocity
alpha particles are compared to a ________ nucleus
helium
the force that keeps an e- in orbit is the?
centripetal & centrifugal force
87º Fahrenheit is equal to _____ Celsius
Tc=5/9(Tf - 32)
Tc = 5/9 (87 - 32)
Tc = 30.5ºC
1/2 the distance from crest of a sine wave to the valley is the
amplitude
in a sine wave, the distance from one valley to another valley (or crest to crest) is
wavelength
of wavelengths that pass a point of observation per sec
frequency
in a sine wave, the shorter it’s wavelength, the _______ its frequency
higher
the energy of a photon is directly proportional to its
frequency
the ___________ describes the relationship btw rad intensity and distance from the rad source
inverse square law
when white light goes through a prism, it gets
refracted
the study of fixed/stationary electric charge
electrostatics
fundamental unit of electric charge is
Coulomb
according to ________, electrostatic force is directly proportional to the product of the electrostatic charges and inversely proportional to the square of the distance btw them
Coulomb’s law
what states that “when an object becomes electrified, the electric charges are uniformly distributed throughout the object or on its surface”
electrostatic law #3
what states that “the electric charge of a conductor is concentrated along the sharpest curvature of its surface”?
electrostatic law #4
unit of electric potential?
volt
study of electric charges in motion is known as
electrodynamics
silicone & germanium are examples of
semiconductors
the property of some materials to exhibit no resistance below certain critical temp is illustrated as a concept known as
superconductivity
any property of the circuit that opposes/hinders the flow of the current is known as
resistance
what factors affect resistance?
material, diameter, length, & temp of conductor
which law states that the voltage across the total circuit or any portion of the circuit is = to the current multiplied by the resistance?
Ohm’s law
if the e- flows alternatively in opposite direction, it is called
alternating current
______ is = to 1 ampere of current flowing through an electric potential of 1 volt
1 watt
any charged particle in motion creates
a magnetic field
the direction of the magnetic field is ________ to the motion of a charged particle
perpendicular
the ability of a material to attract the lines of magnetic field intensity is known as
magnetic permeability
degree to which various material can be magnetized is known as
magnetic susceptibility
what is considered as paramagnetic
MRI contrast
which transformer works under the principle of self-induction?
auto transformer
transformer law formula?
Vs/Vp = Ns/Np
a step up transformer has 500 coils at the primary & 7000 coils at the secondary. If 220 volt is supplied at the primary, how much voltage will be produced at the secondary?
3100v
the transformer loss due to the resistance of the wire is known as
Copper loss
a transformer has 600 coils on its primary side and 30 coils on its secondary side. what s the voltage on the secondary side when the primary side is 220 V?
11V
an electric current can be induced in a coil of wire if it is places near a(n)
electromagnet
the reduction of rad intensity due to scattering & absorption is called
attenuation
gamma rays are produced in the _____ of the atom
nucleus
photons w the highest frequencies have the
shortest wavelengths
like charges _____ and unlike charges _______
repel, attract
electrostatic force is _____ proportional to the distance btw charges and _______ proportional to the product of the charges
inversely, directly
charges on an electrified object are distributed
evenly throughout the object
on the surface of an electrified object the charges concentrate
on the sharpest curvatures
_______ is a source of a direct current
a battery
an alternating current (AC) is represented by a __________ line
sinusoidal
________ uses direct current? (hair dryer, toaster, microwave, flashlight)
flashlight
Ohm’s law? (formula)
I = V/R
SI unit of magnetic field strength
tesla
what type of material can be made magnetic when placed in an external magnetic field?
ferromagnetic
if 3 resistors of 3 ohms, 4 ohms, & 6 ohms ea are connected in a series what will be the total resistance?
Rt = R1 + R2 + R3 Rt = 3+4+6 Rt = 13 Ohm's
if the current flowing through a circuit is 2A and the potential difference is 110V, what will be its resistance?
V = IR --> R = V/I R = 110V/2A R = 55 Ohm's
if a pt receives 100 mR standing at a distance of 72” from an XR source, what will be the rad dose to the pt if the pt is standing at a distance of 40”?
I1/I2 = D2^2/D1^2
100 mR/!2 = 40^2/72^2
1600I2 = 518400
I2 = 324 mR
what determines quality of XR beam?
kVp
what determines quantity of XR beam?
mA & exposure T
heating a coil of wire to produce e-‘s is known as
thermionic emission
the flow of e- from filament to anode is known as
tube current
the alternating current can be converted to direct current w the use of a
rectifier
if a tech uses 70 kVp, 400 mA, & 1/10 s exposure T for a KUB, what will be the mAs produced?
40
what is located btw the auto-transformer & the step up transformer?
kVp meter
what transformer works under the principle of self-induction
auto transformer
what is located btw the step up transformer & XR tube?
rectifier
XR of L-spine needs 40 mAs. the tech wants to use the 200 mA station. what should be the exposure T?
0.20 s
a tech wants to use 110 kVp & 80 mAs for a L-spine. the tech wants to use 200 millisec exposure T. what mA station should be chosen?
400 mA
what is located at the secondary side of the step up transformer?
mA meter
two basic types of induction are _____ induction & ______ induction
self, mutual
a transformer converts
electrical potential to higher/lower intensity
the current to a transformer must be supplied by a(n)
AC source
variations in power distribution to the XR machine are corrected by the
line voltage compensator
the 1st component to receive power in the XR circuit is the
autotransformer
the ______ circuit provides e-‘s for the XR tube current
filament
thermionic emission at the filament determines the _______ across the XR tube during an exposure
milliamperage
a step-down transformer is located in the ______ circuit
filament
the most accurate type of timer is the ______ timer
electronic
the AEC terminates the exposure when
sufficient rad reaches the IR
the ionization chamber is located
btw the pt & the IR
the f(x) of the photodiode is
to convert light to electric signal
the principal material used in the formulation of a solid state diode is
silicon
process by which alternating current is converted into pulsating direct current is termed
rectification
type of unit most likely to possess the smallest voltage ripple is a
high frequency unit (1%)
1 3-phase, 12-pulse wave formula has _____ ripple
4%
a high frequency wave form has ____ ripple
1%
a 3-phase, 6-pulse wave form has ____ ripple
14%
a single-phase wave form has ______ ripple
100%
a 3-phase, 6-pulse unit has an effective kV of about _____ of the peak kVp
86%
during capacitor discharge, the voltage falls at a rate of
1 kV/mAs
the e- cloud around the filament is known as
space charge
tungsten is the material of choice for the target bc?
high Z, high thermal conductivity, high melting point
according to line focus principle, the effective focal spot size is always ________ than the actual focal spot size
smaller
smaller the anode angle the ______ heel effect
larger
anode angle and effective focal spot size are
directly proportional
anode angle and heel effect are
indirectly proportional
to take advantage of the heel effect, the thicker body part must be positioned under the
cathode
the effective focal spot size is larger on the ______ side
cathode
the most frequent cause of abrupt tube failure is
e- arcing from the (open) filament
which kVp selection would result in the most scattered XRs in the img-forming beam? (90, 75, 60, 50)
90 kVp
decreasing kVp will increase
pt dose
contrast res is improved by? (3)
tight collimation, lowering kVp, pt compression
use of a compression device will increase _____
contrast
the use of ______ improves contrast & reduces pt dose
collimation
how can you improve img contrast w a heavy pt without increasing pt dose?
use tight collimation
img contrast improves when more of ______ rad is removed
scattered
a grid is constructed w _______ strips & _______ interspace material
radiopaque, radiolucent
a radiograph w a long scale of contrast will also have _____ latitude & ______ contrast
wide, low
grids are designed to remove scattered XRs before they reach
the IR
what is the grid ratio of a grid w 3-mm height, 0.025-mm thick pb grid strips, and 0.3-mm thick interspace material?
10:1
foreshortening is caused by a(n)
angled body part when the beam is perp to the IR
optical density (OD) is directly controlled by changing the _____
mAs
pt thickness affects img quality by affecting? (3)
magnification, rad contrast, focal spot blur
best way to min. magnification is to use a
long SID & small OID
subject contrast is affected by
pt thickness
3 primary factors influencing the intensity of scatter in the img-forming beam are
kVp, field size, & pt thickness
scatter rad increases as _______ increases
field size
the most commonly used beam restricting device is the ____________
variable collimator
the pos. beam limiting device (PBL) ensures that the XR beam is collimated to
the IR size
________ is the degree of difference in optical density (OD) btw areas of an img
contrast
amount of scatter absorption in a grid depends on? (3)
angle of scattered photon, height of the grid strips, & width of the interspace material
formula for grid ratio?
h/D
purpose of a grid is to achieve
improved img contrast
the interspace material in grids is made of ________
either aluminum or plastic (fiber)
grids generally have a frequency of _______ lines per in
60-110
the most critical consideration when using a crossed grid is ____________
alignment (positioning latitude)
how could contrast be improved on a bedside radiograph of a very large pt? (3)
use grid, lower kVp, use tight collimation
spatial res improves w decreased? (3)
screen/motion/geometric blur
radiographic ___________ is random fluctuation in the optical density (OD) of a radiograph
noise
the slope of the _______ portion of the characteristic curve shows the film contrast.
straight line
if 10% of the view box light is transmitted through an area of film, what is the optical density in that area?
1
a film w a characteristic curve showing a high slope would be useful when ________ is needed
high contrast
the 3 primary geometric factors affecting img quality are?
magnification, distortion, & focal spot blur
distortion can be reduced by
placing the object plane II to the IR
focal spot blur can be reduced by using a
small focal spot
XR img quality is improved when the ______ is increased.
SID
_______ is defined as the ability to img 2 separate objects & visually detect one from the other
resolution
higher speed img receptors generally produce img’s w
increased noise
an img receptor w ________ can be used over a greater range of exposures
wide latitude
formula for optical density (OD)
OD = log10 (Io/It)
densities above 2.5 on a film are represented in the ________ portion of the characteristic curve
shoulder
sharpness of detail can be improved by increasing ______
SID
lowering kVp _____ pt dose & _______ img contrast
increases, increases
modern rad film base is made of ________
polyester
how thick is radiographic film base?
150-300 µm
crystals in film emulsion consist of ______ & ______
silver bromide, silver iodide
latent img formation occurs during film ________
exposure
a contaminant in the silver halide crystal creates the
sensitivity speck
the latent img can be seen
only after development
the latent img is made up of ______ atoms
silver
high contrast film contains ______ silver halide crystals (SHC) of _____ size
smaller, uniform
film is made w double emulsion to enhance film _______
speed
spectral matching is not a consideration when using
direct exposure film
storing film in very low humidity conditions can cause
static artifact
film should be stored at a temp of ______ or below & w humidity no higher than _______
68ºF; 60%
the rollers in the automatic processor are part of the _______ system
transport
replenishment of fixer & developer are controlled by the
microswitch
the undeveloped silver halide is removed from the emulsion during
fixing
name a rare earth phosphor?
lanthanum oxybromide
an increase in _____ will increase both beam quality & beam quantity
kVp
what are the 4 primary exposure factors?
kVp, mA, time, & SID
changes in kVp affect? (3)
OD, img contrast, img noise
an increase in mAs causes (an) _______ in beam quality & (an) ______ in beam quantity.
no change, increase
there is a direct relationship btw the quantity of XRs & the _____
milliamperage
if mAs are increased from 20 mAs to 40 mAs, the pt dose dose will
be doubled
beam penetrability is increased if ______ is increased
kVp
beam quality is improved when the _______ is increased, but ______ has no effect on beam quality.
kilovoltage, milliamperage
both beam quality & beam quantity are increased by
increasing kVp & changing from a single-phase to 3-phase voltage
to reduce img blur, what should tech do?
use shortest exposure T
when looking at exposure techniques, how can you tell which one gives the highest pt dose?
the one with the highest mAs
added filtration has the effect of _____ the beam quality & ______ pt dose
increasing, reducing
when all other exposure factors remain the same, changes in focal spot size result in ____ in beam quality and _____ in beam quantity
no change, no change
film can turn brown during storage due to a retention of ___________
ammonium thiosulfate
filtration is added to XR machines during manufacturing so that the required total of ___ mm Al equivalent filtration is achieved.
2.5
what kind of film is used in mammography?
single emulsion film
an exposure w an off-level grid will show grid cutoff
across the img
what is the formula for Bucky factor?
pt dose w grid/pt dose without grid
grid ratio is the _____ of the grid strips divided by the _____ of the interspace material
height, width
tree artifacts are caused by
friction
a high contrast XR has
short scale contrast
if a tech did a knee w a non-grid exposure using 10 mAs & wanted to use an 8:1 grid, what mAs should be used to produce a XR w the same density?
40
if a tech did a lat C-spine using a 12:1 grid & 10 mAs. if the tech is to be repeated using no grid, what should be the new mAs to produce a XR w the same density?
2
if a tech uses 24 mAs w a 16:1 grid, how much mAs should he/she use w a 6:1 grid?
12
which of the following technique chart causes less rad dose to the pt?
fixed kVp chart
the mAs values must be changed ___% to produce a perceptible change in OD.
30%
low humidity in the darkroom can cause
tree static
the undeveloped silver is removed from the emulsion during ______
fixing
Grid frequency
of pb strips per unit length (in/cm)
Types of grids used in rad
Linear & crossed
Most common grid type used
Linear
Which grid type gives more contrast?
Crossed
High or low ratio grid give more pos latitude?
Low ratio grid
Main disadvantage of II grid
Less contrast, removes less scatter
Main disadvantage of crossed grid?
Less pos latitude, absorbs more primary beam (May need to increase mAs to replace beam, which is more pt dose)
3 factors that control/affect detail
Screen/geometric/motion blur
As speed of IR increases, rad noise ______ & spatial res ______
Increases, decreases
Avg grid frequency used in rad depts?
25-45 lines/cm, 60-110 lines/in
4 most important characteristics of img quality?
Spatial res., contrast res., noise & artifacts
Primary control of contrast?
kVp
Primary control of OD
mAs
3 geometric factors
Magnification, distortion, focal spot blur
What controls detail?
Focal spot size
Detail is influenced by what
SID/OID & motion (screen/geometric/motion blur)
When are grid required?
Anatomical part 10+ cm or more than 60 kVp is needed
High/low grid ratio gives better contrast?
High (absorbs more scatter)
Grid is made w pb strips that are 16 mm long & separated by an interspacing material 2 mm wide. What’s grid ratio?
8:1
How do you calculate the distance until grid cutoff?
D = SID/grid ratio
What happens to img contrast when grids are used?
Img contrast approx doubles
Random fluctuation in the OD of the img
Noise
Ability to img small objects that have high subject contrast
Spatial res
Factors that affect the visibility of detail
Img contrast & OD
Random nature by which XRs interacts w IR
Quantum mottle
What increases quantum mottle? How does it make img appear?
If produced w fewer XRs; grainy
How do you min quantum mottle (3)
High mAs, low kVp, slow IR
Ability to img 2 separate objects and visually distinguish btw the 2
Contrast res
Study of the relationship btw exposure intensity & blackness (density) on img
Sensitometry
Radiographic contrast is the product of ________ & ________
IR contrast & subject contrast
How do you calculate the slope of a characteristic curve
Calculate the avg gradient
Factors that affect magnification (4)
Size, shape, SID & OID
