Ionizing Radiation
radiation that is able to remove electrons from an atom through ionization
Somatic effects
refers to the effects of radiation to the body being irradiated
Genetic Effects
refers to effects of radiation to a germ cell’s genetic code; effects the next generation
Primary radiation
radiation exiting the x-ray tube
Remnant radiation (or Exit Radiation)
x-rays the leave the patient and strike the image receptor
attenuation
absorption and scatter of the x-ray beam as it passes through the patient
heterogenous beam
x-ray beam that has photons of many different energies
photoelectric effect
absorption of x-ray photons in the body
compton effect
scatter of x-ray photons in the body
air kerma
unit of exposure
gray
unit of absorbed dose
gray(a)
unit of radiation absorbed in air
gray(t)
unit of radiation absorbed in tissue
sievert
unit of effective dose or unit of equivalent dose
becquerel
unit of activity
uncontrolled area
general public area, like waiting room or stairways
controlled area
occupied by people trained in radiation safety and wear radiation badges/monitors
x-ray tube leakage may not exceed what?
1mGy(a) per hour at a distance of 1 meter from the housing
minimum lead equivalent for fluoro curtain
0.25mm
minimum lead equivalent for bucky slot shield
0.25mm
NAS or NRC-BEIR
National Academy of Sciences/National Research Counsel on the Biological Effects of Ionizing Radiation
studies biologic effects of ionizing radiation and publishes the data
NCRP
National Counsel on Radiation Protection
publishes radiation protection guidelines for the US
NRC
Nuclear Regulatory Commission
enforces radiation protection standards at the federal level
NCRP Report #102
makes recommendations on equipment design and protection regarding lead shielding and fluoro and mobile exposure rates
NCRP Report #116
makes recommendations pertaining to risk-benefit analysis of radiation exposure; states genetic and somatic effects need to be kept to a minimum; makes annual dose limits
NCRP #160
addresses radiation exposure from all sources to people in the US
effective dose limit
upper boundary dose that can be absorbed (either in a single exposure or annually) with negligible risk of genetic or somatic effects to the individual
cumulative effective dose
lifetime occupational exposure must not exceed radiographer’s age x 10 mSv
equivalent dose
equal to the absorbed dose multiplied by the radiation weighting factor
equivalent dose limit
upper boundary dose that can be absorbed (either in a single exposure or annually) with negligible risk of deterministic effect
Dose Area Product (DAP)
total air kerma striking the patient
probabilistic effects (stochastic)
randomly occurring effects of radiation; probability is proportional to the dose (increased dose = increased probability)
Deterministic Effects
radiation effects that become more severe at higher levels of radiation exposure; do not occur below a certain threshold
GSD (Genetically Significant Dose)
average annual gonadal dose of radiation to individuals of childbearing age; addresses the relationship of gonadal doses to individuals versus an entire population and the overall effects
Linear Energy Transfer (LET)
amount of energy deposited by radiation per unit length of tissue
Relative biologic effectiveness (RBE)
ability to produce biologic damage; varies with the LET
Direct effect
occurs when radiation directly strikes DNA in the cellular nucleus
Indirect effect
occurs when radiation strikes the water molecules in the cytoplasm of the cell
Radiolysis of water
occurs as radiation energy is deposited in the water of the cell; the result of radiolysis is an ion pair in the cell: a positively charged water molecule (HOH+) and a free electron
Mutation
erroneous information passed to subsequent generations via cell division
Law of Bergonie and Tribondeau
ells are most sensitive to radiation when they are immature, undifferentiated, and rapidly dividing
Early somatic effects of radiation
hematopoietic syndrome; gastrointestinal (GI) syndrome; central nervous system syndrome
Late somatic effects of radiation
carcinogenesis; cataractogenesis; embryologic effects; thyroid dysfunction; life span shortening
Cardinal principles of radiation protection
time, distance, shielding
what is the best protection against radiation exposure?
distance
Mean marrow dose
average dose to bone marrow
mass
the amount of matter in an object; generally considered the same as weight
energy
the ability to do work
Potential energy
energy of position
Kinetic energy
energy of motion
chemical energy
energy from a chemical reaction
Electrical energy
result of the movement of electrons
Thermal energy
heat energy resulting from the movement of atoms or molecules
Nuclear energy
energy from the nucleus of an atom
Electromagnetic energy
energy that is emitted and transferred through matter
Velocity (speed)
how fast an object is moving
Acceleration
the rate of change of speed per unit of time
work
force applied on an object over a distance
power
the rate of doing work (measured in watts)
Atomic nucleus
contains protons (positive charges) and neutrons (no charge); contains most of the mass of an atom
Atomic mass
number of protons plus number of neutrons; represented by the letter A
Electron shells
contain orbital electrons (negative charges); electron shells represented by the letters K, L, M, N, O, P, and Q; in a stable atom the number of electrons and protons is equal
Atomic number of an atom
equals the number of protons in the nucleus; represented by the letter Z; the atomic number determines the chemical element; all chemical elements are represented in the periodic table of the elements
Isotopes
atoms with the same number of protons but with a different number of neutrons
Electron-binding energy
force that holds electrons in orbit around the nucleus
Octet rule
the outer shell of an atom may not contain more than eight electrons
Particulate radiation
alpha particles (helium nucleus: two protons and two neutrons); beta particles (electron-like particles emitted from the nucleus of a radioactive atom)
Photon
the smallest amount of any type of electromagnetic radiation; also considered a bundle of energy called a quantum; travels at the speed of light; travels in waves in a straight path
Sine waves
waves of electromagnetic radiation; wave height is called amplitude; distance between the peaks of the waves is called wavelength; as photon wavelength decreases, photon energy increases
Frequency
number of wavelengths passing a given point per unit time; measured in hertz (Hz)
Speed of travel
electromagnetic radiation travels at the speed of light (186,000 miles per second); travel at the speed of light is constant regardless of wavelength or frequency; wavelength and frequency of electromagnetic radiation are inversely proportional
gamma rays
electromagnetic rays produced by the nucleus of radioactive atoms
wave particle duality
the concept that although xray photons exist as waves, they exist with properties of particles
attenuation
partial absorption of the energy of an xray beam as it traverses an object
inverse square law
intensity of an xray beam is inversely proportional to the square of the distance between the source of xrays and the object
law of conservation of matter
matter cannot be created or destroyed; only changed in form
law of conservation of energy
energy cannot be created or destroyed; only changed in form
electrostatics
stationary electric charges (static electricity)
electrification
movement of electrons between objects
law of electrostatics
unlike charges attract and like charges repel; electrostatic charges reside on the outer surface of a conductor and are concentrated at the area of the greatest curvature; only negative charges move
methods of electrification
friction, contact, induction
conductor
material that allows the free flow of electrons
insulator
objects that prohibit the flow of electrons
electric current
the movement of electrons along a conductor or pathway; measured in amperes
electromotive force (EMF)
measured in volts; the force with which electrons move in an electric circuit
electrodynamics
electric charges in motion
semiconductor
material that may act as an insulator or conductor depending on conditions
electric resistance
inhibits the flow of electrons; measured in ohms
electric circuits
path along which electrons flow; may be wired as series circuits or parallel circuits
alternating current
current of electrons oscillate back and forth
direct current
electrons flow in one direction
sine waves
representation of electron flow as alternating current
magnetic field
energy field surrounding an electric charge in motion; can magnetize a material if placed in the magnetic field
magnetic poles
every magnetic has a north and south pole
laws of magnetic
like poles repel; unlike poles retract; governed by inverse square law
electromagnetism
movement of electrons in a conductor produces a magnetic field around the conductor
self induction
opposing voltage created in an inductor by passing alternating current through it
mutual induction
inducing current flow in a secondary coil by varying the current flow in a primary coil
electric generator
device that converts mechanical energy to electrical energy; usually the output is alternating current
single phase, two pulse alternating current
the simplest type of current
three phase, alternating current
may have 6 or 12 pulses per cycle; 6 pulses have 360 pulses per second and 12 has 720
electric motor
electrical energy to mechanical energy
transformer
changes electric voltage and current into higher or lower values; runs on mutual induction so it requires alternating current
step up transformer
increases voltage from the primary to secondary coil; decreases current in same proportion; more turns are in secondary coil than primary; used in x-ray circuit to increase voltage to kilovoltage level
step down transformer
idecreases voltage from the primary to secondary coil; more turns in primary than secondary coil; used in filament portion of xray circuit to increase current flow to cathode
autotransformer
used in xray circuit to provide an increase in voltage before the step up transformer; kvp settings are made here
rectification
changing AC to DC
kvp
controls the energy of xrays produced; direct impact on receptor exposure; governed by 15% rule
SID
distance from xray tube anode to IR; controls magnification and image blur; longer SID = better spatial resolution
grids
absorbs scatter radiation, impacts receptor exposure and contrast
beam restriction
limits size of area of xray beam; affects receptor exposure and contrast due to the reduction of scatter being produced
anode heel effect
lower field intensity towards the anode in comparison to the cathode due to lower x-ray emissions from the target material at angles perpendicular to the electron beam
bit depth
number of bits per pixel; greater bit depth means greater level of grays in an image
contrast
visible difference between two areas of brightness on an xray
contrast resolution
smallest change in signal that can be detected by the receptor
pixel pitch
space between pixels; less space = greater spatial resolution
high contrast
few gray tones, more black and white; caused by low kvp
low contrast
many gray tones; caused by high kvp
subject contrast
affects contrast through variations of atomic number, tissue thickness, and tissue density
OID
distance from the object to the image receptor; controls magnification and image blur; smaller OID = better recorded detail
focal spot size
controls image blur, use smaller focal spot whenever possible to keep xrays coming off the anode from the smallest possible area
distortion
altered size or shape of an object in the image
size distortion
magnification; caused by large OID
shape distortion
elongation or foreshortening
grid ratio
height of lead strips divided by distance between lead strips; ratio=H/D
grid frequency
number of lead strips per inch or centimeter
linear grid
lead strips are parallel with each other
focused grid
lead strips are angled to coincide with divergence of xray beam
grid cutoff
decreased density across periphery of images
grid radius
distance at which focused grid may be used
contrast improvement factor
measure of grids ability to improve contrast
grid conversion factor or bucky factor
amount of mAs exposure increase necessary to compensate for the absorption of image forming rays and scatter in the cleanup process
stationary grids
do not move during the exposure
moving grids
move back and forth during the exposure, eliminate the visibility of grid lines
upside down grid causes what?
decreased density on sides of the image
off-level grid causes what?
visible cutoff across entire image
automatic brightness control
adjusts mA and kVp to make an optimum image
image intensifier tube
consists of input phosphor, photocathode, electrostatic lenses, and output phosphor
photocathode
converts light energy to electron energy
electrostatic lenses
keeps electron beam narrowed as it travels towards output phosphor
output phosphor
converts electron energy to light energy for viewing
total brightness gain
a product of minification gain and flux gain
flux gain
gain in brightness caused by acceleration of electron beam inside image intensifier tube
minification gain
gain in brightness caused by minification of the image at the output phosphor as compared with the input phosphor
direct DR detectors
convert exit radiation directly into electric charges
indirect DR detectors
convert exit radiation to visible light, then into electric charges
pixel
picture element, shade of gray representing a voxel
voxel
volume element, an area of tissue in the patient
histogram
shows distribution of pixel values
receptor exposure
intensity of radiation striking the IR, directly determines quality of a digital image
subtraction
part of post processing, removal of superimposed or unwanted structures on an image
contrast enhancement
part of post processing, altering image to display varying brightness
dead pixel correction
part of post processing, assigning a value to dead pixels based on adjacent pixel values
edge enhancement
part of post processing, improves visibility of small high contrast areas
stiching
connect multiple images into one
window level
adjusts image brightness
window width
adjusts image contrast
spatial frequency resolution
level of detail or sharpness on CR image
look up table (LUT)
a histogram of brightness level values from image aquisition; can be used to correct or enhance luminance values
quantum mottle
grainy/noisy image caused by too few xray photons hitting the IR
pixel density
number of pixels/mm in an image ;determined by pixel pitch
dorsal recumbent
supine or laying on back
ventral recumbent
prone, laying facedown
projection
path of central ray
torts
personal injury law; civil wrong that causes someone else to suffer loss or harm
assault
action that causes fear of harm
battery
inappropriate touching that causes harm
libel
written defamation of character
slander
spoken defamation of character
negligence
unintentionally omitting reasonable care
respondeat superior
employer is responsible for employees actions, “let the master answer”
res ipsa loquitor
cause of negligence is obvious, “the thing speaks for itself”
implied consent
assumes the patient would approve if conscious
medical asepsis
microorganisms are eliminated as much as possible
surgical asepsis
complete removal of all microorganisms
direct contact transmisson
infected person touches the host directly
indirect contact
inanimate object placed in contact with a person
vector transmission
animal contains and transmits organism to humans
the most effective method of preventive the spread of infection
handwashing
normal adult respiration rate
12-16 breaths per minute
systolic pressure
measurement of the pumping action of the heart
diastolic pressure
measurement of the heart at rest
most common oxygen flow rate
3-5 L per minute
most common negative contrast agent
air
common positive contrast agent
iodine or barium
aqueous iodine compound
water soluble sterile contrast agent
iodinated ionic contrast agents
salts of organic iodine compounds; composed of positively and negatively charged ions
iodinated nonionic contrast agents
do not ionize into separate positive and negative charges
anaphylactic reactions
flushing, hives, nausea
cardiovascular reactions
hypotension, tachycardia, cardiac arrest
When performing a quality control test to ensure that adjacent mA stations are accurate, the results must be within this amount of one another
10%
When a quality control test is performed to ensure that the same exposure factors produce consistent x-ray output, successive exposures must be within this amount of one another
5%
When a quality control test is performed to ensure that the collimator is providing appropriate Safety, the result must be within this amount
2% of SID
When performing a quality control test to ensure that the penetrating ability of the x-ray beam is accurate, the result must be within this amount of the control panel setting
±4 kVp
The feature of the image intensifier that automatically adjusts kVp and mAs during fluoroscopy is the
automatic gain control or automatic brightness control
Beam quality is expressed using what unit of measurement?
half value layer
The charge on the atomic nucleus is
positive
The distance from peak to peak of sine waves is called
wavelength
What surrounds an electric charge in motion (or a current)
magnetic field
what transformers operate on mutual imduction?
step up and step down