Comprehensive Exam Flashcards
what does ALARA mean?
As Low as Reasonably Achievable
Which of the following is a cardinal rule of radiation protection?
increase the distance from the source
Increased kVp has what effect on photoelectric (PE) absorption?
decreases PE absorption
To increase the quantity of radiation by adjusting the kVp to the same level as doubling the mAs, you need to increase kVp by a fact of what percentage?
15%
the rate of photoelectric absorption interactions _________ faster than the rate of Compton scattering
decreases
Exposure, dose, and dose equivalent are:
radiologic quantities
What is an expression of the relative risk to humans of exposure to ionizing radiation?
effective dose
factors affecting the photoelectric-compton ratio
Z# of the material
Photon energy
The probability of photoelectric interaction depends on the following:
The atomic number of the tissue atoms with which they interact
The incident x-ray photon energy
how does a higher atomic number (Z) affect PE absorption?
increases PE absorption
a radiolucent structure likely has which of the following properties?
low atomic number
the probability of compton scattering depends on the atomic number. true or false?
false
_____ creates less radiographic density
metal
____ creates more radiographic density
air
to produce a radiographic image that represents anatomy, which interactions must be present?
differential absorption, transmitted photons, photoelectric interactions
_______ dose is calculated for individual organs.
It is based on the absorbed dose to an organ, adjusted to account for the effectiveness of the type of radiation.
This dose is expressed in millisieverts (mSv) to an organ
Equivalent
_______ dose is calculated for the whole body.
It is the addition of equivalent doses to all organs, each adjusted to account for the sensitivity of the organ to radiation.
This dose is expressed in millisieverts (mSv)
Effective
What is atomic number?
the Z#
it represents the nuclear charge
the number of protons & neutrons in an atom
What is described as the rate of change in velocity over time?
acceleration
What is the equation for velocity?
velocity = distance / time
Based on the anode heel effect, an image taken at 40 inches SID distance may demonstrate:
decreases exposure towards the anode end of the beam
Assuming all other factors are accurately adjusted, the exposure time with AEC is adjusted to accommodate changes in:
patient anatomy
In an automatic exposure control system (AEC), where are the detectors placed?
between the patient and image receptor
Which term is the electromotive force or potential energy that produces electron movement?
voltage
The maximum number of electrons in each shell is found by using the equation:
2N^2
(N = shell number, ex: K = 1, L = 2, M = 3)
What is the average energy of the x-ray beam called?
beam quality
Which of the following exposure factors must be selected on the console which increases the quality and penetration of the x-ray beam?
kVp
What term defines the total number of x-ray photons in a beam?
x-ray quantity
Which term describes the reduction of the x-ray beam’s intensity as is passes through matter?
attenuation
What electromagnetic radiation has the lowest frequency?
radiowaves
What electromagnetic radiation has the highest frequency?
gamma rays
Members of electromagnetic spectrum from lowest to highest energy
Radiowaves
Microwaves
Infrared light
Visible light
Ultraviolet light
X-rays
Gamma rays
What unit is used to measure the frequency of a wave?
Hertz
electron shells # of electrons and binding energy from least to most
Q (7) 98 e-
P (6) 72 e-
O (5) 50 e-
N (4) 32 e-
M (3) 18 e-
L (2) 8 e-
K (1) 2e-
As the wavelength of a wave increases, how will frequency change proportionately?
decreases
What effect does frequency increasing have on energy?
increases energy
If the wavelength of a beam of electromagnetic radiation increases by a factor of 2, what happens to its frequency?
decreased by 1/2 (half)
Wavelength and frequency are:
inversely proportional
Which law states that the voltage (V) is equal to the product of the current (I) flowing through a conductor and the resistance (R) of that conductor?
ohm’s law
Which characteristic of a conductor will create the least resistance to the flow of electrons?
decreased temperature
A material that freely allows the flow of electrons is known as:
conductor
What does the anode function as?
a target for electrons, an electrical conductor, a conductor for heat
The property of an element in a circuit that resists or impedes the flow of electricity:
resistance (ohm)
What is the unit of measure for power?
watts
What does the ampere measure?
electric current
The potential difference that will maintain a current of 1 ampere in a circuit with a resistance of 1 ohm is the definition of:
volt
Coulomb’s law (calculation)
F = k (Q1 Q2 / d^2)
a volt is the ratio of _____ to _______
joules to coulombs
volt = joules/coulombs
1 coulomb is equal to the electrical charge of _________ electrons
6.25 x 10^18
How can you double the beam quantity?
double the mAs
In which direction is the correct flow of electrons?
from a negative cathode toward a positive anode
Which type of current is created by use of rectifiers?
direct current
electrons flow in only one direction (cathode to anode)
waveform begins at zero and moves to its maximum potential at its peak
ex: batteries and rectifiers
direct current (DC)
electrons flow in one direction for the first half of the cycle and then in the other for the second half of the cycle
ex: U.S. current (60 Hz)
positive cycle: 1/120 second
alternating current (AC)
the potential difference (voltage) across the total circuit or any part of that circuit is equal to the current (amperes) multiplied by the resistance
ohm’s law
What is it called when a moving magnetic field (created by AC) is placed near a secondary coil, and electricity is induced to flow in the secondary coil
mutual induction
What conditions and materials are necessary for mutual induction to occur?
magnetic flux and a solenoid
The _____ is the SI unit equivalent to the Curie which measures radioactivity
Becquerel
What is used to convert AC to DC?
rectifiers
transformer law for voltage:
Vs / Vp = Ns / Np
transformer law for current:
Is / Ip = Np / Ns
the relation of voltage to current in a transformer is:
Is / Ip = Vp / Vs
A step-up transformer ______ voltage and a step down transformer ______ voltage
increases, decreases
Where is the step-down transformer located?
filament ciruit
By regulation, x-ray tube leakage radiation can be no more than:
100 mR per hour at a distance of one meter
to help dissipate the heat produced during x-ray production, what fills the x-ray tube housing?
oil
Place the following events leading to the production of x-rays in order, from first to last:
1. alternating current is converted to direct current
2. voltage is adjusted at the autotransformer
3. kilovoltage leaves the step up transformer
4. voltage goes to primary side of the step up transformer
2, 4, 3, 1
Place the following events leading to the production of x-rays in order, from first to last:
1. resistance is adjusted at the rheostat
2. filament is heated
3. filament current is increased
4. electrons are boiled off filament
1, 3, 2, 4
Which are a part of an AC induction motor?
stator and rotor
Where are the ionization chambers?
between the patient and image receptor
Electricity coming from the wall. Hz, Volts, etc.
AC at the wall outlet is 60 Hz
Which part of the x-ray circuit functions by means of self-induction?
autotransformer
Where are the rectifiers located?
secondary circuit
Where is the rheostat located?
filament circuit
Where is the timer circuit located?
primary circuit
What is the purpose of the filament circuit?
boil off electrons, provide additional energy
A tungsten button embedded in a copper rod
The target does not move.
Disadvantage: the rapidly building heat can damage the tube, which limits use
stationary (static) anode
Why is molybdenum used in a rotating anode?
it is light but strong
Which is an advantage of angling the anode?
spreads the heat generated over a larger area of the anode
heat units definition & calculation
a measure of the amount of heat stored in a particular device
kVp x mA x s x c
calculation for single phase
mA X time X kVp
calculation for three phase
mA X time X kVp X 1.35
calculation for high frequency:
mA X time X kVp X 1.40
Involves the K-shell (first shell around the nucleus, has the strongest binding energy)
Only the interactions involving K-shell are of sufficient energy to be useful
Characteristics Interactions
The tissue atom is ionized and the inner-shell vacancy makes the
atom unstable
To regain stability, a ________________ occurs, producing secondary x-ray photons
These secondary photons are of low energy, are absorbed by the body in other photoelectric events, and contribute to patient dose
characteristic cascade
photoelectric interactions
The incident x-ray photon interacts with the inner-shell electron of a tissue atom and removes it from orbit
X-ray photons are totally absorbed
photoelectric interaction
During the bremsstrahlung interaction, what happens to the filament electron?
it is attracted to the nucleus
through what type of interaction are the majority of x-rays produced?
bremsstrahlung
What increases the “average” energy of an x-ray beam?
added filtration
What influences quality and quantity of the x-ray beam?
quality: kVp
quantity: mAs
What energy does the incident photon need to enable the photoelectric effect / absorption?
it needs to be the same or greater than the binding energy of an inner-shell electron
What is the minimum amount of energy an x-ray photon must have to create a pair production?
1.02 MeV
Is the x-ray beam heterogeneous or homogenous?
heterogeneous
What metal is used for filtration? Collimators? Protection?
filtration: aluminum
collimators: tungsten
protection: lead
the result of the formation of limb’s as a result of irradiation that stick to adjacent parts of the macromolecule or neighboring molecules, creating an unnatural framework
cross-linking
refers to a breakage of the major structure (framework) of the macromolecule itself
main chain scission
the result of damage to a single chemical bond
point lesions
one half-value layer (HVL) reduces the intensity of the x-ray beam to _____ of its original
one half
measures beam quality
defined as the thickness of absorbing material necessary to reduce the energy of the beam to one-half its original intensity
found by measuring beam intensity with a radiation detector
half value layer (HVL)
what is the normal HVL of a diagnostic beam?
3-5 mm Al
Why would an anode crack?
maximum heat or exposure factors
Anode heel effect. Which side has more intensity?
cathode
Stator and rotor. Where are they?
stator: outside the tube enclosure
rotor: iron core, surrounded by coils, located in center of stator within enclosure
Photoelectron calculation
Ei = Eb + Eke
Ei = Incident photon energy
Eb = Electron binding energy
Eke = Photoelectron kinetic
energy
What tissues have more PE interactions?
those with higher atomic numbers
Where does the technologist get their dose?
compton back scattering
In which interaction with matter does an x-ray interact with an atom without ionizing it?
coherent scattering
SI unit for mass?
kilogram
Which is the most radiosensitive molecule in the body?
DNA
Which describes the force that holds the protons and neutrons. together in the nucleus?
Nuclear binding energy
At what speed do electromagnetic waves travel?
speed of light: 3 x 10^8 m/s
Planks formula for wavelength:
wavelength = constant / frequency
(constant = 3 x 10^8 m/s)
Planks formula for energy:
E = hf
(h = 6.626 x 10^-34 J sec)
Plank’s formula for frequency:
f = c / λ
(constant = 3 x 10^8 m/s)
What is the velocity of electromagnetic radiation?
3 x 10^8 m/s
On which day did Roentgen first discover x-radiation?
November 8, 1895
the length of time it takes for half the remaining atoms in an amount of the element to decay
half-life
inverse square law
I1 / I2 = d2^2 / d1^2
Three-phase, full-wave rectification has what percentage of ripple?
13% to 3.5%
Single-phase full-wave rectified current has what percentage of ripple?
100%
Which has the least amount of ripple?
high frequency generators
(<1% ripple)
An adjustable transformer
controlled by the kilovolt peak (kVp) selector on the
operating console
autotransformer
Where is the autotransformer located?
primary circuit
What is the only adjustable transformer in the x-ray circuit?
autotransformer
essential to tube head assembly
the target window is the primary contributor
Inherent filtration
In a general radiography tube head assembly, this comes in the form of another 2.0 mm Al placed between the target window and the top of the collimator
added filtration
Serves the same role as timer
The patient’s body part of interest is the variable in
determining when to terminate exposure
Uses a device called an ionization chamber
Automatic exposure control (AEC) device
The nature of magnetic materials is that the orbital electrons of their atoms spin in predominately one direction
electromagnetism
The ___________ of a charged particle in motion is perpendicular to the motion of that particle.
magnetic field
How is magnetic field strength measured?
Tesla
Which refers to the relationship between the actual focal spot size, the effective focal spot size, and the anode target angle?
the line-focus principle
