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Element (There are 92 natural ones)
- The quantity of matter in an object.
- A material with definite and constant composition.
- Two or more elements combined.
- Substance that cannot be broken down simpler.
- A definite proportion of chemically united elements.
- Smallest particle of an element.
- Two or more atoms chemically united.
Atomic Z number
Atomic mass units AMU
Atomic mass number
Describe 2n2-the max number of e- occupying a given shell.
- Energy transmitted through matter
- The number of nuclear protons in an atom. Determines what element it is.
- When an atom gains or loses neutrons, becomes isotope.
- Adding or removing electron from an atom.
- The mass of the particles of an atom
- Equal to the number of protons and neutrons
- K= 2(1)squared=2 L=2(2)squared=8
K shell binding energy of tungsten is...
EM electromagnetic radiation
Electromagnetic spectrum- velocity of EM energy is equal to speed of light (3x10^8 meters/sec
- The binding energy of an electron
- 69.5 kev
- a form of energy that is the result of electric and magnetic disturbance in space (light, radio, infrared, etc) and xrays
- the distance between any two points on a wave
- number of waves that pass a point in a time frame (hz)
frequency and wavelength re in what proportion?
low frequency and long wavelength- radio waves
visible light- in the middle
high frequency and short wavelength- gamma and xrays
photon energy and frequency are in what proportion?
Planck's constant = h
E = hv, v = E/h
Directly proportional- if F is doubled, E is doubled
wilhelm roentgen, date?
Nov 8 1895
4 properties of xrays-
- electrically neutral-
- not affected by elec or magnetic fields
travel at 3 x 10^8 m in a vacuum
Describe cathode assembly
filament is made of?
- Cathode- negative side of tube, to produce thermionic cloud, conduct the voltage to the gap, and focus towards the anode.includes the filaments and focusing cup
- Thoriated tungsten wire
Size of thermionic cloud depends on KVP or MAS?
what is the focusing cup made of?
what is the space charge effect?
- E- charges oppose the emission of additional charges- limits xray tubes to 1,000 to 1,200 MA.
what drives a greater percentage of e- towards the anode?
What is the anode?
what metal is the focal track?
- the positive side- can be stationary (rhenium/tungsten) or rotating (molybdenum)
- graphite backed anodes double heat-loading capabilities
the portion of the anode where the high voltage stream will impact is the:
target, focal spot, focal point, focal track
actual focal spot vs effective focal spot:
what is the effective focal spot controlled by?
- Actual focal spot- where the beam strikes
- effective focal spot- where the angle of the beam reduces the spot using the line-focus principle
The actual focal spot which is controlled by the length of the filament and the anode target angle.
most common target angle is?
what is the anode heel effect?
radiation intensity is greater on cathode side
why does the rotor spin?
any photons that escape from the housing (except at the port) are called?
Leakage radiation must not exceed:
to dissipate heat
100 mR/hr at 1 meter
what is off-focus radiation? what does it cause? is it from the patient?
composed of photons that were not produced at the focal spot. causes ghosting . this is NOT patient scatter.
off focus radiation can contribute what percent to the total primary beam?
tube rating charts provide a guide to what?
anode cooling charts provide a guide to what?
what is the formula for the cooling chart?
- the maximum technical factor combinations that can be used without overloading the tube.
- calculating the time necessary for the anode to cool for additional exposures.
- kvp x ma x time x rectification constant
How fast are the electrons in the thermionic cloud traveling?
what happens to the electrons after they strike the target?
In the space of 2cm, they are accelerated to about 1/2 the speed of light
they can have 1000 or more interactions before they are conducted through the anode to the circuit.
what is produced by the incident electrons?
what two types of target interactions produce xray photons?
what does the interaction depend on?
- 99% heat, 1% photons
- bremstrahlung and characteristic.
- the e- kinetic energy and the binding energy of the e- shells of the atom.
when does a brems interaction occur?
how does it result in a photon?
- when an incident e- interacts with the force field of the nucleus (strong positive force)
- the e- changes direction and the resulting photon energy is the difference between the entering and exiting kinetic energy of the e-.
When does a characteristic interaction occur?
how does a photon result?
- when the incident electron interacts with an inner-shell electron
- the e- knocks an inner-shell e- from orbit, ionizing the atom- a hole is created and outer-shell e-'s drop into it, resulting in the energy difference between the 2 shells being emitted as a photon.
why are the resulting multiple photons of the cascade called characteristic photons?
only the drops into which shell produce xray quality photons?
- their energy is the difference between the inner and outer shells between which the electron dropped.
- k shell
between 80 and 100 kvp. what % of the primary beam is brems?
if kvp is below 70, are characteristic photons useful?
- no- tungsten e- removal requires 69.5 kev
what is the kilovoltage peak?
the maximium possible energy of exposure for any photon that exits the Xray tube.
the average beam has keV energy of what percent of the kvp setting?
30 to 40
- quality of the beam- strength
- quantity of the beam- # of e-'s
what does filtering do to the strength of the beam?
decreases intensity, but increases average photon energy
what does ionizing radiation do when it interacts with matter?
What are the two types of particulate radiation?
Which are more harmful and why?
- creates both positively and negatively charged particles, breaks molecular bonds.
- Alpha and beta
- Alpha are large, heavy, and can be stopped easily. They are similar to a helium atom.
- Beta are identical to an electron, but emitted from nuclei of radioactive material (like gamma rays), travel 10-100cm
What are the two medically useful (Xray) ionization processes?
What is direct interaction?
What is indirect interaction?
Photoelectric absorption and Compton scattering
- Radiation to a cell molecule
- Radiation to a water molecule, causing free radical damage (causes 2/3 of all biological effects)
Define somatic effects and genetic effects
- Somatic- affecting the irradiated individual-
- skin erythema, cataracts, malignancies
Annual Effective Dose Equivalent for rad workers?
for students and public?
- 5 rem or 50 mSv
- 1 rem x age = XX rem (30 rem = 300 mSv
- 0.1 rem
Radiation equivalents: study this card, not a question
Exposure per unit mass of air=Roentgen is eqiv to the coulomb/kg or c/kg
Absorbed Dose in material- rad-- 1 gray= 100 rads
rem- absorbed dose in gray plus qualifier for type of radiation = sievert
exposure per unit mass of air- roentgen
integral dose- total radiation to matter
effective dose- to specific organs
what is the SI equivalent of
absorbed dose (gray plus weighing factor)/sievert?
traditional name for exposure per unit mass of air?
What type is our personnel exposure monitoring device?
what is it comercially called?
what type of material is inside?
- an OSL- optically stimulated luminescence.
- the luxel dosimeter
- a thin strip of Aluminum oxide, with copper and tin filters.
what does a TLD device use? (we dont use this)
3 basic principles or cardinal rules of exposure reduction?
what is the law of the relationship between distance and exposure intensity?
time, distance, shielding
the inverse square law
what is the basic formula of the inverse square law?
if the distance is doubled, exposure is reduced by factor of 4. (two squared)
protective lead aprons must posess a minimum of what amount?
0.5 mm Pb eq
a minimum total filtration for the xray equipment is what mm Al/Eq?
Technical factors with a lower patient dose would be in what proporion?
- 2.5 mm Al/Eq
- High kvp, low mAs
what is the dose limit for a fetus?
exposure in pregnancy should not exceed 0.05 rem to fetus
what is the half-value layer?
what is inherent filtration?
Added filtration collimators add how much filtration?
- the amount of absorbing material that reduces the intensity of the primary beam by 1/2.
- comes from the window of the glass envelope, the oil, and the tube housing. usually about 1mm al/eq
- about 1mm al/eq.
Compound filters are also called what? what is a good example of one?
what is the filter that is for unequal subject densities?
what are 2 examples of these?
- K edge filters, to absorb in layers- thoreaus
- a compensating filter-
- wedge and trough filters
does total filtration include use of compound filters?
at what filtration is a point of diminishing returns reached?
- no. it is without these.
- 3.0 mm al/eq
what are the THREE prime factors?
xray quantity, intensity, or exposure is controlled by what?
Xray quality (represented in HVL) or penetrability is controlled by what?
- kvp, mas, and distance
- mas, kvp, distance, and filtration.
- kilovoltage and filtration.
Mas is the measurement of what?
1 amp or 1 coulomb is equal to what unit amount?
a milliamp then is what?
- xray tube curent- number of e- per second
- 6.3 X 10^18
- 6.3 x 10^15
mas and exposure are in what proportion?
mas and xray quantity are in what proportion?
200 mA at 0.083 second =
100 mA at 2/5 second =
- 16.6 mAs
- 40 mAs
the primary controller of film density is what?
the law of the relationship between mAs and density is what?
what does it state?
- reciprocity law
- density should remain unchanged it mAs is the same
kvp controls what?
higher kvp causes an increase in what?
what rule states that a 15% increase in kvp results in doubling of exposure?
- both quantity (at the target) and quality of the beam.
- Speed and energy of the beam, penetrating ability
- the 15% rule
image at 25 mAs at 70 kvp. what kvp would double the exposure?
- 15% of 70 kvp = 10.5 kvp
- 70 + 10.5 = 80.5 kvp (or 81)
the relationship of xray quantity to distance is?
what does the law state?
if distance increases by three, the intensity would decrease by a factor of what?
- the inverse square law
- the intensity at a given distance is inversely proportional to the square of the distance
- Three, squared. or 9.
intensity 1 = distance 2, squared
intensity 2 distance 1, squared
what formula is this?
the inverse square law
an xray exposure of 240 mR at 20 inches,
becomes a 40 inch distance.
what is the new mR?
The exposure maintenance formula states what?
what is the formula?
- Raising exposure factors to compensate for more distance and maintain density.
- mas 1 = distance 1 squared
- ----- ------------------
- mas 2 distance 2 squared
25 mas at 80 kvp, at 40 inches, density is maintained at 56 inches by doing what?
mas 2 becomes 49 mAs
what is the appropriate amount of exposure to the IR?
1 to 2 mR
low energy photons are most likely to interact with what part of the atom?
intermediate energy photons are most likely to interact with what?
high energy photons are capable of interacting with what?
- the whole atom.
- the orbital electrons.(most common in diagnostic xray)
- the nucleus (most common in radiation therapy)
what is the atomic number of tungsten?
what are the five basic interactions between xrays and matter?
- PE absorption
- Coherent scattering
- Compton scattering
- Pair production
photoelectric absorption results when?
what happens to the incident photon?
the ejected e- becomes what?
- the photon interacts with an innershell e-
- it gets absorbed
- a photoelectron of matter with energy equal to the difference between the incident photon and the binding energy.
when the characteristic photons are released from e- falling into the k shell hole in the irradiated matter, what is the radiation called?
lead = 88
2 other names for coherent scatter
what is thompson coherent?
what is rayleigh coherent?
- classical or unmodified
- involves a single electron
- involves all the electrons
three basic rules governing pe interactions:
the incident energy must be greater than?
the photon energy and the e- binding energy are what?
a pe interaction is more likely with an electron that is ? in its orbit?
as photon energy increases, the chance of a photoelectric interaction-
- the binding energy of the inner shell e-
- close to each other
- more tightly bound
at 50 kvp, scatter and PE are about equal (50/50). As kvp goes up, scattering goes ? and pe interaction goes ?
at 130 kvp, scatter and PE are about what percentages?
as kvp goes up, attenuation goes?
as kvp goes up, transmission goes?
as kvp goes up, scatter goes?
as kvp goes up, photoelectric goes?
Compton scattering occurs when an incident photon interacts with an ?
what happens to the e-?
what happens to the incident photon?
- outer shell electron
- it becomes a free e- to fill hole in an atom
- it continues in a different direction with lower frequency and longer wavelength
what is the primary cause of occupational radiation exposure?
compton scatter radiation emitted from the patient
unwanted exposures on the xray image is called
in pair production, the energy of the xray photon is converted to matter in the form of two-
photon energy required for p.p.interaction is?
what is created when a high energy photon comes close to the nucleus?
- 1.02 meV
- a pair of electrons- a negatron (-) and a positron (+)
what happens to the positron?
what is the reaction called?
does it occur in diagnostic imaging?
- it combines with an electron, and creates 2 photons of 0.51 mev each
- annihilation reaction
what is photodisintegration?
is it relevant to diagnostic imaging?
- a photon above 10 mev interacting with the nucleus
- the nucleus emits a fragment
at 50 kvp. 10 cm tissue, what percent of beam is attenuated and what percent is transmitted?
at 130 kvp, what % is attenuated and what % is trans?
- 5.60as kvp increases, non interactive transmission increases
when kvp goes up, the % of PE decreases but Compton increases.
In diagnostic xray, what is the predominant interaction?
when does PE predominate?
- compton scattering
- in low kvp ranges, or when high atomic number contrast is used.
what are the best two ways to minimize scatter?
what are the two main benefits of reducing scatter?
- restricting the beam and using a grid
- reducing patient dose and improving image quality
high atomic number materials attenuate a ? amount than lesser atomic numbers
the order of body tissues from MOST to LEAST in attenuation would be:
- bone, muscle, water, fat, air
the 4 properties affecting recorded detail are:
subject density, subject contrast, subject detail, and subject distortion
DEFINE subject density, subject contrast, subject detail, and subject distortion
- density- changes in amount or type of tissue
- contrast- degree of absorption of different tissues
- detail- part position in the body and in relation to the IR
- distortion- lack of accurate representation of structures
Formula used to determine field size of projected image when using an aperture diaphragragm:
diaphragm is 5 inches from focal spot
aperture is 2 inches
SID 40 inches
what is image size?
SID x diameter of diaphragm
distance from focal spot to diaphragm
image size is 16 inch circle
what is another term for an automated collimator?
collimators add about how much filtration?
what are some ancillary devices?
- positive beam limitation
- 1 mm al/eq
- lead mask, lead blockers (any size/shape)
the sum of protons and neutrons in the nucleus is called the-
isotopes have different mass numbers and the same ? numbers
atomic number is the number of-
atomic mass number minus protons equals number of-
- Mass number
driving the thermionic cloud from the cathode to the anode requires-
tungsten is preferred for the target because of its-
- a large potential difference
- high atomic number
photon energy and frequency are in what proportion?
an xray is a wave and a?
characteristic cascade results in:
- directly proportional
- a photon of energy
which shell electrons posess the most energy?
the outer shell. the inner shells have the most BINDING energy.
during coherent scattering, the scattered photon posesses the same -what- as the incident photon?
energy, frequency, and wavelength
the relationship between intensity of radiation and distance is the: