HomeStretch CRACK Physics X-Ray Production Flashcards
Equation for maximum number of electrons a shell can hold
2n2
for an EM wave, if you increase frequency what happens to wavelength?
high frequency = short wavelength (i.e. smaller)
How much energy does it take to remove an electron from an atom?
15 eV = ionizing
What are rays that originate from the nuclei of an atom called?
How about those that originate interactions between fast-moving electrons and atoms?
Gamma rays
X-rays
alpha particles are what?
same as a helium nucleus (2 protons and 2 neutrons)
what is a beta particle?
electron emitted from the nucleus
Isotopes
same number of protons “Z” but a different number of neutrons and therefore different atomic mass “A”.
Whats the purpose of the envelope?
maintain a vacuum
electrons in from the filament are created on the cathode or anode side?
cathode is the place in the device where the elecrtons enter
What is mA?
milliampere - unit of measurement to describe current
QUANTITY of electrons moving from the cathode to anode
Focal spot sizes for :
Mammo
General X-rays
- Mammo = 0.1 mm and 0.3 mm
- General X-rays = 0.6 mm and 1.2 mm
how to keep your actual focal spot and narrow you effective focal spon - small angle = _______ effective focal spot.
What about the cut-offs for this?
small angle = small effective focal spot (and better spatial resolution)
cut-offs = steeper (smaller) angle = greater Heel effect
also if the target angle is made too small the x-ray beam might not be large enough to expose a standard image receptor.
Heel effect - the strongest x-rays are on what side?
how is it set up in mammo?
how about CXR and AP thoracic spine x-ray?
and how about in general?
Heel effect the CATHODE side has the stronger x-rays and therefore CHEST onto CATHODE side. (Chest wall Closer to Cathode)
CXR/Tspine = orientation is vertical with Cathode Down
In general = “thicker” tissue = cathode
increasing focus to film distance (FFD) does what to the Heel effect?
Larger FFD = decreased Heel effect
Smaller film does what to Heel effect?
Heel effect worsens (increases) with?
Smaller anode angle
smaller FFD
larger film size (FOV)
Heel effect improves (decreases) with?
Larger anode angle
Increased FFD
smaller film size (FOV)
Filter vocab
Inherent filter
Added filter
Total Filtration
Minimum filtration of aluminum required for an x-ray tube operative over 70kVp?
Inherent = normal components of the tube that block soft xrays
Added = any piece of metal added
Total = inherent + added
2.5 mm of aluminum
What does the focusing cup do?
reduces spatial spreading
What are the three kinds of interactions at the anode?
Excitation (heat) = wiggling but not moving
radiative lauses (bremsstrahlung) = general xays (80% of the x-rays produced)
ionization = characteristic x-rays
is keV the same thing as kVp?
highest energy x-ray in the tube depends on what? what about the lowest energy x-ray?
kVp
filtration
higher Z does what to “braking”
increases it! (proportionally) . . .
b emitters like Yttrium? block it with low z like plastic. .
What is the K-Shell binding energy of the republic of Tungston?
how much energy to get some characteristic x-rays from Tungston?
69.5 keV
need more than that. . . ie 69 keV wouldn’t get you any
kVp and characteristic x-ray production from tungsten
below 69.5 kVp
between 80-150
between 150 and 300
above 300 kVp
- below 69.5 kVp = 0
- between 80-150 = 10-25 % K-shell characteristic contribution
- between 150 and 300 = progressive decrease in contribution
- above 300 kVp = negligible contribution
What is “beam intensity”? What are the units?
number of x-rays multiplied by the energy
Roentgens / min (R/min)
-this is not the same as the “total number of xrays”
High Yield Recap of Bremmies
Most (80%) of the x-rays produced
bombarding electron interacts with the entire atom
radiation release due to diversion/slowing down
radiation released spans a large range of energies
x-ray energy depends on tube voltage.
High Yield recap of characteristic radiation
only small % of x-rays produced (10-25% at 80-150kVp)
bombarding e- interact with inner shell e-
radiation released due to higher shell e- moving down into a lower state
radiation released is a specific energy
x-ray energy depends on element of target atom (not tube voltage).
Quality versus quantity
quality = overall average energy of the beam / ability to penetrate an object
quantity = total number of x-rays under the curve in a spectrum diagram
How does target material (Z) influence quantity and quality?
Large Z = more overall X-rays via Brem = change in quantity
Large Z = different characteristic energy peaks = change in quality
How does kVp influence quantity and quality?
max x-ray energy will go up to match the kVp and the average x-ray energy will go up = change in quality
total number of x-rays will go up (more energy was available in those Bremmy x-rays) = change in quantity (beam intensity will increase as a square of kVp)
equation:
Beam intensity =
proportional to (kVp)2
How does mAs influence quantity and quality?
changes in mAs change quantity but not quality
What is the 15% rule?!
if you increase kVp by 15% and decrease the mA by 1/2 you will maintain the same x-ray density on the radiograph.
effect of single and triple phase generators on quantity and quality?
Single phase = more ripple = less quality and less quantity
Triple phase = the opposite
what is half-value layer?
what is 10th HVL?
The ammount of material requeired to attenuate an x-ray to 1/2 the original output.
10 HVL = thickness of material that can attenuate an x-ray to 90%
More filtration = less/more HVL
higher HVL
What does filtration do to quantity and quality?
increased filtration = decreased quantity and INCREASED QUALITY
the average Brems energy is equal to what percent of the kVp selected?
1/3
recap
increasing the kV increases what?
increases max energy, average energy (quality) and increases quantity
recap
increasing the ma does what?
increases quantity of x-rays
no change in characteristic energy, average energy (quality) or max energy
recap spectrum diagrams
adding filtration does what?
increases the average energy of e- (quality)
decreases total quantity of electrons
recap spectrum diagrams
rectifying the current does what?
increases average energy and total quality of xrays
no change in max energy
recap spectrum diagrams
increased atomic number (Z) of the target
increased total quantity of x-rays
change in characteristic energy peaks (which will be higher with a higher Z)
