Please enable JavaScript.
Coggle requires JavaScript to display documents.
Filtration & Prime Factors - Coggle Diagram
Filtration & Prime Factors
Filtration
Increased Filtration
Filters out the lower energy x-ray photons
Half-Value-Layer (HVL)
HVL too low
Too many low-energy photons in the beam
The physicist will add filtration
The amount of filtration needed to reduce the beam to 1/2 of its original intensity.
Measured in mm al/eq
Decrease Filtration
Does NOT add useful image information
Increase Patient dose
kVp
Energy level of the photons
Beam penetrability
how many photons will penetrate anatomy
Quality
Measured in eV (Electron Volts)
Represented numerically by HVL
Increasing kVp
Increases the speed and energy of electrons crossing from cathode to anode.
More Penetration (Travel farther in matter)
No practical value
Doubling kVp = 4x X-ray photon #
Doesn't account for changes in penetration and scatter production
Fewer interactions occur in the body
A higher % of interactions are Compton scatter (not photoelectric)
Lowers contrast
Influences beam quantity
More interactions with higher kVp (more photons produced)
Influences scatter/secondary radiation production
Fewer interactions occur in the body at higher kVp
Should not be used to control IR exposure
mAs
Milliampere (mA)
The measure of tube current
1 Ampere (A) = 1 Coulomb (C)/sec
1C =6.3 x 10^18 electrons/sec
Determines beam quantity or intensity
Changing the mA station changes the filament used
Changes the number of electrons released though thermionic emission
Doubling mA
Doubles the number of electrons emitted
Doubles the number of photons
Doubles patient dose (IF no change is made to exposure time)
1 mA = 6.3 x10^15 electrons/sec
Exposure time (s)
Quantity
Measured in coulomb/kilogram or air kerma
Coulomb/Kilogram
Number of electrons liberated per kilogram of Air (output intensity of x-ray equipment)
Output intensity of x-ray equipment
Air Kerma
Quantity of radiation delivered to a given point (energy deposited)
Energy Deposited
A RATE (how many electrons flow from cathode to anode per second)
mAs Reciprocity
As long as the total mAs is the same, any combination of mA and time can be used to produce the same quantity of radiation.
Primary controller of x-ray intensity
Distance
Source to image-receptor distance (SID)
increasing Distance
Doubling distance
Reduces beam intensity by a factor of 4
Reduces Entrance Skin Exposure (ESE)
Patient Dose
Improves Image Quality
Tube Current
Measured in
The flow of electrons from cathode to anode
DIRECT relationship to intensity
Space Charge Compensator
Corrects for the increase in electron speed to maintain a constant number of electrons/second
15% Rule
Increases kVp 15% (+10kVp) and reduce mAs 50% (1/2)
Decreases kVp 15% (-10kVp) and doubles mAs 50% (x2)
Inverse Square Law
Doubling the distance, reduces the beam intensity by a factor of 4
Applies to all EM Radiation
Direct Square Law (DSL)
Used to maintain the same overall IR exposure
Also known as the "mAs Distance Compensation Formula" or "Exposure Maintenence Formula"
Anode Heel Effect
Smaller & Steeper angle = Smaller Effective Focal Spot
Better Resolution/Detail Sharpness
Smaller anode angle
Increases the impact of the anode heel effect
The x-ray on the cathode side is more intense than that on the Anode side
Longer SID counteracts Anode Heel Effect
X-Ray Machine Indicators
Agfa
Low E = Low LogM 2.05
High E = High LogM 2.35
Low = Low & High = High
Uses LogM
Kodak (Carestream)
Low E = Low EI 1800
High E = High EI 2200
Uses EI
Low = Low & High = High
Fuji
Low E = High S# 400
High E = Low S# 100
Uses S#
High = Low & Low = High
Image contrast is ALWAYS controlled through computer post-processing
