Intro & Physics Flashcards
What are x-rays?
a type of electromagnetic radiation
What is the other word for Photon?
X-rays
What are the properties of x-rays?
No charge or mass Invisible Cannot be felt Travel at speed of light Penetrate all matter to some degree Cause ionization if energy high enough
Ionization
loss of an electron
ALARA
As Low As Reasonably Achievable
What is included in the time component of ALARA?
Rotate personnel in the room
Avoid repeat examinations
Minimize patient holding
What is included in the distance component of ALARA?
Increasing distance between personnel and radiation source reduces exposure significantly
Inverse Square Law
intensity of radiation decreased with the square of the distance from the source
Doubling the distance reduces the x ray intensity to 1/4th(1/2)^2
Tripling the distance reduces the x ray intensity to 1/9th(1/3)^2
How do you reduce scatter?
Minimize the size of the beam
Radiograph
A picture of the pattern of x rays emerging from the patient
What controls the number of x rays produced and proportional?
current (mA) and time the current is “on” (s)
mA
controls the current that goes through the filament and the hotter the filament gets the more electrons are generated
What controls the number of electrons produced?
how long the current is left on
Milliampere (mA)
Number of electrons at cathode is proportional to mA
Seconds
longer time = more electrons produced
Increasing kVp
Greater voltage difference
Electrons travel faster
Have more kinetic energy
Create higher energy x rays
Underexposed radiograph
too Light
Overexposed radiograph
too dark
How do you fix an underexposed radiograph?
Increase mAs
or
Increase kVp
Increasing mAs
Increased number of x rays that strike patient
Increasing kVp
x rays have higher energy
Thorax Radiographs
Air provides contrast
Use high kVp, low mAs
Abdomen Radiographs
Fat provides contrast
Use low kVp, high mAs
When are grids used?
used when patient is more than 10 cm thick
What is the purpose of the Grid?
intercepts scatter from patient before it reaches film
What is the intensifying screen used for?
converts x-ray photon to light photons
What are the advantages to using an intensifying screen?
Permit over 100x reduction in mAs compared to no screens Reduced movement artifact Reduced patient exposure Reduced personnel exposure Increased tube life
