01, 02 Principles and biology Flashcards
(45 cards)
How are x-rays produced?
- pyrex glass tube
- two electrodes in a vacuum: Cathode (negative filament) and Anode (positive)
- generation of electrons,
- accelerate electrons
- abrupt stoppage of electrons
Cathode
-Negative electrode and source of e-s
-tungsten filament wound in molybdenum focusing cup
-strong when thin
-high melting point (6098 degrees)
this is heated and e-s “boil off”
Anode
- positive electrode
- copper to conduct heat with tungsten target
- interacts with electrons to produce radiation
- 99% kinetic energy generates heat, 1% radiation
types of x-ray interactions with patient
- scattered
- absorbed/attenuated
- transmitted
What is the source of “fog” on film
scatter
what does the kilovoltage determine?
x-ray wavelength, ie the penetrating power
What do mAs control?
the amount
inverse square law
- intensity of radiation varies inversely with the square of the source-film distance (SFD)
- I=1/d^2
- i.e. increase d by 2 =decreased intensity by 4X
what are the most attenuating natural tissues of the body?
cortical bone and enamel
what is present in the film to protect the patent from back scatter radiation?
lead foil at the back of the film
what type of film would you use for a periapical radiograph?
No 1, 2
what No. of film for a bitewing?
No. 2 with a bite-tab
what type of film for an occlusal rad?
No. 4
Do fast speed films require more or less radiation exposure than slow speed films?
-less
What is the alphabetical classification of the fastest film available?
F speed (Insight)
What is the primary controlling factor for density?
Milliamperage Seconds (mAs)
if you increase the mAs, what does that increase?
-and when you increase them, what’s the general rule?
the quantity of x-rays produced
-change the mAs by a factor of 2
How do you change the radiographic contrast?
- kVp,
- kilovoltage determines the relative strength of the x-ray photons or penetrating ability
- increasing the kilovoltage produces x-rays which penetrate tissues more deeply
Penumbra
(edge gradient), fuzzy, unsharp margin around a structure on a radiograph
what gives rise to magnification?
-x-rays traveling in diverging straight lines
which cusp tips would have greater magnification, B or L?
Buccal, more magnification and more unsharpness
what are the five keys to accurate image formation?
- small focal spot
- source to object distance as long as possible
- object to film distance as short as possible
- long axis of object parallel to film
- central x-ray perpendicular to film
who discovered x-rays?
Wilhelm conrad roentgen, 1895
x-ray of bertha’s hand
what are the effects of radiation on atoms and molecules?
- excitation (from low energy photons)
- ionization (from high energy photons)
- breakage of molecular bonds
