Principles of Radiology Flashcards
Can xrays be focused on a single point?
No
What property of an xray allows it to penetrate
Short wavelength
What produces an x ray?
Two electrodes in a glass vaccum tube
Which is the positive Electrode?
Anode, the TARGET of negative electrons
Which is the negative Electrode?
Cathode, the expeller of negative electrons
What does the cathode consist of
Tungsten filament wound in molybdenum cup
How does the cathode make electrons?
When the tungsten is heated it boils off electrons
What is the process of “boiling off” electrons that the cathode goes through when heated?
Thermionic emission
What is the anode made of
Copper for heat conduction and tungsten to produce radiation
What percent of the xray kinetic energy produced by the cathode is turned into heat?
99%
What are the 3 ways an x ray can interact with a patient?
Scattered
Absorbed
Transmitted
Why are scattered x rays bad?
They produce fog on a film
They are a source of exposure for patients
What happens when an x ray scatters?
It changes direction and has its energy lowered
What is another word to describe an absorbed xray?
Attenuated
What determines an xray’s absorbtion?
Wavelength/kilovoltage
Tissue thickness
Atomic Number
Density
What color does an absorbed x-ray produce on the film?
White
What measurement refers to the amount of x-rays being directed at the patient?
mA
What measurement is the penetrating power of the x-ray beam?
kVp
What is meant by the term “dead man switch”
It means you have to depress the button to make x-rays….you can’t leave the switch on passively
What is the formula for the inverse square law?
I = 1/d^2
What is the inverse square law?
The intensity of the radiation varies inversely with the square of the source-film distance
What is SFD?
Source-Film Distance
According to the inverse square law, what happens to the intensity of the beam if the SFD is doubled?
Intensity decreases by 4x
Why does the intensity of the beam lessen as the SFD is increased?
There is more time for the x-rays to disperse which makes the beam less focused.
What happens that causes dark/black areas to develop on image?
Primary photons are transmitted through the tissue and are received by the film
Why are absorbed x-rays also called attenuated x-rays?
Because the intensity of the beam is reduced as it passed through tissues. Photons are absorbed by the tissue thereby removing them from the beam
What will result in full beam attenuation
Metallic restorations
What are the two most attenuating natural tissues
Enamel and Cortical bone
What is the letter designating the fastest speed film?
F
What determines the diagnostic quality of Radiographs
The balance between the visibility and sharpness of the image
What does sharpness actually mean
The distinctness between all elements in the film
what does mAs stand for?
Millamperage seconds
What do the mAs of the beam control?
The density, increasing the mAs will increase the quantity of x-rays produced
What is the general rule when adjusting density of the beam?
Increase the mAs by factors of two
what does kVp stand for?
Kilovoltage Pontential
What does the kVp of the beam control?
The strength and penetrating power. Increases the kVp will allow the x-rays to penetrate deeper into tissue
What does Geometric Unsharpness mean
Diffusion of detail
What is Penumbra or Edge Gradient?
Fuzzy margin around a structure on a radiograph
What is Image Magnification vs. Image Shape Distortion?
Magnification is the equal enlargement of all parts of the radiographic image. Distortion is unequal enlargement
Why is there magnification and/or shape distortion?
Because x-rays arise from a field instead of a point and they travel in diverging lines
Which cusps are more magnified and distorted? Buccal or Lingual
Buccal
What are the five keys to an accurate image?
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
What size focal spot will result in a small penumbra?
Small
What magnification results in less penumbra? High or Low
Low
What distances should you strive for to minimize both penumbra and magnification?
Maximize Source to Object
Minimize Object to Film
What steps should you take to minimize geometric distortion?
Keep film parallel to object
Keep film perpendicular to central x-ray
