Exam 1.4: Principles of Radiography and Definitions Flashcards
Physical properties of x-rays
Weightless and undetectable by human senses
What is notable about how x-rays travel?
Travel in straight lines
Cannot be focused on a convergent point
What allows x-rays to penetrate our tissues?
Short wavelength
What is the difference between diagnostic and therapeutic radiation?
Therapeutic radiation causes a biological change
What is the tube made up inside the tube head?
Pyrex glass
What is inside the pyrex glass tube
Two electrodes
Also, no air….vacuum tube
What is the negative electrode called
Cathode
What is the function of the cathode?
It is the source of electrons
What is the cathode made of
Tungsten filament wound up inside a Molybdenum cup
Is the cathode stronger when it is thick or thin?
Thin
How does the cathode “release” electrons
The cathode has a very high melting point, when heated the electrons boil off
What is the name of the positive electrode?
Anode
What is the function of the anode
It is the target of the electrons released by cathode. It releases the radiation
What is the anode made from
copper with a tungsten target
What percent of the energy produced by the anode is immediately lost as heat?
99%
What happens to the x-ray’s energy when it scatters?
It is lowered
What does scatter cause in terms of image errors?
Fog
What is dangerous about scatter?
It is a source of patient exposure
What does it mean when the x-ray is attenuated?
It has been absorbed by the tissue
What values are important when trying to determine if an x-ray will be attenuated?
Wavelength
Tissue thickness
Atomic number
Density
What is removed from the beam as it passes through, and is attenuated by tissue?
Photons
What is the result of attenuation on the image?
Radiopacity
What are the two most attenuating tissues in the body?
Enamel and Cortical Bone
What results in complete attenuation of x-rays?
Metal restorations
In a BW, what percent of x-rays pass through the tissue completely (transmitted) without any interaction at all?
9%
If you want to increase the amount of x-rays in the beam (Cross sectional Density/Flux) what adjustment would you make to the machine?
Increase mA
What value dictates the penetrating power of the beam?
kVp
What is the primary safety feature of well designed x-ray systems?
Dead man switch
What is the inverse square law?
Intensity (I) = 1/d^2
What is the general idea of the inverse square law?
Intensity of radiation varies inversely with the square of the Source-Film Distance
If you increase the Source to Film distance by 2x…what is the effect on the intensity of the beam?
The intensity of the beam is decreased by a factor of 4
What is the purpose of the thin lead sheet in the film?
Receives radiation and protects patient from scatter
Should the raised dot face the tube or the patient?
tube
What are the three types of film?
Periapical (#1,2)
Bitewing (#2)
Occlusal (#4)
What is determined by the film speed?
The efficiency with which a film responds to x-ray exposure
If you increase the speed of the film, how would you adjust exposure time?
You would decrease it
Which speed (High or Low) requires less radiation exposure for the patient?
Fast
Film speed ratings are designated by the letters of the alphabet from A-F….is F the fastest or the slowest film?
F for Fast
What does the sharpness of an image refer to?
AKA Definition, sharp images have a clear demarcation between all elements of the film
What are some qualities that make an image “diagnostic quality”?
Exactness of anatomic detail
Proper balance of visibility and sharpness of redorded detail
What is radiographic density?
White areas vs Dark areas on film
What is the controlling factor of image density?
mAs
milliamperage seconds
If you increase the mAs of the machine, what is the result (in terms of the beam)
The beam will now include more photons
If you are going to increase mAs, try to do it by this amount
2x
What is the controlling factor of contrast?
kVp
What is the kilovoltage of the beam
The strength (not volume/amount) of x-rays. Increased strength means increased penetration of tissue
What characteristic describes the diffusion of detail in an image?
Geometric unsharpness
What would you call a fuzzy, unsharp margin around a structure on a radiograph
Penumbra
What exactly is meant by image magnification?
EQUAL enlargement of all parts of the image.
The shape of the magnified image is in the same proportion as the original
How does image shape distortion differ from magnification
It is enlargement without keeping the enlarged image in the same proportion as the original
If the x-rays are traveling from their source in diverging straight lines, what type of image distortion will occur?
Magnification
If the x-rays originate from an area rather than a point what type of distortion will occur?
Geometric Unsharpness
Why might different parts of the tooth be magnified to different extents
Because the teeth have depth, meaning the buccal cusps will show more magnification than the lingual cusps because they are further away from the film
What are some keys to getting an acute image?
Small focal spot Longest source to film distance Shortest object to film distance Long axis parallel to film Central Ray perpendicular to film
What will increasing the source to object distance and minimizing the film to object distance help mitigate?
Penumbra and Magnification
What will keeping the film parallel to the long axis and the central ray perpendicular to the film help mitigate?
Geometric Distortion
