Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
63 Cards in this Set
- Front
- Back
|
What is considered a good radiographic film?
|
An acceptable image should have diagnostic visual characteristics & minimal projection geometry
|
|
|
What does diagnostic quality depend on?
|
Proper visual characteristics Geometric considerations
|
|
|
List some geometric considerations for good diagnostic quality
|
-Sharpness: how well a boundary between two areas of differing radiodensity is revealed
-Motion unsharpness -Screen unsharpness in extraoral conventional technique -Resolution: how well an image reveals small objects that are close to each other -Anatomical accuracy -Adequate coverage of the anatomical area of interest |
|
|
What are the two important visual characteristics?
|
Density
Contrast |
|
|
What are the characteristics of radiographic density?
|
-Degree of “blackness” on the Image receptor
-Depends on amount of radiation; Greater the amount of x-rays reaching the Image receptor- greater the degree of darkness |
|
|
Darker images are due to...
|
High radiographic density
|
|
|
Lighter images are due to...
|
Low radiographic density
|
|
|
What is density responsible for in a radiographic image?
|
Visible detail
|
|
|
How can you tell that the density is correct in an image?
|
Faint outline of soft tissues should be visualized along with the hard tissues
|
|
|
What is the useful range of radiographic density?
|
0.3 (very light) to 3.0 (very dark)
|
|
|
What are the primary factors controlling radiographic density?
|
mA
kVp source-image receptor distance |
|
|
What are secondary factors controlling radiographic density?
|
Development conditions
Image receptor type Intensifying screens Object density |
|
|
How does mA control density?
|
Blackness varies directly & proportionately with tube current & the exposure time.
Higher the mAs, greater the density |
|
|
How does kVp control density?
|
Greater the kVp, & more penetrating the x-rays
More x-rays strike Image receptor emulsion and Produce greater density |
|
|
How does the source-image receptor distance control density?
|
-Beam intensity varies inversely to the square of the SFD (inverse square law)
-Shorter the distance--> greater the intensity of beam --> higher the Image receptor density -Doubling the distance gives one-fourth the density -Halving the distance gives four times the density |
|
|
How does developmental time affect the radiographic density?
|
-Underdevelopment produces a low-
density image. It may be also because of developer solution that is depleted or too cold for processing. -Over development can produce higher density images (fog). |
|
|
How does image receptor type affect the radiographic density?
|
Higher speed Image receptor requires less mAs to produce a density change compared with slower-speed image receptors
|
|
|
How does conventional intensifying screens affect the radiographic density?
|
Higher-speed screens require less mAs
|
|
|
What does fog affect?
|
-Fog affects the image contrast
-Fog results in an increased image receptor density and decreased contrast on the image |
|
|
What is Radiographic Contrast and what primarily affects it?
|
Differences in the densities on the Image receptor
Primarily affected by kVp |
|
|
High contrast has _____ shades of gray.
|
Few
Also called short-scale contrast |
|
|
Low contrast has _____ shades of gray.
|
More
Also called long-scale contrast |
|
|
What characterizes long-scale contrast?
|
- Higher kVp (80-90 kVp)
- More penetrating x-rays - Density differences are small - Contrast is low Few blacks and whites with more shades of gray |
|
|
What characterizes short-scale contrast?
|
-Lower kVp (60-65 kVp)
-Less penetrating xrays -Density differences are large -High contrast More blacks and whites with fewer shades of gray |
|
|
What should the contrast be for PA films?
|
Show relatively lower contrast - For Osseous changes
|
|
|
What should the contrast be for bitewing radiographs?
|
Should have relatively high contrast - For Dental caries detection
|
|
|
If kVp is increased what should you do to maintain radiographic density?
|
mAs or exposure time should be decreased
|
|
|
What will result in an altered image receptor density?
|
Change in contrast
kVp affects both energy & the number of xrays produced |
|
|
Change in density by changing mAs only will _____ produce an obvious change in contrast
|
NOT
|
|
|
A radiograph is a _____ representation of a _____ object
|
2D, 3D
|
|
|
In Projection geometry what is important to understand?
|
Normal Anatomy
Effect of focal spot size and position (relative to object & Image receptor) on image clarity, magnification & distortion |
|
|
What does sharpness measure?
|
How well a boundary between two areas of differing radio-densities is reveal
|
|
|
What does spatial resolution measure?
|
How well a radiographic image is able to reveal small objects that are close together
|
|
|
What are the three geometric characteristics?
|
Image Unsharpness (Diffusion of detail)
Image Magnification Image Shape Distortion |
|
|
Image unsharpness can be due to what?
|
(1) Geometric unsharpness: Penumbra: unsharp margin surrounding the image.
(2) Motion unsharpness (3) Inherent unsharpness due to conventional extraoral screens |
|
|
What is Penumbra or edge gradient?
|
Almost shadow
unsharp margin or blurred zone on the image is seen as the x-rays originate from focal spot and travel in straight lines, their projections of feature of an object do not occur at exactly the same location on the Image receptor |
|
|
What are two reasons for unsharpness in the clinic?
|
Movement of the patient
Movement of the BID |
|
|
What happens in image magnification and distortion?
|
Objects farther from the Image receptor will always magnify more than objects closer to the Image receptor with similar technique
|
|
|
What causes image magnification?
|
Divergent x-ray photon paths cause enlargement
|
|
|
What minimizes image magnification?
|
Increasing the focal spot-to- Image receptor distance and decreasing the object-to-Image receptor minimizes image magnification
|
|
|
What causes image shape distortion?
|
Unequal magnification
|
|
|
What minimizes image shape distortion?
|
-Position the Image receptor parallel to the long axis of the object
-Orient the CR perpendicular to the object and Image receptor |
|
|
Image unsharpness, distortion & magnification occurs because...
|
1. X-rays originate from an area rather then point
2. X-rays travel in diverging straight lines as they radiate from the source 3. Human structures have depth, width & length |
|
|
What are the five rules for acurate image formation?
|
To minimize loss of clarity:
1. Effective focal spot should be as small as possible 2. Distance between the focal spot & object should be as long as possible 3. Image receptor should be as close to the object as possible 4. Long axis of the object should be parallel to the Image receptor 5.Central ray should be perpendicular to the image receptor to record the structures in their true spatial relationships |
|
|
How do you minimize the loss of clarity through the size of the effective focal spot?
|
-Effective Focal Spot should be as small as possible
-Smaller the focal spot size, the smaller the penumbra, higher the image definition and decreased geometric unsharpness |
|
|
How can the object-image receptor distance affect the image clarity?
|
-Longer the object-Image receptor distance, greater the unsharpness
-Objects closer to the Image receptor have relatively sharper image -Lingual cusps are sharper as they are closer to the Image receptor |
|
|
How does source-object distance affect image clarity?
|
-Radiographic image magnification can be decreased by using longer source-object distance and shorter object-Image receptor distance
-Longer BIDs are recommended because of greater anatomical accuracy |
|
|
What can be minimized by using radiographic intraoral paralleling technique?
|
Image shape distortion
problems arise with bisecting the angle technique |
|
|
What can be decreased by using longer focal spot-object distance by
reducing the divergence of the x-ray beam and by shorter object-image receptor distance? |
Image blurring and magnification?
|
|
|
Divergent paths of _____ cause enlargement of the image
|
Photons
|
|
|
Longer focal spot-to-object distance _____ by using photons whose paths are almost
parallel (longer BID) |
minimizes blurring
|
|
|
Use of longer _____ distance or use of longer _____ would minimize the size of penumbra & magnification
|
Focal spot-image receptor, BID
|
|
|
Whay are longer BID's recommended?
|
Greater anatomic accuracy
|
|
|
Longer the object-image receptor distance, greater the _____
|
Unsharpness
|
|
|
Objects closer to the image receptor have relatively sharper image. This is the result of _____
|
minimizing the divergence of x- ray photons
|
|
|
Why are lingual cusps sharper?
|
They are closer to the image receptor
|
|
|
A radiograph is considered to have anatomic accuracy when...
|
-Proximal contacts of teeth are opened
-Buccal & lingual cusps of post. teeth are superimposed -Buccal and lingual portions of alveolar crest are superimposed -No superimposition of zygomatic arches over the roots of maxillary teeth |
|
|
What are the regions of interest on a bitewing radiograph?
|
crestal alveolar bone and interproximal contacts
|
|
|
Adequate coverage of the region of interest is dependent on what factors?
|
-Proper alignment of Image receptor and radiation beam to the area of interest
-Proper selection of Image receptor type and size -Proper selection of Image receptor-projection technique |
|
|
What does the size of the x-ray focal spot influence?
|
Definition
|
|
|
Why extending the source-image receptor distance by using a longer BID a necessary adjunct to intraoral paralleling technique?
|
To avoid unsharpness of the image
|
|
|
How do you change from a long scale contrast to a short scale contrast and still maintain the density?
|
decrease kVp and increase mA's
|
|
|
True / False
Radiographic fog will increase density & decrease contrast |
True
|
