-
Diagnostic x-ray is one that exhibits proper ______, _______, _______ and is the same ______ as the object being radiographed
- density, contrast, sharp outlines
- shape and size
-
What are some visual and geometric image characteristics
- VisualDensity
- Contrast
- GeometricSharpness
- Magnification
- Distortion
-
Image density is the overall ___________ of the radiograph. Proper density reveals ______
- blackness (darkness)
- white, black and gray areas
-
What are the density influencing factors
- Subject thickness/density
- Three Exposure factors:
- Milliamperage (mA)
- Kilovoltage (kV)
- Exposure time
-
Increase in the thickness of the matter results in _________ radiograph
low image density / lighter
-
Increase in mA= __________ which results in a radiograph that is
- more electrons produced and ultimately more x-rays to expose the receptor.
- darker ↑ density
-
Decrease in mA= ________ which results in a ________ radiograph
- less x-rays on receptor
- lighter radiograph ↓ image density
-
Ideal mA:
7-15 mA required for a diagnostic dental radiograph (newer machines 6-8mA or 7mA fixed)
-
mA and exposure time are ________ related. When the mA is increased the time is
-
Increase in kVp = _______ density
increase
-
Decrease in kVp = ________ density
decrease
-
AN INCREASE OF 15 kVp RESULTS IN _______ IN DENSITY
2X INCREASE
-
The image contrast is the ________. High contrast results in _______ while low contrast results in _______
- difference in the degrees of blackness between adjacent areas on a dental radiograph
- Very light areas and very dark areas
- Many shades of gray
-
What are the influencing factors of contrast
- 1. Inherent qualities of the receptor: determined by manufacturer
- 2. Film processing (Conventional): Increase in development time or temperature = increased contrast
- 3. Subject: size and thickness of patient tissues, density, composition
-
Subject contrast (densities of adjacent tissues)can be compensated for by increasing or decreasing
kV
-
High kV = ______ density with ___ contrast = ______
- high image (darker image)
- low
- many shades of gray
-
Low kV = _____ density and _____ contrast = ________
- low image density (lighter image)
- high
- (black and white)
-
_________ is the ONLY exposure factor that directly influences contrast
kV
-
What is a short scale of image contrast
two densities (black & white)
-
What is a long scale of image contrast
many densities (many grays)
-
What is considered a high and low kV
- greater than 90
- less than 70
-
Penumbra
- Unsharpness, or blurring of the edges
- Fuzzy, unclear area that surrounds a radiographic image
- Every dental image has some degree of penumbra
-
Sharpness: Influencing Factors
- Focal spot size
- Film composition
- Movement
-
Focal spot is the _________. Smaller focal spots result in ________
- (tungsten target at anode)
- sharper images and less heat
-
Faster film contains _______ crystals that produce ______ image sharpness
-
What is magnification and what is the cause
- image is larger than actual size
- divergence of xray beam (xrays travel in diverging straight lines as they radiate from the focal spot)
- all dental radiographs exhibit some degree of magnification (as with penumbra/unsharpness)
-
Magnification: Influencing Factors
- Target (Source) to Receptor Distance:
- Determined by the PID lengthLonger PID=increased source to receptor=less magnification (also less divergent rays)
- Object (tooth) to Receptor Distance:Closer the tooth is to the receptor, less magnification
-
What is Dimensional Distortion and what are the influencing factors
- deviates from true shape and size
- Unequal magnification of different parts of the same object
- Improper object to receptor alignment
- Improper beam angulation
-
X-ray beam must be directed ________ to the long axis of the tooth and receptor to minimize distortion
perpendicular
|
|
