What rule for kVp is used to see a visible change?
SID controls what image characteristic?
Size distortion (magnification)
What is affected by tube object IR alignment and angling of the CR?
Shape distortion (foreshortening or elongation)
***SID does not affect these image qualities
How much of a change in SID is required to actually see a change in visible density? ( in the clinical setting)
Increasing SID, _______ pnuembra
Define radiographic quality
The degree of excellence that anatomical structures are displayed
What are the two photographic properties?
Density and contrast
What are the two geometric qualities?
Sharpness of recorded detail and distortion
What rule for kVp is used to maintain equal image density?
***increase kVp by 15%, decrease mAs by 1/2(50%)
***decrease kVp by 15%, increase mAs by 2
What is the geometric unsharpness formula?
FS x OID/SOD
What is the magnification factor?
What is the % of magnification?
Subtract 1 then x 100
***must first calculate the magnification factor
Foreshortening is caused:
When anatomy is angled, beam is perpendicular to IR, but IR is not parallel to anatomy
Elongation is caused:
When anatomy is angled, beam is perpendicular to anatomy, but beam is not perpendicular to IR and beam is not parallel to anatomy
The ______ the matrix size and the ______ the pixel size = the sharper the spatial resolution
Define dynamic range
The maximum number of gray shades that can be displayed on a monitor
Define bit depth
The pixel's ability to display ranges of gray shades
Define contrast resolution
The ability to distinguish many shades of gray from black to white
Increasing window leveling makes the image ____ on the CRT monitor (darker or lighter)
Decreasing window leveling makes the image _____ on the CRT monitor (darker or lighter)
Increasing window width(ing) results in ___ visible gray shades ( more or less)
Decreasing window width(ing) results in ___ visible gray shades ( more or less)
What must be set first? Window width or window leveling?
Window width to get visible gray scale range then window level for desired brightness
Typical QC testing for monitors could include:
Spatial resolution and noise
Square law formula
Exposure = intensity x time
What is the reciprocity law failure?
When exposure times are too long or short which results in reduced speed. Increase of radiographic technique may be required
Define exposure time (T)
length of time that tube circuit is closed thereby allowing the electrons in the space charge to move (flow) from the filament (cathode) over to the anode thus producing x-rays
***electrons come from the cathode then move to anode
High kVp techniques result in low contrast images for 3 important reasons:
1. Increase penetration of the primary beam through various tissues lengthens the image gray scale
2. Photoelectric interactions are rapidly lost, leaving a high Compton-to-photoelectric ratio: In the image, "white" densities are lost, leaving fog more apparent in the image
3. Scatter radiation produced by the Compton interaction is both more energetic and scatters in a more forward direction, so that an increased amount of scatter reaching the film produces more fog in the image
Anode heel effect
The intensities of primary beam varies along the longitudinal axis of primary which less intensity on the anode side of beam.
Regarding grids, lower ratio = _____ clean-up scatter, _____ density
less clean-up scatter
Regarding grids, higher ratio = _____ clean-up scatter,_____ density