Ch 26-29 Flashcards
(44 cards)
Monitor control function that can change the lightness and darkness of the image on a display monitor but it isn’t related to exposure
Not interchangeable with density; only on digital
The concept of density as it is displayed on a soft-copy monitor for digital images
Brightness
Degree of overall blackening that is the result of black metallic silver deposited in the emulsion of film
Viewable result of a film’s response to exposure
When the IR was primarily film, this term could adequately describe the effects of IR exposure
In the digital environment this important image quality factor hasn’t changed but can be expressed simply as IR exposure because film is no longer the primary IR
Density
Used when switching distances and mAs and want to maintain density/exposure
A direct square law; mAs must increase when distance increases and vice versa in order to maintain IR exposure
mAs1/mAs2 = D1^2/D2^2
Exposure maintenance formula
Along with contrast, one of two photographic properties that allow detail to be seen; in digital imaging it is the critical quality factor to assess and comparable to density in film/screen environment
IR exposure
Digital post-processing that produces changes in brightness
Window level
Along with contrast, one of two photographic properties that allow detail to be seen
Density/IR exposure
What is the controlling factor of density/IR exposure and how is it affected?
mAs
Direct relationship between mAs and density/exposure; one goes up the other goes up
How are density/IR exposure adjustments made for changes in kVp?
Small changes can have profound impact on density/IR exposure
15% rule
How do variations in the anatomical part affect density/IR exposure?
Inverse relationship between tissue thickness/type and density/IR exposure; as tissue thickness, average atomic number of the tissue, and/or tissue density increases, density/IR exposure decreases
Thicker person decreases exposure
What are the relationships to density/IR exposure of grid ratio, frequency, interspace material and grid use?
The more efficient the grid, the less will be the density/IR exposure
Grids with high ratios, low frequency and dense interspace material; moving grids; and improperly used grids (incorrect focal distance, etc.) all reduce density/IR exposure
One of the properties that comprise visibility of detail; the difference between adjacent densities
Contrast
The result of differences in transmission of the beam as it passes through the patient resulting in signal differences to the digital detector
Differential attenuation
The concept of contrast as it is displayed on a soft-sopy monitor for digital images; range of density/brightness of the display monitor light emisson
Dynamic range
The number of shades of gray in a radiographic image
Grayscale
The number of useful visible densities or shades of gray
Scale of contrast
Degree of differential absorption resulting from the differing absorption characteristics of the tissues in the body
Subject contrast
The digital processing that produces changes in the range of density/brightness, which can be used to control contrast
Window width
Short scale
Short/narrow dynamic range
Portable chest x-rays tend to be more high contrast bc of the tech factors you use (no grid)
Low kVp
Dif in adjacent densities is great
Short/narrow dynamics = white & black
High contrast
Long scale
Large/wide dynamic range
Radiographers prefer this for chest x-rays bc it shows more info bc there are a lot of dif tissues w/dif Z#’s so they have more attenuation
High kVp gives long-scale/low contrast bc x-ray photons are greater to interact w/dif tissues & able to knock out e-’s & scatter
Similar densities, dif in adjacent densities is minimal
Large/wide dynamic range = range of exposures you can see is v many (many steps)
Low contrast
Total range of density/IR exposure values recorded by the IR
Physical contrast
Total range of density/IR exposure values that can be perceived by the human eye in a single image
Visible contrast
3 factors that affect subject contrast
Kilovoltage (can control)
Amount of irradiated material
Type of irradiated material (ex: air, bone, contrast media, etc.)
What factors affect image receptor contrast?
Histogram and LUT used affect final image
Use of proper kVp still important
Concept of contrast as it is displayed on a soft-copy monitor for digital images; range of density/brightness on the display monitor light emission
Dynamic range
