Ch 26-29 Flashcards
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
How does density/IR exposure affect image receptor contrast?
When the difference in adjacent densities is great there is high contrast
When there are similar densities/difference in adjacent densities is minimal there is low contrast
How do variations in the anatomical part affect contrast?
Dependent on tissue type, thickness, pathology, etc.
What is the effect of a grid on contrast?
Directly related: increase grid ratio increases contrast
Grids reduce scatter; reduce scatter = increase contrast
How do the histogram and look-up table affect display contrast?
Histogram has idea of what image should look like
LUT looks at image that comes in at standard contrast that machine tells it it should have, tries to fix it to this
Occurs when Nyquist Criterion not met
Low-frequency image wraps around high-frequency image
Visual appearance of two images slightly out of alignment
Aliasing
One of the geometric properties of image quality; the degree of geometric sharpness or accuracy of structural lines actually recorded in the image
Definition/recorded detail/sharpness/spatial resolution
Expression of the boundaries of an image
Edge spread function (ESF)
Background information that the IR receives
Imaging noise
Measurement of recorded detail, sharpness and resolution; the ability of a film/screen system to accurately measure the boundaries of an image
Line spread function (LSF)
Measurement of recorded detail, sharpness and resolution; measures the resolving ability of a film/screen combination
Modulation transfer function (MTF)
The sampling of the spatial resolution frequency signal twice from each cycle in digital systems
Nyquist criterion
Expression of the boundaries of an image; determined by a mathematical measurement of an image produced at a single point
Point spread function (PSF)
A lack of sufficient incoming data to process an image
Quantum mottle/noise
Lack of sharp definition of fine detail
Unsharpness
How is resolution measured?
Line pair per millimeter (lp/mm)
How does the OID affect recorded detail?
Resolution is improved when OID decreases and is degraded whenever it increases
Penumbra decreases when the OID decreases
How does the SID affect recorded detail?
Resolution is improved when SID increases and is degraded whenever it decreases
Penumbra decreases as the SID decreases
What is the relationship between focal spot size and recorded detail?
Focal spot size is controlled by the line focus principle
The focal spot size is a major controller of image resolution because it controls penumbra
As the focal spot decreases in size, penumbra also decreases thus increasing resolution
Penumbra decreases when the focal spot decreases
Imperfect, unsharp shadow surrounding the umbra
With light it is the region of partial illumination that surrounds the complete shadow
Penumbra/edge gradient
Distinctly sharp area of a shadow or the region of complete shadow
Umbra
