Contrast & Patient Factors
As an x-ray beam becomes more penetrating, and tissues are penetrated more uniformly, what happens to subject contrast?
Decreased subject contrast
A patient has difficulty remaining still. Using high mA allows the radiographer to shorten this factor and reduce motion blur.
Exposure time
When this scatter-cleanup device is introduced, mAs usually must be increased because it absorbs scatter and some useful radiation.
Grid
Selecting the wrong examination or projection before exposure can cause the system to apply an inappropriate reference histogram or this grayscale-processing tool.
LUT
A bra clasp or necklace remains in the anatomy during exposure. This is classified as this type of artifact.
Object artifact
Compared with a small extremity, imaging a much thicker body part generally results in greater attenuation and increased production of this unwanted radiation.
Scatter
Decreasing detector-element size generally improves this image-quality characteristic, although fewer photons are collected by each element.
Spatial resolution
Opening the x-ray field substantially larger than necessary increases scatter and patient dose while decreasing this image characteristic.
Contrast
A detector contains one defective pixel. The computer estimates its value using neighboring pixels through this preprocessing operation.
Interpolation
A faint image from an earlier examination remains visible on a newly processed CR image because the imaging plate was not completely cleared. What is the artifact?
Image receptor artifact
These two common positive contrast agents appear very radiopaque because their relatively high effective atomic numbers increase x-ray absorption.
Iodine and Barium
Moving the image receptor farther from the x-ray source while maintaining receptor exposure generally decreases magnification and this type of geometric unsharpness.
Focal spot blur
This beam-modifying process removes low-energy photons that would contribute to skin dose without significantly improving the image.
Filtration
This preprocessing correction compensates for variations in detector response so a uniform exposure produces a uniform image.
Flat-fielding
This form of compression allows the original image data to be reconstructed without permanently discarding information.
Lossless compression
Two neighboring tissues with significantly different mass densities will generally create more of this because they attenuate the beam differently.
Subject contrast
A long bone produces different attenuation patterns when imaged AP versus lateral because this characteristic changes relative to the beam
Object shape/orientation
A radiographer reduces the field size so only the required anatomy is irradiated. This practice reduces both scatter production and unnecessary patient exposure.
Collimation
One of these analyzes the distribution of pixel values, while the other maps those values to displayed shades of gray. What are they?
Histogram analysis and LUT
During an AEC exposure, a radiopaque object covers an active detector chamber. The system may continue exposing longer than necessary, causing an increase in this.
Patient dose
A technique chart works well for one patient but requires adjustment for a patient with a markedly different body type. Most technique charts use this body habitus as their reference.
Sthenic
A patient with a thick abdomen cannot remain still. The radiographer adjusts the mA and exposure time while maintaining the same mAs to prevent this.
Motion blur
For a thick body part with significant scatter and a patient prone to motion, an optimized technique would combine appropriate scatter control, tight collimation, and this mA/time strategy.
High mA with a short exposure time
Excessive unexposed detector area or raw background information causes the system to identify the irradiated region incorrectly. This digital-processing function has failed.
Exposure-field recognition
Poor alignment among the tube, central ray, grid, anatomy, and receptor may produce this grid-related problem in addition to uneven exposure or clipped anatomy.