CH 7 Flashcards
Attenuation
Process by which a beam of radiation is reduced in energy when passing through tissue or other materials
EX: Radiopaque- light/white bone
Radiolucent- dark/black
Automatic rescaling
Process by which images are produced with uniform brightness and contrast, regardless of the amount of exposure
Computed radiography (CR)
- first version of digital imaging
- uses storage phosphor plates to produce images
- placed in a reader that scans the plate and transferred it’s energy into an image on the monitor
Contrast
Difference between ranges of adjacent IR exposures represented as gray tones in an image
Contrast resolution
Ability to distinguish between very subtle differences in image receptor exposures and differentiate them from the noise in the image
Data drop
Condition due to extreme overexposure which causes digital detector elements to become overwhelmed with photon energy and leads to drop of data during image reconstruction
Detector element (DEL)
Pixel size element of the DR IR that has a fixed dimension in x- or y- orientation
Detector saturation
Data drop that involves areas or regions of the digital detector
Digital radiography (DR)
Digital image acquisition systems that convert x-ray energy into a digital electronic signal for manipulation and display using direct or indirect (turns I are until light then converted into image) conversion
Primary radiation
Exiting X-ray tube
Scatter radiation
Bounces off patient
Absorbed radiation
Stays in patient
Remnant radiation
Strikes image receptor
Radiographic exposure factors
mAs- milliampere seconds, directly controls quantity of X-ray photons
kVp- kilovoltage peak, controls penetrating ability of X-ray beam
SID- affects relative intensity of beam
Factors that affect radiographic quality
Image signal: visibility of image
image resolution: sharpness/accuracy
Balance between the two required for optimum image quality
Two types of image signal
- IR exposure: signal value, numerical value assigned to the amount of x-ray exposure IR receives (brightness)
- Contrast: signal difference, difference in adjacent structures on image
Two types of image resolution
- Spatial resolution: sharpness, describes the degree of accuracy of structural lines recorded
- Contrast resolution: ability to distinguish between very subtle differences and signal values and differentiate them from noise
What are factors that affect signal value?
- mAs/kVp/SID
- patient size/thickness, Atomic number of anatomy, Pathology
- beam modification: filtration/collimating
- grids
- type of IR: CR/DR indirect and direct
Subject contrast
Differences in the intensity of x-ray beam after it has been attenuated or absorbed by patient
Radiographic contrast
Difference between adjacent exposure values on the radiographic image
Image contrast
brightness
Contrast media
Substance that’s injected into or ingested by patient to better visualize structures
Spatial resolution factors
Temporal resolution: motion distortion
Beam, geometry: object unsharpness due to shape of an atomic structure, use a small focal spot for better resolution, greater SID, smaller OID
Fluoroscopy
Use of x-rays to create a real time image of patient anatomy and function
- need image intensifier and flat panel digital fluoroscopic detector
