chp2 Flashcards
What is pixel?
picture element
smallest element in a digital image
What is analog?
device or system that captures or measures continuously changing signal.
What is pixel size?
the size of the pixel is directly proportional to the amount of spatial resolution or detail in the image.
What is an example of pixel size?
the smaller the pixel the greater the detail
What is pixel bit depth?
the number of bits within the pixel
How many shades of grey can the eye see?
35
What is a factor in determining the image contrast resolution?
grey level
What is field of view (FOV)?
the amount of body part or patient included in the image
What is exposure index?
the amount of exposure received by the IR (image receptor) not by the patient
What is ALARA?
as low as reasonably acheivable
What is air kerma?
unit of measurement of radiation energy absorbed in a unit of air
How is air kerma expressed?
J/kg or gray (Gy)
What is the indicated equivalent air kerma?
Measurement of radiation incident on the image receptor derived from pixel values produced by the exposure to an image receptor
What is the target equivalent air kerma value?
set values, established by either the system manufacturer or the system user, that represents an optimal exposure for each specific body part and view
What is the deviation index (DI)?
difference between the actual exposure and the target exposure it is expressed as a formula
What are the some reasons you cannot solely determine image quality by the deviation index?
- a prostheses within the image
- gonadal shield within the image
- failure of the system to recognize the collimated borders
- unexpected body part in the image
What is brightness?
amount of luminescence
What is window level?
adjusting brightness of an image, this can also be used to make an image darker
What is contrast resolution?
ability of the digital system to display subtle changes in the shade of gray
What does contrast resolution depend on?
scatter
What is spatial resolution?
the ability of the imaging system to demonstrate small details of an object
What is dynamic range?
ability to respond to varying levels of exposure
What equals more detail?
less lines
What equals less detail?
more lines
What is a matrix?
square arrangement of numbers in columns and rows
What is modulation transfer?
the ability of a system to record available spatial frequencies
What is noise?
anything that interferes with the image
What is equipment noise and how does it affect the radiographer?
noise that is highly dependent on manufacturer; technology, and detector quality. This cannot be controlled by the radiographer
What is latitude?
The amount of error that can be made in exposure factor choice and still result in the capture of the quality image
What is latitude dependent on?
the image detector; the higher the dynamic range, the more values can be detected
What is detective quantum efficiency(DQE)?
measurement of percentage of x-rays that is absorbed when it hit the detector
What is modulation transfer function?
The ability of a system to record available spatial frequencies
