Ch 9: Digital Imaging Characteristic Flashcards
CR
Film
cassette
computed radiography
“old school”
DR
direct digital radiography
dynamic range
range of intensities the IR can detect
Why is dynamic range good?
can adapt the image and change brightness and window level to make the image quality better
Why is dynamic range bad?
can easily overexpose your patient if you aren’t watching your technique or EI
matrix
size is how many pixels are in your image/field
define matrix
how digital image is recorded
pixel density
number of pixels per unit area
pixel pitch
distance between pixels (center to center)
Can you change your bit depth?
No - specific to each xray unit/system
bit depth
determines how many shades of gray the system can create
affects contrast
won’t use every shade of gray for each image
higher bit system allows for longer contrast scale (more shades of gray available)
quantum mottle
“dotty” static-y appearance on computer
too low of EI/technique
saturation
dark portion of image
too high of EI/technique
too much info that computer cannot fix
Why might the window level be adjusted during postprocessing of an image?
to manipulate brightness levels
What determines the contrast resolution (shades of gray) of a digital imaging system?
bit depth
The sensor chamber for the AEC are located:
between the grid and image receptor
In the image intensifier the function of the input phosphor is to:
absorbs the remnant photons exiting the patient to visible light
The range of exposures a digital system can retain and use to create the image is:
dynamic range
The electric timer must be set to what back-up time in case the automatic exposure control (AEC) fails to terminate?
1.5 times the exposure time
What term is defined as the distance from the center of one pixel to the center of an adjacent pixel?
pixel pitch
The automatic exposure control (AEC) is a device that measures the quantity of radiation that will reach the ___________ before terminating the exposure?
IR
Grayscale on a digital system is:
scale of contrast
What are some patient factors that would affect image quality when using AEC?
patient size
pathology
orthopedic hardware
A radiographic image displays with obvious quantum noise (mottle). What does this say about EI and the exposure amount? How would you fix it on the repeat image?
EI would be low
IR would be underexposed
increase your mA
