Textbook - Chapter 3 + 4 Flashcards
what is interpolation?
mathematical method of creating missing data
what are the 4 principal components of a computer?
input, output, central processing unit and memory
what are examples of input devices?
keyboard, mouse, touch-sensitive plasma screen, and CT detector mechanism
what are examples of output devices?
monitor, laser camera, printer and archiving equipment
what is the cpu?
the part of the system that interprets the computer program instructions and sequence tasks
what are the three principle types of solid-state memory?
- rom
- ram
- worm
which type of solid-state memories are part of the system’s primary memory?
- rom
- ram
what are rom used for?
- imprinted at the factory
- stores frequently used instructions to start the system
what are ram used for?
- has instructions that are frequently changed
image reconstruction
use of raw data to create an image
attenuation profile
system accounting for the attenuation properties of each ray sum and correlating it with the position of the ray
ray
path the x-ray beam takes from tube to detector
ray sum
detector senses each arriving ray and measure how much of the beam has been attenuated
views
compete set of ray sums
back projection
compilation of information from all the attenuation profiles to create an image
what are some drawbacks to back projection?
it produces a streak artifact in a star pattern
how do you minimize streak artifacts?
filters
filters are applied to only ______ data.
raw
SFOV
determines the area that the raw data is acquired
out-of-field artifacts
when parts of the patient is outside the SFOV causing inaccuracies in the images
DFOV
section of data selected to be displayed on the image
too large DFOV = image to be _______
small
small images due to too large of a DFOV will result in?
- more data in each pixel = decrease in spatial resolution
CT display monitor
used to display patient information, scan protocol data, provides many graphic aids to assist in image interpretation
DAC
digital to analog converters
what do DACs do?
change the digital signal from computer memory back to analog so the image can be displayed on the monitor
multiformat cameras
transfers images displayed on monitors to film
laser cameras
bypasses putting the image onto the display monitor and transfers it directly to the film
window width
determines the quantity of HUs represented as shades of gray on a specific image
if the value is higher than the selected range of the window width, what colour will the object be?
white
if the value is lower than the selected range of the window width, what colour will the object be?
black
window level
selection of HUs that are displayed on the image
what should the window level be set at?
a point where the value of the average attenuation number is similar to that of the tissue of interest
why is it good practice to widen the window width if a patient is obese or have metallic artifacts?
what does a wider window width do?
- increases anatomic diversity
- decreases image contrast
what size of window width is good for metallic artifacts and obese patients?
wider window widths
what size of window width is good for tissues of similar densities like the brain?
lower/narrow window widths
what does a narrower window width do?
provides greater density discrimination and contrast
dual window setting
when two images of different window widths are superimposed on each other to create a single image
