CR
computed radiography
Pixels
- the smallest unit in the image
- a single shade of gray
Many pixels make up the _____
matrix
Digital processing uses mathematical formulas called what?
algorithms
In digital, contrast is controlled by what two things?
kVp and LUT
LUT
look up table
As kVp increases, the beam penetrability ______, and patient dose _______
increases, decreases
Brightness
the intensity of light that represents individual pixels in the image on the computer monitor
Does a change in mAs have an effect on the brightness of an image?
No
PACS
picture archiving communication system
Post Processing
altering the image before it is sent to PACS
Contrast resolution
the different between light and dark areas of an image
What controls contrast in post processing?
LUT (look up tables)
Bit depth
determined by the manunfacturer
Spatial Resolution
- the recorded sharpness of detail of structures on the image
- factors: focal spot size, motion, geometric factors, and acquisition pixel size
- measured in line pairs per millimeter (lp/mm)
The smaller the pixel, the ______ the spatial resolution
greater
Spatial Resolution for eyes, CR/DR, and hardfilm
Eyes- 3 lp/mm
CR/DR- 4 lp/mm
Hardfilm- 15 lp/mm
Exposure Indicator
- Exposure value or S#
- a number value given to an image to tell you whether or not you are in range
Kodak
- Exposure value
- direct relationship
Fuji and Konica
- S#
- indirect relationship
Is the technologist monitor of diagnostic quality?
No
Noise
- random disturbances or occurrences that reduce clarity
- looks grainy
SNR
signal to noise ratio
High SNR
- want a high SNR to show low contrast, soft structures
- need enough mAs to obtain
- less noise - better picture
Low SNR
- bad, looks grainy
- not enough mAs
Range for Kodak
1800-2100
How to increase or decrease exposure value for Kodak
- to increase by 300 points, add 1/2 of your mAs
- to decrease by 300 points, cut 1/2 of your mAs
Konica Range
75-450
Fuji Range
- Different for every exam
- Extremities usually between 75-150
- Chest usually between 200-600
How to increase or decrease S# for Konica and Fuji
- double your mAs, cuts S# in half
- halving your mAs, doubles S#
Rules for CR
1. One body part per film
2. Needs at leave 60 kVp for algorithms to work (up to 120kVp)
3. Need to be in the middle of the IR
4. Grids are needed for any body part over 10cm
5. Every hospital has a different protocol
Brightness is to CR as ______ is to hardfilm
density
Increase kVp, _______ radiographic exposure
increase
kVp Range
about 48-130
mAs Range
about .5-630
Increase mAs, _____ radiographic exposure
increase
Windowing
- user can adjust image contrast and brightness on the monitor
- can adjust window width (contrast) and window level (brightness)
Smoothing
reduces the display of noise in an image
Magnification
all or part of an image can be magnified
Edge Enhancement
- makes the edges of structures appear more prominent
- spatial resolution of the image does not change
Equalization
- presents a more uniform image appearance
- makes low brightness brighter and high brightness dimmer
Subtraction
- background anatomy can be removed to allow visualization of contrast media-filled vessels
- used in angiography
Image Reversal
the dark and light pixel values of an image are reversed, x-ray image reverses from a negative to a positive
Annotation
text can be added to images
Digital archive
a digital storage and image management system, stores patient files and images
Display matrix
series of "boxes" that give form to the image
Display pixel size
pixel size of the monitor, related to the display matrix
Exposure latitude
range of exposure intensities that will produce an acceptable image
Exposure level
a term used by certain equipment manufacturers to indicate exposure indicator
Flat-panel detector with thin-film transistor (FPD-TFT)
- a method of acquiring radiographic images digitally
- replaces the film-screen system
- made with amorphous selenium or silicon
- cassette-based or cassette-less
Photostimulable phosphor (PSP) plate
- a method of acquiring radiographic images digitally
- main components include a PSP image plate, an image plate reader, and a workstation
- cassette-based or cassette-less
Parallel grid
- more absorbed on the outside
- image darker in center
- don't want this
Focus grid
- more even
- focuses towards the center
Grid cutoff
- if grid isn't angled properly
- want angle to go with the lines on the grid
Off-focus grid
using the wrong grid 40 vs. 72in
Upside down grid
black in middle, white on sides