Chapter 1 (pages 49-59) Flashcards
What is CR
Computed Radiography
What is DR
Digital Radiography
Properties of digital images
2 dimensional image
Made up by a matrix of pixels
Requires software and hardware applications to develop image
What are pixels?
The smallest unit in an image - many pixels make up the matrix
What are the mathematical formulas used for digital processing?
Algorithms
Function of algorithms
Enhance and optimize the look or appearance of an image on the computer screen
Differences between analog and digital films
Analog images are processed with chemicals
Digital is processed using algorithms
Analog doesn’t have much “latitude” where as digital has alot
Digital can be produced across a large rance of factors and have a large dynamic range
Image Quality Factors (digital)
Brightness
Contrast
Spacial Resolution
Distortion
Exposure Indicator
Noise
What is brightness?
The intensity of light that represents individual pixels in the image on the computer montior
In digital images, does mAs effect brightness?
No
What is post processing?
Altering the image before it is sent to the PACS or radiologist; will reduce the amount of latitude the radiologist has on his side to window and level an image
What is contrast resolution?
The difference between light and dark areas of an image
In digital, can contrast be altered?
Yes, by post processing LUT
What is pixel and bit depth?
Pixel demonstrates a single shade of gray. The range of possible shaes of gray is determined by bit depth. Bit depth is determined by the manufactuer.
What is spatial resolution?
Is the recorded sharpness of detail of structures on an image
What are the controlling factors for spatial resolution (digital)
Focal spot size
Motion
SID
OID
Pixel size
How does pixel size effect spatial resolution?
The smaller the pixel size, the greater the spatial resolution
What is Exposure Indicator for CR/DR
A number value given to an image to tell you whether or not you are in what techs call “range” basically this is telling you that the image may need to be repeated
What is the relationship between exposure indicator and range for Kodak, Fuji and Konica?
Kodak - direct
Fuji and Konica - Indirect
What is noise?
Random disturbances or occurances that reduces clarity. It looks grainy or mottled
When do you want a high SNR?
To show low contrast soft structures.
What is SNR?
Signal to Noise ratio
The number of xray photons that strike the IR is considered the signal, the other factors that contribute negatively are considered noise
What causes low SNR?
Not enough mAs
Post Processing Options
Windowing and Leveling
Smoothing
Magnification
Edge Enhancement
Equalization
Subtraction
Image Revesral
Annotation
What is windowing and leveling (post processing)?
Adjust window width which contains contrast
Adjust window leveling which controls the brightness
What is smoothing (post processing)
Reduce the display of noise
What is magnification (post processing)?
All or part of an image can be magnified
What is edge enhancement (post processing)?
Pixels are altered to make the edges of structures look more prominent
What is equalization (post processing)?
Pixels are altered to present a more uniform image.
What is subtraction (post processing)?
Background anatomy can be removed
What is image reversal (post processing)?
Dark and light pixels are reversed
What is annotiation (post processing)?
Adding text to images
What is density?
Color of blackness that hits the IR
A 15% increase in kVp will cause density to:
Increase; similar to doubling the mAs
What is the process of developing PSP
Scan barcode
Run cassette
PSP comes out
Turns protons to electrons
Run laser over the middle, gives a # (S# or EI)
Creates manifest image
Laser light goes back over it and releases electrons
PSP is now clean
What is bit depth equation?
2^bits per color
What is the line pairs per mm (lp/mm) for analog and digital
Analog - 15 lp/mm
Digital - 3-4 lp/mm
Is a higher or lower SNR better?
Higher
10:1 is better than 5:1
How does PSP effect spatial resolution?
The thicker the PSP, the better the spatial resolution
How do you increase your exposure value in Kodak systems and how much will it increase?
Add 1/2 your mAs technique to increase exposure value by 300
How do you decrease your exposure value in Kodak systems and how much will it decrease?
Cut 1/2 your mAs technique to decrease exposure value by 300
For Fuji/Konica, what happens when technique is increase?
S# goes down
Fuji/Konica - how do you increase your technique and how does it effect your S#
Double your mAs - cuts S# in half
Fuji/Konica - how do you decrease your technique and how does it effect your S#
!/2 your mAs - doubles S#
4 ways ALARA can be acheieved
- Personnel monitoring device
- Mechanical holding devices (patient immobilization)
- Close collimation, filtration, optimum technique, avoidance of repeats
- Time, distance, shielding
How does the field size look on the skin compared to the actual size of the anatomic area?
Smaller because of beam divergence
How does limiting the xray field reduce patient dose?
Volume of tissue irradiated is smaller
Amount of scatter is decreased
