Memory & Display Flashcards
What is memory responsible for?
Greyscale - allows to differentiate tissues
What does memory enable?
Free frame
Cine-loop
Ability to post-process
What is another name for memory?
Scan converter
What is the function of modules or circuits?
Store US information and enables machine to build an image
How does the system write memory?
Vertical to horizontal since monitors write their information horizontally
Where does the image go after memory?
Display or recording device
What was the scan conversion process historically?
Analog process
What do the current systems use to convert memory?
Distal scan converter
What is the difference b/w analog and digital?
Analog- continuous values, prone to drift, less reproducible
Digital- discrete values, stable, reproducible
What is a analog scan converter similar to?
CRT
What was the phosphate face in the analog scan converter replaced with?
Wafer silicon
What is the wafer silicon called in the analog scan converter?
Dielectric matrix
What happens to the electrons when emitted from the filament?
Pass through deflection plates and strike silicon wafer
What kind of charge is produced when the electrons strike the silicon wafer?
Positive charge
What is the positive charge proportional to?
Amplitude of signals strengths
Why is the analog scan converter prone to drift?
The positive charges fade over time and are erased
What was the main advantage of the analog scan converter? (2)
Allows for a grey scale
Acts as a buffer b/w image and display with good short term memory
What was a disadvantage with analog scan converters?
Prone to drift with no long term memory
Why do we used digital scan converters today?
Reliable and versatile
Can connect to other systems or cameras
Superior resolution
What does a digital scan converter consist of?
A matrix typically 1024X768 - divided into a rectangular square of pixels (picture elements)
What does each pixel contain and represent?
Contains a digital number to represent amp of received echo
How do we know the amp from the matrix size?
Multiple the matrix = # of pixels = amp
Ex: 1024X768=786432
Therefore the amp is 786432
What does each pixel on the matrix represent?
Each pixel stores data corresponding to a specific tissue - it represents the greyscale for returning echos
Each pixels corresponds to a specific depth
In what code does the computer operate?
Binary code
What is the data in each square of the matrix equal to?
A 1 or 0 therefore a shade of grey…
How do we display more then 1 shade of grey per square?
Matrices can be stacked on top of one another which each square in every matrices having its own #
What happens when there are multiple matrices stacked on top of each other? Why?
More matrices = more shapes of grey due to the different combinations of binary digits
What is the smallest form of display?
Pixel
How does having more pixels affect resolution?
Better resolution
What is a bit?
One binary digit - either 1 or 0
What is a byte?
8 bits
What is a word?
Combination of bits expressed as a unit
What is word length?
of bits in a word
What is bit depth?
The word address at each address location
What is RAM?
Random access memory
Fast, re-writable, cheap and erased when machine is turned off
What is ROM?
Read only memory
Permanent and used for system functions (pre-sets)
What determines how good our contrast resolution will be?
Bit depth
What is contrast resolution?
How well the tissue differentiation is (distinguish tissue from background)
What increases contrast resolution?
Increase of BD
What helps control the contrast resolution?
Dynamic range
What does “n” represent in the formula for calculating shades of grey?
N is the bit depth or # of bits used at each address location to store the echo data received
What would the bit depth be of 4?
n = 4 = 16 shades of grey (bit depth)
2. 2
How many bits does a typical US machine have?
8
The binary system replies on 2 digits (1 or 0) which represents what?
Represents a circuit that is either on or off
What is the advantage of having a binary system for the computer?
Allows for a stable and fast process since the computer only has to process 2 numbers
Binary is great for computers but sonographers prefer a more meaningful decimal #
We can calculate the decimal # from the binary # by placing the binary # in the table….
See page 9 of notes
What part of the system is resolution limited by?
Type of display used
What are 2 considerations made when assessing monitor resolution?
Number of pixels
Size of pixels
Hoe does changing the amount of pixels affect monitor resolution?
Increase amount of pixels= better resolution
How does changing the depth affect monitor resolution?
Decrease the depth= improved resolution
What type of monitors are used for digital display today?
LCD
What type of monitors were used in earlier units?
CRT
Other modes: A, B and M mode used oscilloscope
How did an oscilloscope work?
Could only display using an X & Y axis at
Refer to picture on pg 12 of the notes
Was the oscilloscope compatible with video signal?
No
How does the CRT tube work?
Accepts a video signal and is capable of displaying a wide range of greys
Is the CRT equipped for displaying color? What is the color useful for?
It is capable and useful in Doppler applications
What are the colours used in the CRT? How?
CRT had 3 electron guns - cause phosphor to light up as either red, blue and green
What is a CRT?
Large glass vacuum tube that contains a cathode or source of electrons (negative)
Where is the electron aimed?
Phosphor plates (positive)
What are electric or magnetic deflections plates used for?
Used to steer the beam
What does the phosphor brightness depend on?
of electrons that strike it
What is the # of electrons dependent on?
Amplitude of the video signal
Stronger the amp= stronger electrons
Stronger electrons= brighter shade of grey
What is a raster format?
Specific method used to move the electron beam
How is the beam moved in raster format?
From left to right in addition to interlacing (writes odd then even lines)
Why is interlacing used?
Gives us the ability to see things in real time by writing all the odd lines and then even lines - reduced our ability to see flicker
What does a complete frame consist of?
525 horizontal lines produced at 30Hz (FR) — might see flicker
Each frame has 2 fields- odd and even- what are they produced at?
60Hz - eliminates flicker
Refer to page 14 for picture
Why are computer monitor superior to CRTs?
Have more scan lines and pixels
Pixels are smaller
How many scan lines does a CRT use? Monitor use?
CRT 525 lines
Monitor 1024X768 or higher
What kind of manner are the lines written? What does this mean?
Lines are written in a progressive manner which allows FRs typically higher then 60Hz
