1
Q
memory/scan converter
A
- allows us to store image
- responsible for gray scale
- enables freeze frame and cine loop and post processing
2
Q
memory - how memory works basic
A
- module’s or circuits are designed to store ultrasound information and enables the machine to build up the image
- from the memory the image goes to a display or recording device
3
Q
historical memory
A
- scan conversion was an analog process
+ not stable - current systems use a digital scan converter
4
Q
analog vs. digital
A
- analog like a ramp or analog clock
+ gives us every single bit of information even stuff we don’t need - digital like stairs or digital clock
+ only gives us the information we need, only the relevant information
5
Q
analog characteristics
A
- continuous values
- prone to drift
- less reproducible
6
Q
digital characteristics
A
- discrete numbers
- stable
- reproducible
7
Q
analog scan converter
A
- like a cathode ray tube but with a silicon wafer called dielectric matrix
- no cine in analog scan converter
- MAIN ADVANTAGE = allows for gray scale
- also acts as buffer between image and display with good short term memory
- DISADVANTAGE = prone to drift and there was no long term memory
8
Q
digital scan converter
A
- reliable and versatile can be connected to many other systems or cameras and have superior resolution
- consists of a matrix (group of squares) 1024x768 which are divided into small rectangular pixels
9
Q
pixels
A
- aka picture element
- contains a digital number to represent the amplitude of the received echo
- 1024 x 768 matrix has 786 432 pixels
- smallest form of display
- MORE PIXELS = BETTER RESOLUTION
10
Q
matrix
A
- checker board arrangement of pixel locations on a grid
- each square of the matrix stores data that represents gray scale info of the returning echoes
- each square corresponds to a particular depth
11
Q
binary code
A
- computers operate in binary code
- uses only 1’s and 0’s
- data contained within each square of the matrix is equal to a one or zero
- could only show two shade of gray with this set up
12
Q
how to show multiple shades of gray
A
- additional matches are staked one on top of the other so that every pixel location can be represented by several 1’s or 0’s
- the combo of many binary digits represent multiple shades of gray
13
Q
bit
A
- one binary digit
- 1 or 0
14
Q
byte
A
- 8 bits of data
+ 10011010
15
Q
word
A
- combination of bits expressed as a unit
16
Q
word length
A
- number of bits in a word
17
Q
BIT DEPTH
A
- WORD LENGTH AT EACH ADDRESS LOCATION
+ TELLS US HOW MANY SHADES OF GRAY
18
Q
RAM
A
- random access memory
- fast rewritable cheap and erased when the machine is turned off
- needs to be transferred to ROM
19
Q
ROM
A
- read only memory
- permanent and used for system functions
+ pre sets
20
Q
bit depth & shades of gray relationship
A
Increase the # of bits = Increase the # of shades of gray
- directly related
21
Q
bit depth (formula)
A
- 2^n calculates how many shades of gray there is
- “n” = bit depth or number of bits used at each address location to store the echo data received
22
Q
binary system
A
- 1 or 0 represents a circuit that is either on or off
- very stable and very fast because computer only had to process 2 numbers
23
Q
how to convert binary to decimal and vice versa
A
- create a box starting with 1 on the far right side then 2, 4, 8
+ 128 / 64 / 32 / 16 / 8 / 4 / 2 / 1 - input the binary digit under the numbers in the chart and add together any number with a 1 underneath it
+ 128 / 64 / 32 / 16 / 8 / 4 / 2 / 1
1 0 1 0 1 0 1 0
= 170 - decimal to binary = start with the largest number and add together the digits in the box until you reach the decimal number putting 1’s under the numbers you are adding and 0’s under the ones you aren’t
24
Q
monitor resolution
A
- us systems operate to provide the best resolution images but limited by type of display used
- 2 considerations made
+ number of pixels
+ size of pixels - want SMALL PIXELS and LOTS OF THEM
25
pixel size and number
- more pixels in a finite space the better the resolution will be
- because the size of the pixel must decrease to fit the monitor
- depth also impacts the resolution
26
how to calculate resolution
- divide the depth of the field by the # of pixels in the matrix
- less info per pixel is better
- 1024 x 1024 matrix with a 10 cm depth of field has the best resolution of 0.1mm / pixel
27
display
- modern day ultrasound use LCD monitor for display
- earlier units used a CRT while other modes of ultrasound like A Mode and B Mode use and oscilloscope (tv that can show picture)
- mostly talk about CRT
28
oscilloscope
- first to use a CRT
- could only display using an X and Y axis and not compatible with a video signal
- usually display A mode, B mode, M mode
- NO PICTURE
29
television CRT
- accepts a video signal and is capable of display of wide range of grays
- is equipped the CRT is also capable of displaying color which is useful for doppler application
- RED GREEN AND BLUE
30
CRT
- large glass vacuum tube that contains a cathode source of electrons (negative)
- the electron beam is aimed at phosphor plate (positive)
- electric or magnetic deflection plates are used to steer the beam and the phosphor brightness will depend on the number of electrons that strike it
- number of electrons is dependent on the amplitude of the video signal
31
how to obtain color
- three electron guns that cause phosphor to light up either RED, GREEN or BLUE
- different mixes of these colours can produce all of the colours you see when you watch tv
32
display - raster format
- to move the electron beam a specific method is used called raster format
- beam is moved from left to right and INTERLACING is used to write first the EVEN lines then the ODD lines
33
interlacing
- method to help reduce the appearance of flicker to viewer
- a complete frame consists of 525 horizontal lines produced at 30 Hz
- each frame has two fields ODD AND EVEN produced at 60Hz
- not seeing complete picture every time but increases frame rate
34
computer monitors
- superior to CRT have ore scan lines and pixels and pixels are smaller
- higher resolution
- monitors use 1024 x 768 or higher scan lines
- lines written in PROGRESSIVE MANNER with frame rates higher than 60 Hz
35
progressive
- better temporal resolution
- no interlacing
- writes scan lines left to right, top to bottom
Physics 2
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