Module 2.1 : Memory and Display

Question 1

memory/scan converter

Answer 1

• allows us to store image
• responsible for gray scale
• enables freeze frame and cine loop and post processing

Question 2

memory - how memory works basic

Answer 2

• 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

Question 3

historical memory

Answer 3

• scan conversion was an analog process
  + not stable
• current systems use a digital scan converter

Question 4

analog vs. digital

Answer 4

• 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

Question 5

analog characteristics

Answer 5

• continuous values
• prone to drift
• less reproducible

Question 6

digital characteristics

Answer 6

• discrete numbers
• stable
• reproducible

Question 7

analog scan converter

Answer 7

• 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

Question 8

digital scan converter

Answer 8

• 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

Question 9

pixels

Answer 9

• 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

Question 10

matrix

Answer 10

• 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

Question 11

binary code

Answer 11

• 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

Question 12

how to show multiple shades of gray

Answer 12

• 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

Question 13

bit

Answer 13

• one binary digit

- 1 or 0

Question 14

byte

Answer 14

• 8 bits of data

+ 10011010

Question 15

word

Answer 15

• combination of bits expressed as a unit

Question 16

word length

Answer 16

• number of bits in a word

Question 17

BIT DEPTH

Answer 17

• WORD LENGTH AT EACH ADDRESS LOCATION

+ TELLS US HOW MANY SHADES OF GRAY

Question 18

RAM

Answer 18

• random access memory
• fast rewritable cheap and erased when the machine is turned off
• needs to be transferred to ROM

Question 19

ROM

Answer 19

• read only memory
• permanent and used for system functions
  + pre sets

Question 20

bit depth & shades of gray relationship

Answer 20

Increase the # of bits = Increase the # of shades of gray

- directly related

Question 21

bit depth (formula)

Answer 21

• 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

Question 22

binary system

Answer 22

• 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

Question 23

how to convert binary to decimal and vice versa

Answer 23

• 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

Question 24

monitor resolution

Answer 24

• 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

Question 25

pixel size and number

Answer 25

• 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

Question 26

how to calculate resolution

Answer 26

• 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

Question 27

display

Answer 27

• 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

Question 28

oscilloscope

Answer 28

• 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

Question 29

television CRT

Answer 29

• 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

Question 30

CRT

Answer 30

• 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

Question 31

how to obtain color

Answer 31

• 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

Question 32

display - raster format

Answer 32

• 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

Question 33

interlacing

Answer 33

• 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

Question 34

computer monitors

Answer 34

• 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

Question 35

progressive

Answer 35

• better temporal resolution
• no interlacing
• writes scan lines left to right, top to bottom