physics exam 4

most commonly used displays in olden days

tv (most common) or cathode ray tube

why was tv most commonly used before

excellent gray scale rendition at low cost

advantages of crt monitors (4)

-better viewing angles

-brighter image

-more robust

-cheaper

crt monitor scanning

rapid left to right or raster scan sequence

crt monitor has how many display lines and fps

525 horizontal display lines and 30 fps

crt form of display is called

interlaced

televisions are interlaced to eliminate

flicker

humans can detect flicker in noninterlaced displays with frame rates of _ but not with interlaced display with rates of _

30 hz, 60hz

most us systems use _ display

lcd

in an analog system the electrical voltage/current is generated that is _ to the quantity being observed

proportional

in a digital system the quantity being observed is expressed as a

number

image processor performs what functions (4)

-scan conversion

-preprocessing

-storing image frames

-post processing

receiver is the _ end and scan converter is the _ end of the system

front, back

receiver is where all processing takes place [before or after] signal is sent to back end for conversion and storage

before

scan converter two roles

stores and performs scan conversion for image to be viewed on video monitors (raster scanning)

grayscale imaging was initially made possible with the use of _

scan converters

storage of image info in the scan converter is called

writing

scan converter translates the info from _ format into _ format

spoke, video

2 types of scan conversion

analog, digital

first form of scan converter

analog

primary method of storing data for analog scan converters

videocassettes

analog number can have _

unlimited and continuous range of values

analog numbers are _ numbers

“real world”

how are analog scan converters shaped and how do they work

funnel shaped vacuum tube w/ electron gun located w/in its smaller end and electrons that contain image information are shot out of the electron gun

analog scan converters store

electrical charges

the greater the stored charge the greater the _ of the echo

amplitude

limitations of scan converters (9)

-image fade

-image flicker

-instability

-deterioration

-bad detail resolution

-limited frame rate

-difficult and time consuming to copy

-poor video quality if heads of the player get dirty

-rollers wear out

advantage of analog scan converters

good spatial resolution/image detail bc there is a large number of storage elements w/in matrix

digital scan converters use tech to convert images into _, and it is called

numbers, digitizing

digital numbers are associated with/ computer devices and have only _ values

discrete

digital scan converters store an image in computer memory as a series of

0s and 1s

advantages of digital scan converters (5)

-uniformity consistent gray scale quality

-stability

-durability

-speed

-accuracy

digital info is far less susceptible to _

contamination

why is converting info from analog to digital advantageous

digital info is less susceptible to contamination

before the image is displayed on a monitor the digital information must be converted back to _

analog form

5 step process of analog to digital conversion

1. electrical signals created by transducer during reception are converted from analog to digital by the analog to digital (A-D) converter

2. digital info is stored in scan converter’s computer memory

3. image info still in digital form continues to be processed by the ultrasound system’s computer

4. digital signals are translated back into analog form by a digital to analog (D-A) converter to be able to be displayed on conventional tv (which are analog)

5. signal in analog form is presented on the video display for interpretation

any processing of reflected signals before storage is called

pre processing

any processing after storage in the digital scan converter is called

post processing

in digital format, values are represented in _ with fixed _ between levels

discrete levels (more specific), steps

two important elements of a digital scan converter

pixel, bit

pixel def

smallest building block of a digital picture

each pixel’s shade of gray is determined by the cluster of _ assigned to it

bits

more shades of gray appear on an image with _ bits per pixel

more

images with many gray shades have superior _ resolution

contrast

pixel density def

number of picture elements per inch

higher pixel density is achieved with _ pixels

smaller

_ resolution improves with higher pixel density and creates a greater detailed image

spatial

how to determine number of shades of gray

2^n ; n = number of bits

most instruments use at least _ bits to represent _ in each pixel location

8, echo amplitude

8 bits provides _ amplitude levels at each pixel location

256

gray scale encodes each pixel value to a

brightness level

the gray scale map is selectable by the

operator

human eye is capable of seeing fewer than _ shades of gray so the minimum number of gray levels on the monitor should be _ and how many bits is that

64, 6 bits

BIT comes from the term

binary digit

BIT is

smallest amount of computer memory, can be either 0 or 1

byte is

a group of eight bits

a word is made up of

two bytes or 16 bits

who controls preprocessing

sonographer

can preprocessing be reversed

no

all receiver functions are [pre, post] processing

pre

preprocessing buttons you can change (6)

-tgc/amplification/gray scale maps

-log compression/dynamic range/compression/reject/power/persistence

-write magnification

-edge enhancement

-image updating

-write zoom

the purpose of tgc and amplification are to compensate for

a loss of energy in the reflected signal caused by attenuation

magnification/zoom magnifies structures by

making region of interest (roi) appear bigger

two different forms of magnification used in us

write, read

write zoom tries to _ maintain by _

maintain pixel density, zooming the image live which produces better spatial resolution

read zoom relies on _ which enlarges the _ in that region

stored images, pixel density

is write or read zoom better

write

write zoom ins aka

acoustic approach

write zoom is done _ data acquisition

during (live)

with write zoom, the number of pixels or scan lines in the roi image is _ than that in the roi portion of the original image

greater

increased number of pixels and line density in write zoom roi improves _ resolution

spatial

how does pixel size change with write zoom

stays the same

you need a _ image to use write zoom

live

who controls post processing

sonographer

can post processing changes be reversed

yes

posit processing we can changes (6)

-any change after freeze frame

-read magnification

-black and white inversion

-contrast variation

-measurements on some machines

-grey scale color maps on some machines

read zoom is aka

non acoustic zoom

the number of pixels or scan lines in read zoom magnified image is _ as the original image

the same

advantage of read magnification

can be used on a frozen image

disadvantage of read zoom

potential for data to appear coarse bc pixels are enlarged (resolution is somewhat compromised, but spatial resolution is still same)

when you apply the freeze button, the scanner

stops acquiring image data and the last values written in memory are frozen

persistence uses _ to create an image that is _

frame averaging, smoother and has less noise

smoothing/spatial averaging is a processing technique used to reduce

noise

disadvantage of smoothing/spatial averaging

lose spatial detail (bc pixels nearby have been averaged into surrounding pixels)

temporal compounding/persistence/temporal averaging is an image processing technique that continues to

display information from older images

edge enhancement is an image processing method that makes pictures look

sharper

edge enhancement works by

increasing image contrast in the area immediately around the edge

edge enhancement creates subtle _ on either side of boundaries to make them appear more defined

bright and dark highlights

bi stable images are composed of what two shades

black and white

contrast determines the range of _ w/in the image

brilliancies

brightness determines the _ of the displayed image

brilliance

what is coded excitation

sophisticated method of improving image quality; creates long sound pulses containing wide ranges of frequency

coded excitation was developed within the context of

bio effects (fda established max peak intensities)

coded pulse is _ but still keeps intensities below the fda limit, giving improved _

strong, penetration

coded excitation happens where

in the pulseer

spatial compounding is a method of

using sonographic info from several different imaging angles to produce a single image

spatial compounding works by acquiring

multiple frames from different viewing angles and then combined (overlapped or compounded) to form a single real time image

the more frames in the compound acquisition sequence the better the

compound image quality

compound imaging reduces

speckle and shadowing artifact

limitations of compound imaging

reduced frame rates/temporal resolution