Understanding Ultrasound Physics: Chapter 15 Display and Image Storage Flashcards

A television tube, which is a special form of cathode ray tub (CRT), is a glass vacuum tube shaped like a funnel.

charged particles

electrons fly through electronic controlled, time-varying magnetic fields that focus and seep the electron beam across the inside of the wide end of the tube. The interior surface of the screen is coated with phosphors, which glow when struck by electrons

525 closely-spaced lines.

The electron beam first writes the odd fields within 1/60 of a sec

After the odd fields are written the electron beam writes the even fields within 1/60 of a sec or 60 Hz

is the combination of one odd field and one even field

time is 1/30 of a second or 30 HZ or 60 Hz

the way television are written with odd and even fields

Humans can detect flicker in non-interlaced displays with frame rates 30 Hz, but not with an interlaced field of 60 Hz

Bi means 2

bistable images are composed of only two shades Black and White

present multiple levels of grey

white, light grey, dark grey etc.

user control

determines the range of brilliances within the displayed image.

bistable images with only black and white

determines the brilliance of the displayed image.

store information and later display

The scan converter translates the information from the spoke format into the video format.

storage of the image information

image information is converted from the scan converter for display on CRT

scan converters that use computer technology rather than older analog

real world

unlimited # of choices

continuous value

computer world

limited choices

discrete values

picture divided into millions of tiny dots, each containing an electrical storage item. The electrons stored in the bucket are read to retrieve the image.

matrix at the larger end of CRT tube where images are stored

image detail

excellent - large number of storage units within the matrix

Image fade - stored charges on the silicon wafer dissipate over time

Image flicker - caused by switching between read and write modes

instability - picture quality depends on many factors including length of use, room temp, and humidity

Deterioration - image degrades as the device ages.

Uniformity - consistent grayscale quality throughout the image.

Stability - does not fade or drift

Durability - not affected by age or heavy use

Speed - nearly instant processing

Accuracy - error free

picture element

smallest building block of an element

is the # of pixels per inch

Spatial resolution

Low Pixel Density
-few pixels/inch
-larger pixel
-less detail image
-lower spatial resolution

High Pixel Density
-many pixels/inch
-smaller pixel
-more detail image
-higher spatial resolution

is the smallest amount of computer memory

a bit is bistable, having values of either 0 or 1

is a group of bits and is simply a series of zeroes and ones

0101010011

used in everyday life are based on ten choices 0 through 9

is a group of eight bits of computer memory

10011111

made up of two bytes or 16 bits

fewer shades of grey
degraded contrast resolution

more shades of grey
improved contrast resolution

raise 2 by the power of (# of bits)

8 different shades of gray

2 * 2 * 2 = 8

256

2 * 2 * 2 * 2 * 2 * 2 * 2 * 2 = 256

2^8

4

4 bits are required to store 9 to 16 shades of grey

1. converted from analog to digital for by the analog-to-digital scanner (A-to-D)

2. The digital information is stored in the scan converter's computer memory. Preprocessed

3. processing continues after storage

4. digital signals converted back to analog by a digital-to-analog converter (D-to-A)

5. signal is presented in the video display.

any processing of the electrical signals before storage

yes

time gain compensation
log compression
write magnification

No

any processing after storage in the digital scan converter

yes

yes

any change after freeze frame
black/white incersion
read magnification
contrast variation

enlarging a portion of an image to fill entire screen

region of interest

occurs after storage in the scan converter

the system reads and displays only the original data pertaining to the ROI

* Spatial resolution is not changes because the number of pixels is unchanged

applied during data acquisition, before storage in the scan converter

1. scans an image

2. converted and stored

3. ROI identified

4. image discarded re-scan only the ROI and writes new data

increased number of pixels in the image improves spatial resolution

yes if the ROI is shallower than the original image's DOV

Read magnification
-uses old data
-post processing
-larger pixels
-same # of pixels
-unchanged spatial resolution
-unchanged temporal resolution

Write magnification
-uses new data
-pre processing
-smaller pixels
-more pixels
-improved spatial resolution
-possible improved temporal resolution

Examples
-charts from pen writers

Advantages
-portability
-does not require device to read

Disadvantages
-bulky, hard to store
-difficult to make copies
-cannot display dynamic images

Examples
-CD
-computer memory
-magnetic tape
-video tape

Advantages
-can be erased by strong magnetic fields
-store huge amounts
-can store and play dynamic images
-can record color

Disadvantages
-can be erased by magnetic field

Examples
-photographs
-flat film
-multiformat camera film

Advantages
-high resolution
-accepted in the medical community
-can produce color images

Disadvantages
-bulky, hard to store and retrieve
-requires chemical processing
-atifacts can arise from dirt or chemical contamination

Examples
-laser disc
-compact disc

Advantages
-store huge amounts
-inexpensive
-not erased by exposure to magnetic field

Disadvantages
-require a display system
-No standardized format for image display and storage

picture archiving and communications system

describes the digital ultrasound laboratory in which images and reports are digitized and stored on a large computer network.

instant access

no degradation

store and forward

Magneto-optical, or M-O storage is based on a combination of magnetic and laser (optical) technology. PACS often uses M-O disc storage.

store large amounts

high degree of security - not erased by magnetic field

C) There are 600 horizontal scan lines from top to bottom, painted in order from 1 to 600

normal CRT creates images using 256 horizontal scan lines that appear on the screen iin an interlaced format

A) interlaced

D) scan converter

B) low-resolution image

D) digital with 1000 x 1000 pixels

4 bits = 16 shades
2 * 2 * 2 * 2 = 16

2 bits = 4 shades
2 * 2 = 4

C) it displays up to 3 gray shades, simultaneously

post A) modifying a frozen image
post B) read zoom
pre C) write zoom
post D) adjusting the brightness on the CRT
pre E) increasing the receiver gain

analog A) the signal from the transducer to the receiver
digital B) the input signal to the digital-to-analog
digital C) the output signal from the analog-to-digital
analog D) the input signal to the analog-to-digital
analog E) the output signal from the digital-to-analog
analog F) a typical video signal

C) identical regions stored in the scan

B) the information is vulnerable

D) images have higher resolution than what appears on the system's display