Displays

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

Electrons

charged particles

How does CRT work?

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

Fields

525 closely-spaced lines.

Odd fields

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

Even fields

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

Frame

is the combination of one odd field and one even field

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

interlaced

the way television are written with odd and even fields

Why are CRTs interlaced?

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

Bistable

Bi means 2

bistable images are composed of only two shades Black and White

Grayscale

present multiple levels of grey

white, light grey, dark grey etc.

contrast

user control

determines the range of brilliances within the displayed image.

High contrast

bistable images with only black and white

Brightness

determines the brilliance of the displayed image.

Scan converter

store information and later display

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

writing

storage of the image information

read

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

Digital Scan converters

scan converters that use computer technology rather than older analog

Analog numbers

real world

unlimited # of choices

continuous value

Digital numbers

computer world

limited choices

discrete values

matrix

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.

silicon wafer

dielectric matrix

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

Spatial resolution

image detail

excellent - large number of storage units within the matrix

Limitations of analog scan converters

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.

Advantages of digital scan converter

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

Pixel

picture element

smallest building block of an element

Pixel Density

is the # of pixels per inch

improves with Higher pixel denesity

Spatial resolution

Low Pixel Density vs. High Pixel Density

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

Bit

is the smallest amount of computer memory

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

Binary Number

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

0101010011

Decimal numbers

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

byte

is a group of eight bits of computer memory

10011111

word of computer memory

made up of two bytes or 16 bits

Fewer bit per pixels

fewer shades of grey
degraded contrast resolution

more bit per pixels

more shades of grey
improved contrast resolution

Calculating the number of gray shades

raise 2 by the power of (# of bits)

What is the number of shades that can be represented by 3 bits?

8 different shades of gray

2 * 2 * 2 = 8

What is the number of shades that can be represented by 8 bits?

256

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

2^8

How many bits are needed to store 10, 11, and 15 shades of grey?

4

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

Analog and digital image information

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.

Preprocessing

any processing of the electrical signals before storage

Can the sonographer control preprocessing?

yes

time gain compensation
log compression
write magnification

Is preprocessing reversible?

No

Postprocessing

any processing after storage in the digital scan converter

Can a sonographer control postprocessing?

yes

is post processing reversible?

yes

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

magnification

enlarging a portion of an image to fill entire screen

ROI

region of interest

Read magnification

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

Write magnification

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

Can write magnification improve temporal resolution?

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

Read magnification vs. write magnification

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

Paper Media

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

Magnetic Media

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

Chemically mediated photographs

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

Optical Media

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

What is a PACS system?

picture archiving and communications system

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

PACS advantages

instant access

no degradation

store and forward

What is magneto-optical storage?

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

M-O Storage advantages

store large amounts

high degree of security - not erased by magnetic field

All of the following are true of ordinary cathode ray tubes except:

A) it contains large vacuum tubes with a phosphor-coated screen

B) Electrons are emitted by a gun and swept across the screen by varying magnetic fields

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

D) There are 60 fields generated each second that combine into 30 frames per second

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

Which of the following correctly describes a typical television display?

A) interlaced
B) progressive scan
C) bistable
D) non-interlaced

A) interlaced

Which electronic component is required for grayscale imaging?

A) VCR
B) non-interlaced
C) computer memory
D) scan converter

D) scan converter

All of the following are disadvantages of analog scan converters except:

A) image fade
B) low-resolution image
C) image filter
D) deterioration

B) low-resolution image

Which of the following scan converters will provide the best spatial resolution?

A) digital with 256 x 256 pixels
B) digital with 512 x 512 pixels
C) digital with 128 x 128 pixels
D) digital with 1000 x 1000 pixels

D) digital with 1000 x 1000 pixels

How many gray shades can be represented by a group of

* 4 bits?
* 2 bits?

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

2 bits = 4 shades
2 * 2 = 4

Which of the following statements regarding a pixel is false?

A) smallest part of a digitized image
B) a collection of bits, assigned to each pixel, stores the shade of gray.
C) it displays up to 3 gray shades, simultaneously
D) image quality is improved when the number of pixels is high

C) it displays up to 3 gray shades, simultaneously

Are the following procedures usually pre- or post-processing?

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

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

Are the following forms of information usually digital or analog?

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

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

All of the following are characteristics of write magnification except:

A) pre-processing function
B) more pixels in the region of interest
C) identical regions stored in the scan
D) it is the preferred method of image magnification

C) identical regions stored in the scan

What is the primary disadvantage of video tape and computer disc methods of image archiving?

A) these methods are very costly
B) the information is vulnerable
C) only low resolution images are stored
D) only black and white images are stored

B) the information is vulnerable

All of the following are advantages of PACS systems except:

A) data will not deteriorate over time
B) images can be delivered to distant locations on the imaging network
C) older, achieved studies and reports can be reviewed easily
D) images have higher resolution than what appears on the system's display

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