Image Storage and Display

8/13/2019 Image Storage and Display

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ALZAIEM ALAZHARI UNIVERSITY

FACULTY OF RADIOLOGICAL SCIENCES ANDMEDICAL IMAGING

MEDICAL DIAGNOSTIC ULTRASOUND (M.S.C)

BATCH(9)-SMESTER(1)

IMAGES STORAGE AND DISPLAY

PRESENTED BYNuhla Mohamed haj shareef

Tahani gebril Adam

Saadia Mohamed abaker

Suha ahmed alsaied

Yossria moustafa saad aldeen

STUDENTS OF GROUP (1)

SUPERVISOR: Dr: AHMED ABDELRAHEEM

20th.FEB.2013


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Introduction

The US system is a pulsed system . The

US pulse propagates into the body

tissues at all acoustic interfaces in the

body a portion of incident US energy is

reflected and return to transducer.(


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Introduction(cont.)

Then the transducer converts the

returning echoes into electric signals

which are amplified, electronically

processed and formatted into appropriate

form and displayed in differen forms on

the monitor.(berwin)


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Digital scan converter(DSC)

A scan converter is a device which

convert echo voltage signals to digital values

using a process called analog to digital

conversion(ADC) brwin


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Figure (1): Digital Scan Converter (DSC) ()


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DSC(cont.)

Analog values are represented by

proportional, continuously variable physical

quantities such as electric voltages.

Digital values are represented by discrete

number in binary system.(essitioal


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DSC(cont.)

A scan converter is a device which stores

echo signals (ultrasound images) in

a memory according to their location in thescanning process and outputs the echo

information in a format that is different from

the one in which it was received (hence

the term scan conversion).(2)


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DSC (cont.

A digital scan converter assigns a numerical

(digital) value to each echo according to the

echo amplitude. These digital values are then

assigned shades of gray, providing the basis

for grayscale display.


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DSC(cont.)

Role of the scan converter:

1. It stores images during scan build-up, for

reviewing and recording.

2. It performs scan conversion, enabling image

data to be viewed on video monitor(essitional


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Advantages of digital system(cont.)

3. Mass production of RAM chips in recent

years has dramatically increased the

capacity of digital memories. This permits

modern DSCs to store multiple frames of

data in memory that can be instantlyrecalled by the sonographer at touch of a

button.(1)


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Binary system

The binary system is a number system that is

used by digital systems because it consists of

two digits, namely the digits 0 and 1.

These two digits can be used in different

combinations to represent many different

values.(brwin


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Figure (2): comparison between the

decimal system and binary system ()


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Binary system(cont.)

The binary system is a particular numbering

system for digital systems because the

electrical components are designed and able

to work in this environment reliably, quickly,

and efficiently.(briwn


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Pixels and Bits

All digital devices employ as a basic unit a

stable electronic circuit, which we will refer to

as a bit which is smallest piece of information

that a digital device can stored and

manipulate.


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Pixels and bits (bit depth)(cont.)

digital scan converter memory Divided in to

matrix of small square or address known as

pixel or picture elements. (1)

A single matrix element can store only a one

or zero in each memory location (pixel). (3)


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Bit depth(cont.)

This would allow only black and white

imaging. Gray scale imaging requires more

matrices, more bits. (3)


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Gray scale capacity

The number of different shades of gray that

can be used in image depend on the bit

capacity or bit depth of DSC.

The bit capacity is determined by the

complexity of the digital computer circuits.

Number of gray shades =2*(brwin


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Contrast resolution

contrast resolution (gray scale resolution) is

ability of US system to separate echoes by

displaying them with different shades of gray.(

brwin

contrast resolution can be described in terms

of dynamic range of echoes that can be

assigned a shade of gray


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Memory resolution and field of view

The anatomic area stored at each pixel depends

on the image size (field of view).

Consider an image stored in a DSC memory in

which the field of view is 20 cm and the matrix

size is 512* 512. The depth of tissue that can be

stored in each pixel in the vertical axis of the DSC

can be determine as follow :


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Memory resolution and FOV(cont.)

20cm/512 pixels = 200mm/512 pixel=

0.4mm/pixel. (1)

Axial resolution is the ability of the transducer

to detect two closely spaced reflectors as two

separated echoes.


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For two similar reflectors to be resolved in the

image, the echoes from the tow reflectors

must be stored in separate memory pixels. In

our example, each pixel represents a distance

of 0.4 mm.


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Therefore, two reflectors must be at least 0.4

mm apart if they are to be resolved as

separate echoes in the displayed image

(spatial resolution of memory). (1)


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Preprocessing

it includes all functions performed on echoes

before the image stored in memory.(receiver

function ,write magnification and assignment

of gray shades.(briwin


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Assignment of gray shade

The assignment of grayscale digital values is

done prior to storing echoes in digital memory.

there are four to six preprocessing schemes

(algorithms) to choose. Some algorithms

emphasize low level echoes while othersemphasize mid range echoes or high level

echoes.(brwi


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Figure (3) assignment of gray scale()


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Write zoom

Is magnification of a region of an ultrasound

image prior to storage in memory.(brwin

instruments that have this feature allow the

operator to first select the region to be

enlarged by applying cursors to the original

image.


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Write zoom(cont.)

When write zoom is enabled the transducer

re-scan the region. Only echo data a rising

from zoomed region are written to memory ,

and all pixels in memory are used to

represents this region.(essienal


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persistence

Is the averaging of sequential frames together

for the purpose of providing a smoother

image appearance and reduction of

noise.(diagnostic


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Edge enhancement

It is filtering technique that is designed to

improve the detection of interfaces and the

boundaries between structures. (brwin


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Smoothing (filtering)

smoothing is an electrical preprocessing technique

applied to the rectified echo signal (known as the

video signal) to smooth out adjacent peaks.(

brwin

The filter is one that passes a range of frequencies(its band width) and remove those above and

below acceptance band width.(diagnosti


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Fill-in interpolation

This is a preprocessing technique. Interpolation

means that image data of missed pixels are

calculated from image data in nearby pixels

that are situated along beam line(essional


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Post processing

Post processing includes all functions

performed on echoes after the information is

digitized and stored in memory.(freeze frame,

black/white image inversion, read

magnification and contrast variation.(brwin


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Read zoom

Is magnifying image data that is already existing

within scan converter memory as these data are

read out to the video monitor . The stored image

data from pixels within the region of interest are

expanded to fill the whole screen in the viewing

monitor. it may be done on frozen

image.(essienal


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Black/white image inversion

This is post processing function that allows the

operator to change the orientation of the

displayed image ,for example ,left-to-right, or

top-to-bottom.brwi


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Types of digital memories

A. Random Access Memory(RAM):

is temporary memory used by the system

to store images as they are acquired in real-

time. This type of memory is volatile (the

image data may be lost spontaneously).


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Types of digital memories(cont.)

B. Read Only Memory(ROM):

Is digital memory that contain information that can

be accesses(read) by the user but not changed.

C. Programmable Read Only Memory(PROM):

PROM functions similarly to ROM except the

software can be updated by the manufacture from

time to time.


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Image Display

Cathode ray tube video monitor(CRT):

It consist of a large cathode ray vacuum tube

with phosphor screen at one end, and an

electron gun at the other. The phosphor

screen emits light in response to the electron

beam.


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Cathode ray tube(cont.)

the brightness of the light is directly

proportional to the intensity of the electron

beam current. The electron beam is repeatedly

scanned in a raster format from left to right

across the phosphor screen.


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Cathode ray tube (cont.)

T.V have brightness, contrast and focus controls.

These controls affect the image displayed in

T.V screen and do not affect the image stored

in the DSC.

Current US scanners use either black-and-white

and/or color video monitors for image display.


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Cathode ray tube (cont.)

Ideally, scanning should be performed in a

room which is dimly lit and preferably with

back lighting to minimize glare on the display

monitor which is distracting and can lead to

operator eye strain.


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Liquid Crystal Display(LCD)

LCDs have been used for decades in

monochrome clock and watch displays. In the

last decade the technology has been improved

so that thousands of LCD pixels can be arranged

in a matrix to form a large, full color flat screen

display such as those found in notebook an

laptop.


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LCD(cont.)

An in the last few years these displays have

become large and cheep enough to replace

the traditional CRT as a computer display.


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Plasma display panel(PDP)

Plasma use a matrix of pixels contain a rare

gas. When ionized by an electrical charge, the

pixels produce an ultraviolet light which

strikes a color phosphor at the back of pixel

causing it to glow.


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PDP(cont.)

This process can be carried out up to 85 times

per second fast enough to give a brilliant full-

color real-time display .PDPs are being

produced for the high end home market and

are very expensive.

Ad f fl h l i


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Advantages of flat screen technologies

over CRT

small size and weight.

produce, bright, sharp display.

using less power than CRT.

I di d A hi i


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Image recording and Archiving

techniques

Types of recording media:

Chemical media:

Transparency film.

Polaroid print.

Black and white paper print.

Color paper print.


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Image recording and archiving(cont.)

Magnetic media:

Videotape.

Magnetic tape.

Computer disk.

Optical media:

Laser disk.

Compact disk.(CD-ROM, DVD).


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US transparency film

Transparency film is single-sided which means it

has a recording surface(emulsion) on one side.

The emulsion side of the film must be placed in

the film cassette to face the cameras CRT

screen. It processed through standard

automatic wet processing as for x-ray film.


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Transparency film(cont.)

Film exposure is determined by:

the brilliance of the display screen.

Brightness and contrast settings of the

cameras CRT screen.


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Characteristics of transparency film

8*10 or 14*17 depending on type of multi-

format .

Single emulsion.

Wide latitude for good grayscale recording.

Spectral sensitivity of film must be matched to

CRT phosphor.


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Construction of transparency film

Base: is rigid plastic on which emulsion is

layered.

Emulsion: is a mixture of gelatin and silver

halide crystals.

Super coat: cover the emulsion and protects it.


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Film processing

Latent image: is the change produced in silver

halide after exposure but before

development.

Development: change latent image to

manifest image.

Fixing : stops development.

Washing :removes residual chemicals.

Drying :dries film.


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Factors affects the appearance of film

Temperature of developer.

Concentration of developer.

Time in developer.


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Advantages of US film

It is reasonably priced, although it is not

cheap.

It is durable, making it good medium for

archiving.

It has excellent spatial and contrast resolution.


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Video paper printer

Uses thermal paper.

Offers reasonable grayscale and/or color.

Compatible with TV signal from digital scan

converter.

Poor archiving.


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Magnetic tape

Different formats-VHSSVHS .

Compatible with TV signal.

Excellent for recording moving structures.

Awkward for review.

Suboptimal resolution.


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Computer disks

Magnetic medium.

Limited data storage.

Fragile(susceptible to being damaged by

magnetic fields)


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Optical discs

Laser disc

Compact disc


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Picture Archiving and communication


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Picture Archiving and communication

system(PACS)

Filmless system.

Network of computers connected to US

scanners allowing archiving of US images on

hard drives or optical disks.

Allows remote access and viewing of images

during real time scanning or later.


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PACS(cont.)

Consistent and reliable archiving of digital still

and cine images

Images can be backed up cheaply and easily

providing additional archival security for long

term availability.

Advantages and disadvantages of


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Advantages and disadvantages of

recording media

media advantages disadvantages

Single

emulsion

film

Good resolution

Long term

archiving

Expensive

Inconsistent results with

multi format camera

Polaroid film Rapid Poor archiving

Poor contrast resolution

Paper film Rapid

inexpensive

Poor resolution

Poor archiving

VCR motion Poor resolution

Poor access


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References (cont.)

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Image Storage and Display

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