Ch 15- Display & Image Storage

Bistable images are composed of ____ shades: _____

two; black and white

Gray scale images display ____ levels of brightness

multiple

(white, light grey, medium grey, etc.)

The numerous levels of gray scale allow the system to assign different gray shades to different ____

echo amplitudes

What does contrast determine?

the range of brilliancies (brightness) within the displayed image

Bistable images are ____ contrast, gray scale images are ____ contrast

high; low

What does brightness determine?

the brilliance of the displayed image

Gray scale imaging was first made possible with the use of ____

scan converters

Scan converters ____ information first, then ____ it later

store; display

Scan converters translate information from ____ format to ____ format

spoke; video

Modern digital scan converters use ____ technology

computer

Analog numbers are "real world" numbers that have ____ values with an ____ number of choices

continuous; unlimited

Ex. weight= 163.998

Digital numbers are "computer world" numbers that have ____ values with a ____ number of choices

discrete; limited

Ex. weight = 164

What type of scan converter is a funnel-shaped vacuum tube with an electron gun at its smaller end?

analog scan converter

In an analog scan converter, ____ are fired from the gun, then strike a ____ ____ where they are stored

electrons; dielectric matrix

The dielectric matrix may be thought of as what?

a picture divided into millions of tiny dots, each containing an electrical storage element (electron bucket)

Stored electrons in each bucket are ____ to retrieve information

read

Analog scan converters have excellent ____ ____

spatial resolution (image detail)

What limitations do analog scan converters have?

1. image fade

2. image flicker

3. instability

4. deterioration

(FFID)

What is digitizing?

using computers to convert images into numbers

How do digital scan converters work?

- digitize images

- images are stored in computer memory as a series of 0's and 1's

- numbers are retranslated into an image before display

What are the advantages of digital scan converters?

1. uniformity

2. stability

3. durability

4. speed

5. accuracy

(USDSA)

What are the two important elements of a digital scan converter?

1. pixel

2. bit

What is a pixel?

picture element; smallest building block of a digital picture

What is pixel density?

pixels per inch

High pixel density is achieved with ____ pixels

small

High pixel density requires ____ pixels per inch

many

Spatial resolution improves with ____ pixel density

high

What is a bit?

binary digit; smallest amount of computer memory

A bit is ____, having a value of either 0 or 1

bistable

What is a binary number?

group of bits

Ex. 01010100110011010

What is a byte?

8 bits

What is a word?

2 bytes or 16 bits

Fewer bits per pixel:

____ shades of gray

____ contrast resolution

fewer

degraded

More bits per pixel:

____ shades of gray

____ contrast resolution

more

improved

Pixels have better ____ resolution, bits have better ____ resolution

spatial; contrast

How many possible shades of gray are displayed with 5 bits of memory?

2 x 2 x 2 x 2 x 2 = 32 shades of gray

During reception, a transducer produces ____ voltage electrical signals, making them susceptible to ____

low; noise

Digital information is ____ susceptible to noise

less

Translating image information from ____ to ____ and back again is a 5 step process

analog; digital

What are the 5 steps of translating image information from analog to digital and back again?

1. analog to digital (A-to-D)

2. preprocessing

3. post processing

4. digital to analog (D-to-A)

5. video display

Summarize the following:

1. analog to digital (A-to-D)

2. preprocessing

3. post processing

4. digital to analog (D-to-A)

5. video display

1. electrical signals created during reception are converted from analog to digital

2. digital information is stored in the scan converter

3. digital image information continues to be processed

4. digital signals in bistable form need to be converted back to analog

5. analog signal displayed on TV

What is pre-processing?

manipulation of image data BEFORE storage

Can pre-processing be reversed or undone?

no

What are examples of pre-processing?

1. TGC

2. log compression

3. write magnification

4. persistence

5. spatial compounding

6. edge enhancement

7. fill-in interpolation

What is post-processing?

manipulation of image data AFTER storage

What are examples of post-processing?

1. any change after freeze frame

2. black/white inversion

3. read magnification

4. contrast variation

5. 3D rendering

Magnification (zoom) enlarges a ____ of an image to fill the entire screen

portion

What is ROI?

region of interest; the selected part of the image

What is RES?

regional expansion selection

What are the 2 forms of magnification?

1. read magnification

2. write magnification

Read magnification occurs during ___

post-processing

What are the 3 steps of read magnification?

1. system scans anatomy

2. image is converted from analog to digital and stored

3. ROI is identified and system reads and displays original data, ROI is NOT rescanned

In read magnification, spatial resolution is ____ because number of pixels in ROI is ____

unchanged; unchanged

Write magnification occurs during ____

pre-processing

What are the 4 steps of write magnification?

1. system scans the anatomy and creates image

2. image is converted from analog to digital and stored

3. ROI is identified, old data is discarded

4. system rescans only the ROI and writes new data into scan converter

In write magnification, spatial resolution is ____ because there is a ____ number of pixels

improved; greater

With write magnification, temporal resolution may improve if bottom of ROI is ____ than the original depth

shallower

Backing material in transducers create ___ pulses but produce ___ intensity

short; high

- The FDA established ___ peak intensity levels for sound beams

- Imaging transducers cannot exceed these limits, which impacts ____

- What is the solution for this?

- maximum

- image quality

- coded excitation

Coded excitation creates ___ sound pulses containing a ___ range of frequencies

long; wide

Coded excitation creates a ___ pulse but keeps intensity ___ FDA's limit, improving ___ and ___

strong; below; penetration; resolution

Coded excitation occurs in the ___

pulser

Coded excitation provides:

____ signal-to-noise ratio

____ axial resolution

____ spatial resolution

____ contrast resolution

____ penetration

higher

improved

improved

improved

deeper

Spatial compounding is a method of using sonographic info from several different ___ to produce a ___

angles; single image

Spatial compounding starts by acquiring ___ frames from ___ views

multiple; different

- Spatial compounding starts by acquiring multiple frames from different views

- Frames are then ___ to form a ___

combined; single image

The more frames in the compound sequence, the ___ the compound image quality

better

What are limitations of spatial compounding?

- reduced frame rates

- reduced temporal resolution

What type of steering is used in compounding imaging?

electronic

Electronic steering is only available with ___ transducers

phased array

Frequency compounding is an advanced technique that reduces ___ and ___

speckle; noise

With frequency compounding, instead of using a ___ range of frequencies to create an image, the reflected signal is divided into ___ of ___ frequencies

large; sub-bands; limited

- With frequency compounding, instead of using a large range of frequencies to create an image, the reflected signal is divided into sub-bands of limited frequencies

- Images from sub-bands are then ___ to create a ___

combined; single image

Noise levels of reflections are different from each sub-band, and when combined, noise level is ___

reduced

What is an image processing method that makes pictures look sharper?

edge enhancement

Edge enhancement works by ___ image contrast around the edges

increasing

Edge enhancement creates subtle ___ and ___ highlights on either side of the boundaries to make them appear more ___

bright; dark; defined

Temporal compounding is an image processing technique that does what?

continues to display information from older images

What is temporal compounding also called?

persistence

temporal averaging

Temporal compounding produces a ___ image with:

___ noise

___ signal-to-noise ratio

___ image quality

smoother

reduced

higher

improved

Temporal compounding is most effective with ___ moving structures

slow

What are limitations of temporal compounding?

reduced frame rate

reduced temporal resolution

Fill-in interpolation is a method of constructing what?

new simulated data points to fill in gaps between scan lines

Is interpolation a form or pre or post processing?

pre-processing

As line density increases, spatial resolution is ___

improved

What is the theory that tissues will deform differently after applying force?

elastography

___ data and ultrasound ___ are combined into images called elastograms

stiffness; reflections

What is PACS?

Picture Archiving and Communications System

What are 3 advantages of PACS?

1. instant access

2. no degradation of data

3. "store and forward" technology

What are the primary digital storage devices used in PACS?

computer hard drives

What is DICOM?

Digital Imaging and Computers in Medicine

DICOM is a set of ___ that allows imaging systems to share information on a ___

rules; network

When a system adheres to ___ standards, the system, can connect to a ___ network

DICOM; PACS

Types of data storage

- paper

- magnetic

- chemically mediated photographs

- optical