Imaging Processing and Display- Prep/ Edel

What are the three display modes

A- mode, B-mode, M-mode

A-mode

amplitude

• displays relative amplitude of reflected US waves

• visualizes depth and strength of reflector, similar to depth

A mode x axis

depth

Y-axis A mode 

amplitude 

Amplitude is stronger to more ____ in the body due to attenuation 

shallow 

Each spike of A-mode is relative to _____ and the spike is the strength of the reflection

reflection

Where would we see the spike on the graph of A mode

in the beginning (we would not have that great of a spike deeper in the body due to attenuation)

A mode is still used in ____ 

optamology 

B-Mode

Displays the amplitude as pixel brightness

• stronger signals appear brighter, ranging from black to white

what was the first mode of greyscale imaging

B mode

X- axis on B mode

depth

Y-axis B mode

amplitude of signal (assigned brightness pixel based on number)

intense high amplitude is____ 

bright 

weak/ low amplitude

dark

How is B mode displayed

• as sound is transmitted from transducer an invisible dot is produced on system display 

• when sound encounters a boundary and a reflection is produced, the returning echo operates a shade of gray which is assigned to the correlative dot on the imaging display 

• brightness of the dot is displayed on the monitor is proportional to the reflected signal amplitude 

Motion (m-mode) 

one line of B mode moving across the screen 

• ideal for measuring dynamic structures like in echo

• enables easy measurement of vessel diameter, wall thickness, chamber size, valve motion

• ECG tracing fro precise cardiac cycle timing

What mode gives the best temporal resolution

M-mode

Y-axis M-mode

depth

X-axis M-mode

time

M-mode registry question: what is the appearance of M-mode 

series of wavey horizontal lines 

Steps for M-mode

• single sound pulse needed to produce one scan line on B-mode

• Single B-mode line used for m-mode display

• image produced

Sample rate of M-mode is _____, why?

rapid, due to using only a single scan

rate of PRF for M-mode

rate equivalent to PRF of US unit

Bi-Stable display

composed of two shades (black and white)

• high contrast, narrow dynamic range

• decreased contrast resolution

Greyscale 

the amplitudes are assigned a different shade of grey 

• increased contrast resolution 

• lower contrast, higher dynanic range 

contrast.

the range of shades of grey displayed

brightness

luminance of a visual target

• proportional to the intensity of the echo

Scan converter 

changes the format of the data (modern converters are digital)

• data acquired 

• “written” into storage 

• Date is “read” to be displayed 

What made the earliest form of greyscale possible 

scan converter

What functions as an analog to digital converter?

receiver channels

Analog scan converter

original equipment

• funnel shaped vacuum tub through which electrons are fired

• contains a dielectric matrix or silicon wafer which stores info for later retrieval

Drawback to analog scan converter 

image fluctuations 

• image fade- stored charge dissipates over time 

• image fliker- swiitching btwn read and write modes

• instability- quality of image dpnds on external condition

• deterioration 

Digital scan converter

computerized storing of info

• binary Numbers are stored data

• they can be retrieved with no changes in value

anything that occurs prior to scan converter =

preprocessing

anything that occurs after scan converter is 

post processing 

preprocessing

• synchronizer

• pulser

• beam former

• transducer

• receiver (amplification, compensation, compression, reject)

postprocessing

• digitally stored

• displayed

• archived

advantages of digital scan converters 

• uniformity- consistent grayscale 

• stability- does not fade

• durability- age and amount of use has no effect

• speed- nearly instant

• accuracy- virtually error free 

Pixel

(PICture ELement)

smallest building block of digital image

smallest controllable element of a picture represented on a screen

in US a shade of grey is assigned to each ____

pixel (variable depending on amplitude)

In color doppler color is represented by _____ intensities 

3-4 (red, green, yellow, magenta, blue, red, cyan, black) 

Low pixel density

• few pixels per unit area

• larger pixel size

• less detail

• poor spatial resolution

High pixel density

• many pixels per unit area

• smaller pixel size

• greater detail

• higher spatial resolution

What pixel size gives the best spatial resolution 

smaller (high pixel density) 

Each ___ determines the pixel shade

bit

Bit

(BInary DigiT)

a value of either 0 or 1

0 = ____ pixel

black

1= ____ pixel 

white 

byte

group of 8 bits

word

computer memory consisting of two bytes or 16 bits

the more _____ the more shades of grey

bits

formula for shades of grey

2^n

4 bits have how many shades of grey 

16

8 bits have how many shades of grey

256

Grey scale assignment - memory

• shad number assignment corresponds to amplitude before storage

• each amplitude numerical value is allotted to corresponds to grey shade

• shades transformed to binary language for digital storage

preprocessing 

manipulation of info prior to storing info 

post processing

manipulation of info after its been stored

Preprocessing functions

TGC

log compression

Write magnification

persistence/temporal compounding

spatial compounding

edge enhancement

interpolation

postprocessing functions 

ANY change to frozen image

black/white inversion

read magnification 

changes to variations in contrast

3D render 

Read magnification

occurs after the image data has been stored, postprocessing

• only original data used (enlargement of pixels)

“book already published”

Write magnification 

occurs during data acquisition and before storage, preprocessing 

• sono designates ROI, system rescans ROI and writes new data

• pixels are the same size as the original 

“still writing book” 

What magnification gives more improved spatial and temporal resolution

Write magnification (pixel density is maintained)

Read mag. qualities

• used already acquired data

• post. processing

• larger pixel size

• same # of pixels

• same spatial resolution 

• no change in temp resolution 

write mag qualities 

• acquired new data in ROI

• preprocessing 

• identical pixel size

• more pixel than original ROI 

• improved spatial resolution 

• may improve temporal resolution (smaller scan area) 

coded excitation is produced where

in the beam former

What is coded excitation 

a sophisticated method that improves image quality 

• encoded (binary) electrical impulses are applied to the transducer active element (occurs in pulser) 

• also sets the max peak intensity for the acoustic beam 

creates a long pulse waves containing wide range of freq. 

Clinical impact of coded excitation

increase axial resolution, increase S/N ratio, better customization for imaging application and enhanced contrast resolution

Edge enhancement

processing technique that enhances the edges, computer identifies sharp boundariis and those with large differences in echogenicity

How does edge enhancement work 

increased image contrast in area surround this “edge” making them more defined 

Interpolation

fills in the gaps between scan lines (when using a sector of curved linear probe, gaps are created)

• gaps are filled with simulated data that is generally undetectable by sono

• done so by averaging shades of grey based on the real scan lines

interpolation is a ____ function

preprocessing

interpolation ____ spatial resolution 

increases 

Elastography

imaged based on mechanical properties of the medium (stiffness)

• form of US palpation

Shear wave elastography

sideways directed waves are created by transmitted sound beam rather than transducer pressure

3D rendering 

creation of realistic image w/ shadows and texture from 3D data 

• volumetric data is stored

3D render is a ____ function

post-processing

image matrix

composed of columns and rows of pixelss which when aligned theyproduce B-mode image

• 2D pic element- pixel

• 3D picture element- voxel

spatial compounding

using different angles to create multiple scan lines 

• electronic beam steering rapidly acquires data from multiple incident “view angles” into a single “compounded image” 

clinical impact of spatial compounding

• decreased speckle

• increased contrast resolution

• decreased frame rate, decreased temp resolution

What is the purpose of spatial compounding?

artifact reduction

Persistance aka 

temporal compounding

superimposition or compounding of new data over the last acquired image frame 

• sound reflected from a boundary is compromised of more than one freq. these reflected freq (sub-bands) are used to generate image data. 

• Each sub-band is averaged or compounded and noise is subtracted. 

Clinical impact of persistance (temporal resolution)

• smooths image

• decrease noise and speckle

• increase contrast

What is the tradeoff with compounding

decreased axial and temporal resolution

(since sub-bands contain a narrow bandwidth)

Dynamic range 

shades of grey displayed 

• range oof returning signals too large to be displayed visually, they must be compressed

The more data processed the more of a _____ in dynamic range

decrease

• earliest data acquisition has the widest dynamic range

• each level of the system dynamic range decrease due to attenuation/compression

Dynamic range levels

• transducer - 120 dB

• receiver- 110dB

• scan converter- 45dB

• display- 25dB

• archive- 20dB

compressed signal = _____ dB 

subtracted 

uncompressed signal = _____ dB

add

contrast resolution

Number of shades of grey displayed

• allows us to differentiate tissues 

Contrast

ability of the system to detect a difference in brightness where echo amplitudes between discrete adjacent structures

(if able to do so, high contrast)

Dynamic range at the receiver is 100dB. The signal btwn the reciever and scan converter endures 60dB of compression. Signal dynamic range is what?

40dB

What system component has the greatest dynamic range?

transducer

Why is imaging data stored digitally instead of analog

digital data prevents image degration over time

Function of compression in US

condense signal range while maintaining highest and lowest values

Where does coded excitation occur

pulser

What form of compounding superimposes new data over last acquired imaging frame?  

temporal compounding 

Purpose of coded excitation

to improve contrast resolution and penetration without increasing output

Drawback of temporal compounding (persistance)

decreased frame rate and temporal resolution

Modern transducers 

• multiple elements in an array 

• use time delays for element activation 

• synthesize US waves w/ combined pulses

• focus controlled by electronic time delays 

• adjusts image detail at various body depths 

____ focal depth with increased freq and increased diameter

increased