Transcript Session 8 - Display Systems - my Tri

Display Modes
A-Mode or Amplitude Mode
B-Mode (Brightness Mode)
M-Mode (Motion Mode)
A-Mode
a one-dimensional display or image
each pulse produces a new line of
information on the display
temporal resolution = PRP
an uncommon display, except in
ophthalmologic sonography used
for precise intraocular length
measurements
A-Mode
Height of the spike is proportional to the amplitude
A-Mode
Depth…
horizontal axis corresponds to the reflector’s depth or distance
B-Mode (Brightness Mode)
- basis for gray scale,
two-dimensional (2D) imaging
US unit tracks the position of
the transducer to place a dot on
the screen corresponding to the
transducer position (X, Y
locations), creating a 2D image
B-Mode (Brightness Mode)
Each pulse from the
transducer creates a single
scan line from a series of
returning echoes
A complete scan line
resulting from one emitted
pulse. occurs in < 1/1000
of a second (< 1 msec)
Scan Line
One pulse of ultrasound
generates a single scan
line (from a series of
returning echoes).
A complete scan line
resulting from one emitted
pulse. This is accomplished
in < 1/1000 of a second.
Echoes are presented in sequence on a
scan line as they return from tissue.
(A) The first echo is displayed. (B) The
second echo is added. (C) More echoes
are added. (D) All the echoes from a
single pulse have been received and
displayed as a completed scan line.
B-Mode
0
1
A shade of gray is assigned to
the amplitude of the echo
2
3
4
Stronger echo amplitude
= brighter dots
Vertical axis represents depth
M-Mode (Motion Mode)
- one-dimension image used to
investigate moving structures with
respect to time
Temporal resolution = PRP;
each pulse produces a new line of
echo information on the display
evaluates motion pattern of moving
structures such as in the heart
M Mode
A dot records
echo position in
relation to time
(horizontal axis)
with the vertical
axis representing
depth
D
E
P
T
H
TIME >>>>
Echo amplitude is
represented by
the dot’s
brightness
B Mode
M Mode
A Mode
Scanning Imaging
Static scanning (B scan)
Real-time
Static Scanning (B scan)
An articulated arm scanner scans the patient
from many different directions creating a 2Dimage from multiple B-mode pulses
Multiple dots are combined to delineate the echo
pattern of internal structures within the body
Superimposition of multiple scan lines creates a
two-dimensional image that portrays the general
contour of the patient and the internal organs
Compound B-mode scanning produces a static
image that can be thought as a stop-action
photograph of the reflecting surfaces
B Scan
B Scan
Static Scanner
B Scan
Real-time
Produces a video giving the impression of
constant motion of the scanned anatomy
Consists of a series of frames displayed in
rapid sequence creating the impression of
constant motion
Provides rapid, convenient image
acquisition with the display changing
continuously as the scan plane is moved
through the tissues
Real Time
Who’s that pregnant with twins??
A real time image
before computer
technology could
handle increased
lines/frame & faster
frame rates.
How many shades
of gray can you
see?
Temporal Resolution
Resolution related to time & motion
Time from the beginning of one frame to the
beginning of the next one (the time required
to generate one complete frame)
Expressed in milliseconds (ms)
Ability to accurately determine the position of
a structure at a particular instant in time
Depends on extent of movement of the
structure & the frame rate
Important in imaging rapidly moving
structures
Temporal Resolution
Each frame is made of many scan lines;
when you  # of scan lines - the frame
rate 
Improves as the frame rate increases (a
greater # of frames/ second) because less
time elapses from one frame to the next
Temporal Resolution
Depends upon 2 factors:
1. # of images created/second (frame rate)
- higher frame rates (greater number of
frames created/second), the better the
temporal resolution. To  temporal resolution,
frame rate must be 
2. Higher frame rates are needed to
evaluate motion or moving structures,
such as adult, pediatric and fetal hearts
Spatial (detail) resolution
ability to see detail on the image
affected by the # of scan lines & focuses
 # of scan lines  spatial resolution
More detail is needed to scan organs
in the body so a slower frame rate
is tolerated
When temporal resolution ,
spatial resolution  !
Scanning Speed Limitation
Real-time scanning consists of multiple
frames/second that are made up of
multiple scan lines per frame
Its advantage is temporal resolution
To create each scan line, the ultrasound
unit must wait until all echoes have been
received from the selected depth before
sending out the next pulse, if not range
ambiguity occurs
Range Ambiguity
When structures beyond the indicated
range are depicted in an image
Cause – time between the transmitted
pulse & detected echo is not coreectly
measured
Occurs when an echo (from the previous
pulse) is received after the next pulse is
transmitted
Scanning Speed Limitation
US unit can’t work any faster than the
sound wave can travel, so propagation
speed plays a major role in limiting the
scanning speed
The # of focuses that the sonographer
uses while imaging will slow down the
process of obtaining a scan line
Imaging depth controls determine when
the next pulse is sent out (PRF)
The # of foci used in imaging will slow down
the process of obtaining a scan line
Imaging depth
controls determine
when the next pulse
is sent out (PRF)
Frame Rate
- # of frames/second (fps).
Human eye can see flickering (each individual
frame being produced) at frame rates < 15 -20 fps
Acceptable frame rates are 30 fps-60 fps
Factors affecting frame rate are:
• depth of field
• # of lines used to create the image
• # of focal zones used
Sound travels 1,540 m/s (154,000 cm/s) in ST
A pulse can travel to & from a depth of 77,000 cm/s
Imaging with multi focus- and annular arrays
(multiple pulses to various depths to create a single
composite scan line) requires even more time
Creating a single frame with a large # of scan lines
requires TIME. Presenting many frames in rapid
sequence requires TIME.
Frame Rate
To avoid misplacing the proper location
from returning echoes on the display:
imaging depth (cm) X lines/frame
X pulses/line [number of focal zones]
X frame rate  77,000 cm
Frame Rate
Consider the following scenario:
You are imaging a liver that extends to
10 cm deep with a 5.0 MHz probe. What
is the maximum PRF permitted to avoid
range ambiguity?
10 cm X 13 μs/cm = 130 μs - which means 1 pulse/130 μs
PRF = # pulses/sec = 1 pulse/130 μs = .0077 pulses/μs
7,700 pulses/sec = 7.7 KHz
PRF = 7.7 KHz
Maximum Frame Rate
=
=
c
= PRF
2 X Distance X # lines/frame [lpf]
lpf
7.7 KHz = 77 fps
100
Imaging depth
# of pulses (foci) per line
lines per frame
frame rate
ALL OF THE ABOVE battle over time
Therefore, a compromise to balance
these factors must be based on
meeting the clinical need.
PRF = # focuses X lines/frame X frame rate
PRF ↑ when you ↑ any of the following:
–# of focuses
–# of lines per frame
– frame rate
Consider this:
FRAME RATE ↓ with:
↑ # of focuses
↑ # of lines per frame
↑ in scanning penetration
Frame Rate
Solution depends on area of interest:
Imaging depth
Multiple focal zones
Line density
Frame rate
Imaging Depth
Complete depth that sound travels per
pulse
Controlled by the sonographer to visualize
the anatomy to be imaged that may lie
superficially or deep in the body
The deeper the system images, the longer
the listening time for each pulse
Deeper imaging results in:
longer listening time
longer pulse repetition period
lower PRF (# pulses/second)
more time for each scan line
Multiple Focal Zones
US pulse has only a single focal zone
(region within the beam that provides the
finest lateral resolution)
Using multiple sound beams with different
focal depths to create a single image line,
results in optimal lateral resolution all
depths  superior image quality
Multiple Focal Zones
A pulse is required for:
– each focus
– each scan line
– each frame
– More foci/image line = more pulses/image line
Multiple focal zones are controlled by the
sonographer & are only used with phased
array transducers (linear, curved, and
annular)
More foci per image line result in:
more pulses/line
superb lateral resolution at all depths
more time/image scan line
more time needed to create a frame
Line Density
# of scan lines that create a single image
Set automatically by the US system & is
not controlled by the sonographer
The greater the line density, the more
pulses/image sector
Increased Line Density results in:
greater detail within the image
less “space” between image lines
more sound pulses per image
more time needed to create a frame
Line Density
For a sector scan:
lines/degree
For a rectangular
scan: lines/ cm
Frame Rate
determined by the US system & is not
directly controlled by the sonographer
when a rapidly moving structure is
imaged at an unsuitably low frame rate,
the images are said to ‘flicker’
More Frames per Second result in:
1. greater accuracy in locating moving
structures
2. less time to make each frame
3. decreased line density
THE DILEMMA
SO... to optimize these conditions:
adjust the maximum imaging depth to
the area of interest
Determine the # of foci per scan line.
Superior lateral resolution over a range
of depths requires more foci. This
determines the number of sound pulses
required to make each scan line.
THEN…
The frame rate & line density are
determined by the ultrasound system
to balance the goals of temporal
resolution (frame rate) & image
quality (line density).
THE DILEMMA
Deeper Imaging
Depth
Multiple Focal
Zones
Higher Line
Density
Higher Frame
Rate
longer listening
time
more sound
pulses/line longer
greater spatial
detail in the image
greater accuracy in
locating moving
structures 
temporal resolution
decreased line
density; less
detail resolution
Less imaging
depth due to
speed limitation
less time allocated
to make each
frame/scan line
Amount of time
short/frame; long
with high frame rates
T/R time
longer pulse
repetition period
superb lateral
resolution at all
depths
lower PRF (# of
pulses/second)
more time per
image scan line
more time required
for each scan line
more time needed
to create a frame
 space between
image lines  real
detail
more sound
pulses/image 
listening time
more time needed
to create a frame
Amount of time long
Amount of time long
Amount of time long
Recording Techniques
Before an image is recorded, the contrast
& brightness controls of the monitor are
adjusted for optimal image quality
Contrast & brightness controls of the
recording devices are then matched to the
image on the monitor.
– Adjusting the contrast & brightness controls of
the monitor without changing the contrast &
brightness controls of the recording device,
can lead to producing films that appear with
increased gain or decreased gain,
i.e., too light or too dark
Recording Devices
Hard copy film & paper
Thermal processors
Laser imaging systems
Digital recording devices
videotape player
M-mode records
Magneto-optical (MO)
Picture Archiving & Communication
Systems
Teleradiology
Hard Copy Film and Paper
Transparent film uses a single emulsion film
Film is a cellulose acetate sheet coated with
a gelatin emulsion containing silver bromide
crystals
After exposure to light from the camera
monitor, the film is developed in a chemical
processor
Changes in the temperature of the
chemicals will affect the quality of the film
Age & concentration of the chemicals can
also affect the film
Thermal Processors
uses a paper medium to record the
image
less resolution & shades of gray than
single emulsion film
less archival stability
Color Thermal Printers
contain a ribbon of colored inks
(black, cyan, yellow, & magenta)
printing on photo paper
produces good quality color images
used for color Doppler hard copy
imaging
Laser Imaging Systems
capable of higher resolution, better gray
scale uniformity & less image distortion
Initial cost outlay
automated film handling & developing –
saves sonographer processing time
15+ images available per sheet of film
Digital Recording Devices
- store the image on computer disks
or in computer memories for viewing
on monitors or later transfer to film
Videotape Player
used to record moving or real-time images
record color as well as black & white
images
tapes store the image information on a
magnetic medium
Follow recommended procedures when
handling and storing tapes
Most common format is VHS
Super VHS (S-VHS) has better spatial
resolution, less distortion & stores more
information
Fiber optic recorder
(M-mode recorders)
paper developed by exposure to
visible light
dry silver paper as recording medium
-better gray scale
Trend
digital archiving & image storage
Magneto-optical (MO)
Magneto-optical (MO) is also known as
optical technology. It is a combination of
optical & magnetic technologies
Stores lots of information onto disk
(optical portion). MO drives can be
rewritten and erased
Not susceptible to magnetic fields like
regular diskettes or digital tapes so
information storage is safe
Picture Archiving &
Communication Systems (PACS)
a computer network for the acquisition, display, &
storage of images.
provide for electronically communicating images
to work stations, devices, and storage external to
the instrument, the examining room,
& even the building where the scanning is done.
protocols for communicating images and
associated information between imaging devices
and workstations have been standardized in the
Digital Imaging & Communications in Medicine
(DICOM) Standard
Picture Archiving &
Communication Systems (PACS)
Other names are digital imaging network
(DIN) & information management archiving
and communications systems (IMACS)
Acquisition, display, hard copy, & computer
components must be interconnected using
a local area network (LAN)
Allows digitized images from multiple
imaging modalities to be stored for later
retrieval, display, manipulation &
interpretation
Picture Archiving &
Communication Systems (PACS)
US scan data is digitized & transferred to
the network. Standards for encoding
patient file information developed by ACR
(American College of Radiology) & NEMA
(National Electrical Manufacturers Assoc.)
Provides for more centralized processing
by reducing the need for multiple hard
copy devices for each ultrasound or
imaging modality system
Teleradiology
- is the electronic transfer of images from
one location to another
Allows multiple hospitals to have quick
access to images
Transmission methods include telephone
lines, coaxial cables, fiber optic cables,
microwave dishes, laser systems,
satellites, & T-1 (multiple) telephone lines
Digital information is compressed and
converted to transmission methods such
as pulsed tone signals for sending over
telephone lines