Pulse-Echo Imaging Instrument

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Pulse-Echo ImagingInstrument
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Pulse-Echo Instrumentation

1. Voltage activation of the PE crystal
2. Ultrasound formation
3. Propagation
4. Reflection
5. Charge formation of crystal
6. Processing
7. Display

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Pulse-Echo Instrumentation
Transmitter
Display
Receiver Amplifier
Detector
Scan Converter
TRX
TGC
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Pulse-Echo Instrumentation
Pulser Components

• HV pulse generator
• The clock generator
• The transducer

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Pulse-Echo Instrumentation
Generated Wave
Applied Voltage


P
V
TIME
TIME
-
-
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Pulse-Echo Instrumentation
The Pulser rate is known as the pulse repetition
frequency (PRF). Typical PRF 3,000 5,000. PRF
automatically adjusted as a function of imaging
depth.
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Pulse-Echo Instrumentation
Switch that controls the output power of the HV
generator is the attenuator.
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Pulse-Echo Instrumentation
ATTENUATOR
TRX
PULSER
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Pulse-Echo Instrumentation

• CLOCK GENERATOR
• Controls the actual number of pulses which
• activate the crystal.
• Responsible for sending timing signal to the
• Pulse generator
• TGC circuitry
• Memory

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Pulse-Echo Instrumentation
TGC UNIT
CLOCK GENERATOR
HV GENERATOR
MEMORY
TRS
CRT DISPLAY
TRX
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Pulse-Echo Instrumentation

• Sensitivity refers to the weakest echo
• signal that the instrument is capable of
• detecting and displaying.
• Factors that determine sensitivity are
• Transducer frequency
• Overall and TGC receiver gain
• Reject control
• Variable focal zone on array real-time
• instruments.

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Pulse-Echo Instrumentation

• Increasing the voltage causes
• Greater amplitude greater penetration
• Longer pulses degrades axial resolution
• Increase exposure

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Pulse-Echo Instrumentation
Transducer has dual roles transmitting and
receiving signals. The transducer is capable of
handling a wide range of voltage amplitude. The
Receiver is capable of handling only smaller
signals Therefore it is desirable to isolate the
pulser circuit from the receiver circuit.
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Pulse-Echo Instrumentation
The Transmit Receive Switch TRS positioned at
the input of the receiver and is designed to pass
only voltages signals originating at the
transducer by the returning echoes.
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Pulse-Echo Instrumentation

• The Receiver Unit consist of
• Radiofrequency Amplifier
• Time gain compensation unit
• Demodulation Circuit
• Detector Circuit
• Video Amplifier

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Pulse-Echo Instrumentation
MEMORY
PULSER
TGC UNIT
RF RECEIVER
TRS
TRX
CRT DISPLAY
DEMODULATOR
DETECTOR
VIDEO AMPLIFIER
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Pulse-Echo Instrumentation

• Radio-Frequency Amplifier
• Amplify weak voltage signals.
• This is called GAIN

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Pulse-Echo Instrumentation
Electric signals generated by the transducer are
weak and needs amplification. The gain is the
ratio of the output to input Voltage or
Power. Gain Voltage Out Voltage In
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Pulse-Echo Instrumentation

• The Imaging effect of adjusting gain are
• Increasing the gain - increased sensitivity,
  better penetration
• Decreasing the gain decreased sensitivity, less
  penetration
• Too high a gain overloads the display, loss or
  spatial resolution

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Pulse-Echo Instrumentation
Normal Gain
Saturation Level
Amplitude
Distance
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Pulse-Echo Instrumentation
Excess Gain
Saturation Level
Amplitude
Distance
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Pulse-Echo Instrumentation
Primary objective of grayscale pulse-echo imaging
is to make all like reflectors appear the same in
the Image regardless where they are located in
the sound beam.
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Pulse-Echo Instrumentation
Time Gain Compensation TGC - electronic process
of adjusting the overall system gain as a
function of the transmit time.
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Pulse-Echo Instrumentation

• TGC Controls
• Near Gain
• Slope Delay
• Slope
• Knee
• Far Gain
• Body Wall

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Pulse-Echo Instrumentation
MAX GAIN
KNEE
Gain dB
NEAR GAIN
SLOPE
DELAY
Depth cm
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Pulse-Echo Instrumentation
MAX GAIN
KNEE
NEAR GAIN
Gain dB
SLOPE
Depth cm
Body wall
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Pulse-Echo Instrumentation
KNEE
Gain dB
SLOPE
CUT-OFF
DELAY
Depth cm
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Pulse-Echo Instrumentation
The slide potentiometer allows adjustment of
receiver gain for small discrete depth
increments.
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Pulse-Echo Instrumentation
Slide Potentiometer

Gain dB
Depth (Time)
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Pulse-Echo Instrumentation
Frequency Tuning of the Receiver The frequency
band width of the receiver refers to the range of
ultrasound signal frequencies that the receiver
can amplify with a maximum gain.
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Pulse-Echo Instrumentation

• Types of Amplifiers
• Wide-Band
• Narrow-Band

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Pulse-Echo Instrumentation
Wide-band amplifier
Narrow-band amplifier
Gain
Gain
Frequency MHz
Frequency MHz
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Pulse-Echo Instrumentation
Receiver Unit
Receiver A
Receiver B
Output To System
TRX
Receiver C
Receiver D
Frequency Selector Switch
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Pulse-Echo Instrumentation
DYNAMIC RANGE The dynamic range is a measure of
the range of echo signal amplitudes. The dynamic
range can be measured at any point. The dynamic
range decreases from transducer, to receiver to
scan converter and finally to display.
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Pulse-Echo Instrumentation

• Large range in signal amplitudes is due to
• Normal variation in the reflection amplitude.
• Frequency dependent tissue attenuation.

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Pulse-Echo Instrumentation
RF amplifier can handle a wide range of signal
amplitude at its input but cannot accommodate
the corresponding output using linear
amplification.
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Pulse-Echo Instrumentation
Linear amplification - all voltages amplitudes,
regardless of size at the point of input are
amplified with the same gain factor.
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Pulse-Echo Instrumentation
LOGARITHMIC AMPLIFICATION In Logarithmic
amplification weak echoes amplitudes are
amplified more than strong echoes. This can
reduced the dynamic range by as much as 50. The
process of reducing the signal DR by electronic
means is called COMPRESSION
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Pulse-Echo Instrumentation
Linear Amplification
A
Gain
B
Logarithmic Amplification
Input signal
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Pulse-Echo Instrumentation
R-F amplifier can also set the electronic level
in the machine. S-N level compares real echo
signals the system can handle versus the non-echo
signals presents (Noise). The Higher the SN
ratio better the operation of the system.
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Pulse-Echo Instrumentation
Pre-amplification is a technique to reduce system
noise. Positioning of part of the amplifier
circuitry in the transducer housing reduces
system noise.
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Pulse-Echo Instrumentation
REJECTION Rejection is the receiver function
that enables the operator to systematically
increase or decrease the minimum echo signal
amplitude which can be displayed. Alternate
names Threshold, Suppression.
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Pulse-Echo Instrumentation
Saturation Level
Dynamic Range
Rejection Level
Noise Level
Zero Signal Level
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Pulse-Echo Instrumentation
SIGNAL PROCESSING RF waveform oscillating type
of voltage signal (AC) First Step in processing
the signal is Demodulation. Demodulation is the
process of converting the electric signal from
one form to another.
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Pulse-Echo Instrumentation

• DEMODULATION
• Rectification
• Detection

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Pulse-Echo Instrumentation

• RECTIFICATION
• Rectification results in the elimination of the
  negative portion of the RF signals
• Half Wave Rectification
• Full wave Rectification

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Pulse-Echo Instrumentation
Half-Wave Rectification
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Pulse-Echo Instrumentation
Full-Wave Rectification
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Pulse-Echo Instrumentation
DETECTION The main effect of detecting the
rectified RF signal is to round out or smooth the
signal as to have a single broad peak. The
rectified RF signal following detection is
referred to as a Video Signal.
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Pulse-Echo Instrumentation
Smoothing
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Pulse-Echo Instrumentation

• The video signal is then further amplified by the
• VIDEO AMPLIFIER.
• The output from the video amplifier is forwarded
  to
• CRT or
• Scan converter

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Pulse-Echo Instrumentation
DIGITAL SCAN CONVERTER The device that stores
the echo signal is called a Scan converter.
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Pulse-Echo Instrumentation

• All Scan Converters are designed to
• Store echoes in appropriate location
• Encode echoes in shade of gray
• Read out echoes in a horizontal raster format

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Pulse-Echo Instrumentation

• 4. Digital Memory is divided into small squares
  Pixel.
• 5. The Pixels form the Image Matrix
• 6. Total of storage location rows x columns
• 7. x and y location ADDRESS

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Pulse-Echo Instrumentation










Matrix
Rows x, coordinates
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Pulse-Echo Instrumentation










Matrix
Columns, y coordinates
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Pulse-Echo Instrumentation










Matrix
Pixel
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Pulse-Echo Instrumentation
10x 10y

8x 7y


5x 5y

3x 3y

1x 1y
X, Y ADDRESS
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Pulse-Echo Instrumentation
In the Scan converter the echoes are processed on
a first-come first-in basis.
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Pulse-Echo Instrumentation

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Pulse-Echo Instrumentation










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Pulse-Echo Instrumentation


X X
X X
X X
X X
X X
X X


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Pulse-Echo Instrumentation


X X
X X
X X
X X
X X
X X


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Pulse-Echo Instrumentation


50 50
50 50
50 50
50 50
50 50
50 50


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Pulse-Echo Instrumentation


50 50
50 50
50 50
50 50
50 50
50 50


Raster Process
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Pulse-Echo Instrumentation

• DIGITAL SCAN CONVERTER
• Convert echo voltage signal into a numerical
  value.
• Each numerical value corresponds to a shade of
  gray.

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Pulse-Echo Instrumentation
The number of shades of gray is determined by the
BIT CAPACITY. of shades of gray 2
bit capacity
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Pulse-Echo Instrumentation
Echoes dB
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Pulse-Echo Instrumentation
Bit Shades of Gray
1 2
2 4
3 8
4 16
5 32
6 64
7 128
8 256
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Pulse-Echo Instrumentation
Gray Scale Resolution dynamic range (dB)
of gray shades
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Pulse-Echo Instrumentation
Operator can select different A/D conversion
scheme (Preprocessing). Each preprocessing curve
is called an algorithm and assigns a specific
percentage amount of shades of gray to regions of
the echo amplitude.
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Pulse-Echo Instrumentation
Available Shade of gray
100
1
2
50
3
4
0
Echo Strength
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Pulse-Echo Instrumentation
POST PROCESSING Assignment of specific display
brightness to numerical echo amplitudes read out
of the digital memory.
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Pulse-Echo Instrumentation
9 7 8 8
8 9 8 7
7 8 8 9
8 8 8 8
8 8 8 8
8 8 8 8
SMOOTHING
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Pulse-Echo Instrumentation

• The DSC is not necessary for image display,
• but is needed for the following post-processing
• functions.
• Video Invert
• Display Invert
• Display Subdivision
• Zoom Magnification

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Pulse-Echo Instrumentation

• Zoom Magnification
• Read Zoom
• Write Zoom

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Pulse-Echo Instrumentation

• Resolution at the DSC
• Find Matrix size
• Determine FOV ( width/length)
• Calculate pixels/cm
• Find linear distance/pixel resolution

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Pulse-Echo Instrumentation
Data Post- Processing
Data Pre- Processing
RAM
Data Reformatting
Data Collection Formatting
ADC
Display
Echo Signal
Positional Data
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Pulse-Echo Instrumentation

1. ROM
2. PROM
3. RAM