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Pulse-Echo Imaging Instrument. Pulse-Echo Instrumentation. Voltage activation of the PE crystal Ultrasound formation Propagation Reflection Charge formation of crystal Processing Display. Pulse-Echo Instrumentation. Transmitter. Display. Receiver Amplifier. Detector. Scan Converter.

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Pulse-Echo Imaging Instrument


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pulse echo instrumentation
Pulse-Echo Instrumentation
  • Voltage activation of the PE crystal
  • Ultrasound formation
  • Propagation
  • Reflection
  • Charge formation of crystal
  • Processing
  • 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

+

+

V

P

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

TRX

TRS

CRT

DISPLAY

DEMODULATOR

DETECTOR

VIDEO

AMPLIFIER

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Pulse-Echo Instrumentation
  • Radio-Frequency Amplifier
  • Amplify weak voltage signals.
  • This is called GAIN
pulse echo instrumentation18
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
  • 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

In the Scan converter the echoes are processed on a first-come first-in basis.

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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

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
  • 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

Pre-

Processing

Data

Post-

Processing

RAM

Data

Reformatting

ADC

Data

Collection

&

Formatting

Echo

Signal

Positional

Data

Display