ut testing instrumentation
DESCRIPTION
My ASNT UT Level III Pre-exam Study notes. Not proven yet! The exam is due next month.TRANSCRIPT
Pulse-Echo Instrumentation
The Circuitry:
Voltage activation of the PE crystal Ultrasound formation Propagation Reflection Charge formation of crystal Processing Display
Transmitter
TGC
ReceiverAmplifier Detector Scan
Converter
Display
TRX
Pulse-Echo Instrumentation
TGC – Time Gain Compensation Circuit
Pulse-Echo InstrumentationPulser Components
1. HV pulse generator
2. The clock generator
3. The transducer
TIME
TIME
+ +
-
P
Generated WaveApplied Voltage
V
-
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.
Pulse-Echo Instrumentation
Switch that controls the output power of the HV generator is the attenuator.
Pulse-Echo Instrumentation
PULSER
ATTENUATOR
TRX
Pulse-Echo Instrumentation
CLOCK GENERATOR
Controls the actual number of pulses which activate the crystal.Responsible for sending timing signal to the
1. Pulse generator2. TGC circuitry3. Memory
Pulse-Echo Instrumentation
CLOCKGENERATOR
HVGENERATOR
TGC UNIT
MEMORY
CRT DISPLAY
TRS
TRX
Pulse-Echo Instrumentation
Sensitivity refers to the weakest echo signal that the instrument is
capable of detecting and displaying.
Factors that determine sensitivity are
1. Transducer frequency2. Overall and TGC receiver gain3. Reject control4. Variable focal zone on array real-time instruments.
Pulse-Echo Instrumentation
Increasing the voltage causes
1. Greater amplitude – greater penetration
2. Longer pulses – degrades axial resolution
3. Increase exposure
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.
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.
Pulse-Echo Instrumentation
The Receiver Unit consist of
1. Radiofrequency Amplifier
2. Time gain compensation TGC unit
3. Demodulation Circuit
4. Detector Circuit
5. Video Amplifier
Pulse-Echo Instrumentation
PULSER TGC UNITMEMORY
CRT DISPLAY
TRSTRXRF
RECEIVER
DEMODULATOR
DETECTOR
VIDEOAMPLIFIER
Radio-Frequency Amplifier
• Amplify weak voltage signals.
• This is called GAIN
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 OutVoltage In
Pulse-Echo Instrumentation
The Imaging effect of adjusting gain are:
1. Increasing the gain - increased sensitivity, better penetration
2. Decreasing the gain – decreased sensitivity, less penetration
3. Too high a gain – overloads the display, loss or spatial resolution
Pulse-Echo Instrumentation
Saturation Level
Distance
Am
plitu
de
Normal Gain
Pulse-Echo Instrumentation
Saturation Level
Distance
Am
plitu
de
Excess Gain
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.
Pulse-Echo Instrumentation
Time Gain Compensation TGC
TGC - electronic process of adjusting the overall system gain as a function of the transmit time.
Pulse-Echo Instrumentation
TGC Controls
• Near Gain
• Slope Delay
• Slope
• Knee
• Far Gain
• Body Wall
Pulse-Echo Instrumentation
GaindB
Depth cmDELAY
SLOPE
KNEE MAX GAIN
NEAR GAIN
Pulse-Echo Instrumentation
GaindB
Depth cm
SLOPE
KNEE MAX GAIN
NEAR GAIN
Body wall
Pulse-Echo Instrumentation
GaindB
Depth cmDELAY
SLOPE
KNEE
CUT-OFF
Pulse-Echo Instrumentation
The slide potentiometer allows adjustment of receiver gain for small discrete depth increments.
Pulse-Echo Instrumentation
GaindB
Depth (Time)
Slide Potentiometer
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.
Pulse-Echo Instrumentation
Types of Amplifiers
• Wide-Band• Narrow-Band
Pulse-Echo Instrumentation
Frequency MHz
Gain Gain
Frequency MHz
Wide-band amplifier Narrow-band amplifier
Pulse-Echo Instrumentation
Receiver B
Receiver A
Receiver C
Receiver D
TRXOutputTo System
Frequency SelectorSwitch
Receiver Unit
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.
Pulse-Echo Instrumentation
Large range in signal amplitudes is due to:
1. Normal variation in the reflection amplitude.2. Frequency dependent tissue attenuation.
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.
Pulse-Echo Instrumentation
Linear amplification - all voltages amplitudes, regardless of size at the point of input are amplified with the same gain factor.
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
Pulse-Echo Instrumentation
Input signal
GainA
B
Linear Amplification
Logarithmic Amplification
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.
Pulse-Echo Instrumentation
Pre-amplification is a technique to reduce system noise.
Positioning of part of the amplifier circuitry in the transducerhousing reduces system noise.
Pulse-Echo Instrumentation
REJECTIONRejection 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.
Pulse-Echo Instrumentation
NoiseLevel
DynamicRange
Saturation Level
Rejection Level
Zero Signal Level
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.
Pulse-Echo Instrumentation
DEMODULATION
Rectification
Detection
Pulse-Echo Instrumentation
RECTIFICATION
• Rectification results in the elimination of the negative portion of the RF signals
• Half Wave Rectification
• Full wave Rectification
Pulse-Echo Instrumentation
Half-WaveRectification
Pulse-Echo Instrumentation
Full-WaveRectification
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.
Pulse-Echo Instrumentation
Smoothing
Pulse-Echo Instrumentation
The video signal is then further amplified by the VIDEO AMPLIFIER.
The output from the video amplifier is forwarded to
1. CRT or
2. Scan converter
Pulse-Echo Instrumentation
DIGITAL SCAN CONVERTER
The device that stores the echo signal is called a Scan converter.
Pulse-Echo Instrumentation
All Scan Converters are designed to
1. Store echoes in appropriate location
2. Encode echoes in shade of gray
3. Read out echoes in a horizontal raster format
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
Pulse-Echo Instrumentation
Matrix
Rows x, coordinates
Matrix
Columns, y coordinates
Matrix
Pixel
1x1y
3x3y
5x5y
8x7y
10x10y
X, Y ADDRESS
In the Scan converter the echoes are processed on a first-come first-in basis.
Pulse-Echo Instrumentation
XXXX
XXXX
XXXX
XXXX
XXXX
XXXX
5050
5050
5050
5050
5050
5050
5050
5050
5050
5050
5050
5050
Raster Process
DIGITAL SCAN CONVERTER
• Convert echo voltage signal into a numerical value.
• Each numerical value corresponds to a shade of gray.
Pulse-Echo Instrumentation
The number of shades of gray is determined by the BIT CAPACITY.
# of shades of gray = 2
Pulse-Echo Instrumentation
EchoesdB
Pulse-Echo Instrumentation
214283
16432564612872568
Shades of GrayBit
Pulse-Echo Instrumentation
Gray Scale Resolution = dynamic range (dB)# of gray shades
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.
Pulse-Echo Instrumentation
100%
50%
0%
% AvailableShade of gray
Echo Strength
1
2
34
Pulse-Echo Instrumentation
POST PROCESSING
Assignment of specific display brightness to numerical echo amplitudes read out ofthe digital memory.
Pulse-Echo Instrumentation
9887
7898
8879
8888
8888
8888
SMOOTHING
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
Pulse-Echo Instrumentation
Zoom Magnification
• Read Zoom
• Write Zoom
Pulse-Echo Instrumentation
Resolution at the DSC
1. Find Matrix size
2. Determine FOV ( width/length)
3. Calculate pixels/cm
4. Find linear distance/pixel = resolution
Pulse-Echo Instrumentation
DataReformatting
DataPost-Processing
DataCollection&Formatting
ADC
DataPre-Processing
Display
RAM
EchoSignal
PositionalData
Pulse-Echo Instrumentation
1. ROM
2. PROM
3. RAM
Pulse-Echo Instrumentation