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Beam Former

QuestionAnswer
Organization of a pulse-echo imaging system Beam Former, signal processor, image processor, display
Components of the beam former, where the action takes place Pulser, pulse delays, transmit/receavie switch, amplifiers, analog/digital converter, echo delays, and summer
Function of the beam former Generating voltage that drive the trandsucer,Determin PRF,coding, frequency,&intensity.Scanning, focusing,& apodizing the transmitted beam.Amplifying the returning echo voltage. Compensating for attenuation. Digitizing the echo voltage stream &dircecting,
Pulser produces electric voltages that drive the transducer forming the beam that sweeps through the tissue to be imaged
When sound reaches the transducer from that point on everything is electrical
The voltage repetition frequency (VRF) = The pulse repetition frequency (PRF) Mirror image of each other
PRF ranges from? "Number of pulses occuring in one second" 4-15 khz
The voltage repetition period (VRP) = The pulse repetition period (PRP)
All echo from one pulse must be received before before the next pulse is sent out. This limits the PRF at deeper depths
The number of complete screens of information produced per second Frame rate
For deeper imaging, echoes take longer to return, thus forcing a? Reduction in PRF and the number of images that are generated each second ( frame rate)
Imaging depth (cm) x PRF (kHz) must be less than or equal to 77. If over you will have? Overlapping information
As operating frequency is reduced and penetration increased PRF is decreaed to avoid echo misplacement
The pulser also determines the amplitude and the intensity of the sound pulse. The greater the amplitude of the electrical voltage pulse the greater the amplitude of the sound pulse Intensity
Greater amplitude = Greater intensity
How do we make intensity bigger? Sonographer changes it with accoustic output or power botton
The greater the voltage amplitude produced by the pulser The greater the intensity of the ultrasound pule produced by the transducer
Voltage amlitudes can be as high as 100 volts
Acoustic output is the same as Power, which means sound
The amount of intensity sent into the body.Always indicated on the image screen Acoustic output or power
The power button/acoustic output on the machine controls the amount of? Energy being sent into the body when scanning
Theses delays control the sequencing of electrical voltage being applied to the individual transducer elements Pulse delays
Task performed by pulse delays Beam Scanning & Steering, Transmit focusing, Dynamic aperature & Apodization
We decide where we want our focus and depth Transmit focusing
Large group of elements with more voltage needed Dynamic aperture
Element hit in the center Dynamic apodization
A more complicated form of pulse delays Coded Excitation
Function of Coded excitation Multiple transmit focuses, Separation of harmonic bandwidth,Increase penetration & depth, Reduction of speckle, Brighter echos, Gray-scale imaging of blood flow
Operation of coded excitation generating more than one pulse per scan line.With "listening time" between each group of pulses. Uses a series of pulses & gaps rather than a single pusle
How many elements in an array 128
One pulse hits the beam former at a time but voltage that exits the beam former must have many different Channels or routes to the 128 transducer elements in a single probe
Transmission Channel Each independent delay to a single Element constitutes a channel. Equipment can have 32,64, or 128 channels
Is one that has internal amplitude, frequency or phase modulation used for pulse compression Coded Pulse
The conversion, using a matched filter of a relatively long coded pulse to one of a short duration, excellent resolution & equivalent high intensity sensitivity Pulse compression
Maximizes the signal to noise ratio of the returning signal. The longer the coded pulse the higher will be the signal to noise ration Matched filter implementation
Is chosen to attain adequate axial resolution and intrapulse coding
Is chosen to achieve the desired sensitivity Pulse duration
The matched filter decoding process can be thought of as a Sliding correlation of the parts of the coded pulse with a matched filter
Directs the driving voltage from the pulser to the transducer when the sound is being sent into the body and directs the returning echo voltage from the transducer to the next part of the machine ( amplifier T/R switch
Electrical= voltage
Electrical voltages produced by the pulser are sent/routed to the transducer. The transducer converts electrical pulses to acoustic pulses Route
The sound is reflected off the structures and returns to the transducer in the form of sound echos. The transducer than converts sound energy back to electrical energy Route
After the echoes are converted back to electrical energy, the beam former performs Dynamic Receive Focusing
Additional beam former responsibilities Amplification and compensation
The conversion of the small voltages received from the transducer to large ones. These can survive the remaining portion of equipment. Amplification/Gain
Gain is the ratio of? With units of? Output to Input electrical power & dB
Gain compensates for Attenuation and is responsible for amplification of echos
Input = energy that goes into the amplifer
Output = energy that comes out of the amplifer
Output divided by Input = Gain
The power ratio = the valtage ratio squared
Amplifiers usually have ___ to ____dB of gain 60 to 100
Voltage applied to the amplifier depends on the strength of the returning echo
Useful dB values: 3,10 & 20 dB = 2, 10, 100 x's brighter
Determins how much amplification is accomplished in the beam former Gain control
Creates overall brightening of the image. A decrease in amplification creates an overall darkening of the image Amplification/Gain
Names of compensation Gain, time varied gain (TVG), sensitivity time control ( STC), Most common :Time-gain compensation (TGC), Depth gain compensation (DGC)
Reflectors or echoes from greater depth are attenuated more than echoes from a shorter depth
Compensation Compensates for Attenuation
What is a DGC Slope The rate of increase of gain with depth, corresponds to the attenuation in the tissue.Slope should be 1dB/cm/mhz w/units in dB
The DGC curve is set by the operator. The object of DGC is to achieve uniform Brightness across the image
Time gain compensation is accompished in the bean former
Compensation takes into account reflector Depth
Compensation amplifies echoes differently according to their arrival Times
Compression decreases the ____ range to a range that the ___ & human ____ can handle. Dynamic, display, vision
In some equipment, some amplification is accomplished by a small amplifier in the transducer assembly, which allows less lose of info because the signal is amplified before it enters the cable to the machine Preamplification
Compensation equalizes differences in recieved echo amplitude because of Reflector depth
Controlled by the sonographer Power, amplification,2D Gain, Compensation
Equalizes differences in received echos amplitude because of reflector depth Compensation
After amplification the echo voltages are digitized,they pass through. Analog to digital converters (ADCs)
Analog to digital converters convert the analog voltage representing echos to? Numbers for digital signal processing and storage.
After amplification and digitizing, the echo voltage pass through digital delay lines to accomplish reception dynamic focus & steering functions Echo Delays
After all the channel signal components are delayed properly to accomplish the focus and steering functions, they are added together in the Summer(Adder)
Reception apodization and dynamic aperture functions are accomplished as part of the Summing Process
Is responsible for the electronic beam scanning,steering,focusing, apodization and aperture functions with arrays Beam Former
Created by: yovana2011