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Beam Former
| Question | Answer |
|---|---|
| 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
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