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Chapter 14 Edelman
Pulsed Echo Instrumentation
| Question | Answer |
|---|---|
| The two main functions of an ultrasound system | Preparation and transmission of electrical signals to the transducer, which creates a sound beam and Reception of electrical signals from the transducer, with subsequent processing into images |
| The six components of an ultrasound system | Transducer, pulser and beam former, receiver, display, storage, and master synchronizer |
| The pulser | Creates and controls the electrical signals sent to the transducer. The pulser determines the amplitude, pulse repetition period, and pulse repetition frequency |
| The beam former | Determines the firing delay patterns for phased array systems (apodization, steering and focusing). |
| True or false: the sonographer can adjust the magnitude of the pulser's electrical voltage spike, ranging from 0 to nearly 100 volts. | True |
| True or false: changes in pulser voltage modify the brightness of the entire image displayed. | True |
| True or false: when the pulser is set to low voltage, the PZT vibrates gently and transmits a weak sound beam. The reflected echoes are weak, and the entire image is dark. | True |
| Lower pulser voltages are desirable because they decrease transmitted acoustic energy and minimize the likelihood of what? | Bioeffects or tissue damage |
| Noise describes what? | Random and persistent disturbance that obscures or reduces a signal's clarity. |
| When SNR is high | The image is good (the signal is much stronger than the noise) |
| When SNR is low | The image is poor (the strength of the signal is close to the strength of the noise) |
| When transducer output is low | Noise is more likely to degrade the image. |
| As output power is increased | SNR increases and the image improves |
| True or false: increasing output power is the most common way to improve SNR | True |
| The pulser controls output power and what else? | The time between one voltage spike and the next or PRP |
| Beam former or digital beam former | Receives the pulser's single electrical spike and distributes it to the numerous active elements of an array transducer |
| The beam former also adjusts electrical spike voltages to reduce lobe artifacts in a process called | Apodization |
| True or false: the beam former works during both transmission and reception | True |
| True or false: the beam former also controls dynamic receive focusing and dynamic aperture by varying the number of crystals used | True |
| True or false: to protect the delicate receiver components of the transducer, the beam former uses a "switch" to direct electrical signals | True |
| A channel is made up of what three things? | A single PZT element, the electronics in the beam former/pulser and the wire that connects them |
| True or false: most systems have between 32 and 256 channels | True |
| The receiver | Transforms the electrical signals from the transducer (produced by reflected sound) into a form suitable for display |
| Order of receive operations: | 1. amplification 2. compensation 3. compression 4. demodulation 5. reject |
| The first function of the receiver is amplification, also called receiver gain. In the amplification process, each electronic signal returning from the transducer is _______ _________. | Made larger |
| Why is amplification required? | Because the electrical signals are too low to be displayed on the monitor. |
| True or false: all electrical signals in the receiver are affected identically by amplification. Thus, SNR is not improved through amplification. | True |
| Amplification is measured in units of what? | Decibels |
| The master synchronizer | Works with all the different components to make sure they all work together and at the right time |
| During transmission, the transducer takes ________energy and turns it into ________ energy. | Electrical; acoustic. This is called the reverse piezoelectric effect |
| During reception, the transducer takes _______ energy and turns it into _________ energy. | Acoustic; electrical. This is called the piezoelectric or ferroelectric effect. |
| TI | Thermal index (related to the liklihood of bioeffects, which is the increase in temperature of human tissue) |
| MI | Mechanical Index (related to the liklihood of thermal effects) |
| Signal strength is measured in what? | Decibels |
| Compensation is the second function of the receiver. W/o compensation every US image would become progressively darker with increasing depth. Compensation is controlled with what? | TGC's (time-gain compensation) |
| Compression is the third function of the receiver. It occurs how many times? | Twice |
| The second part of compression does what? | Compresses the gray scale to within what the human eye can detect, which is 20 shades of gray |
| Demodulation takes the electrical signals of the returning sound wave and turns it into something that can be ________ __ _____ _________. | Viewed on the monitor |
| This part of demodulation converts all negative voltages into positive voltages. | Rectification |
| This part of demodulation places a smooth line around the "bumps" and evens them out. | Smoothing or enveloping |
| Reject | |
| Does output power improve SNR? | Yes |
| Does receiver gain (also called amplification) alter SNR? | No |
| If an entire image is too bright, what should you do first? | Reduce output power |
| If an entire image is too dark, what should you do first? | Increase receiver gain |
| What does ALARA stand for? | As low as reasonably achievable. And it refers to when modifications to either output power or receiver gain need to be made, the first choice should be the one that will minimize the patient's US exposure. |
Created by:
gillybruursema
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