Pass Ultrasound Physics Exam Study Guide Review Volume I and II
By
Mansoor Khan MBBS, RDMS, RDCS
©Copyright 2014 Pass Ultrasound Physics Exam Study Guide Review 1
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The Pass Ultrasound Physics Exam Study Guide Review is protected by copyright. No part of this study guide review may be reproduced in any form without written permission from the copyright owner.
Introduction
This Pass Ultrasound Physics Exam Study Guide Review is in easy to understand question and answer format with over 700 questions. This study guide review is designed to help students and sonographers practice and prepare for the questions which appear on the ARDMS Sonography Principles and Instrumentation exam. It is divided into two Volume I and Volume II. The Volume I contains questions and answers from chapters such as Pulse Echo Instrumentation, Ultrasound Transducers, Sound Beam, Bioeffects, Intensity, and Resolution. The Volume II contains questions and answers from chapters such as Pulse Ultrasound Principles, Pulse Echo Principles, Doppler Physical Principles, Hemodynamics, Propagation of ultrasound wave through tissues, Artifacts and Ultrasound Physics Elementary Principles. The material is based on the ARDMS exam outline. It explains the concepts in very simple and easy to understand way. You can increase your chances to pass Ultrasound Physics and Instrumentation SPI exam by memorizing these questions and answers. After studying this study guide review you will feel confident and will be able to answer most of the questions easily which appear on the ARDMS Sonographic Principles and Instrumentation Exam. The Pass Ultrasound Physics Exam Study Guide Notes Volume I & II will be a great compliment to this study guide review and I highly recommend it if you are preparing to sit for ARDMS Sonographic Principles and Instrumentation exam.
Thank You. Mansoor Khan MBBS, RDMS, RDCS
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Table of Contents Pulse Echo Instrumentation .......................................................................................................................... 6 Output Power ............................................................................................................................................ 8 Pulsar....................................................................................................................................................... 12 Beam Former .......................................................................................................................................... 14 Noise ....................................................................................................................................................... 16 Receiver ................................................................................................................................................... 20 Amplification ........................................................................................................................................... 21 Compensation ......................................................................................................................................... 23 Compression ........................................................................................................................................... 29 Dynamic Range ....................................................................................................................................... 30 Demodulation ......................................................................................................................................... 35 Reject ...................................................................................................................................................... 37 Display ..................................................................................................................................................... 39 Display Modes ......................................................................................................................................... 41 Scan Converter ........................................................................................................................................ 43 Ultrasound Transducers .............................................................................................................................. 48 Active Element ........................................................................................................................................ 49 Matching Layer ....................................................................................................................................... 59 Damping Material ................................................................................................................................... 61 Bandwidth ............................................................................................................................................... 64 Quality Factor .......................................................................................................................................... 66 Types of Ultrasound Transducers ............................................................................................................... 72 Mechanical Transducer ........................................................................................................................... 72 Array Transducer ..................................................................................................................................... 74 Linear Sequential Array Transducer ........................................................................................................ 76 Linear Switched Array Transducer .......................................................................................................... 77 Phased Array Transducer ........................................................................................................................ 79 Linear Phased Array Transducer ............................................................................................................. 82 Annular Phased Array Transducer .......................................................................................................... 86 ©Copyright 2014 Pass Ultrasound Physics Exam Study Guide Review 3
Focusing and Steering ............................................................................................................................. 89 Sound Beam ................................................................................................................................................ 97 Huygens' Principle ................................................................................................................................. 103 Bioeffects .................................................................................................................................................. 105 Cavitation .............................................................................................................................................. 106 Mechanical Index .................................................................................................................................. 109 Thermal Index ....................................................................................................................................... 109 Intensity .................................................................................................................................................... 114 Resolution ................................................................................................................................................. 119 Lateral Resolution ................................................................................................................................. 119 Axial Resolution..................................................................................................................................... 121 Temporal Resolution ............................................................................................................................. 126 Pulse Echo Principles ................................................................................................................................. 129 Spatial Pulse Length .............................................................................................................................. 129 Pulse Duration ....................................................................................................................................... 130 Pulse Repetition Period ......................................................................................................................... 132 Pulse Repetition Frequency .................................................................................................................. 134 Duty Factor ............................................................................................................................................ 136 Doppler Instrumentation .......................................................................................................................... 142 Doppler Shift ......................................................................................................................................... 143 Aliasing .................................................................................................................................................. 148 Pulsed Wave Doppler ............................................................................................................................ 150 Continuous Wave Doppler .................................................................................................................... 152 Color Doppler ........................................................................................................................................ 154 Spectral Analysis ................................................................................................................................... 158 Hemodynamics ......................................................................................................................................... 159 Flow ....................................................................................................................................................... 164 Hydrostatic Pressure ............................................................................................................................. 167 Propagation of Ultrasound ....................................................................................................................... 169 ©Copyright 2014 Pass Ultrasound Physics Exam Study Guide Review 4
Attenuation ........................................................................................................................................... 181 Impedance ............................................................................................................................................ 185 Reflection .............................................................................................................................................. 186 Incidence ............................................................................................................................................... 189 Artifacts ..................................................................................................................................................... 197 Ultrasound Physics Elementary Principles ................................................................................................ 213 Frequency ............................................................................................................................................. 217 Period .................................................................................................................................................... 220 Wavelength ........................................................................................................................................... 222 Amplitude .............................................................................................................................................. 225 Power .................................................................................................................................................... 229 Intensity ................................................................................................................................................ 229
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Pulse Echo Instrumentation Q1. Name the components of an ultrasound system? Answer: The components of an ultrasound system are transducer, pulsar, receiver, scan converter, display, and master synchronizer.
Q2. What is the Master Synchronizer? Answer: Master Synchronizer is a component of ultrasound machine which maintains and organizes the proper timing and interaction of all components of the ultrasound machine so that ultrasound system can operate as a single integrated system.
Q3. What is an ultrasound transducer? Answer: The ultrasound transducer is a part of ultrasound machine. It contains a piezoelectric material which converts electrical energy into acoustic energy during the transmission phase, and converts acoustic energy into electrical energy when the echoes return to the transducer after traveling in the body during reception phase.
Q4. What is Channel? Answer: A channel in ultrasound system consists of a single crystal, the beam former, pulsar electronics, and the wire connecting them.
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Q5. What is a receive channel? Answer: Each active element in an ultrasound transducer is connected to an amplifier and processing chain. The amplifier and processing chain are collectively known as the receive channel. There are 256-512 active receive channels are present in ultrasound systems. The benefits of more receive channels in ultrasound systems is greater processing flexibility.
Q6. What is Switch? Answer: Switch in ultrasound system protects the delicate receiver components from the high voltage signals created during pulse creation. It directs low voltage signals from the transducer to the appropriate processing components within the system.
Q7. What is interpolation? Answer: Fill in Interpolation is a technique in which made up pixels are used to fill the areas between the scan lines where there is no information available.
Q8. What is frequency compounding? Answer: Frequency compounding is the technique of imaging with multiple frequencies and averaging them out. Frequency Compounding improves contrast resolution and reduces speckle which improves the image quality.
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Q9. What is Dynamic Frequency Tuning? Answer: Dynamic frequency tuning is a technique in which high frequency portion of the ultrasound pulse is used to create images from the shallow depths, and the low frequency portion of the ultrasound pulse is used to create the images from the greater depths.
Q10. All of the following are components of an ultrasound system except? a. b. c. d. e. f.
transducer pulsar alternator synchronizer display receiver
Answer: c. alternator Alternator is not the component of the ultrasound machine.
Output Power Q11. What does the output power control? Answer: Output power is the amount of voltage applied to the piezoelectric element to produce an ultrasound pulse. Output power controls the amplitude of the voltage that excites the piezoelectric crystals.
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Q12. What is the relationship between pulsar voltage and the returning echo strength and increasing pulsar voltage will have what effect on the image? Answer: There is a direct relationship between pulsar voltage and the returning echo strength. By increasing the pulsar voltage increases the strength of the returning echo signal and increases the brightness of the image.
Q13. What is the range of pulsar output voltage which excites a piezoelectric crystal in the ultrasound transducer? Answer: The strength of pulsar output voltage that excites the piezoelectric crystals ranges from 1-300 volts and lasts less than 1 microsecond.
Q14. What is the range of input voltage signal to the receiver of an ultrasound system? Answer: The signal produced by the transducer upon receiving the returned echoes and sent to the receiver of the ultrasound system is extremely small and is in the micro volt to milli volt range.
Q15. What determines the strength or intensity of the ultrasound wave? Answer: The output power generated by pulsar determines the strength or intensity of the ultrasound wave produced by the transducer. The greater the strength of electrical signal from the pulsar that excites the piezoelectric crystal, the greater the intensity of the ultrasound wave produced.
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Q16. Can sonographer change the output power? Answer: The sonographer can increase or decrease the strength of output power from the pulsar. The different names used for output power control are output gain; transmit output, acoustic power, pulsar power, and energy output.
Q17. What two measurements are used to standardize the output gain? Answer: Thermal index and mechanical index are the two measurements used to standardize the output gain.
Q18. What does ALARA principle mean? Answer: The ALARA stands for As Low As Reasonably Achievable and is related to the output power. During the exam, the sonographer should use minimum possible output power to obtain the images. Sonographer should choose settings that will maximize image quality while minimizing patient exposure to high ultrasound intensity.
Q19. Following ALARA principle, what is the first thing to do if the image is too dark? Answer: Try increasing receiver gain first If the image is too dark, first try to increase the receiver gain. In most of the cases, the image will become bright and will be able to see structures.
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Q20. Following the ALARA principle, what is the first thing to do if the image is too bright? Answer: Try decreasing output gain If image is too bright, first try to decrease the output gain. Decreasing the output gain will decrease the risk of possible bioeffects.
Q21. What is the difference between Output Gain and Receiver Gain? Answer: Output Gain is the amount of voltage applied to the piezoelectric crystal to produce an ultrasound pulse. The strength of the ultrasound wave produced depends upon the strength of the voltage applied to excite the crystal. The stronger the voltage applied the stronger will be the ultrasound wave produced. Output gain improves the signal to noise ratio. Increasing the output gain increases the risk of potential bioeffects. Receiver Gain increases the strength of the small electric voltages received from the transducer to a level suitable for further processing. In amplification process all electrical signals are amplified equally, that’s why amplification or receiver gain increases the brightness of the entire image. There is no risk of bioeffects by increasing the receiver gain.
Q22. What happens by changing the output power gain? Answer: Changing output power gain does the following:
changes brightness of entire image alters signal-to-noise ratio has bioeffect concerns
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Q23. What happens by changing the receiver gain? Answer: Changing receiver gain does the following:
changes brightness of entire image does not affect signal-to-noise ratio no bioeffect concerns
Pulsar Q24. What is a Pulsar? Answer: Pulsar is a component of ultrasound machine which determines amplitude, pulse repetition period and pulse repetition frequency of ultrasound waves. The pulsar functions during transmission.
Q25. What are the functions performed by the pulsar? Answer: The following are the functions performed by the Pulsar:
generates the electrical signals which are applied to the piezoelectric elements controls the timing of electrical signals controls the strength and amplitude of the electrical signal determines the pulse repetition period determines the pulse repetition frequency
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Q26. What control does a sonographer use to modify pulsar voltage? Answer: The sonographer uses output gain control to change pulsar voltage. The output gain control is also known as power, output, transmitter output, acoustic power, pulsar power, and energy output.
Q27. What is the relationship between pulsar voltage and the returning echo strength? Answer: There is a direct relationship between pulsar voltage and the returning echo strength. Increasing the pulsar voltage, increases the strength of the returning echo signals and increases the brightness of the image. Decreasing the pulsar voltage, decreases the strength of the returning echo signal and decreases the brightness of the image.
Q28. How the pulsar determines the pulse repetition period? Answer: The pulsar determines the time between one voltage spike and the next which is called pulse repetition period.
Q29. What type of pulsar generates a constant electrical signal in the form of a sine wave? Answer: In continuous wave transducer, the pulsar generates electrical signals continuously and produces continuous sound waves.
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Q30. What type of pulsar generates a single electrical spike, which creates a single sound pulse? Answer: In pulsed wave transducers, the pulsar generates a single electrical spike, which creates a single sound pulse.
Q31. What type of pulsar generates numerous electrical spikes, which create a single sound pulse? Answer: In phased array transducers, the pulsar generates numerous electrical spikes, which create a single sound pulse.
Beam Former Q32. What is Beam Former? Answer: Beam Former is a component of ultrasound machine. Beam Former receives the electrical voltages from the pulsar during transmission and distributes it to the active elements of a phased array transducer.
Q33. What are two important functions of the beam former? Answer: Beam former creates the appropriate phase delays and pulse sequencing to create the transmit beam and also creates the appropriate phase delays and pulse sequencing to create the receive beam. Beam former also determines the firing delay patterns in phased array transducers for steering and focusing of the ultrasound beam. ©Copyright 2014 Pass Ultrasound Physics Exam Study Guide Review 14
Q34. How the beam former works during transmission? Answer: During transmission, beam former receives the electrical voltage from the pulsar and distributes it to the active elements of a phased array transducer. During transmission, the beam former also adjusts electrical voltages to different PZT crystals to prevent side lobes and grating lobes. It is also called apodization.
Q35. How the beam former works during reception? Answer: During reception, the beam former creates time delays for dynamic receive focusing. It also varies the number of crystals used and controls dynamic aperture.
Q36. What are the advantages of digital beam formers? Answer: The advantages of digital beam former are:
no mechanical parts needed it is software programming and can be updated easily it can be used with wide range of frequencies
Q37. What is Dynamic Aperture? Answer: The beam former varies the number of crystals used in order to control Dynamic Aperture during reception.
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Q38. What is Apodization? Answer: During transmission the beam former adjusts electrical voltages in phased array transducers to prevent grating lobes and side lobes. This process is called Apodization.
Noise Q39. What is Noise? Answer: Noise is low level signals that degrade the image. Noise is random and persistent disturbance that obscures or reduces the clarity of a signal.
Q40. What is the most common method of overcoming noise? Answer: The noise can be reduced by increasing the output power. The signal to noise ratio increases by increasing the output power. Increasing the output power also increases the risk of exposure to possible bioeffects.
Q41. What is Signal to Noise Ratio? Answer: A ratio between original signal and the degraded signal is called signal to noise ratio. Signal to Noise Ratio is a comparison between the amount of meaningful information and contamination in an image. It is amplitude of the signal divided by the amplitude of the noise.
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Q42. To improve image quality, what type of signal-to-noise ratio is desired? Answer: To improve image quality, high Signal-to-Noise Ratio is desired.
Q43. How signal to noise ratio can be improved? Answer: The signal to noise ratio can be improved by:
using a lower frequency transducer moving transmit focus deeper using a larger aperture transducer using a different imaging plane maneuvering to remove attenuators such as lungs and gas using an endocavity probe
Q44. What is the relationship between output power gain and signal to noise ratio? Answer: There is a direct relationship between output power gain and signal to noise ratio. Increasing the output power increases the signal to noise ratio and is a common method of overcoming noise. High signal to noise ratio improves the image quality.
Q45. What is apparent SNR? Answer: When the overall gain is increased, the signal and noise are amplified by the same amount, which gives the appearance of improved signal to noise ratio also called apparent SNR.
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Q46. What is noise floor? Answer: Noise floor is the amplitude level below which the signals are not detected because of the presence of noise. The lower the noise floor the smaller the signals that can be detected.
Q47. What is electronic noise? Answer: The random signals caused by electric amplification of small returning echoes are called electronic noise. Electronic noise is caused by random excitations of electrons within the electronics.
Q48. What does electronic noise looks like in Doppler spectrum, or 2D image? Answer: The electronic noise looks like random white speckles with high receiver gain in Doppler spectrum, or 2D image.
Q49. What does electronic noise looks like in color Doppler? Answer: The electronic noise looks like random color pixels where there is no flow in color Doppler.
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Q50. What is electrical interference? Answer: The electrical interference occurs when the transducer receives energy from other electrical devices or electromagnetic waves such as radio transmission. The electrical interference can be carried through the air or from the power supplying the system.
Q51. How does electrical interference look like on the image? Answer: The electrical interference looks like a bright flashlight down the middle of an image or a barber pole flashing on the image.
Q52. How does electrical interference appear on spectral Doppler spectrum? Answer: The electrical interference appears on spectral Doppler as bright white horizontal or zigzag lines in the spectrum called Doppler tones.
Q53. What is Coded Excitation? Answer: Coded excitation uses a series of pulses and gaps rather than a single pulse. It is a sophisticated form of transmission in which the driving voltage pulses have intrapulse variations in amplitude, and frequency. The advantage of coded excitation is that it improves the signal to noise ratio which improves the image quality.
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Receiver Q54. What is a Receiver? Answer: Receiver is the electronic component of ultrasound machine which processes the electrical signals received from the transducer during the reception phase. The electronic signals produced by returning sound waves are weak. The receiver increases the strength of these weak electrical signals, processes them and transforms them into a suitable form for display as an ultrasound image. Receiver is also known as signal processor.
Q55. What are the five functions performed by the receiver during reception phase? Answer: The five functions performed by the receiver during reception phase are amplification, compensation, compression, demodulation, and reject. All these five functions of the Receiver should be performed in the proper order i.e. amplification, compensation, compression, demodulation, and rejection.
Q56. All of the following are functions of the receiver except? a. b. c. d.
suppression attenuation demodulation amplification
Answer: b. attenuation Attenuation is not the function of the receiver.
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Q57. Place these functions of the receiver in the order? a. b. c. d. e.
compensation demodulation compression amplification reject
Answer: d, a, c, b, e The functions performed in the order are amplification, compensation, compression, demodulation and reject.
Amplification Q58. What is Amplification? Answer: Amplification is the first function of the receiver. The returning echo signals are very weak and produce very weak electrical signals. Amplification increases the strength of these electrical signals received in the transducer to a level suitable for further processing. All electrical signals are made larger equally in the amplification process. Amplification is also called overall gain or receiver gain.
Q59. What is the effect of amplification on signal to noise ratio? Answer: The amplification does not affect the signal to noise ratio because the returning echo signals and noise are amplified equally.
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Q60. Does amplification improve signal to noise ratio? Answer: The amplification does not improve the signal to noise ratio. Both returning echo signals and noise are amplified equally. The signal to noise ratio is improved by increasing the output power.
Q61. Does amplification increase the risk of patient exposure to ultrasound energy? Answer: Amplification does not increase the risk of patient exposure to ultrasound energy. Only the returning echo signals are amplified in the receiver, therefore patient is not exposed to bioeffects of ultrasound energy.
Q62. What is the typical value for amplification of a signal received by the receiver? Answer: The signals that first reach the receiver are extremely weak. The amplification of these signals by receiver ranges from 50 to 100 decibels. This amplification prepares the signal for further processing by the receiver and other ultrasound system components.
Q63. Can sonographer adjust the receiver gain? Answer: The sonographer can increase or decrease the receiver gain. This determines the overall brightness of the image during an exam.
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Q64. What is Pre Amplification? Answer: Pre amplification is the process of improving signal quality before it is amplified. Pre amplification prevents electronic noise from contaminating the small signals received by the transducer. Pre amplification is performed close to the crystal within the transducer during reception.
Q65. An image on an ultrasound system displays echoes from structures in all regions very bright. Which ultrasound machine control will help to decrease the overall brightness of the image? Answer: Decrease the overall amplification or gain. When the amplification or overall gain is set too high the ultrasound system is not able to distinguish between large amplitude and low amplitude echoes and all structures are displayed too bright. By decreasing the overall gain you will be able to differentiate strong reflectors from weak reflectors.
Compensation Q66. What is Compensation? Answer: Compensation is the second function of the receiver. Its function is to compensate for the loss of echo strength caused by the depth of the reflector and create an image which is uniformly bright from top to bottom. The signals are treated differently based on reflector depth. Compensation is also called Time Gain Compensation (TGC) or Depth Gain Compensation (DGC). The unit for compensation is Decibels (dB).
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Q67. What is the effect of compensation on the image? Answer: TGC compensates for attenuation. The purpose of compensation is to produce images of uniform brightness from top to bottom or from near field to far field. Compensation treats echoes differently, depending upon the depth from which they return.
Q68. Describe the process of compensation? Answer: The process of adjusting for attenuation is called compensation. The ultrasound waves become weaker as they travel deep in the body. The sound waves reflected from the deeper regions of body are weak and have low intensity; therefore, the echoes returning from greater depths have lower amplitude than those returning from shallow depths. This process is called attenuation. The process to compensate for the loss of echo strength caused by the depth of the reflector is called compensation. The amplitude of received weak echo signals is increased in the receiver which makes these signals suitable for further processing in ultrasound machine to create an image.
Q69. What is the function of TGC control? Answer: The time gain compensation (TGC, DGC) control adjusts for the attenuation of sound as it propagates through the body.
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Q70. What control will you use when only deep reflectors are displayed, not shallow ones on the image? a. b. c. d.
adjust compensation use higher frequency transducer decrease output power adjust the reject level
Answer: a. adjust compensation Increase the time gain compensation (TGC) in the shallower region. When the structures at shallower depths are not displayed that means TGC is set too low for that regions. The time gain compensation (TGC) or depth gain compensation (DGC) adjusts the brightness of echoes reflected from structures at different depths. Increasing the TGC gain in that area will make structures visible at shallower depths.
Q71. What control will you use when only shallow reflectors are displayed but no deep reflectors on the image? a. b. c. d.
use a higher frequency transducer increase the power output adjust compensation adjust the reject level
Answer: c. adjust compensation Increase the time gain compensation (TGC) in the deeper region. The echoes of structures located in deeper regions are not displayed due to attenuation of sound wave while it travels in the body. When the structures at greater depths are not displayed that means TGC is set too low for that region. Increasing the TGC gain in that area will make weak reflectors visible.
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Q72. The echoes from three structures located at 2 cm, 4 cm, and 6 cm depths appear progressively darker. How does compensation will help to fix this problem? Answer: Time Gain Compensation (TGC) will amplify weak and low intensity echoes returning from structures at 4 cm and 6 cm depths so that they can appear as bright as similar structures located at 2 cm depth. Compensation produces an image of uniform brightness from top to bottom.
Q73. When performing an ultrasound exam why the sonographer needs to use the TGC? Answer: TGC is needed to amplify weak and low intensity echoes returning from deeper structures so that they can appear as bright as similar structures located at more shallow depths.
Q74. When TGC is adjusted which component in the ultrasound system implements the changes? Answer: Receiver When TGC is adjusted the receiver in the ultrasound system implements the changes.
Q75. On a TGC curve, what does the X axis and Y axis represent? Answer: On a TGC curve: X axis represents amount of compensation Y axis represents depth
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Q76. The reflections at superficial depths undergo a small amount of compensation. What is this called on TGC curve? Answer: Near Gain The ultrasound waves at superficial depths attenuate less and need small amount of compensation. On TGC curve this is called near gain.
Q77. On TGC curve the depth at which compensation begins is called what? Answer: Delay On TGC curve, the depth at which compensation begins is called delay. This is the region of minimum amplification and is associated with area close to the transducer. The low frequency transducers are more likely to have longer delay in the TGC curve. A long delay in TGC curve is consistent with less compensation in the area close to the transducer.
Q78. Transducer A has frequency of 5 MHz and transducer B has frequency of 2.5 MHz. Which transducer will have longer delay in TGC curve? Answer: Transducer B will have longer delay in TGC curve. The low frequency transducers are more likely to have longer delay in the TGC curve. A long delay in TGC curve shows less compensation needed in the area close to the transducer.
Q79. As the ultrasound wave travels in the body, it becomes weaker. Compensation increases the strength of returning weak ultrasound waves. What is this area called on the TGC curve? Answer: Slope On TGC curve, the area where compensation corrects for attenuation is called slope.
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Q80. The depth at which maximum compensation is used, what is this area called on TGC curve? Answer: Knee On TGC curve, the area where maximum compensation is used is called knee.
Q81. The area where maximum amount of compensation is used is called what on TGC curve? Answer: Far Gain On TGC curve, the area where maximum amount of compensation is used is called far gain.
Q82. During an exam, sonographer is using a 5 MHz transducer and is given a new transducer to use. The new TGC slope is to the lower left of the old slope. The frequency of new transducer is higher or lower than the old one? Answer: The frequency of new transducer is less than 5 MHz. By using a lower frequency transducer, the ultrasound beam undergoes less attenuation. Therefore, less TGC will be needed to compensate for the attenuation. On the diagram, the TGC curve will be shifted downward and to the left.
Q83. During an exam, sonographer is using a 5 MHz transducer and is given a new one to use. The new TGC slope is to the upper right of the old one. The frequency of new transducer is higher or lower than the old one? Answer: The frequency of new transducer is more than 5 MHz. By using a higher frequency transducer, the ultrasound beam undergoes more attenuation. Therefore, more TGC will be used to compensate for attenuation. On the diagram, the TGC curve will be shifted upward and to the right.
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Q84. In what region of the ultrasound beam TGC is most effective to improve image quality? Answer: TGC is most effective in focal zone area of ultrasound beam in improving image quality. Compensation for attenuation in focal zone area will help to produce superior quality images with detailed information.
Q85. What does the far gain setting on a TGC curve represents? Answer: The far gain setting on a TGC curve represents the maximum compensation that a reflected ultrasound wave undergoes during the compensation process.
Compression Q86. What is Compression? Answer: Compression is the third function of the receiver. Compression decreases the dynamic range of the electrical signals by decreasing the difference between the smallest and largest electrical voltages passing through the system. Compression keeps electrical signals within the operating range of the ultrasound system electronics. Compression is done without altering the relationships between the voltages. The largest electrical voltages stay largest, and smaller electrical voltages remain smallest. Electrical signals are treated differently based on strength. Compression also changes the gray scale mapping and keeps gray scales within the range of what we can see. Compression decreases the dynamic range of the signals and increases the image contrast.
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Q87. What is the function of compression? Answer: The function of compression is to keep electrical signal levels within the range of the electronics of the ultrasound system and keep grayscale content within the range of detection of the human eye.
Dynamic Range Q88. What is Dynamic Range? Dynamic Range is the ratio of the largest to the smallest signal strength or amplitude of a component such as transducer, receiver, scan converter, or display. It is the ratio between the largest signal amplitudes and the smallest signal amplitudes processed by a device. The dynamic range of a signal decreases the more it is processed and is expressed in units of decibels.
Q89. What are the different types of dynamic range? Answer: The different types of dynamic range are input dynamic range, output dynamic range, display dynamic range, and gain dynamic range.
Q90. What is input dynamic range? Answer: The ratio of the maximum input signal to the minimum input signal is called input dynamic range. Input dynamic range is the range of the signal amplitudes a system can receive and process without causing harmonic distortion.
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Q91. What is output dynamic range? Answer: The ratio of the maximum output signal to the minimum output signal is called output dynamic range.
Q92. What is the default dynamic range? Answer: The input dynamic range is the default dynamic range.
Q93. Which component of the ultrasound system has the largest dynamic range? Answer: Within different components of the ultrasound system, the amplifier has the largest dynamic range.
Q94. Which component of the ultrasound system has the lowest dynamic range? Answer: Within different components of the ultrasound system, the display has the lowest dynamic range.
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Q95. What does the dynamic range of the receiver of an ultrasound system refers to? Answer: The dynamic range of the receiver of an ultrasound instrument refers to the range of echo signal amplitudes that can be processed without distortion.
Q96. What is a bit? Answer: A bit is the smallest amount of computer memory. A group of bits is assigned to each pixel in order to store the gray scale color for that pixel. The more bits per pixel, the more shades of gray.
Q97. How to calculate the number of shades of gray in a pixel? Answer: The number of shades of gray in a pixel can be calculated by the following formula. To calculate the number of shades of gray in a pixel, multiply 2 by as many times as there are bits in a pixel. 1 bit per pixel = 2 shades (white and black) 2 bits per pixel = 2 x 2 = 4 shades of gray 3 bits per pixel = 2 x 2 x 2 = 8 shades of gray 4 bits per pixel = 2 x 2 x 2 x 2 = 16 shades of gray 8 bits per pixel = 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 = 256 shades of gray
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Q98. What will result in the greatest number of shades of gray in a digital image display? Answer: Large pixels with many bits per pixel will result in the greatest number of shades of gray in a digital image display. The more bits per pixel the more shades of gray.
Q99. What is the largest number of shades of gray that can be stored with 4 bits in a pixel? Answer: A maximum of 16 shades of gray can be stored with 4 bits in a pixel. To calculate the number of shades of gray in a pixel, multiply 2 by as many times as there are bits in a pixel. There are 4 bits in this pixel, therefore, multiply 2 by itself 4 times. Shades of gray = 2 x 2 x 2 x 2 = 16 shades of gray A pixel with 4 bits will have 16 shades of gray.
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Q100. What is the largest number of shades of gray that can be stored with 8 bits in a pixel? Answer: A maximum of 256 shades of gray can be stored with 8 bits. How to calculate the number of shades of gray in a pixel? 1 bit per pixel = 2 shades (white and black) 2 bits per pixel = 2 x 2 = 4 shades of gray 3 bits per pixel = 2 x 2 x 2 = 8 shades of gray 4 bits per pixel = 2 x 2 x 2 x 2 = 16 shades of gray 8 bits per pixel = 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 = 256 shades of gray
Q101. Two ultrasound systems are used in an ultrasound exam. System A has been assigned 8 bits per pixel; the System B has been assigned 4 bits per pixel. Which ultrasound system will have the ability to display more shades of gray? Answer: The ultrasound system A will have the ability to display more shades of gray. The more bits per pixel the more shades of gray. The pixels with more bits per pixel will result in the greatest number of shades of gray in a digital image display.
Q102. What happens when number of bits assigned to a pixel is increased in an image? Answer: As the number of bits assigned to a pixel are increased in a digital image, the number of shades of gray that can be viewed in an image increase.
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Q103. Can the gray scale be changed by the sonographer? Answer: True. The gray scale can be changed by the sonographer. Compression changes the gray scale mapping. Compression keeps electrical signals within the operating range of the ultrasound system electronics and the gray scale within the range of what we can see. Compression can be adjusted by sonographer therefore gray scale can be changed by the sonographer.
Q104. What is Bistable? Answer: A video display with the ability to show only black and white colors is called bistable.
Demodulation Q105. What is Demodulation? Answer: Demodulation is the process which changes the shape of the electrical signal from one form to another which is more suitable for display. Demodulation is the function of the receiver. Demodulation is done in two steps. These steps are called rectification and smoothing.
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