Understanding Sound Waves: Axes, Relationships, and Acoustic Parameters, Exams of Medical Sciences

Download Understanding Sound Waves: Axes, Relationships, and Acoustic Parameters and more Exams Medical Sciences in PDF only on Docsity! ARDMS- SPI Rated 100% Correct. The horizontal axis, or x-axis - Correct Answer Runs side to side The vertical axis, or y-axis - Correct Answer Runs up and down Unrelated - Correct Answer Two items that are not associated Related or Proportional - Correct Answer Two items that are associated or affiliated However, the relationship between the items does not have to be specified Directly related or Directly proportional - Correct Answer Two items that are associated such that when one item increases, the other increases Inversely related or inversely proportional - Correct Answer Two items are associated such that when one item increases, the other decreases Reciprocal Relationship - Correct Answer When two numbers with a reciprocal relationship are multiplied together, the result is one Reciprocal numbers are inverse because when one increases, the other decreases For a numerical answer to a question to be comprehensive, it requires a - Correct Answer Unit "Increase by a factor" means - Correct Answer To multiply by that number "Decrease by a factor" means - Correct Answer To divide by that number Scientific or engineering notation is a shorthand manner to represent what types of numbers? - Correct Answer Very large or very small numbers A number in scientific notation form with a positive exponent has a value - Correct Answer Greater than 10 A number in scientific notation form with an exponent of zero has a value - Correct Answer Between 1 and 10 A number in scientific notation form with a negative exponent has a value - Correct Answer Less than 1 10⌃9 - Correct Answer Prefix: giga Symbol: G Meaning: billion 10⌃6 - Correct Answer Prefix: mega Symbol: M Meaning: million 10⌃3 - Correct Answer Prefix: kilo Symbol: k Meaning: thousand 10⌃2 - Correct Answer Prefix: hecto Symbol: h Meaning: hundred 10⌃1 - Correct Answer Prefix: deca Symbol: da Meaning: ten 10⌃-1 - Correct Answer Prefix: deci Symbol: d Meaning: tenth 10⌃-2 - Correct Answer Prefix: centi Symbol: c Meaning: hundredth 10⌃-3 - Correct Answer Prefix: milli Symbol: m Meaning: thousandth 10^-6 - Correct Answer Prefix: micro Symbol: μ Meaning: millionth 10^-9 - Correct Answer Prefix: nano Symbol: n Meaning: billionth List all these metric terms in increasing order: A. mega B. micro C. milli D. hecto E. deca Some parameters are determined by the tissue through which the sound is traveling, also called a __________. - Correct Answer Medium What is period? And what is it determined by? - Correct Answer The time it takes a wave to vibrate a single cycle, or the time from start of a cycle to the start of the next cycle It is determined by the source What is frequency? And what is it determined by? - Correct Answer The number of cycles that occurs in one second Determined by the sound source only 1 cycle/second = - Correct Answer 1 Hertz If the frequency of a sound wave is less than _____, it is below the threshold of human hearing and cannot be heard. These are defined as ____________. - Correct Answer 20 Hz, infrasonic Audible sound waves that humans can hear are frequencies between _______________________. - Correct Answer 20 Hz and 20,000 Hz What is ultrasound's frequency? - Correct Answer Greater than 20,000 Hz or 20 kHz Why is frequency important in diagnostic sonography? - Correct Answer It affects penetration and image quality Period and frequency are __________ related to each other. - Correct Answer Inversely When two reciprocal parameters are multiplied together, the result is: - Correct Answer 1 What three parameters describe the size, or magnitude, or strength of a sound wave? - Correct Answer Amplitude, power, intensity What is Amplitude? - Correct Answer The "bigness" of a wave. It is the difference between the maximum value and the average or undisturbed value of an acoustic variable Also the difference between the minimum value and the average value of the acoustic variable What is Amplitude determined by? And is it adjustable? - Correct Answer Initially, amplitude is determined only by the sound source, however amplitude decreases as sound propagates through the body (attenuation) Yes, a control on ultrasound systems allows the sonographer to alter initial amplitude What is the difference between amplitude and peak-to-peak amplitude? - Correct Answer Amplitude is measured from the middle value to the maximum value. Peak-to- peak amplitude is the difference between maximum and minimum values of an acoustic variable Peak-to-peak is twice the value of the amplitude What is power? - Correct Answer The rate of energy transfer or the rate at which work is performed. Power, like amplitude, describes the "bigness" of the wave What is power determined by? And can it be changed? - Correct Answer Determined by the sound source only It CAN be changed How are amplitude and power related? - Correct Answer Both describe the size, or magnitude of a wave. When power increases, so does amplitude Power is proportional to... - Correct Answer amplitude^2 What is intensity? - Correct Answer The concentration of energy in a sound beam Intensity = Power/area What is intensity determined by? And is it adjustable? - Correct Answer Sound Source Yes, it is adjustable How is intensity related to power and amplitude? - Correct Answer Intensity is proportional to power Intensity is proportional to amplitude^2 What is the distance or length of one complete cycle called? - Correct Answer Wavelength What is wavelength determined by? And is it adjustable? - Correct Answer Both the medium and source No, it is not adjustable What is the relationship between wavelength and frequency? - Correct Answer As long as a wave remains in one medium, wavelength and frequency are inversely related As frequency increases, wavelength decreases. The lower the frequency, the longer the wavelength What is the wavelength of 1 MHz sound in soft tissue? - Correct Answer 1.54 mm What is the wavelength of other frequency sound waves in soft tissue? - Correct Answer Sound with a frequency of 2 MHz has a wavelength of 0.77 mm in soft tissue. 1.54mm/2 = 0.77 mm What is the wavelength equation? - Correct Answer wavelength = (1.54mm/μsec)/(frequency) Why is wavelength important in diagnostic ultrasound? - Correct Answer Wavelength plays an important role in image quality Shorter wavelength sound usually produces higher quality images with greater detail (higher frequency) What is the distance that a sound wave travels through a medium in 1 second called? - Correct Answer Propagation Speed What does the speed of sound range from? - Correct Answer 500m/s to 4000m/s What is Propagation Speed determined by? And is it adjustable? - Correct Answer The Medium No, it is not adjustable What is the speed of sound in soft tissue? - Correct Answer 1,540 m/s 1.54 mm/μsec 1.54 km/s 1 mile per second What has the slowest propagation speed? And the longest? - Correct Answer Slowest: Lung (Air, Gas) Longest: Bone What is the speed of sound in Blood? - Correct Answer 1,560 m/s What is the order for speed of sound from lowest to highest in Water, Metals, and Air? - Correct Answer Air, Water, Metals What determines the speed of sound in that medium? - Correct Answer Stiffness, density What describes the ability of an object to resist compression? - Correct Answer Stiffness; A stiff material will retain its shape if it is squeezed; whereas a non-stiff material will change its shape How does stiffness affect speed? - Correct Answer Stiffness and Speed are directly related As materials become stiffer, the speed of sound in the material increased Non-stiff media are described as... - Correct Answer Elastic or compressible What describes the relative weight of a material? - Correct Answer Density The effects of sound waves on tissue in the body are called __________. - Correct Answer Bioeffects Which of the following are considered acoustic variables? Frequency, density, particle motion, temperature, period, and pressure - Correct Answer Density, particle motion, and pressure Which of the following are considered acoustic parameters? frequency, density, distance, pressure, and period - Correct Answer Frequency and period The effects of tissue on sound waves are called _________ _________ ____________. - Correct Answer Acoustic Propagation Properties The effects of a medium on an ultrasound wave are called _________ ____________ _________. - Correct Answer Acoustic Propagation Properties How are frequency and period related? - Correct Answer Inversely How are amplitude and power related? - Correct Answer Directly How are amplitude and intensity related? - Correct Answer Directly How are power and intensity related? - Correct Answer Directly How are wavelength and intensity related? - Correct Answer Unrelated How are wavelength and frequency related? - Correct Answer Inversely How are acoustic velocity and density related? - Correct Answer Inversely How are elasticity and speed of sound related? - Correct Answer Inversely How are acoustic velocity and compressibility related? - Correct Answer Inversely How are stiffness and sound speed related? - Correct Answer Directly How are frequency and sound speed related? - Correct Answer Unrelated How are frequency and intensity related? - Correct Answer Unrelated How are power and frequency related? - Correct Answer Unrelated What are the five parameters to describe pulsed sound? - Correct Answer Pulse duration, pulse repetition period, pulse repetition frequency, duty factor, and spatial pulse length What is pulsed ultrasound? - Correct Answer A pulse of an ultrasound is a collection of cycles that travel together. The entire pulse moves as a single item What are the two components of pulsed ultrasound? - Correct Answer Transmit, talking, or "on" time Receive, listening, or "off" time What is the actual time from the start of pulse to the end of that pulse called? - Correct Answer Pulse duration (a single "on" time) What is pulse duration determined by? And can it be adjusted? - Correct Answer Sound source, NO Pulse duration (μsec) = - Correct Answer # cycles x period (μsec) or #cycles/frequency (MHz) Pulse duration is directly proportional to ___________. - Correct Answer # cycles in a pulse and to period Pulse duration is ____________ proportional to frequency. - Correct Answer Inversely What creates pulses of long duration? - Correct Answer Many cycles in the pulse, and individual cycles with long periods What creates pulses of short duration? - Correct Answer Few cycles in the pulse, and individual cycles with short periods Which type of pulse duration is more desirable in diagnostic imaging? - Correct Answer Shorter duration pulses are desirable for imaging because they create images of greater accuracy What is Spatial Pulse Length? - Correct Answer The distance that a pulse occupies in space from the start to the end of a pulse. What determines Spatial Pulse Length? And is it adjustable? - Correct Answer Both the source and the medium. No it is not adjustable. Spatial Pulse Length (mm) = - Correct Answer # cycles x wavelength (mm) Spatial Pulse Length is _________ proportional to frequency. - Correct Answer Inversely What is the difference between pulse duration and pulse length? - Correct Answer Pulse duration is the TIME that a pulse in "on" pulse length is the DISTANCE of the pulse end to end Two characteristics that create long pulses are: - Correct Answer Many cycles in the pulse Cycles with longer wavelengths Two characteristics that create short pulses are: - Correct Answer Fewer cycles in the pulse Cycles with shorter wavelengths Which types of pulse length is more desirable in diagnostic imaging? - Correct Answer Shorter pulses are desirable because they create more accurate images What is the time from start of one pulse to the start of the next pulse called? - Correct Answer Pulse Repetition Period Pulse Repetition Period is determined by the ___________ _________ that the sonographer selects. - Correct Answer Imaging depth What is PRP determined by? And is it adjustable? - Correct Answer Sound Source Yes, it is adjustable When the system is imaging at shallow depths, the time from one pulse to the next is __________. - Correct Answer Short What is depth of view? - Correct Answer The maximum distance into the body that an ultrasound system is imaging How are PRP and depth of view related? - Correct Answer Directly related What are the two components of pulse repetition period? - Correct Answer Transmit time (pulse duration) and the receive time Which component of PRP can the sonographer change? - Correct Answer Receive time or "listening time" (alter the depth of the image) What is pulse repetition frequency? - Correct Answer The number of pulses that an ultrasound system transmits into the body each second What is the PRF determined by? And is it adjustable? - Correct Answer Sound Source, Yes What is the duty factor if the pulse duration is 1 millisecond, and the pulse repetition period is 1 second? - Correct Answer The duty factor is 0.001 or 0.1% (0.001 divided by 1.0 = 0.001) What is Intensity? - Correct Answer A beam's power divided by its area What is temporal intensity? - Correct Answer Refers to all time, transmit (pulse duration) and receive What is pulsed intensity? - Correct Answer The average intensity for the pulse duration only What does spatial refer to? - Correct Answer Location or space. What is the beam's intensity at the location where it is maximum called? - Correct Answer Spatial peak intensity The average intensity across the beam's entire cross-sectional area is called ____________. - Correct Answer Spatial average intensity Spatial peak intensity is always _______ than the spatial average. - Correct Answer Higher The term temporal refers to ______. - Correct Answer Time Measuring the intensity of the beam at the instant in time of its maximal value is called the _________________. - Correct Answer Temporal peak intensity What is SPTP? - Correct Answer Measured at the location where intensity is maximum (highest value intensity) What is SPPA? - Correct Answer Measured at the location where intensity is maximum, averaged over the transmit time (pulse duration) What is SPTA? - Correct Answer Measured at the location where intensity is maximum and averaged over all time, both the transmit and receive times (Used to test for bioeffects) What is SATA? - Correct Answer Measured over the entire cross-sectional area of the sound beam, and over all time (lowest value intensity) All intensities have units of __________. - Correct Answer W/cm^2 What is the number that describes the spread of a beam in space called? - Correct Answer The Beam Uniformity Coefficient (SP/SA factor) Unitless with a value of 1 or greater What describes the relationship of beam intensities with time? - Correct Answer Duty factor For continuous wave ultrasound, the beam is always "on" and the pulse average and temporal average intensities are ____________. - Correct Answer The same SPTA = SPPA and SATA = SAPA When pulsed and continuous wave sound beams have the same SPTP intensities, the __________ wave beam has the higher SPTA intensity. - Correct Answer Continuous When pulsed and continuous wave sound beams have the same SATP intensities, the __________ wave beam has the higher SATA intensity. - Correct Answer Continuous ________ average intensity is averaged only during the pulse duration ("on" time). - Correct Answer Pulse ________ average intensity is averaged during the PRP (both the "on" and "off" times) - Correct Answer Temporal The rank of intensities from largest to smallest is: - Correct Answer SPTP -> SPPA -> SPTA -> SATA As sound travels in the body, it weakens, or __________. - Correct Answer Attenuates After a sound wave is received by the transducer, converted into electricity and returned to the ultrasound system, it is strengthened or __________. - Correct Answer Amplifide When a waves intensity doubles, the relative change is... - Correct Answer +3 dB When the intensity increases 10-fold, the relative change is... - Correct Answer +10 dB. When the intensity is reduced to 1/2 its original value, the relative change is... - Correct Answer -3 dB. When the intensity is reduced to 1/10 its original value, the relative change is... - Correct Answer -10 dB. A reduction in the intensity of a sound beam to one-half of its original value is _____ dB. - Correct Answer -3 dB A reduction in the intensity of a sound beam to one-quarter of its original value is _____ dB. - Correct Answer -6 dB -10 dB means that the intensity is reduced to ______ of its original value. - Correct Answer One-tenth dB is a mathematical representation with a _________ and _____________ scale. - Correct Answer Logarithmic and relative True or False. We need one intensity to calculate decibels. - Correct Answer False A waves intensity is 2 mW/cm^2. There is a change of +9 dB. What is the final intensity? - Correct Answer 16 Mw/cm^2 Every dB change means that the intensity will ______. - Correct Answer Double Every 10 dB change means that the intensity will _______. - Correct Answer Increase ten times If the final intensity of a sound beam is more than the initial intensity, then the gain in dB is ________ . - Correct Answer Positive If the initial intensity of a sound beam is less than the final intensity, then the gain in dB is _______. - Correct Answer Positive What is attenuation determined by? - Correct Answer Path length, and frequency of sound Distance and Attenuation are ___________ related. - Correct Answer Directly Frequency and Attenuation are _________ related. - Correct Answer Directly As sound strikes a boundary, a portion of the wave's energy may be redirected, or _________, back to the sound source. - Correct Answer Reflected Reflection is likely to occur when... - Correct Answer The boundary is large What is specular reflection? - Correct Answer When the boundary is smooth, the sound is reflected in only one direction in an organized manner What is diffuse reflection? - Correct Answer When a wave reflects off an irregular surface, it radiates in more than one direction (also called backscatter) What are the advantages and disadvantages of diffuse reflection? - Correct Answer Advantage: interfaces as suboptimal angles to the sound beam can still produce reflections that the transducer will receive Disadvantage: the backscattered reflections will have a lower strength than specular reflections As frequency decreases, depth of penetration _________. - Correct Answer Increases As path length increases, the half boundary layer __________. - Correct Answer Remains the same Impedance is a characteristic of ___________. - Correct Answer Only the medium As the path length increases, the attenuation coefficient of ultrasound in soft tissue __________. - Correct Answer Remains the same Acoustic impedance = ________ x _____________. - Correct Answer Impedance = density (kg/m^3) x propagation speed (m/s) Two media A and B have the same densities. The speed of sound in medium A is 10% higher than in medium B. Which medium has the higher acoustic impedance? - Correct Answer Medium A Impedance is important in _______ at boundaries. - Correct Answer Reflections Which is better to use while examining a carotid artery., a 7.5 or 3.0 MHz transducer? - Correct Answer 7.5 MHz transducer (superficial) What are the three types of angles? - Correct Answer Acute - <90 degrees Right - exactly 90 degrees Obtuse - >90 degrees All angles that do not equal 90 degrees are called _________ angles. - Correct Answer Oblique What does normal incidence mean? - Correct Answer The incident sound beam strikes the boundary at exactly 90 degrees. (also called: perpendicular, orthogonal, right angle) What is an oblique incidence? - Correct Answer When the incident sound beam strikes the boundary at any angle other than 90 degrees What is the sound wave's intensity immediately before it strikes a boundary called? - Correct Answer Incident intensity What is reflected intensity? - Correct Answer The intensity of the portion of the incident sound beam that, after striking a boundary, continues forward in the same general direction it was traveling incident (starting) intensity = - Correct Answer Reflected intensity + transmitted intensity What is the intensity reflection coefficient (IRC)? - Correct Answer The percentage of the intensity that bounces back when a sound beam strikes the boundary between two media What is the intensity transmission coefficient (ITC)? - Correct Answer The percentage of ultrasound intensity that passes in the forward direction when the beam strikes an interface between two media IRC (%) + ITC (%) = - Correct Answer 100% A sound wave with intensity of 50 W/cm^2 strikes a boundary and is totally reflected. What is the intensity reflection coefficient? - Correct Answer 100% A sound wave with intensity of 50 W/cm^2 strikes a boundary and is totally reflected. What is the reflected intensity? - Correct Answer 50 W/cm^2 IRC (%) = - Correct Answer (Z2-Z1/Z2+Z1)^2 x 100 If the two media have identical impedances, there will be... - Correct Answer No reflection If two media have slightly different impedances, there will be... - Correct Answer A small reflection If two media have substantially different impedances, there will be... - Correct Answer A large reflection A pulse of ultrasound is propagating in soft tissue, such as liver. The pulse strikes a boundary with a different soft tissue at normal incidence. What portion of the intensity is reflected back toward the transducer? Why? - Correct Answer A very small percentage of sound, typically less than 1%, is reflected at a boundary between two soft tissues Very little reflection occurs when the impedances have similar, but not identical, values Sound is traveling in a medium and strikes a boundary with normal incidence. If 63% of the wave's intensity is reflected back toward the transducer what percentage is transmitted? - Correct Answer 37% ITC (%) = - Correct Answer (transmitted intensity/ incident intensity) x 100 or 1 - intensity reflection coefficient Sound is traveling from bone to soft tissue. The impedances of the media differ significantly, and 90% of the beam's intensity is reflected. What percentage of the intensity is transmitted? - Correct Answer 100% of the energy must be accounted for If 90 % is reflected 10% must be transmitted In ___________ incidence, it is complicated to tell whether the sound ill reflect or transmit after striking a boundary. - Correct Answer Oblique What two principles always apply to reflection with oblique incidence? - Correct Answer Conservation or energy reflection angle = incident angle incident intensity (W/cm^2) = - Correct Answer reflected intensity + transmitted intensity angle of incidence = - Correct Answer angle of reflection If the sound beam bends or changes direction after is strikes an interface at an oblique angle, this is called... - Correct Answer refraction What is refraction? - Correct Answer a change in direction of wave propagation when traveling from one medium to another. Refraction only occurs if two conditions are satisfied: - Correct Answer oblique incidence (not normal) and propagation speeds of the two media are different What is snell's law? - Correct Answer sin(transmission angle)/sin (incident angle) = speed of Medium 2/speed of Medium 1 Under what conditions will the transmission angle equal the incident angle? - Correct Answer if the two media are the same Under what conditions will the transmission angle be greater than the incident angle? - Correct Answer when medium 2 is greater than medium 1 Under what conditions will the transmission angle be less than the incident angle? - Correct Answer when medium 2 is less than medium 1 A pulse of ultrasound propagates in soft tissue, such as liver. The pulse strikes a soft tissue - soft tissue interface with oblique incidence. Some of the sound energy is transmitted. To what extent is the transmitted beam refracted? - Correct Answer The transmitted beam undergoes little to no refraction. A transmitted beam is refracted when the incidence is oblique and the propagation speeds are different. A sound wave strikes a boundary at normal incidence. The impedances of the two media are identical. What percentage of the sound wave is refracted? - Correct Answer 0%, refraction cannot occur with normal incidence What property has units of rayls? How is it determined? - Correct Answer Impedance Impedance = density x speed The more cycles in a pulse, the _______ the numerical value of the range resolution is. - Correct Answer greater If a new pulsed transducer has many more cycles in its pulse, the image accuracy ________. - Correct Answer degrades _____ frequency transducers generally have the best range resolution. - Correct Answer high In soft tissue, a 3 cycle, 1 MHz pulse has a length of a pulse is 4.5 mm. What is the axial resolution? - Correct Answer 2.25 mm. Two different transducers create sound pulses. One transducer is labeled 5 MHz and the other, 3 MHz. Which transducer is more likely to create a more accurate image with relation to axial resolution? Which transducer probably has a lower numerical measure of axial resolution? - Correct Answer The 5 MHz transducer. The higher frequency transducer creates a shorter pulse and thus has a lower numerical measure of axial resolution. Lower numbers mean improved image quality. Wha happens during transmission? - Correct Answer electrical energy from the system is converted into sound What happens during reception? - Correct Answer the reflected sound pulse is converted into electricity What is the piezoelectric effect? - Correct Answer the property of certain materials to create a voltage when they are mechanically deformed What is the reverse piezoelectric effect? - Correct Answer when a voltage is applied to piezoelectric materials, they change shape What are the materials that change sound into electricity (and vice versa)? - Correct Answer piezoelectric or ferroelectric What materials are commonly used in clinical transducers? - Correct Answer lead zirconate titanate (PZT) also known as ceramic, active element, or crystal What are the 7 components of a basic transducer? - Correct Answer case, electrical shield, acoustic insulator, PZT or active element, wire, matching layer, and backing material (also called the damping element) What is the case? - Correct Answer the cylindrical tube, constructed of metal or plastic, that protects the internal components of the transducer from damage. What is the electrical shield? - Correct Answer Thin metallic barrier lining the inside of the case. What is acoustic insulator? - Correct Answer A thin barrier of cork or rubber that isolates or "uncouples" the internal components of the transducer from the case. Prevents vibrations in the case from inducing an electrical voltage in the PZT of the transducer. What is the wire? - Correct Answer Provides an electrical connection between PZT and the ultrasound system. What is the matching layer? - Correct Answer increases the efficiency of sound energy transfer between the active element and the body, and protects the active element What is the backing material (or damping element)? - Correct Answer bonded to the back of the active element, it reduces the "ringing" of the pulse. The matching layer and gel _________ the efficiency of sound transfer between the transducer's PZT and the skin. - Correct Answer increase How thick are the matching layer and the active element of a basic ultrasound transducer? - Correct Answer The thickness of the matching layer is one quarter of the wavelength of sound in the matching layer. The thickness of the active element is one-half of the wavelength of sound in the active element. What are the characteristics of damping material? - Correct Answer high degree of sound absorption, and acoustic impedance similar to PZT. What are additional consequences related to the use of a backing material? - Correct Answer decreased sensitivity wide bandwidth low quality factor What does decreased sensitivity mean? - Correct Answer the transducers with damping material are less able to convert low-level sound reflections into meaningful electrical signals during reception. What is bandwidth? - Correct Answer the range, or difference, between the highest and lowest frequencies in the pulse. Thus, imaging probes are identified as short pulse, wide bandwidth. Long duration events are _______ bandwidth, whereas short duration events are _______ bandwidth. - Correct Answer narrow, wide quality factor = - Correct Answer main frequency/bandwidth A shorter pulse has a _________ Q-factor. - Correct Answer lower A longer pulse has a ______ Q-factor. - Correct Answer higher How is PZT created? - Correct Answer created by exposing the material to a strong electrical field while being heated to a substantial temperature. (polarization) What is the Curie temperature, and what is its importance? - Correct Answer the temperature that the PZT is polarized is called the Curie temperature or Curie point. If the polarized PZT is heated above the Curie temperature, the crystal's piezoelectric properties are destroyed. (depolarized) What is the difference between sterilization and disinfection? Which method is used on transducers? - Correct Answer Sterilization is the destruction of all microorganisms by exposure to extreme heat, chemical agents, or radiation. Disinfection is the application of a chemical agent to reduce or eliminate infectious organisms on an object. Ultrasound transducers only require disinfection. Pulse length is ______ related to pulse duration. - Correct Answer directly Q-factor is ___________ related to bandwidth. - Correct Answer inversely Pulse duration is __________ related to bandwidth. - Correct Answer inversely T or F. Shorter duration events (such as dampened pulses) are more likely to be wide bandwidth. - Correct Answer True. What occurs when a PZT crystal's temperature is elevated above the Curie point? - Correct Answer the PZT is depolarized In a continuous wave transducer, electrical frequency = - Correct Answer acoustic frequency The frequency of sound emitted by a continuous wave transducer is determined by what? - Correct Answer the frequency of the electrical signal created by the ultrasound system What characteristics of the active element determine the frequency of sound created by a pulsed wave transducer? - Correct Answer speed of sound in the PZT and the thickness of the PZT How does the speed of sound in PZT affect frequency? - Correct Answer in a pulsed wave transducer, the speed of sound in PZT and the frequency of sound are directly related. When the speed of sound in PZT is faster, the frequency of sound created by a pulsed wave transducer is higher. At the starting point, the beam width is... - Correct Answer exactly the same as the transducer diameter. What are the five terms that describe the shape and regions of a sound beam? - Correct Answer focus, near zone, focal length, far zone, focal zone Where is the beam narrowest? - Correct Answer focal point (one-half the width of the beam as it leaves the transducer) What is the near field? Another name for it? - Correct Answer the region from the transducer to the focus, fresnel zone What is the focal length or NZL? - Correct Answer the distance from the transducer to the focus What is the far zone? Another name for it? - Correct Answer the region starting at the focus and extending deeper, fraunhofer zone At depths more than two bear zone lengths, the beam is _______ than the active element. - Correct Answer wider What is the focal zone? - Correct Answer a region around the focus where the beam is relatively narrow and image detail is superior (half located in near and other half located in far) The focus marks the end of the _________. - Correct Answer near zone At the depth of the focus, the sound beam starts to __________ or widen, which marks the beginning of the ____________ zone. - Correct Answer diverge, far (Fraunhofer) At depths more than twice the focal length, the beam's width __________ that of the transducer. - Correct Answer exceeds Adjustable focus systems are called ______________. - Correct Answer Phased array What characteristics of a fixed-focus transducer determine the focal depth? - Correct Answer transducer diameter and frequency of the sound How does transducer diameter affect the focal depth? - Correct Answer increasing diameter results in a deeper focus; therefore, transducer diameter and focal depth are directly related. (beams from larger diameter active elements will have deeper focus) How does frequency affect focal depth? - Correct Answer Higher frequency sound results in a deeper focus; therefore, frequency and focal depth are directly related Even with high frequency sound, an extremely small diameter locates the focus ___________. - Correct Answer shallower focal depth (cm) = - Correct Answer diameter (mm)^2 x frequency (MHz)/61.6 or diameter (mm)^2/40 x wavelength (mm) A pair of 6 MHz probes are identical except for active element diameter. The active element diameters are 6mm and 10mm, respectively. The sound beam of which probe will have a shallower focus? - Correct Answer 6mm active element. Smaller diameter crystals produce beams with shallower foci. A pair of 9 mm diameter probes are identical except for frequency, which is 3 MHz and 6 MHz, respectively. Which beam will have a shallower focus? - Correct Answer 3 MHz beam. (focal depth increases with increasing frequency) True or False. Transducer frequency and near zone length are inversely related. - Correct Answer False. (directly related) True or False. Wavelength and near zone length are inversely related. - Correct Answer True True or False. Active element diameter and near zone length are directly related. - Correct Answer True Beam divergence describes... - Correct Answer the gradual spread of the ultrasound beam in the far field. How does transducer diameter affect beam divergence in the far field? - Correct Answer Smaller diameter crystals produce beams that spread out, or diverge, more in the far zone. (crystal diameter and beam divergence are inversely related) Larger diameter crystals produce beams that diverge less in the far field Larger diameter crystals and higher frequency sound improve ______________ in the far field. - Correct Answer lateral resolution How does frequency alter beam divergence in the far field? - Correct Answer Lower frequency sound beams spread out or diverge more in the deep far zone. (frequency and beam divergence are inversely related) A pair of 6 MHz probes are identical except for active element diameter, which is 6 mm and 10 mm, respectively. Which beam will be more compact in the far field? - Correct Answer 10mm active element has a less divergent beam. (larger diameter crystals produce beams that diverge less in the far field) A pair of 9 mm diameter probes are identical except for frequency, which are 3 MHz and 6 MHz. Which sound beam will spread out more in the far field? - Correct Answer 3 MHz beam is more divergent. (beams are more compact as frequency increases) True or False. Transducer frequency and beam divergence are inversely related. - Correct Answer True. True or False. Active element diameter and beam divergence are inversely related. - Correct Answer True. What are sound waves are produced by? What shape do they diverge in? - Correct Answer tiny pieces of PZT, V-shape When is the V-shaped wave created? And what are they called? - Correct Answer when the source is about the size of the sound's wavelength. Called spherical waves, diffraction patterns, or HUYGEN'S wavelets Huygen's principle states... - Correct Answer that a large active element may be thought of as millions of tiny, distinct sound sources. Where does destructive interference occur? - Correct Answer in the areas where the sound beam is absent What does resolution refer to? - Correct Answer accuracy in imaging Lateral resolution distinctly identifies two structures that are very close together when they are _________ to the sound beam. - Correct Answer perpendicular What is lateral resolution determined by? - Correct Answer the width of the sound beam (narrower beams have better resolution) Synonyms to lateral resolution are: - Correct Answer angular, transverse, azimuthal resolution (LATA) Where is lateral resolution best? - Correct Answer at the focus where the beam is narrowest. lateral resolution (mm) = - Correct Answer beam diameter (mm) Which type of resolution is superior in clinical imaging systems: lateral resolution or axial resolution? - Correct Answer Axial resolution because ultrasound pulses are shorter than they are wide. Higher frequencies improve both axial and lateral resolutions because... - Correct Answer axial: the shorter pulses associated with high frequency sound What was the form form of grayscale imaging? - Correct Answer B-Mode What is M-mode? - Correct Answer Motion, horizontal wavy lines represent the changing depth of the reflecting surfaces are produced on the paper. X-axis = time, Y- axis = depth What is M-mode primarily used for? - Correct Answer assess the motion of cardiac walls and structures What is the only display mode that provides information regarding reflector motion with respect to time? - Correct Answer M-mode With A-mode, what does the X-axis display? - Correct Answer depth of the reflector With M-mode, what does the Y-axis display? - Correct Answer depth of the reflector Which mode provides the foundation for real-time, grayscale anatomic imaging? - Correct Answer B-mode, or brightness mode With A-mode, what does the Y-axis display? - Correct Answer amplitude of the reflected signal In M-mode, what does the X-axis display? - Correct Answer time With B-mode Which axis is related to the strength of the reflection? - Correct Answer the z-axis How does an ultrasound system create high quality, two-dimensional images? - Correct Answer Two characteristics of sound that make it difficult to create two-dimensional images are: sound travels only in a straight line, and sound beams must be narrow to optimize lateral resolution. The use of multiple pulses to create a two-dimensional image overcomes both of these difficulties. In a mechanical transducer, the PZT crystal is _______________ to create the image. - Correct Answer physically moved Mechanical transducer image shape: - Correct Answer fan or sector-shaped Mechanical transducers have a _________ focal depth. - Correct Answer fixed When there is any damage done to the crystal in a mechanical transducer, - Correct Answer the entire image is lost Array transducers are comprised of... - Correct Answer a single slab of PZT cut into a collection of separate pieces called elements. Each active element is connected by a wire to its own electronic circuitry int he ultrasound system. The linear phased array has ___ moving parts. And the beam is steered and focused using an electrical techniques called _________. - Correct Answer no, phasing What is the image shape created by a phased array? - Correct Answer fan or sector- shaped Elements of a phased array are what shape? - Correct Answer rectangular and narrow Sound beams are focused ___________ with linear phased array transducers. - Correct Answer electronically Advantage of phased array systems is: - Correct Answer the availability of electronically controlled, adjustable focusing, which allows the sonographer to match the beam's characteristics to the clinical circumstances. Damage to one of the elements of a phased array transducer results in... - Correct Answer inconsistent or erratic beam steering and focusing. How many elements in a phased array probe are excited to create a single sound pulse? - Correct Answer All the active elements in a linear phased array probe are fired to create each sound beam. What is the beam former? - Correct Answer the electronics within the ultrasound system that create the voltages to the transducer element When the spike line is straight, an ____________ is created. - Correct Answer unfocused sound beam How does the pattern of electrical spikes from the beam former focus the sound beam during transmission? - Correct Answer When the outer crystals are excited earlier than the inner crystals, the curved pattern creates a focused sound beam. This means the beam will be directed straight ahead. Brightness of the display is affected by? - Correct Answer Receiver amplification (gain) Acoustic speckle is an artifact produced by what? - Correct Answer interference of tiny acoustic wavelets Side lobe artifact is a result of what condition? - Correct Answer Acoustic energy radiating in a direction different than the main axis of the beam