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Questions and Answers
What is the most likely outcome of decreasing the number of pulses per image?
What is the most likely outcome of decreasing the number of pulses per image?
Which of these factors does NOT directly influence frame rate?
Which of these factors does NOT directly influence frame rate?
What is the trade-off associated with increasing the line density?
What is the trade-off associated with increasing the line density?
What is the relationship between the number of focal zones and temporal resolution?
What is the relationship between the number of focal zones and temporal resolution?
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Which scenario would likely result in the poorest temporal resolution?
Which scenario would likely result in the poorest temporal resolution?
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Which of the following correctly describes the relationship between period and frequency?
Which of the following correctly describes the relationship between period and frequency?
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What is the correct definition of pressure, in the context of sound waves?
What is the correct definition of pressure, in the context of sound waves?
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Which of the following parameters of a sound wave is determined solely by the medium through which it travels?
Which of the following parameters of a sound wave is determined solely by the medium through which it travels?
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In a longitudinal wave, how do the particles of the medium move in relation to the direction of the wave?
In a longitudinal wave, how do the particles of the medium move in relation to the direction of the wave?
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Which of the following is NOT a unit of measurement for distance in the context of particle motion?
Which of the following is NOT a unit of measurement for distance in the context of particle motion?
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What effect does a compression have on the pressure and density of a medium?
What effect does a compression have on the pressure and density of a medium?
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Which parameter of a sound wave CANNOT be adjusted by the sonographer?
Which parameter of a sound wave CANNOT be adjusted by the sonographer?
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Which of the following is the prefix that represents a factor of 10^-6?
Which of the following is the prefix that represents a factor of 10^-6?
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What is the frequency range for ultrasound waves?
What is the frequency range for ultrasound waves?
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If the period of a wave decreases, what happens to its frequency?
If the period of a wave decreases, what happens to its frequency?
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Which of the following correctly describes the relationship between a wave's power and amplitude?
Which of the following correctly describes the relationship between a wave's power and amplitude?
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What determines the propagation speed of a sound wave?
What determines the propagation speed of a sound wave?
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What happens to the speed of sound when the stiffness of a medium increases?
What happens to the speed of sound when the stiffness of a medium increases?
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What type of interference occurs when two waves are out of phase and combine?
What type of interference occurs when two waves are out of phase and combine?
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What is a key factor determining the spatial pulse length?
What is a key factor determining the spatial pulse length?
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What is the relationship between frequency and wavelength?
What is the relationship between frequency and wavelength?
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What is the relationship between frequency and attenuation in soft tissue?
What is the relationship between frequency and attenuation in soft tissue?
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Which type of reflection occurs when sound reflects off a smooth surface?
Which type of reflection occurs when sound reflects off a smooth surface?
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In which medium is the attenuation much less than in soft tissue?
In which medium is the attenuation much less than in soft tissue?
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What condition is required for refraction to occur?
What condition is required for refraction to occur?
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What defines the intensity transmission coefficient (ITC)?
What defines the intensity transmission coefficient (ITC)?
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What characterizes Rayleigh scattering?
What characterizes Rayleigh scattering?
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What occurs with reflection at normal incidence?
What occurs with reflection at normal incidence?
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Which of the following is true about acoustic impedance?
Which of the following is true about acoustic impedance?
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What is the region surrounding the focus where the beam is relatively narrow and produces a good picture called?
What is the region surrounding the focus where the beam is relatively narrow and produces a good picture called?
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In the far field, how does beam diameter affect lateral resolution?
In the far field, how does beam diameter affect lateral resolution?
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What effect does focusing have on a sound beam?
What effect does focusing have on a sound beam?
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Which type of transducer is always fixed focus and may have the poorest lateral resolution?
Which type of transducer is always fixed focus and may have the poorest lateral resolution?
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What defines axial resolution in ultrasound imaging?
What defines axial resolution in ultrasound imaging?
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Which statement accurately describes phased array transducers?
Which statement accurately describes phased array transducers?
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What is the term for the spread of the sound beam in the deep far zone?
What is the term for the spread of the sound beam in the deep far zone?
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How does diffraction relate to ultrasound beam formation?
How does diffraction relate to ultrasound beam formation?
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What does the 13 microsecond rule indicate in soft tissue imaging?
What does the 13 microsecond rule indicate in soft tissue imaging?
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Which of the following describes the characteristic of a high Quality Factor (Q)?
Which of the following describes the characteristic of a high Quality Factor (Q)?
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What happens to the PZT properties when it is heated above the Curie temperature?
What happens to the PZT properties when it is heated above the Curie temperature?
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When comparing thin and thick crystals in pulsed transducers, how does crystal thickness affect frequency?
When comparing thin and thick crystals in pulsed transducers, how does crystal thickness affect frequency?
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What is the purpose of the matching layer in a transducer?
What is the purpose of the matching layer in a transducer?
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Which of the following statements about imaging transducers is accurate?
Which of the following statements about imaging transducers is accurate?
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What is the relationship between beam width and image quality as sound travels?
What is the relationship between beam width and image quality as sound travels?
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Which of the following correctly describes a damping element in transducers?
Which of the following correctly describes a damping element in transducers?
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Study Notes
Physics Chapters 1-12 Review
- All numerical values require corresponding units
- Macro = Bigger, Micro = Smaller
- Common metric prefixes are 10⁹ (billion; giga), and 10⁻⁶ (millionth; micro)
- Sound waves carry energy, characterized by compressions (increased pressure and density) and rarefactions (decreased pressure and density)
- Sound cannot travel in a vacuum
- Sound is a mechanical, longitudinal wave (not transverse), traveling in a straight line
- Three acoustic variables for sound waves include pressure (force per area, measured in Pascals), density (mass per volume, measured in kg/cm³), and distance (particle motion, measured in mm or cm)
- Transverse waves: particle movement is perpendicular to the wave's direction (90°)
- Longitudinal waves: particle movement is parallel to the wave's direction
- Parameters for sound waves include period, frequency, amplitude, power, intensity, wavelength, and speed
- Period and frequency are inversely related to each other, determined by the sound source
- Amplitude, power, and intensity are directly related and adjustable by the sonographer
- Wavelength depends on both the sound source and the medium
- Speed depends only on the medium
Three Bigness Parameters
- Amplitude, power, and intensity describe the strength of a sound beam
- All three are adjustable by the sonographer
- Period: time for one complete cycle (measured in microseconds); unchangeable by the sonographer
- Frequency: number of cycles per unit time (measured in Hertz or Hz); determined by the sound source and unchangeable
- Audible frequencies range from 20 Hz to 20,000 Hz
- Ultrasound frequencies are greater than 20,000 Hz
- Infrasound frequencies are less than 20 Hz
- Period and frequency are inversely related; if period decreases, frequency increases, and vice-versa.
Propagation Speed
- Determined solely by the medium
- Speed and wavelength are directly related
Phase Relationships
- Constructive interference: combined wave amplitude is greater than the original waves
- Destructive interference: combined wave amplitude is less than one of the original waves
Pulse Duration & Spatial Pulse Length
- Pulse duration is the time from the start to the end of a pulse
- Spatial pulse length is the distance from start to end of the pulse
- Shorter pulses create higher image quality
- The relationship between pulse duration and spatial pulse length is that shorter pulses have a shorter spatial pulse length
Pulse Repetition Period and Pulse Repetition Frequency
- PRP is the time from the start of one pulse to the start of the next pulse
- PRF is the number of pulses per unit time
- Increasing PRP decreases imaging depth, and vice-versa
Intensity
- The concentration of power in a sound beam
- Two types: Spatial and Temporal
- Key words related to intensity: peak, average, spatial peak, temporal peak, spatial average, temporal average
- SPTA (spatial peak, temporal average) is the most relevant to thermal bioeffects.
Attenuation
- Attenuation is the decrease in intensity as sound travels through a medium
- Three components of attenuation: absorption, scattering, and reflection
- Attenuation is different in air, lung, bone, water, and soft tissue, with soft tissue typically having medium attenuation
- Lower frequency sound penetrates further in soft tissue than higher frequency sound, attenuating less
- Reflectors create specular or diffuse reflection depending on the shape.
Refraction
- Refraction is the bending of sound at a boundary between two different media
- Refraction occurs when sound travels from one medium to another at an oblique angle.
- Snell's law describes the physics of refraction
Time of Flight
- Time needed for a pulse to travel to and from a reflector
- Can be used to determine reflector depth
Basic Transducers
- Piezoelectric materials (e.g., PZT) convert energy into sound waves
- PZT crystal properties are destroyed if heated above Curie temperature
- The active element is a piezoelectric crystal; it is ½ wavelength thick
- Don't use a transducer with a cracked case to avoid patient electrical shock
- Matching layer is a quarter wavelength thick; between the skin and active element for increased transmission
Bandwidth and Quality Factor
- Bandwidth is the range of frequencies
- Imaging transducers use backing material, but therapeutic transducers do not
- Quality factor is a unitless number related to damping
Pulsed Transducers
- The main and central frequency depend on crystal thickness and propagation speed
Anatomy of a Sound Beam
- Sound beam width changes during travel, narrowing to a focus and then diverging
- Near zone (Fresnel zone) is where the beam is relatively narrow
- Far zone (Fraunhofer zone) is where the beam diverges
- Focal zone is where the beam is narrow
- Focal depth is determined by the transducer diameter and frequency
- Beam divergence describes the spread of sound in the deep far zone
- Diffraction is the wave-like behavior of sound
Axial and Lateral Resolution
- Axial resolution is the ability to distinguish two structures positioned along the beam axis
- Lateral resolution is the ability to distinguish two structures positioned side-by-side perpendicular to the beam axis
- Lateral resolution is equal to the beam diameter
Two-Dimensional Imaging
- Mechanical scanning moves the active element or a mirror, creating a scan plane
- Phased arrays achieve adjustable focus electronically.
- Malfunctional elements in phased arrays can distort the image.
Contrast, Spatial, and Temporal Resolution
- Contrast is visualized in gray shades
- Spatial resolution is image detail determined by axial, lateral resolution, and line density
- Temporal resolution is the time for creating an image frame; limited by imaging depth and speed of sound in medium; higher frame rates for shallow imaging
- Frame rate is determined by imaging depth and number of pulses per image
Frame Rate vs. Image Quality
- As temporal resolution improves, image quality may degrade, and vice versa
- Factors affecting frame rate and temporal resolution include line density, number of focal points, and sector angle
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Description
This quiz will test your understanding of key concepts covered in Physics Chapters 1-12. It includes important definitions, properties of sound waves, and the distinctions between macro and micro phenomena. Prepare to review acoustic variables, wave types, and their respective parameters.
