## Questions and Answers

What is the symbol used to represent the period of a sound wave?

T

If one cycle of a sound wave takes 0.2 μs to occur, what is the frequency of the wave?

5 MHz

What is the unit of measurement for wavelength?

millimeters

Can the wavelength of a sound wave be controlled by the sonographer?

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What is the formula to calculate wavelength?

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What is the effect of shorter-wavelength sound waves on the diagnostic quality of ultrasound images?

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What is the propagation speed of a sound wave dependent on?

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What is the speed of sound wave propagation in a specific medium?

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What is the primary effect of a decrease in area on the intensity of an ultrasound pulse?

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What is the term used to describe the weakening of an ultrasound pulse as it travels through a medium?

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What is the maximum amount of variation that occurs in an acoustic variable, such as pressure, in an ultrasound wave?

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What is the primary purpose of the dead time in a pulsed ultrasound wave?

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What is the term used to describe the range of frequencies emitted by a pulsed ultrasound transducer?

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What type of ultrasound diagnostic images are generated by pulsed wave transducers?

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What is the primary application of continuous wave ultrasound?

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What is a limitation of continuous wave ultrasound?

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What is the effect on PRF when the imaging depth is increased?

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What is the relationship between PRP and PRF?

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What is the typical unit of measurement for PRP?

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What happens to the pulse-repetition period when PRF increases?

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What is the formula to calculate pulse duration?

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What is the effect on pulse duration if the number of cycles in a pulse is decreased?

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What is the duty factor in terms of PRP?

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What is the typical range of PRP values in clinical imaging?

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What is the primary purpose of the listening time in pulsed ultrasound?

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What is the unit of measurement for pulse duration in the calculation of duty factor?

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What is the typical range of duty factors for Doppler ultrasound?

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What determines the axial resolution in ultrasound imaging?

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What is the formula to calculate the spatial pulse length (SPL)?

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How does the spatial pulse length (SPL) change with increasing frequency?

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What is the primary factor that determines the spatial pulse length (SPL)?

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Can the sonographer adjust the duty factor during an ultrasound examination?

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What is the approximate speed of sound in fat?

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Which of the following best describes amplitude in relation to a sound wave?

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What is the unit of power commonly used in diagnostic ultrasound?

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What happens to intensity when the area over which the power is spread increases?

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What is the primary factor that determines the speed of sound in different materials?

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What is the purpose of power in ultrasound?

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What is the unit of intensity?

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What is the relationship between power and intensity?

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## Study Notes

### Sound Wave Parameters: Period

- The period (T) is determined by the sound source and cannot be altered by the sonographer.
- Each cycle occurs in a specific time, and the period is the time for one cycle to occur.
- If one cycle takes 0.2 μs to occur, the frequency is 5 MHz.

### Sound Wave Parameters: Wavelength

- Wavelength (λ) is the length of a cycle in space.
- Units for wavelength are measured in meters, millimeters, or any standard unit of length.
- Typical values in soft tissue range from 0.1 to 0.8 mm.
- The wavelength cannot be modified by the sonographer.
- Wavelength is calculated as Speed divided by Frequency (λ = c / f).

### Sound Wave Parameters: Propagation Speed

- Propagation speed (c) refers to the rate at which a sound wave moves through a medium.
- Within a specific medium, sound waves travel at a consistent speed, regardless of their frequency.
- The speed of sound wave propagation varies across different mediums.
- The average propagation speed of sound in tissues:
- Air: 330 m/sec
- Fat: 1450 m/sec
- Water: 1480 m/sec
- Soft tissue: 1540 m/sec
- Bone: 4100 m/sec

### Sound Wave Parameters: Amplitude

- Amplitude is created by the number of molecules displaced by a vibration.
- Amplitude is indicative of the strength or intensity of a sound wave.
- Amplitude is typically measured in units of pressure, such as Mega Pascals (MPa).

### Sound Wave Parameters: Power

- Power is the rate at which work is performed or energy is transferred.
- In ultrasound, power refers to the generation of ultrasound waves by the transducer and their propagation through tissues.
- The standard unit of power is the Watt (W).
- Power in diagnostic ultrasound is commonly expressed in milliwatts (mW).

### Sound Wave Parameters: Intensity

- Intensity (I) is the rate at which energy passes through a unit area.
- Intensity is equal to the power in a wave divided by the area (A) over which the power is spread.
- Intensity units include milliwatts per centimeter squared (mW/cm²) and watts per centimeter squared (W/cm²).

### Pulsed Wave

- A pulse has a distinct beginning and end.
- Pulsed ultrasound comprises two main components: The Cycle (the "on" or "transmit" time) and The Dead Time (the "off" or "receive" time).
- Pulsed transducers are designed to generate multiple, sequential, short pulses, allowing for the simultaneous use of the same crystal or group of crystals for both sound transmission and echo reception.

### Pulsed Repetition Frequency (PRF)

- Pulse Repetition Frequency (PRF) refers to the number of sound pulses generated by the transducer per second.
- The determination of PRF is attributed to the sound source and can be adjusted by the sonographer.
- There is an inverse relationship between imaging depth and PRF, meaning as imaging depth increases, PRF decreases.

### Pulse Repetition Period (PRP)

- Pulse-repetition period (PRP) refers to the time from the beginning of one pulse to the beginning of the next one.
- PRP is the reciprocal of Pulse Repetition Frequency (PRF), expressed in milliseconds or any unit of time (PRP = 1 / PRF).
- The determination of PRP is influenced by the sound source, and it can be adjusted by the operator.

### Pulse Duration (PD)

- Pulse duration (PD) is the time that it takes for one pulse to occur.
- PD is equal to the period (the time for one cycle) times the number of cycles in the pulse (n) and is expressed in microseconds (PD = n × T).
- Sonographic pulses are typically two or three cycles long, while Doppler pulses are typically 5 to 30 cycles long.

### Duty Factor (DF)

- The duty factor is the percentage of time that the ultrasound system transmits sound.
- DF is the fraction of the PRP that the sound is on.
- Typical DFs for sonography are in the range of 0.1% to 1.0%, and for Doppler ultrasound, the range is 0.5% to 5.0%.
- The sonographer can adjust the duty factor when changing imaging depth.

### Spatial Pulse Length (SPL)

- SPL is the length of a pulse from front to back.
- SPL is equal to the length of each cycle times the number of cycles in the pulse (SPL = n × wavelength).
- SPL determines axial resolution.
- Because wavelength decreases with increasing frequency, SPL decreases with increasing frequency.

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## Description

Understanding the period of a sound wave and its relation to frequency. Learn how to calculate frequency from period and vice versa.