Ultrasound Wavelength and Frequency

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Questions and Answers

What does Pulse Repetition Frequency (PRF) refer to?

The percentage of time the ultrasound system transmits sound

The time it takes for one pulse to occur

The time between two consecutive sound pulses

The number of sound pulses generated per second (correct)

What happens to PRF when imaging depth increases?

It becomes irrelevant

It increases

It remains constant

It decreases (correct)

What is the relationship between PRP and PRF?

PRP is directly proportional to PRF

PRP is the square root of PRF

PRP is the reciprocal of PRF (correct)

PRP is the square of PRF

What is the unit of Pulse Repetition Period (PRP)?

Milliseconds Signup and view all the answers

What determines Pulse Duration (PD)?

The number of cycles in the pulse Signup and view all the answers

What happens to Pulse Duration (PD) if the frequency is increased?

It decreases Signup and view all the answers

What is the formula to calculate Pulse Duration (PD)?

PD = n × T Signup and view all the answers

What is the duty factor (DF)?

The percentage of time the ultrasound system transmits sound Signup and view all the answers

What is the typical range of Pulse Repetition Period (PRP) in clinical imaging?

100 microseconds to 1 millisecond Signup and view all the answers

What happens to intensity when the area of an ultrasound pulse is decreased?

It increases Signup and view all the answers

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

Attenuation Signup and view all the answers

What is the maximum amount of variation that occurs in an acoustic variable?

Amplitude Signup and view all the answers

What is the definition of a pulse in ultrasound?

A wave with a distinct beginning and end Signup and view all the answers

What are the two main components of pulsed ultrasound?

The Cycle and the Dead Time Signup and view all the answers

What is the purpose of the Dead Time in pulsed ultrasound?

To receive the echoes Signup and view all the answers

What is the frequency bandwidth in pulsed ultrasound?

A range of frequencies Signup and view all the answers

What type of ultrasound is predominantly used in echocardiography?

Continuous wave Signup and view all the answers

What is the limitation of continuous wave ultrasound?

It is incapable of creating anatomic images Signup and view all the answers

What is the frequency of a cycle that takes 0.2 millionths of a second to occur?

5 MHz Signup and view all the answers

What is the unit of measurement for wavelength?

millimeter Signup and view all the answers

Can the wavelength be modified by the sonographer?

No Signup and view all the answers

What is the formula to calculate wavelength?

Wavelength = Speed ÷ Frequency Signup and view all the answers

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

They have superior spatial resolution Signup and view all the answers

What is the propagation speed of sound waves in a medium?

It is the same for all frequencies Signup and view all the answers

What determines the speed of sound wave propagation?

Medium through which it travels Signup and view all the answers

What is the wavelength of a sound wave with a frequency of 5 MHz and a propagation speed of 1.54 mm/μs?

0.31 mm Signup and view all the answers

Why is wavelength an important parameter in ultrasound imaging?

It influences the diagnostic quality of ultrasound images Signup and view all the answers

What is the characteristic of normal incidence in ultrasound?

The ultrasound path is perpendicular to the boundary. Signup and view all the answers

What factor affects the degree of reflection and refraction in ultrasound?

Acoustic impedance differences of the two media. Signup and view all the answers

What is the process of conversion of sound energy into heat within a medium called?

Absorption Signup and view all the answers

What is the result of slower molecular relaxation in a medium?

Increased absorption Signup and view all the answers

What type of reflection occurs at large and smooth interfaces?

Specular reflection Signup and view all the answers

What is the result of higher frequencies in ultrasound?

More heat production Signup and view all the answers

What is the characteristic of non-specular reflection?

The ultrasound beam is scattered in multiple directions. Signup and view all the answers

What is the result of the acoustic impedance difference between two media?

Increased reflection Signup and view all the answers

What is the characteristic of specular reflection in ultrasound imaging?

The image is hyperechoic (brighter). Signup and view all the answers

What is the result of less uniform tissue in diffuse reflection?

A more hypoechoic image Signup and view all the answers

What is the reason for the bright signal in the sonogram of the bone?

The bone is highly reflective of sound waves Signup and view all the answers

What is the term for the image artifacts produced by backscatter?

Speckle Signup and view all the answers

What is the condition for refraction to occur?

The sound wave hits the boundary at an oblique angle Signup and view all the answers

What is the law that defines the refraction of sound waves?

Snell's Law Signup and view all the answers

What is the term for the way sound waves spread out in different directions?

Scattering Signup and view all the answers

What is the result of the difference in propagation speeds of sound in different media?

Refraction Signup and view all the answers

What is the factor that determines the direction of the refracted beam?

The speed of sound in the second medium Signup and view all the answers

What is the term for the reflection of ultrasound waves back to the transducer?

Backscatter Signup and view all the answers

Study Notes

Sound Wave Parameters

A cycle takes 0.2 millionths of a second to occur, which means 5 million cycles occur in 1 second, resulting in a frequency of 5 MHz.
Wavelength (λ) is the length of a cycle in space and is typically measured in meters, millimeters, or any standard unit of length.
Wavelength ranges from 0.1 to 0.8 mm in soft tissue and cannot be modified by the sonographer.
Wavelength is calculated as Speed divided by Frequency: λ (mm) = c (mm/μs) ÷ f (MHz).
Wavelength is a crucial parameter that influences the diagnostic quality of ultrasound images, with shorter-wavelength sound waves having superior spatial resolution but less penetration.

Propagation Speed

Propagation speed (c) refers to the rate at which a sound wave moves through a medium.
Sound waves travel at a consistent speed within a specific medium, regardless of their frequency.
The speed of sound wave propagation varies across different mediums.
A decrease in area (focusing) increases intensity because power is more concentrated.
Attenuation is the weakening of an ultrasound pulse as it travels through a medium.

Pulsed Wave

A pulse, by definition, must have 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 wave transducers are responsible for generating all types of ultrasound diagnostic images, including both real-time and static.
The frequency bandwidth of a pulsed transducer emits ultrasound waves that span a variety of frequencies.

Continuous Wave (CW)

Continuous wave (CW) ultrasound is predominantly employed in echocardiography for acquiring CW Doppler information.
Continuous wave sound is incapable of creating anatomic images.

Pulse Repetition Frequency (PRF) and Pulse Repetition Period (PRP)

Pulse Repetition Frequency (PRF) refers to the number of sound pulses generated by the transducer per second.
There is an inverse relationship between imaging depth and PRF, meaning as imaging depth increases, PRF decreases.
Pulse Repetition Period (PRP) is the time from the beginning of one pulse to the beginning of the next one and is the reciprocal of PRF: PRP = 1 / PRF.
The determination of PRP is influenced by the sound source and 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(μs) = n × T(μs).
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.

Types of Incidence

Normal Incidence occurs when the ultrasound path is perpendicular to the boundary.
Oblique Incidence occurs when the ultrasound beam strikes the interface between two media at an angle other than 90°.

Incident Sound in Ultrasound

The degree of reflection and refraction is influenced by the acoustic impedance differences of the two media.

Factors Contributing to Attenuation

Absorption is the conversion of sound energy into heat within a medium.
Factors affecting absorption include relaxation time and frequency.
Reflection is the redirection of part of the ultrasound wave back towards the source.
The degree of reflection is influenced by the acoustic impedance difference between the two media.
Scattering refers to the way sound waves spread out in different directions when they encounter tissues with irregular surfaces or interfaces similar in size to the wavelength of the sound.
Refraction is the change in direction of a sound wave as it passes across a boundary between two different media at an oblique angle, not perpendicular to the boundary.

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Description

Quiz about ultrasound wavelengths, frequencies, and their relationships in soft tissue, including units of measurement and factors influencing wavelength.