Ultrasound Lecture 3: Ultrasound Wave Characteristics and Speed of Sound

Phase

relationship of one wave to another

Interference

two or more ultrasound waves having different frequency/phase

In Phase Waves

undergoes constructive interference that results in increased amplitude.

same area of compression and rarefaction (AT SYNC)

Out-of-Phase Waves

undergoes destructive interference that results in 0 amplitude.

NOT IN SYNC, some parts of the waves has been cancelled out.

Standing Waves

two waves travelling in opposite direction with the same aplitude.

vibrating in place and is moving at an alternating pattern of nodes and antinodes.

nodes

point of 0 amplitude.

antinodes

point of maximum amplitude.

Beat Frequency

rate at which the warbling pattern of noise.

sounds with slightly different frequencies combine.

Continuous wave

cycles repeat indefinitely

employed in procedures such as fetal heartbeat and doppler studies.

requires assessment of structure/organs that are continuously moving.

Pulsed Wave

pulses separated by gaps in time.

contains two or more cycles followed by a resting time.

listening time

part where the transducer receives the echo coming from different parts of the body.

Pulse Repetition Frequency

no. of pulse in 1 second

Special Pulse Length

Length of space that a pulse takes up.

Pulse duration

Time it takes for one pulse to occur

Pulse Repetition Period

time or duration of the beginning of the pulse to the next.

Duty Factor

percent/fraction of time that pulsed ultrasound is on.

Deep Imaging

occurs with lower pulse repetition frequency (PRF)

Shallow Imaging

occurs with a higher pulse repetition frequency (PRF).

Huygens Principle

Nature of wave propagation

describes the production of ultrasound wavefront from individual wavelets.

perpendicular

Wavefront is always _____ to the direction of the wave.

Propagation of speed

speed at which sound moves through a medium.

dependent on density and compressibility of medium.

Decibel

Relative intensities of two sounds

Alexander Graham Bell

originally came from “bel scale“ of…

Acoustic Impedance

medium impedes the motion that constitutes the sound wave.

degree of how much is transmitted and reflected.

same Z

total transmission of energy and no reflection

small difference in Z

less reflected but majority is transmitted.

high difference in Z

large amount of energy is reflected, but small amount is transmitted.

1%

most soft tissues interfaces reflect energy of ___ or less.

air-water interface

all sound in air is reflected at an _____

acoustic impedance mismatch

happens between soft tissues, causing most of the sound to be reflected.

difference in Z between two substances.