L3: Ultrasound wave Characteristics and Speed of Sound

Lecture 3: Ultrasound

PHASE

Refers to the relationship of one wave to another

INTERFERENCE

Interaction of two or more ultrasound waves having different frequency or phase

STANDING WAVES

Two waves travelling in opposite directions with the same amplitude, they interfere and create a ____________

STANDING WAVES

It appears to stand still, vibrating in place and always consist of an alternating pattern of nodes and antinodes

BEAT FREQUENCY

The rate at which the warbling pattern of noise, known as beats, when sound waves with slightly different frequencies combine. Pulsation caused by beats

CONTINUOUS WAVE

Cycles repeat indefinitely. Employed in procedures involving fetal heartbeat and doppler studies

PULSED WAVE

pulses separated by gaps in time

PULSED WAVE

Contains two or more cycles followed by a resting/listening time. Employed in most imaging studies, involving A-mode, B-mode, M-mode and real time imaging

Pulse Repition Frequency (PRF)

No. of pulse occurring in 1 second. How frequent is the transducer emitting pulse

Spatial Pulse Length (SPL)

Length of space that a pulse takes up

Pulse Duration (PD)

Time it takes for one pulse to occur

Duty Factor (DF)

Percent/fraction of time that pulsed ultrasound is on

Pulse Repitition Period (PRP)

Time or duration from the beginning of one pulse to next

Christian Huygens

Dutch mathematician who discovered nature of wave propagation

Huygens Principle

Every point on wave-front may be considered a source of secondary spherical wavelets, which spread in forward direction at the speed of light. The new wave-front is the tangential surface to all these secondary wavelets. Describes the production of ultrasound wavefront from individual wavelets

Perpendicular

Wavefront is always ___________ to the direction of the wave

Nodes and Antinodes

It appears to stand still, vibrating in place and always consist of an alternating pattern of _____ and _________

Less listening

Shorter PRP

Higher PRF

Higher duty factor

Shallow Imaging

____ listening

____ PRP

____ PRF

____ duty factor

More listening

Longer PRP

Lower PRF

Lower duty factor

Deep imaging

____ listening

____ PRP

____ PRF

____ duty factor

PROPAGATION OF SPEED

Speed at which sound moves through a medium. Dependent on density and compressibility of medium

DECIBEL

Logarithmic scale

Alexander Graham Bell

Originally came from the “bel scale” of ___________________

ACOUSTIC IMPEDANCE

The acoustic properties of a medium are quantified in terms of its _________________, which is a measure of the degree to which the medium impedes the motion that constitutes the sound wave

Rayl

Unit of Acoustic Impedance

INTENSITY REFLECTION COEFFICIENT

Proportion of energy reflected from an interface between two substance