
The effects of the medium upon the sound wave.
Acoustic Propagation Properties

The effects of the sound wave on biologic tissue
Biologic Effects

Sound is what kind of wave?
Mechanical, longitudinal

Period
Definition?
Determined by?
Changed by sonographer?
The time required to complete a single cycle
determined bysource
changed by sonographerno

Frequency
Definition?
Units?
Determined by?
Changed by sonographer?
 DefinitionThe number of certain events that occur in a particular time duration
 Units per second, hertz, Hz
 Determined bySource
 Changed by sonographerno

Ultrasound Range?
Greater than 20,000Hz, not audible

Audible Sound
2020,000 Hz

Infrasound?
Less than 20 Hz


Intensity is proportional to?
Amplitude^{2}

Formula for wavelength?
wavelength (mm)= prop. speed (mm/us) / frequency (MHz)

Formula for wavelength in soft tissue?
wavelength= 1.54mm/frequency (MHz)

Wavelength is determined by?
Source and Medium

Propagation speed is determined by?
 Medium only,
 density and stiffness

Propagation Speed formula?
 speed= frequency x wavelength
 (m/s) =(Hz) x (m)

InPhase waves interfere how?
Constructively

Pulse duration formula?
PD= number of cycles in pulse x period
or
PD=number of cycles in pulse / frequency

Pulse Repetition Period definition?
The time from the start of one pulse to the start of the next pulse. Includes "on time" and "off time"

PRP
Determined by?
Changed by sonographer?
 Determined by source
 Changed by sonographeryes
 (amount of listening time is determined by image depth)

PRF definition?
The number of pulses that occur in one second



Depth and PRF are related how?
Inversely proportional

Depth and PRP are related how?
directly proportional


Duty Factor formula?
DF = PD/PRP x 100

Duty Factor
Definition?
Determined by?
Changed by sonographer?
 Definition The percentage of time the system is transmitting sound. (% of "on time")
 Determined by source
 changed by sonographeryes

SPL formula?
SPL= number of cycles x wavelength

SPL determines resolution?
Axial resolution

PRP, PRF, and DF are all affected by what?
Depth of view

What intensity is most relevant with respect to tissue heating?
SPTA

What is the log of:
a100?
b10,000?

