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Ultrasound
High frequency "sounds" inaudible to the human hear. >20kHz

Sound
 traveling variation of acoustic variables
 ; audible 20Hz  20kHz

Frequency
number of cycles in a wave that occur in one second.

Acoustic variables
 Pressure
 Density
 Particle Motion

Wave
traveling variation of some quantity or quantities

Hertz
one cycles per second (Hz)

Kilohertz
 1000 cycles per second
 kHz

Megahertz
 in million cycles per second
 MHz

Infra
"below" audible sounds and is a frequency too low for human hearing

ultrasound
"above" a frequency too high for human hearing.

Period
time it takes for one cycle

Frequency and period relationship?
 Inverse.
 As frequency increases period decreases.

Wavelength
the length of a cycles in space

Propagation Speed
speed at which a wave moves through a medium

Frequency and Wavelength relationship?
 inversely
 as frequency increases, wavelength decreases

Propagation speeds in solids and gases
 highest in solids
 lower in gases

Propagation speed in tissue
1.54 mm/microsec.

Harmonics
even and odd multiples of fundamental frequency

What is PRF?
 Pulsed Repetition Frequency
 # of pules per second

What is PRP
time from beginning of one pulse to the next

PRF and PRP relationship?
inversely
 PRF increases
 PRP decreases

Pulse duration
TIME for a pulse to occur

Duty Factor
fraction of TIME that pulsed ultrasound is on

PRP increases, PRP decreases and Duty Factor...
increases

Spatial Pulse Length
DISTANCE in space that a pulse takes up

# of Cycles in a pulse increases, SPL increaces. If frequency increases, wavelength and SPL....
decrease

What do shorter pulses do to image resolution
improves resolution

Bandwidth
range of frequencies contained in a pulse

Intensity (I)
rate at which energy passes through a unit area

How is Intesity related to power?
 proportional
 Intensity = power (mW)/area (cm^2)

If beam power increases, intensity increases. If beam area ____, intensity _____.

If frequency increases penetration ______
decreases

Attenuation
weakening of sound as it propagates

If the attenuation coefficient ______, attenuation ______

If path length _____ attenuation ______

As frequency ______ increases, attenuation ______.

Perpendicular Incidence
denotes a directoin of travelĀ of US wave perpendicular to the boundary between two media.

Impedance
determines how much of an incident sound wave is reflected back into the first medium and how much is transmitted into the second medium.

If density _____, impedance ______.
If propogation speed _______, impedance _____.
 increases
 increases
 increases
 increases

Oblique incidence
denotes a direction of travel of the incident US that is NOT perpendicular to the boundary between two medium.

Refraction
"turn aside"  change of direction of sound when it crosses a boundary

Scattering
redirection of sound in many directions by rough surfaces, like tissue and blood.

Backscatter
sound scattered in the direction from which it came.

Speckle
grainy dots or "noise" in the display representing interference between constructive and destructive.

