SPI Fundamental Basics

Acoustic variables vs acoustic parameters

Pneumonic for the Metric System

Good 

Man

king

henry

died

bloated

drinking

chocolate

milk

many (micro, u)

nights

Definition of media

multiple tissues

What are acoustic Propagation Properties

effects of soft tissue on the US

What are biologic effects

effects of the sound wave upon the biologic tissue

What is sound

a type of WAVE that carries ENERGY, not matter, from place to place. Created by vibrations, compressions and rarefractions, needs a medium to travel, mechanical, longitudinal wave, travels in a straight line

What are compressions

areas of increased pressure and density

What are rarefractions

areas of decreased pressure and density

What are acoustic variables

identify which waves are sound waves. Discern from other waves like heat light etc.

-Pressure

-DIstnace

-DEnsity

What is pressure and its units

Concentration of force within an area (force/area) Units: pascals (Pa)

What is density and its units

Concentration of mass within a volume Units: kg/cm³

What is distance its units

Measure of particle motion Units: cm, feet, miles

What is a mechanical wave

convey energy from one location to another through vibration of molecules in that medium

What is a longitudinal wave

(slinky) particles move parallel or same direction as the wave

What is a transverse wave

ocean wave (sterotypical wave) particles move perpendicular (Right angles or 90 degrees)

What is interference

 more than one sound beam traveling at the same time (they mesh to form a single wave)

In step/in phase

2 waves are in sync. Peaks and troughs meet at the same location. CONSTRUCTIVE INTERFERENCE (greater amplitude)

Out of phase/ out of step

2 waves are out of sync DESTRUCTIVE INTERFERENCE (smaller amplitude)

What happens when two out of phase waves are of equal amplitude

cancel each other out COMPLETE DESTRUCTIVE INTERFERENCE (no sound wave)

What do acoustic parameters describe

describe the features of a particular sound wave

What are the seven acoustic parameters

Period

Frequency

Amplitude

Power

Intensity

Wavelength

Speed

Which two parameters are reciprocals

Period and frequency

What is period, its units, can it be changed by the sonographer?

the time required to complete a single cycle, micro sec (any unit of time) typically .06-.5 useconds, NO cannot be changed by the sonographer. Determined by sound source

What is frequency, its units, can it be changed by the sonographer?

number of cycles that occur in a particular time duration, units: per second, 1/second, Herts, Hz, typically 2 MHz to 15MHz, NO cannot be changed by sonographer, determinded by sound source

What affects penetration and axial resolution (image quality)

frequency

What is audible sound

heard by man, frequencies between 20 Hz and 20,000 Hz

What is Ultrasound

frequencies exceeding 20,000 Hz (20 kHz), so HIGH that sound is not audible

What is infrasound

frequencies less than 20 Hz, so LOW that sound is not audible

Equation for frequency and period

period= 1/frequency (inverse relationship)

What are the 3 parameters that describes a sound beam’s strength

Amplitude, Power, Intensity

What is amplitude, its units, can it be changed by the sonographer?

the difference between the average value and the maximum value, units: the acoustic variables (pascals, grams, cm sometimes decibles), YES can be changed by sonographer

As sound propagates through the body what happens to the amplitude, power and intensity

they ALL decrease

What is Power, its units, can it be changed by the sonographer?

the rate that work is performed, units: Watts, YES can be changed by sonographer

What is the relationship between power and amplitude

Power is proportional to the wave’s amplitude squared

Power=(Amplitude)²

If the amplitude is tripled what happens to the power

power increased by a factor of nine

3×3=9

If the amplitude is halved what happens to the power

decreased by a factor of four (quartered)

1/2×1/2= 1/4

What is intensity, its units, can it be changed by the sonographer?

concentration of energy in a sound beam, watts/cm², typicallyt .001-100 watts/cm², YES cna be changed by sonographer

What is the equation for intensity

Intrensity (Watts/cm²)= Power (watts)/beam area (cm²)

What is the relationship between intensity and amplitude

amplitude² !!

What is wavelength, its units, can it be changed by the sonographer?

The LENGTH or distance of a single cycle, Units: meters, mm etc, NO cannot be changed by sonographer, determined by BOTH source and medium

AKA may be called range resolution

What does wavelength influence

axial resolution (image quality)

Equation for wavelength

wavelength mm= propagation speed (mm/us)/frequency (MHz)

^=C/F

In soft tissue what do you divide by frequency

divide 1.54 mm by frequency in MHz

What is propagation speed, its units, can it be changed by the sonographer?

The rate that sound travels through a medium (velocity or speed), Units: m/s, mm/us, NO cannot be changed by sonographer, determined by the medium only-density and stiffness

What happens if different frequencies travel through the same medium

ALL SOUND travels at the SAME speed through any specific medium. Sound with frquenices of 5MHz and 3MHz travel at the same speed through the same medium

Average speed of all sound through soft tissue

1540 m/s= 1.54 km/s= 1.54 mm/us

General Rule of speeds through mediums between liquid, solids and gases

solid (fastest)>liquid>gas (slowest)

What is the relationship between speed and wavelength

Directly related. Sound in a slow medium has a short wavelength

Rule of thumbs

stiffness and speed= same direction

density and speed= opposite direction

What is stiffness

Related to change in shape “squishability” the stiffer the object the faster it will travel through. bone is stiff, not dense- speed is high in bone

What is density

related to weight. Opposite thumbs. As density increases, speed decreases

What is bulk modulus

same as stiffness, when bulk modulus increases speed increases

What is responsible for changes in period, frequency and wavelength

a new transducer with a different frequency is used

What is a cycle, not to be confused with what?

a single wave (don’t confuse it with a pulse.)

What is a pulse

a collection of cycles