Ultrasound Physics Formulas + Relationships

Acoustic Parameters

100

How are period and frequency related? 

Inversely related.

200

The 3 magnitude parameters 

Amplitude, Power, Intensity

300

How is amplitude related to power and intensity?

Proportional to amplitude squared

400

General speed of sound in soft tissue 

1,540 m/s

500

What is the formula for wavelength?

/\ (lambda)= PS/f

Pulsed sound

100

Sharp pictures create more diagnostic image, _ pulses create sharper pictures.

Shorter 

200

The length or distance a pulse occupies in space from start to finish

Spatial pulse length 

300

PRP, PRF, and duty factor are all controlled by

Imaging depth 

400

Units of duty factor and typical duty factor in clinical imaging

Unit less, it is a percentage. 1% or less in clinical imaging.

500

What is the formula for pulse duration?

PD= # of cycles x period 

Attenuation

100

Changes in attenuation are expressed in _ which represent relative changes.

Decibels 

200

3 types of attenuation 

-absorption

-reflection 

-scattering 

300

Relationship between Raleigh scattering and frequency 

Raleigh scattering is proportional to frequency^4 

400

Place in order from low to high attenuation: soft tissue, bone, blood, muscle, air

Blood, soft tissue, muscle, bone/air

500

Formula for finding attenuation coefficient in soft tissue 

A.c (dB/cm) = 0.5 x frequency (Mhz)

Acoustic Impedance

100

Acoustic impedance is determined by…

Density and propagation speed of the medium.
formula: a.i (rayls) = density x prop. speed

200

Because of the conservation of energy, if the incident sound beam is equal to 50 W/cm^2 and the reflected sound beam is equal to 15 W/cm^2, what is the transmitted sound beam?

35 W/cm^2

300

which is easier to find using the other, IRC or ITC?

if we have the IRC or if we find it with the formula it is easier to find ITC since it is whatever is left over (to equal 100%)

400

Snell’s Law Shortcuts:

If the new sound beams propagation speed is higher…

if it’s lower…

if it’s the same…

higher= angle will be higher 

lower= angle will be lower

same= angle is the same 

500

A sound beam has reached the critical angle, how much of the wave is transmitted? 

None, beyond critical angle there is total internal reflection. 

Ranging

100

Range equation 

Distance= time x speed 

200

 Rule that tells us for each _ us of go-return-time, an object is 1cm deeper in the body. 

13 microsecond rule, 13us

300

Formula for the go-return-time 

Also known as PRP

PRP (us)= imaging depth (cm) x 13 us/cm

400

Two ways to solve for PRF

Reciprocal of PRP so PRF= 1/PRP or 

77,000 (cm/s) / imaging depth (cm)

500

If you double imaging depth, what happens to PRP and PRF?

PRP doubles and PRF halves.