Ultrasound physics Ch 4

period common values

.06-.5 micro sec

Frequency common values

2-15 MHz

Amplitude common values

1-3 MPa

Power common values

4-90 milliwatts

intensity common values

.01- 300 W/cm^2

wavelength common values

.1 - .8 mm

Prop. speed common values

1,500- 1,600 m/s
1.54 mm/micro sec
1.54km/ sec

-Decreases as sound travels through the body
-can be changed by sonographer

Amplitude, power, intensity

Pulsed ultrasound

pulses of US needed to create an image

A pulse of US is

a collection of cycles that travel together

5 additional descriptions of pulsed ultrasound

-pulse duration
-PRP
-PRF
-duty factor
-spacial pulse length

Pulse duration

time from start to finish of a pulse
-number of cycles in each pulse (usually 2-4)

Spacial pulse length

distance from start to end of pulse

SPL equation

# of cycles x wavelength

SPL and # of cycles in a pulse relationship

Direct. Increasing cycles= increase in SPL

SPL and wavelength relationship

direct. increasing wavelength= increase in SPL

SPL and frequency relationship

inverse. more cycles= shorter SPL

What is the difference between SPL and pulse duration?

duration is the time it takes for one pulse, SPL is the distance of that pulse

fewer cycles in a pulse=

shorter pulse

a long wavelength=

longer pulse

a lower frequency=

longer pulse

PRP

Start of one pulse to start of next pulse

B

Which PW wave would be utilized for shallow imaging?

PRF

number of PULSES that occur in one second (not cycles)

PRF equation

PRP (sec) x PRF (Hz) = 1

PRP and PRF are

reciprocals

Depth and PRP

increase depth= increase PRP

depth and PRF

increase depth= decrease PRF

A

Which has greater pulse duration and period?

What parameters are affected by depth

PRP and PRF

PRP

Period

Peak to peak amplitude

Pulse duration

Amplitude

Duty factor

percentage of time US system is transmitting a pulse

duty factor equation

Duty Factor (%) = Pulse Duration / Pulse Repetition period X 100

Parameters that describe both pulsed and CW

period, frequency, wavelength, propagation speed

Pulse duration determined by

Source/not adjustable

PRP determined by

Source/adjustable

PRF determined by

Source/ adjustable

Spatial pulse length determined by

source and medium/not adjustable

duty factor determined by

source/ adjustable

Shallow imaging: listening time

less

shallow imaging: PRP

less

shallow imaging: duty factor

increases

Shallow imaging: PRF

increases

Deeper imaging: duty factor

less

deeper imaging: PRP

increases

deeper imaging: listening time

increases

deeper imaging: PRF

less

deeper imaging: SPL

not affected