Basic Physics Exam 1

CH1,2,3,4, and 23

7 Parameters

1. period

2. frequency

3. amplitude

4. power

5. intensity

6. wavelength

7. propagation speed

Source

Ultrasound system and transducer

Medium

the tissue the sound is traveling through

Period

time it takes for a wave to vibrate a single cycle (start of one cycle to the next)

Typical Values for Period

0.06 - 0.5 microseconds

What is period determined by?

sound source

Frequency

Number of particular events that occur in a duration of time

Typical Values for frequency

2MHz- 15MHz

What is frequency determined by?

sound source

Infrasound frequency

<20 Hz

Audile frequency

20 Hz - 20000 Hz (20kHz)

Ultrasound frequency

>20kHz

How are period and frequency related?

Inversely and reciprocal

Bigness parameters

Amplitude

Power

Intensity

Can sonographer adjust bigness parameters?

Yes

Amplitude

difference between max and average value of acoustic variable

Peak-to-Peak amplitude

difference between minimum value and maximum value

Amplitude Units

any acoustic variables ( pascals, g/cm³, or cm, inches

What is amplitude determined by?

sound source

Typical amplitude values

1 MPa - 3MPa

Power

Rate of energy transfer or rate at which is performed

Typical Power values

.004-.09 Watts

What is power determined by

Sound source

Is power adjustable

yes

How are amplitude and power related

power is directly related to the square of amplitude

The concentration of energy in a sound beam

intensity

units for intensity

w/cm²

typical values for intesity

.01-300 W/cm²

Intensity formula

Intensity=power/area

How is intensity determined

sound source

is intensity adjustable

yes

Distance or length of one complete cycle

wavelength

typical values for wavelength in soft tissues

.1-.8 mm

what is the only parameter determined by both sound source and medium

wavelength

how are wavelength and frequency related

inversely

wavelength formula

wavelength (mm) = 1.54 (mm/microsecond)/ frequency (Mhz)

Rate at which a sound wave travels through a medium

propagation speed

typical values for propagation speed

500 m/s - 4000 m/s

how is propagation speed determined

medium

propagation speed of lung

500 m/s

propagation speed of fat

1450 m/s

propagation speed of soft tissue

1540 m/s

propagation speed of liver and blood

1560 m/s

propagation speed of muscle

1600 m/s

propagation speed of tendon

1700 m/s

propagation speed of bone

3500 m/s

propagation speed of air

330 m/s

propagation speed of water

1480 m/s

how does stiffness affect speed

increases speed

5 parameters of pulsed sound

1. pulse duration

2. pulse repetition period

3. pulse repetition frequency

4. duty factor

5. spatial pulse length

pulse duration

duration of time from start of pulse to the end (talking time)

typical values for pulse duration

.3-2.0 microseconds

how is pulse duration determined

sound source

is pulse duration adjustable

no

pulse duration formulas

1. pulse duration= #cycles x period

   1. pulse duration= # cycles/frequency

Spatial pulse length

distance a pulse travels from the beginning of that pulse to the end of that pulse

typical values of spatial pulse length in soft tissue

.1-1.0 mm

how is spatial pulse length determined

sound source and medium

how is spatial pulse length related to # of cycles in the pulse

directly

how is spatial pulse length related to wavelength

directly

how is spatial pulse length related to frequency

inversely

pulse repetition period

the time from the start of one pulse to the start of the next pulse

typical values for pulse repetition period

100 microseconds - 1 millisecond

how is pulse repetition period determined

sound source

how is pulse repetition period adjusted

changing the depth

pulse repetition frequency

number of pulses transmitted into the body by the US system

typical values for pulse repetition frequency

1000- 10000 hertz

how is pulse repetition frequency determined

sound source

how is pulse repetition frequency adjusted

changing the depth

how are PRP and PRF related

inversely and reciprocals

duty factor

percentage or fraction of time that the system transmits a pulse

typical values for duty factor

.2%-.5%

how is duty factor determined

sound source

how is duty factor adjusted

changing the depth

duty factor formula

duty factor= pulse duration / PRP x 100

pressure

concentration of force in an area

density

concentration of a mass in a volume