Particle Motion And Wave Propragation Flashcards
At the most basic levels of sonography what are the five steps ?
- Operator control
- Transducer activation (Sending)
- Sound interaction
- Transducer action (receiving)
- Image display
What is the Piezoelectric effect?
When pressure waves are applied to certain crystals they produce electric pulses or a voltage
What is reverse piezoelectric effect?
When electric pluses or voltages are applied to certain crystals they produce sound waves
What does the term acoustic mean?
Refers to sound
What is propagation?
Refers to travel
What is acoustic Propagation?
Refers to the effect tissues cause on sound
What does Bioeffects mean?
Refers to the effects of a ultrasound on tissue
What is sound?
Sound is a propagation variation (a wave).
What can an sound waves carry?
Sound waves can carry energy not matter
Does sound waves require a medium to travel?
Yes
What are variables?
Qualities of waves
What variables apply when sound travels through mediums?
- Pressure
- Density
-Rarefaction-low density
-compressions-high density - Particle motion
- Temperature
What is density?
The concentration of particles or mass per unit of volume
What is rarefactions
Regions of low density
What are compressions?
Areas of high density
In terms of sound what role does temperature play?
Sound is an energy.
Energy creates heat
What are sound waves?
Sound is a mechanical wave and therefore, requires a medium to travel
What are the two types of sound waves?
Longitudinal and transverse waves
What are longitudinal waves?
Back and forth particle motions parallel to direction of wave travel
What are transverse waves?
Perpendicular motion to wave travel
What types of mediums support longitudinal waves?
Solids, liquids and gases
What mediums can support transverse waves?
Solids only
What is mode conversion?
When one type of wave is converted into another form.
An example of this may occur at a tissue bone interface
In terms of waves what is common to all waves? 6
- Frequency
- Period
- Wavelength
- Propagation speed
- Amplitude
- Intensity
What is Frequency?
Simply a measurement of how often something happens.
With sound we can say it is the number of complete variations goes through in one second
What is the unit of frequency?
Hertz (Hz)
What frequency does ultrasounds run on?
MHz (megahertz)
What is period (T)?
The time it takes for one cycle to occur
How is Period measured?
Period is measured in seconds, or in ultrasound in microseconds
What is wavelength?
The length of space one cycle takes up
What is the formula for frequency?
F=1/T and W=C/F
What does the Frequency formula tell us about the relationship?
If Frequency increases time and wavelength decrease. and vice versa
What is propagation speed (c)?
The speed with which the wave moves through a medium
How much is Propagation speed (c)?
1.54 mm/us or 1540 m/sec
What are variables we need to find wave strength?
Amplitude, intensity, and power
What is amplitude?
Maximum variation of an acoustics variation
What is intensity?
Power of wave divided by the area
It is also equal to amplitude squared
What is power?
Total energy over the entire cross- sectional area
What is the formula for power/intensity?
I= P/A
In a sound beam where is the intensity the greatest?
Greatest and the centre and falls off near the periphery
What is Spatial intensities?
The greatest intensity found across the beam. This is called the spatial peak.
Where is the Spatial peak found? And what is it?
Near the centre of the beam, and is the place of the beam with the greatest intensity
What is spatial average? And where is it found?
Average intensity measured over the entire beam, it is usually found at edge of the transducer or the edge of the flashlight
How are SP(spatial peak) and SA(spatial average) related
They are related based on the uniformity ratio (BUR)
What is the Uniformity ratio (BUR)
BUR= SP/SA
What is Temporal Peak (TP)?
The greatest intensity found in the pulse
What is pulse average?
Average for all values found inside a pulse
Can TP and PA be used interchangeably?
Yes, they are almost identical and can be used interchangeably
How do we convert the SP to SA
Divide it by BUR
How do we convert SA to SP
X BUR
How do we convert TP to TA?
We X DF
How do we convert the TA to TP
We divide by DF
Considering SPTA what different modes of ultrasounds from lowest value to the highest are available
- M mode
- Real Time B mode
- Doppler
- Continuous wave (no dead time SPTP)
Ultrasound machines are calibrated to what speed?
1540 m/s
If Ultrasounds machines are calibrated to C, Does that velocities do the same?
No velocities actually differ in different tissues and as a result artifacts may occur
What is the actual velocities found in fat?
1460 m/s
What is the actual velocity found in bone?
4080 m/s
What is the distance equation?
D = C x T
In the distance equation what is D?
D is the distance to the reflector and back
What is C in the distance equation?
C is the average speed of sound in soft tissue
What is T in the distance formula?
T is the time for the round trip
How do we get the distance to the reflector?
We get the distance and then divide it by 2
What is the 1 CM rule?
In 13 microseconds the sound wave travels to and back from a object 1 cm away
What are two categorizes of waves and what type of wave is used in ultrasound?
Two types of waves are electromagnetic and mechanical.
Ultrasound uses mechanical
Which combined intensity has the lowest value
SATA
What is the purpose of describing intensities in both space and time?
This terminology is needed to asses for bioeffects since we must consider the amount of sound transmitted into the patient along with the time of exposure
How does the intensity change when the area of the sound beam is reduced by half?
It is halved because intensity is indirectly proportional to the area
