Exam 1 Flashcards
Importance of Physics
- Learn DMS
- Understand Artifacts
- Prep for instrument performance measurements
- Become aware of safety and risk factors
Doppler Effect
Christian Doppler
1840
Piezoelectric Effect
Piere and Marie Curie
1880
Distance Formula
Distance = Rate of speed X time of trace
Rate of speed in soft tissue?
1540 m/s
Or
1.54 mm/us
13 microsecond rule
Time for sound to travel 1cm and back in soft tissue
Linear Scan
- Rectangular Display
- Pulses travel in the same direction
Sector Scan
- each pulse shares origin
- subsequent pulses go out in different directions
Doppler Effect -> in ultrasound
If an echo generating structure is moving, the echo will have a different frequency than pulse enjoyed by the transducer
Metric Measurements
Mega(M)
Million (10^9)
Metric Measurements
Kilo(k)
Thousand(10^3)
Metric Measurements
Hecto(h)
Hundred (10^2)
Metric Measurements
Centi(c)
Hundredth(10^-2)
Metric Measurements
Mili(m)
Thousandth(10^-3)
Metric Measurements
Micro(u)
Millionth(10^-6)
Metric Measurements M k h c m m(u)
Mortal kombat has crazy many murders(u)
Sound
The sensation produced by vibrations through a medium; gas, liquid, etc
Wave
A disturbance that travels through a medium and moves its energy from one location to another
Compression
An area of increased particle density
Top of wave
Refraction
An area of decreased particle density
Bottom of wave
Acoustic Variables
Pressure
Density
Particle Motion (Disturbance)
Temp
Acoustic Variables
Pressure
Concentration of force
Units: Pascals (Pa), lbs/sq in, atmospheres
Acoustic Variables
Density
Concentration of mass or weight
Units: kilo per cubic cm
Acoustic Variables
Particle Motion
Distance
Units: meter, cm, feet
Acoustic Variables
Temp
Measurement of heat
Units: Degrees
Ultrasound Pulse Principles
- Pulse Repetition Frequency
- Pulse Repetition Period
- Pulse Duration
- Duty Factor
- Spatial Pulse Length
Range Equation
Distance = Rate x Time
What is a Pulse?
- a short burst of sound energy
- a collection of a number of cycles
- all these cycles travel together
- each Pulse has a beginning, middle, & end
PRF
Pulse Repetition Frequency
- number of pulses the ultrasound transducer emits in 1 second of time
- units: Hz or kHz
- typical range of PRF is 1-10 kHz
PRP
Pulse Repetition Period
- the time from the beginning of one pulse to the start of the next Pulse
- PRP includes the time the machine is producing the pulse and the time it is listening for the pulse to return
What is the relationship between PRP & PRF?
They are reciprocals
Ex)
-PRF=(1/PRP)
-PRP=(1/PRF)
Can PRP be changed?
Yes, because PRF is the reciprocal of PRR and PRP can be adjusted on the US machine
PD
Pulse Duration
- the time (duration) of an ultrasound pulse
- units: time (microseconds)
- typical PD for US is 0.5-0.3 microseconds
PD equation
Pulse Duration = # of cycles in a pulse x period
PD increases if?
- Period increases
- # of cycles in pulse increases
- frequency decreases
DF
Duty factor
- the fraction of time that the ultrasound machine is sending out a pulse of sound
- DF is expressed as a decimal point or fraction
DF equation
Duty factor = Pulse Duration / Pulse Repetition period
Acoustic Variables
Pressure
Density
Particle vibrations/movements
Temperature
Bigness Parameters
Amplitude
Power
Intensity
Attenuation
Amplitude
The maximum variation in an acoustic variable
Decibels
- not an exact number
- used to express a ratio or difference between a reflected signal and source signal
- based info logarithmic scale of numbers
Positive decibels
\+3dB = doubling intensity (2x the original)] \+6dB = quadrupling intensity (4x the original) \+9dB = 8x the original \+10dB= 10x the original \+20dB = 100x the original
Negative decibels
- 3dB = halfing intensity (½ the original)
- 6dB = quartering intensity (¼ the original)
- 9dB = ⅛ the original
- 10dB = 1/10 the original
- 20dB = 1/100 the original
Logarithm (log)
-a mathematical numerical rating system
-the number of 10s that are multiplied together to equal a number
Ex) Log of 100 = 2
How can a sonography change the amplitude?
Adjusting the Power Control
Power
-rate of energy transference
The number of pulses emitted in 1 second is termed what?
Pulse Repetition Frequency
The beginning of one pulse to the beginning of the following pulse is termed pulse is termed what?
Pulse Repetition Period
What is the relationship between PRF and PRP?
They are reciprocals
When we increase depth what happens to the Pulse Repetition Period
PRP increases
When we increase depth what happens to Pulse Repetition Frequency?
PRF Decreases
What term measures the duration of the US pulse?
Pulse Duration
What formula for Pulse Duration? What are the units?
PD= (# of cycles in pulse) x (period)
What term do we use for the fraction of time the US machine is sending out a pulse?
Duty Factor
What is the equation for the above term? What are the units?
DF = PD / PRP DF% = PD / PRP x 100
What term do we use for the length of an US pulse?
Spatial Pulse Length
What is the equation for SPL?
SPL = (# of cycles in pulse) x wavelength(mm)
What are the units for PRP?
Seconds
What are the units for PRF?
Hz of kHz
What is the term when the US machine has just sent out a pulse and is waiting for it to come back?
Receiving time
If Period decreases, what happens to the Pulse Duration?
PD decreases
What happens to SPL if Frequency increaseS?
SPL Decreases
Three components of attenuation?
Reflection
Absorption
Scatter
As path length increases, the attenuation of ultrasound in soft tissue?
Path length increases = path length increases
Units of attenuation?
dB/cm
T/F
In a given medium, the attenuation is unrelated to the speed of sound
True
What are the units of half layer thickness?
Cm & mm
As Frequency decreases, what happens to the depth of penetration?
It increases
T/F Amplitude, power and intensity can be changed by the sonographer?
True
Which intensity is related to tissue heating?
SPTA
What is the importance of describing sound beam intensities in a variety of ways with regard to space and time?
Intensity is important in bio effects
What are the units of the transmitted intensity of a sound wave?
Watts/cm^2
As the sound travels in the body, what happens to the intensity of the wave?
Intensity decreases
What determines the initial amplitude if a wave?
The transducers capability determines the initial amplitude
Requirements for refraction
- oblique incidence
- different propagation speeds between the media
Refraction
Bending of a beam of sound, or change in direction of a beam of sound as it passes from one medium to another
Oblique incidence
Anything besides 90 degree incidence
- reflection uncertain
- transmission uncertain
Relation of incidence angle and reflection angle “Law of Reflection”
Incidence angle = reflection angle
40 degree = 40 degree
Average impedance for soft tissue
1,630,000 Rayls
Or
1.63 x 10^6
2 factors for reflection to occur
1) angle @ which sound strikes the boundary must be 90 degrees
2) the 2 tissues or mediums must have different acoustic impedances
IRC & ITC relationship
- IRC & ITC must = 100% of original intensity
- all sound must be accounted for
Ex: if IRC is 3% then ITC should be 97%
Reflected sound
The sound that is reflected @ the boundary or interface & returns to the transducer
Transmitted sound
Transmission
The sound that continues to propagate I. The direction it was going, after hitting a boundary of interface
Incident sound
The sound that is coming from the sound source & going to the medium
How is Rayleigh scattering affected by Frequency?
Frequency increases, scattering increases
Scattering
- occurs when sound encounters irregular, boundaries or tissue
- redirected into many directions
2 types of scattering
Backscatter (diffused reflection): sound returns toward the transducer
Rayleigh scattering : sound is redirected in all directions
dB in relation to increasing or decreasing power or gain
+dB = increases in value (turn up power or gain)
-dB = decrease in value (turn down power or gain
Relationship between Period & Frequency (PRP & PRF)
Reciprocals (inversely related)
-PRF = 1/PRP or PRP = 1/PRF
Sound speed in different tissues
Solids are faster than liquids, liquids are faster than gases
Density of medium
Density increase = speed of sound decrease
Density decrease = speed of sound increase
Hardness of medium
- Dominant role
- the stiffer or less elastic a medium is the faster the sound travels in it
- stiffness increase then the speed increases
- stiffness decreases then the speed of sound decreases
2 properties of medium affecting speed of sound
1) hardness of medium (stiffness)
2) density of medium ( related to weight)
What affects propagation speed
- only the medium affects propagation speed
- if the medium does not change, the speed of sound will not change
What affects wavelength?
- transducer Frequency
- the medium sound travels in
Wavelength
- Reciprocal of frequency
- length of space that one wave occupies
- units: mm, meters, inches, etc
- US units = mm
- US wavelength = 0.1-0.8
Ultrasound Frequencies
Usually between 2.0-12.0mHz
Choice of frequency affects:
1) penetration
2)image resolution - increased frequency
Frequency is determined by the transducer
Categories of sound
Infrasound: <20Hz
Audible sound: within range of hearing 20Hz - 20,000Hz
Ultrasound: >20,000Hz
Image depth equation
(Rate x Time) / 2
