Physics Test 1 study guide
DECIBELS decrease in Amplification
If signal that attenuates by 3dB, the signal strength has decreased by 1/2; If the signal that attenuates by 10dB, the signal strength is 1/10 as strong
DECIBELS Increase in Amplification
If signal that increases by 3 dB the signal is 2x stronger; If signal increases by 10dB it is 10x stronger; ie (27 increased to 30. There is a 3dB increase making the amplification doubled.
How do you calculate the Incident Intensity?
Incident Intensity = Reflected % + Transmitted % ??
What is the relationship between PRF & PRP?
Indirectly related
What is the relationship between Wavelength and Frequency?
Indirectly related. Wavelength increases the frequency decreases as signal takes longer to return.
Relationship between Density & Speed?
Indirectly related; Density increases, Speed decreases (beer belly patient)
What are the 3 categories of sound?
Infrasound - <20 Hz Audible - 20Hz to 20,000Hz or 20KHz (heard by man) Ultrasound - >20,000Hz
Intensity
Intensity doesn't have a symbol. Definition - Concentration of energy in a sound beam. Units - Watts/square centimeters, or W/cm2 (watts from Power and cm2 from the beam area). Determined by the sound source/machine. Sonographers ARE able to adjust intensity. I = P/A
What is the relationship between Intensity, Power, and Amplitude?
Intensity increase = Power increase Intensity is proportional to Power. Intensity is proportional to Amplitude². Intensity (watts/cm²) = Power(watts)/Beam Area (cm²)
What is the relationship between Frequency & PRP?
Inversely related; If depth increases, the PRP decreases; meaning get more pulses in shorter distance as wave return quicker, ie the "off time" decreases. Frequency increases, the PRP decreases
Wavelength
Symbol λ, other name is lambda. Definition - Distance or length of a single cycle. Units - mm, meters (units of length). Determined by BOTH the sound source and the medium. Not adjustable by the sonographer. λ = C/F
What is the relationship between Power and Amplitude?
Power and Amplitude is proportional to one another.
Power
Power has no symbol. Definition - Rate that work is performed, or rate of energy transfer. Units - Watts. Determined by the sound source. Power CAN be adjusted by the sonographer.
What is the relationship between power & amplitude?
Power is proportional to amplitude² If Power doubles, then amplitude² increases by 4.
What are the 3 acoustic variables that identify sound waves?
Pressure - concentration of force within an area. force/area; units pascals. Density - Concentration of mass within a volume. units kg/cm³ Distance - Measure of particle motion. units mm, cm
What is the relationship between Power & Amplitude(squared)
Proportional. Power decreases by 2, amplitude decreases by 4.
What is the biggest influence on PRP?
Depth; PRP is depth dependent. If depth increases, the off time will increase. Meaning takes longer to receive the following pulse.
What is the relationship between Period and Frequency?
inversely related As frequency increases, the wave will decrease. If the frequency decreases, the wave will increase. They are reciprocals.
Acoustic propagation properties
the effects of the medium upon the sound wave (ie what does the bone do to the sound wave? What does the body do to the sound wave?)
biological effects
the effects of the sound wave upon the biological tissue through which it passes (what the sound wave does to the medium "tissue). Extreme high frequency can & will burn tissue.
What is the wavelength of soft tissue if the Frequency is 1 MHz? If Frequency is 2 MHz?
λ = C/F In soft tissue divide 1.54 mm by the frequency of the transducer. 1MHz wavelength of 1.54 mm. 2 MHz wavelength is 0.77 mm
What is the equation for Spatial Pulse Length (SPL)
# cycles x wavelength
What is the Pulse Duration(us) equation?
# of cycles x Period (T) or # cycles/frequency(MHz)
What is the definition of Pulse Repetition Frequency (PRF Hz)
# of pulses per 1 second
What is PRF?
# of pulses per second; measured in hz
What is the Duty Factor (%) equation?
(Pulse Duration/PRP) x 100 = %
What is 40us converted to seconds
.00004 s
5 things to know about sound waves
1.) Sound waves carry energy 2.) Sound waves are mechanical waves 3.) Sound waves can only travel through a media (water, tissue, etc) 4.) Sound waves can only travel in a staight line. (Waves can bounce off walls, but NO bending) 5.) Sound waves are LONGITUDINAL waves
What is the propagation speed of soft tissue?
1.54 mm/us
What is 5 MHz converted to Hz
5,000,000 Mz
50m converted to mm
50,000
What is the Coefficient attenuation (AC) (dB/cm) over 5cm of tissue with 5MHz of sound
AC= Frequency/2 or .5 x Frequency
What are the 3 things that make up the "Bigness of a Wave"?
Amplitude Intensity Power
Amplitude
Amplitude has no symbol. Definition - The bigness "energy" of the wave. It is the difference between maximum & minimum values compared to the average. Unit - pressure(pascals), Density(g/cm³) Determined by the source/machine. Amplitude CAN be adjusted by the sonographer. Amplitude is measured from base to peak or baseline to trough. Peak to peak amplitude is measured from peak to trough.
Rarefaction
An area where the particles in a medium are spread out; located at the trough of a wave. (low acoustic variables)
What is the wavelength determined by? Medium and/or Source
Both; Only parameter that is determined by both medium & source.
What are other names to describe "Stiffness"?
Bulk modulus Low elasticity Low compressibility
What are the 3 types of Interferences?
Constructive, Destructive, and Combination.
Relationship between Stiffness & Speed?
Directly Related; Stiffness increases, speed increases
What is the relationship between PRP & Depth?
Directly related; If depth increases, the PRP increases as the "off time" increases as it takes longer for pulse wave to return
True or False; PRP (Pulse Repetition Period) is directly related to the Period (T).
False!! PRP has NOTHING to do with the Period (T). It is only depth dependent.
Compression has what type of pressure?
High Pressure (Pascals)
True or False, The normal Duty Factor for pulsed wave ultrasound is 100%.
False; It is 1%. If it is 100% that indicates continuous wave as there is no off time, the on time is continuously on. If DF is 0%, it means that the machine is not running.
What is the Equation for Frequency(MHz)?
Frequency (MHz) = c/wavelength
What is the relationship between Frequency (F) and Period (T)
Frequency and Period are indirectly related. Frequency increases, Period will decrease; Frequency decreases, the Period will increase.
What is the relationship between wavelength and frequency?
Frequency and Wavelength are INDIRECTLY related
What is the relationship Frequency vs Penetration & Frequency vs Detail
Frequency increase, Penetration decrease INDIRECTLY related; Frequency increases, Detail increased DIRECTLY related
Why do different mediums have different propagation speeds?
It's due to their stiffness and speed.
Rarefraction has what type of pressure?
Low Pressure (Pascals)
Propagation Speed of structures in the body
Lung has propagation speed of .5 mm/μs (Slowest) Fat has propagation speed of 1.45 mm/μs Soft tissue has propagation speed of 1.54 mm/μs Muscle has propagation speed of 1.6 mm/μs Bone has propagation speed of 3.5 mm/μs (Fastest)
What is Propagation Speed determined by? Medium or Source
Medium only, (Bone is the fastest at 3.5mm/us & Lung is the slowest at .5mm/us
Combination Interference
Most common interference; Waves striking the medium at different angles at different times.
If PRP gets longer, what happens to the PRF?
PRF decreases
What is the equation for PRP us?
PRP = PD us + Off Time us
what are the 7 Acoustic Parameters?
Period, Propagation Speed, Power, Frequency, Wavelength, Amplitude, and Intensity. *3PWIFA*
Period
Symbol = T Equation T = 1/F Definition = The time required to complete a single cycle (1 compression & 1 rarefraction). He can also be described as the time from the start of a cycle to the start of the next cycle. Unit of measurement - μs; microseconds. Determined by the machine (source). Period is NOT adjustable by sonographer.
Propagation Speed
Symbol - C. Definition - The rate that sound travels through a medium, also called Velocity or speed. Units - m/s, mm/μs. Determined by the medium ONLY. NOT adjustable by the sonographer. Propagation speed of soft tissue 1,540m/s, = 1.54km/s = 1.54mm/μs C = λ x F
Frequency
Symbol - f definition - events per interval of time, ie how often something happens. How many cycles are completed in 1 second. Units - Hz Determined by the source. Frequency is NOT adjustable by the sonographer; however one could change the probe to a multi hertzing (linear transducer) F = C/λ
Once you calculate the AC, what is the total attenuation?
Take the AC(dB/cm) x distance = dB/cm
What happens to PRP is the depth Increases?
The PRP will increase as the off time will increase.
Compression
The part of a longitudinal wave where the particles of the medium are close together; located at the peak of a wave (high acoustic variables)
What is the Pulse Repetition Period ms, us (PRP)?
The time from the start of one pulse to the start of the next pulse; On Time + Off Time.
What is a Longitudinal wave?
The wave energy moves parallel to the direction of the vibration. (side to side)
What is a Transverse wave?
The wave energy moves perpendicular to the direction of the vibration; example shaking rope up and down.
What is the definition for Pulse Duration?
Time that it takes for 1 pulse to occur in us.
True or false; Medium affects the sound wave as it travels through it.
True
True or false, decreased penetration = images with greater accuracy?
True; Decreased penetration = Increased frequency
Constructive Interference
Waves that the peak and trough allign; (can have different amplitudes); When in phase waves combine they create a large wave (waves add together).
Destructive Interference
Waves that the peak and trough do NOT allign; When waves are combined, they create smaller waves (they subtract from one another); If waves are 180° they cancel each other out.
