Ultrasound Basic Physics Principles Flashcards
Directly Proportional
related so that one becomes larger or smaller when the other becomes larger or smaller
Related
- Being connected; associated.
2. Having a close harmonic connection.
Proportional
- Forming a relationship with other parts or quantities; being in proportion.
- Properly related in size, degree, or other measurable characteristics; corresponding.
- Having the same or a constant ratio.
- One of the quantities in a mathematical proportion.
Inversely Proportional
related so that as one becomes larger the other becomes smaller
Reciprocal Relationship
A number related to another in such a way that when multiplied together their product is 1. For example, the reciprocal of 7 is 1/7 ; the reciprocal of 2/3 is 3/2 .
Acoustic Propagation Properties
The medium has an effect on the variables of the wave.
Biologic Effects
Effect of the ionizing radiation on living organisms.
Pressure
concentration of force
units: lb/sq inch, Pascals Pa
Density
concentration of mass or weight
units: kg/cubic cm
Distance
measure of particle motion
units: cm, feet, miles
Transverse Wave
The molecules vibrate at 90 degrees to the direction of energy travel
Longitudinal Wave
The molecules vibrate in the same direction as the energy travels
In-phase wave
Two waves with the same frequency are “in phase” if they have the same phase and therefore line up everywhere
Out-of-phase wave
Two waves are out of phase if the peaks of one wave align with the troughs of the other
Constructive Interference
Peaks encounter peaks, troughs encounter troughs
= stronger wave results
Destructive Interference
Peaks encounter Troughs, troughs encounter Peaks
= smaller wave results
Source
- Physics- The point or part of a system where energy or mass is added to the system.
- A person or thing from which something comes into being or is derived or obtained.
Medium
substance that the sound travels through
Period
The time of a cycle
Frequency
How many cycles per second
Amplitude
Strength of the beam
Power
Rate that work is performed; rate of energy transfer
Intensity
Concentration of energy in certain areas of the sound beam (used for bioeffects)
Wavelength
The distance that one complete cycle occupies; the cycle length
Propagation speed
The speed at which sound wave moves through the medium
Density
The concentration of matter (mass per unit volume)
Stiffness
the resistance of material to compression
Pulsed Sound
- A pulse is a collection of cycles that travel together
- In continuous wave US cycles repeat continuously
Pulse Duration
Time from the start of one pulse to the end of the pulse
Spatial Pulse Length
- The distance a pulse occupies in space
- DISTANCE from the start of the pulse to the end of the pulse
- Units: meter, mm, any unit of distance
Pulse Repetition Frequency
- Number of pulses that occur in a single second
- Similar to frequency (number of events occurring per second)
- Units: Hz or per second
Pulse Repetition Period
- Time from the start of one pulse to the start of the next
- Includes both the time that the pulse is on and the time that it is off (dead time)
- Determined by: sound source
- Units: Seconds, microseconds
Duty Factor
- Percentage of time that the system is transmitting a pulse (or ‘on’ / not listening)
- Units – No units (unitless)
Spatial
- Related to space / areas of the beam
- Spatial intensity is greatest at the center of the beam and at the focus of the beam
Peak
the highest intensity area or time of the sound beam (maximum value)
Average
take peak, low, and medium intensities and average them together to get average intensity (mean value)
Temporal
- Temporal non-uniformity
- Occurs with time
Pulsed
- In continuous wave US cycles repeat continuously
- Continuous wave US cannot form images
- Must have listening time to form images
- A pulse is a collection of cycles that travel together
Decibel
- Decibel is 1/10th of a Bel
- Relative, not absolute units
- Two intensities or amplitudes are required for computation of decibels
- Decibels involve the use of mathematical logarithms
Attenuation
a reduction in intensity as wave travels through a medium
Reflection
- Occurs when sound energy strikes a boundary and some gets sent back to transducer. For reflection to occur, we MUST HAVE…..
1. An acoustic interface between two media……and…
2. The media must have different impedances for reflection to occur
Specular Reflection
- very smooth surfaced, mirror-like reflector
- Reflector is very large compared to sound beam’s wavelength
- Reflection is well-defined and regular
Backscatter
- Backscatter – scatter returning in the same general direction as the transducer
- But sound is disorganized and random
- Occurs when boundary has irregularities about the same size as the sound’s wavelength
Diffuse / Scattering / Non-Specular Reflection
- the random redirection of sound waves in multiple directions
- Produced when sound beam strikes a rough surface
- Where surface irregularities are same size or smaller than the wavelength
Scattering
- Attenuation process in which the beam interacts with interfaces smaller than the wavelength of the beam
- Causes the US energy to be dispersed in multiple directions
Rayleigh Scattering
- sound scatters symmetrically in all directions
- Not related to incidence angle
- Directly proportional to the frequency4
- If frequency is doubled, Rayleigh scattering is 16 times greater
Absorption
- Conversion of sound to heat
- Transfer of energy from the sound beam to the tissue
- Directly proportional to frequency
- Higher frequency; higher absorption, more attenuation
Attenuation Coefficient
are numerical values that express how different materials will attenuate the sound beam per unit path length
Half Value Layer Thickness
is the thickness of the material at which the intensity of radiation entering it is reduced by one half
Impedance
a material’s resistance to sound traveling through it (unit is Rayl)
Normal Incidence
Incoming sound strikes the boundary at 90 degrees
Oblique Incidence
sound beam strikes at any angle other than 90 degrees
Refraction
A bending from the straight line path or a change in direction of a sound wave traveling from one medium to another (goes in same general direction)
Snell’s Law
For two given media, the sine of the angle of incidence bears a constant relation to the sine of the angle of refraction
Range Equation
a relationship between the distance to a reflector and the time it takes for a pulse of ultrasound to propagate to the reflector and return to the transducer.
13 Microsecond Rule
In soft tissue, every 13 microsec of go-return time means the reflector is 1 cm deeper in the body
