Ultrasound Basic Physics Principles Flashcards
a mathemamatical relationship whereby two phyical are related; increasing or decreasing together, and with a constant ratio
Directly Proportional
Describes a relative relationship between two variables
Related or Proportional
Implies an opposite relationship between two variables.
Inversely Proportional
the absolute inverse of a quantity.
Reciprocal Relationship
The term for sound energy travel from one thing to another through a medium
Acoustic Propagation Properties
An undesired biological change to tissues as a result of interaction with the ultrasound beam (ex. heat)
Biologic Effects
concentration of force, units: lb/sq inch, Pascals Pa
Pressure
concentration of mass or weight, units: kg/cubic cm
Density
measure of particle motion, units: cm, feet, miles
Distance
A wave that oscillates perpendicular to the axis along which the wave travels.
Transverse Wave
waves that molecules vibrate in the same direction as the energy travels
Longitudinal Wave
Two waves with the same frequency, therefore line up everywhere
In-phase wave
Waves with the same frequency but different phases
Out-of-phase wave
Greater wave interference +
Constructive Interference
Lesser wave interference -
Destructive Interference
transducer
Source
The material through which a mechanical waves propagate
Medium
The time of a cycle
Period
How many cycles per second
Frequency
Strength of the beam
Amplitude
Rate that work is performed; rate of energy transfer
Power
Concentration of energy in certain areas of the sound beam
Intensity
The distance of one cycle
Wavelength
The speed at which the cycles travel
Propagation speed
The concentration of matter (mass per unit volume)
Density
The resistance of material to compression
Stiffness
Collection of cycles that travel together
Pulsed Sound
Time from the start of one pulse to the end of the pulse, # of cycles in the pulse x period or # of cycles in pulse/frequency
Pulse Duration
The distance a pulse occupies in space
from the start of one pulse to the end of the pulse,
units: meter, mm, any unit of distance,
# of cycles in the pulse x wavelength
Spatial Pulse Length
Time from the start of one pulse to the start of the next, units: seconds, microseconds
Pulse Repetition Period
Number of pulses that occur in a single second, units: Hz or per second
Pulse Repetition Frequency
Percentage of time that the system is transmitting a pulse (or ‘on’ / not listening)
Duty Factor
space related (physical dimension)
Spatial
the highest intensity area or time of the sound beam (maximum value)
Peak
take peak, low, and medium intensities and average them together to get average intensity (mean value)
Average
(time related) variations
Temporal
a collection of cycles that travel together
Pulsed
1/10th of a Bel, Bel is a logarithmic ratio of the relative power in two acoustic beams
Decibel
reduction in intensity as wave travels through a medium
Attenuation
When some of the energy of the beam is reflected back to form an echo, while the remainder of the beam carries on traveling forward through the tissue
Reflection- Specular
When the interface is rough and the undulations are approximately one wavelength or less then sound is reflected in all directions
Reflection- Diffuse
the random redirection of sound waves in multiple directions
Scattering
sound scatters symmetrically in all directions
Rayleigh Scattering
Transfer of energy from the sound beam to the medium (tissue) through which it is traveling.
Absorption
attenuation occurring per/cm sound travel
Attenuation Coefficient
The distance the sound beam penetrates into the tissue when its intensity is reduced to half the original value
Half Value Layer Thickness
a material’s resistance to sound traveling through it (unit is Rayl
Impedance
Perpendicular, Orthogonal, Right Angle, Ninety Degrees (PORN) – Occurs when the sound beam strikes a boundary between 2 media at exactly 90 degrees
Normal Incidence
sound beam strikes at any angle other than 90 degrees
Oblique Incidence
When the beam encounters an interface between two different tissues at an oblique angle, the beam will be deviated as it travels through the tissue.
Refraction
formula which gives the relationship between the angle of incidence and the angle of refraction when beam of sound passes through an interface between two tissues where the speed of sound is different
Snell’s Law
Relationship between round trip pulse-travel time (sound to interface and echo coming back from it), propagation speed, and distance to a reflector.
Range Equation
In soft tissue, every 13 microsec of go-return time means the reflector is 1 cm deeper in the body.
13 Microsecond Rule
