Ultrasound Physics Flashcards
____ is caused by a mechanical deformation induced by an external force with a resultant increase in the pressure of the medium
COMPRESSION
This occurs following the compression event - as the backward motion of piston reverses the force, the compressed particles transfer their energy to adjacent particles with a subsequent reduction in the local pressure amplitude.
RAREFACTION
Distance compressions or rarefactions.
Distance between any two points that repeat on the sinusoidal wave of pressure amplitude.
WAVELENGTH
Determined by the frequency and speed of sound.
Number of times the wave oscillates through one cycle each second.
FREQUENCY
Infrasound is
Less than 15Hz
Audible acoustic spectrum
15Hz to 20kHz (20,000Hz)
Ultrasound spectrum is
Above 20kHz
Diagnostic ultrasound uses 2-10MHz
Time duration of one wave cycle
PERIOD
Fundamental property that generates echoes (and contrast) in an ultrasound image.
Difference in the speed of sound at tissue boundaries
Defined as the peak maximum or peak minimum value from the average pressure on the medium in the absence of a sound wave
PRESSURE AMPLITUDE
Pascal (Pa) - Newton per square meter
Thickness that reduces the ultrasound intensity by 3dB
HVT (HALF VALUE THICKNESS)
Occurs by reflection or refraction usually by small particles within the tissue medium, causing the beam to diffuse in many directions (which gives rise to characteristic texture and gray scale in the acoustic image)
SCATTERING
Describes the change in direction of the transmitted ultrasound energy with non perpendicular incidence.
REFRACTION
This occurs at tissue boundaries where there is a difference in the acoustic impedance of adjacent materials.
Reflection
Is the process whereby acoustic energy is converted to heat energy whereby sound energy is lost and cannot be recovered
Absorption
The si unit for acoustic impedance
R a y l
is equal to 1 kg per meter squared second
When the wavelength of ultrasound beam is much greater than structural variations of the boundary
Smooth interface
Determined by the speed of sound change that occurs at a boundary
Angle of refraction
Term used for describing scatter characteristics where in higher scatter amplitude is seen
Hyperechoic
Hypo- lower scatter amplitude
It converts electrical energy into mechanical energy by physical deformation of the crystal structure
Piezoelectric material
These are molecular entities containing positive and negative electric charges that have an overall neutral charge. When mechanically compressed by an externally applied pressure the alignment of the dipose is disturbed from the equilibrium position to cause an imbalance of the charge distribution.
Electrical dipoles
Most common synthetic piezoelectric ceramic material
Led zirconate titanate (PZT)
Layered on the back of the piezo electric element this material absorbs the backward directed ultrasound energy and attenuates three ultrasound signals from housing.
Damping block
This is the primary use of acoustic coupling gel
Removing air pockets which could attenuate and reflect sound beams
Acoustic impedance is similar to soft tissue
Lower frequency ultrasound is transmitted into the patient and the higher frequency harmonics created from the interaction with contrast agents and tissues are received as echoes
Harmonic imaging
What are the basic elements of a CMUT (capacitive micromachined ultrasound transducers)?
Capacitor cell with a fixed electrode (backplate)
Free electrode (membrane)
The near field is a jason to the transducer phase and has a converging beam profile, also known as
Fresnel zone
These are unwanted emissions of ultrasound energy directed away from the main pulse caused by the radial expansion and contraction of the transducer element during thickness contraction and expansion
Side lobes and grating lobes
Refers to the ability to discern two closely spaced objects in the direction of the beam
Axial resolution
Also known as azimuthal resolution refers to the ability to discern as separate two closely space objects perpendicular to the beam direction
Lateral resolution
Hypo intense signal area distal to an object or interface and is caused by objects with high attenuation or reflection of the incident beam without the return of echoes
Shadowing
This occurs distal to objects having very low ultrasound attenuation such as fluid field cavities arise from increase transmission of sound by these structures
Enhancement
Displayed as a series of parallel bonds extending posterior to a collection of gas
Ring-down artifacts
This occurs with multi elementary transducers and result from the division of a smooth transducer surface in the a large number of small elements
Grating lobes
Pseudosludge is an example of _____
Side lobe
Created when a high prf limits the amount of time spent listening for echoes during the prp
Ambiguity
Represented as a rapidly changing mixture of colors typically seen distal to a strong reflector such as a calculus and is often mistaken for aneurysm when evaluating vessels
Twinkling artifact
May be used to identify small renal stones
Rate of energy production absorption or flow
Power
SI unit: Watts (1Joule per second)
The rate at which sound energy flows through a unit area and is usually expressed in watt per square centimeter
acoustic intensity
This is the ratio of the acoustical power produced by the transducer to the power required to raise tissue in the beam area by 1° c
Thermal index
Cavitation is a consequence of negative pressures that induce bubble formation from extraction of result gases in the medium. While ___ is a value that estimates the likelihood of cavitation by the ultra sound beam
Mechanical index
Determined by the average ultrasound intensity in the focal zone and the absorption coefficient of the tissue
Heat deposition
