SPI 2 Flashcards
Absorption
Process where sound energy is dissipated in a medium
Heat
Acoustic
Having to do with sound
Acoustic impedance
Resistance to sound as it propagates through a medium
Acoustic variables
Effects on the sound beam caused by the medium
Pressure, density, distance
Amplitude
Strength of the compression wave; maximum variation of an acoustic variable
Attenuation
Weakening of sound as it propagates through a medium
Attenuation coefficient
Attenuation occurring with each centimeter that sound travels
Bandwidth
Range of frequencies found in pulse Ultrasound
Compression
Region of high pressure or density in a compression wave
Continuous wave
A nonpulsed wave in which cycles repeat indefinitely
Cycle
One complete variation in pressure or other acoustic variable
Decibel
A unit used to compare the ratio of intensities or amplitudes of two sound waves or two points along the wave
Density
Concentration of mass weight or matter per unit volume
Duty factor
Fraction of time that pulse Ultrasound is on
Frequency
Number of cycles in a wave occurring in one second
Half value layer
Thickness of tissue required to reduce the intensity of the sound beam by one-half
Aka- depth of penetration
Harmonic frequency
Echoes twice the frequency transmitted into the body that reflect back to the transducer, which improves image quality
Impedance
Determines how much of an incident sound wave is reflected back from the first medium and how much is transmitted into the second medium
Incident angle
Direction and of incident beam with respect to the media boundary
Intensity
Rate at which energy transmits over a specific area
Oblique incidence
Incident Ultrasound traveling at an oblique angle to the media boundary
Period
Time to complete one cycle
Pressure
Concentration of force
Propagation speed
Speed at which a wave moves through a medium
Pulse
Collection of a number of cycles that travel together
Pulse duration
Portion of time from the beginning to the end of a pulse
Sonography 2-3 cycles
Doppler 5-30 cycles
Pulse repetition frequency
Number of pulses per second
Pulse repetition period
Time between the beginning of one cycle and the beginning of the next cycle
Q factor
For short pulses the Q factor is equal to the number of cycles in a pulse; the lower the Q factor the better the image quality
Rarefraction
Regions of low pressure or density in a compression wave
Rayleigh’s scatter
Occurs when the reflector is much smaller than the wavelength of the sound beam
Reflection
Redirection (return) of a portion of the sound beam back to the transducer
Refraction
Change in direction of the sound wave after passing from one minute to another
Scattering
Redirection of sound in several directions on encountering a rough surface (non speculate reflection)
Spatial pulse length
Distance over which a pulse occurs
Speckle
Multiple echoes received at the same time generating interference in the sound wave, resulting in a grainy appearance of the US
Specular reflections
They compromise the boundaries of organs and reflect sound in only one direction. Angle dependent
Stiffness
Resistance of a material to compression
Temporal
Relating to time
Wavelength
Distance of one cycle
Sound categories
Infra - below 20Hz (below human hearing)
Audible- above 20Hz and below 20,000Hz (human hearing)
Ultrasound- over 20,000 Hz (above human hearing)
Sound waves carry?
Energy
Sound waves have areas of?
Compression (high pressure) and rarefraction (low pressure)
Frequency is proportional to?
Image quality and attenuation
Frequency is inversely proportional to
Wavelength, period and depth
Period is proportional to?
Wavelength
Period is inversely related to
Frequency
Propagation speed is proportional to
Stiffness in a medium
Propagation speed is inversely related to?
Density of a medium
Dense structures or pathology do what to propagation speed?
Decrease
Stiff structures do what to propagation speed?
Increase
Bone
Propagation speed of soft tissue
1.54 mm/ms
Wavelength is proportional to?
Period and depth
Wavelength is inversely related to?
Frequency
Amplitude
Sound strength
Amplitude is proportional to
Power
Amplitude does what through tissue?
Decreases
Intensity is proportional to
Power and amplitude of the wave squared
Intensity is inversely related to
Beam area
Power
Rate at which energy is transmitted into the body
Power is proportional to
Intensity
Pulse Ultrasound
A few pulses of Ultrasound followed by a longer pause of no ultrasound
Two components: transmitting and receiving
Bandwidth relationships
Inversely related to SPL and Q factor
Duty factor relationships
Directly related to PRF and pulse duration
Inversely related to PRP
Pulse duration relationships
Directly related to duty factor and number of cycles in pulse
Inversely related to PRF
PRF relationships
Proportional to duty factor
Inversely related PRP and imaging depth
PRP relationships
Proportional to imaging depth
Inversely related to PRF
Spatial pulse length relationships
Directly related to wavelength and number of cycles per pulse
Inversely related to frequency
Sound travels through tissues at different speeds depending on?
Density and stiffness of a medium
Sound travels faster in media that is denser than air because of
reduced compressibility
Normal incidence
Allows reflection of sound beam.
Oblique incidence
When incident sound beam strikes another boundary at any angle other than 90 degrees
What must take place for reflection to occur?
A difference in acoustic impedance between two structures and striking the boundary at a perpendicular angle
Harmonics frequency improves
Spatial and contrast resolution
Harmonics frequency decreases
Axial resolution
Harmonics frequency sound beams are
Narrower with lower side lobes increasing lateral resolution
Increasing depth does what to harmonics frequency?
Increases harmonic signals
Tissue harmonics created when?
During transmission
Contrast harmonics are created
During receiving
What must take place for refraction to occur?
Oblique incidence and a change in velocity or propagation speed between two media
Absorption
Conversion of sound to heat
Reflection
Redirection of sound beam back to transducer
Scattering
Redirection of sound in multiple directions
Attenuation relationship
Proportional to frequency and depth
Attenuation coefficient relationship
Proportional to frequency and depth
Density relationship
Proportional to impedance and propagation speed
Half value layer relationship
Inversely related to frequency
Impedance relationship
Proportional to density and propagation speed of the medium
Divergence
Widening of sound beam in the far field
Aperture
Size of transducer element
Apodization
Excitation of elements in an array to reduce grading lobes
Array
Collection of active elements connected to individual electronic currents in one transducer assembly
Axial resolution
Ability to distinguish two structures along a path parallel to the sound beam
Channels
Multiple transducer elements with individual wiring and system electronics
Constructive interference
Occurs when two waves in phase with each other create a new wave with amplitude greater than the original two waves;in phase
Convex array
Curved linear transducer containing multiple piezoelectric elements
Curie point
Temp to which a material is raised while in the presence of a strong electrical field, to yield piezoelectric properties.
What happens when temperature exceeds Curie point?
Crystal properties will be lost
Damping
Material attached to rear of transducer element reduce ringing
Destructive interference
Occurs when two waves out of phase with each other create a new wave with amplitude less than the two original waves
Diffraction
Deviation in the direction of the sound wave that is not a result of reflection, scattering, or refraction
Dynamic aperture
Aperture that increases as the focal length increases; minimizes change in the width of the sound beam
Element
Piezoelectric element of the transducer assembly
Elevational resolution
Detail resolution located perpendicular to the scan plane; it is equal to the section thickness and is the source of slice thickness artifact
Far zone
Region of the sound beam in which the diameter increases as the distance from the transducer increases
Focal length
Distance from a focused transducer to the center of the focal zone; distance from a focused transducer to the spatial peak intensity
Focal point
Concentration of the sound beam into a smaller area
Focal zone
Area at region of focus
Fraunhofer
Far zone
Fresnel
Near zone
Grating lobes
Additional weak beams emitted from a multi element transducer that propagate in directions different from the primary beam
Huygens principle
All points on a wave front or at a source are point sources for the production of spherical secondary wavelets
Interference
Occurs when two waves interact or overlap resulting in the creation of a new wave
Lateral resolution
Ability to distinguish two structures lying perpendicular to sound path
Matching layer
Material attached to front face of the transducer element to reduce reflections at the transducer surface
Near zone
Region of beam between the transducer and focal point which decreases in size as it approaches the focus
Operating frequency
Natural frequency of the transducer
Operation frequency is determined by
Propagation speed and thickness of element in pulse Ultrasound and by the electrical frequency in continuous wave
Phased
Multiple focal zones, beam steering and beam focusing
Applies voltage pulse to all elements in the assembly as a group, but with minor time differences.
Sequenced array
Operated by applying voltage pulses to a group of elements in succession
Side lobes
Additional weak beams traveling from a single element transducer in directions different from the beam
Subdicing
Dividing each element into small pieces to reduce grading lobes