# Shared Flashcard Set

## Details

Ultrasound Physics
Terms and facts for Ultrasound Physics
158
Physics
Professional
03/14/2012

Term
 X^0
Definition
 Any number raised to the zero power, or the exponent is 0 is 1.Ex. 10^0=1
Term
 Multiplying with Exponents
Definition
 When the base is the same add the exponents.Ex. 10^2 * 10^2= 10^4
Term
 Negative Exponents
Definition
 Take the reciprocal.Ex. 10^-2= 1/10^2
Term
 Dividing with Exponents
Definition
 When the base is the same subtract the exponents.Ex. 10^4/10^2=10^2
Term
 Giga
Definition
 G, 10^9Reciprocal: nano
Term
 Mega
Definition
 M, 10^6Reciprocal: micro
Term
 Kilo
Definition
 k, 10^3Reciprocal: milli
Term
 Hecto
Definition
 h, 10^2Reciprocal: centi
Term
 Deca
Definition
 da, 10^1Reciprocal: deci
Term
 Deci
Definition
 d, 10^-1Reciprocal: deca
Term
 Centi
Definition
 c, 10^-2Reciprocal: hecto
Term
 Milli
Definition
 m, 10^-3Reciprocal: Kilo
Term
 Micro
Definition
 u, 10^-6Reciprocal: Mega
Term
 Nano
Definition
 n, 10^-9Reciprocal: Giga
Term
 Directly Proportional
Definition
 An increase in one variable results in an increase in the related variable.
Term
 Indirectly Proportional
Definition
 An increase in one variable results in a decrease in the related variable.All inverse relationships are non-linear.
Term
 Logarithm
Definition
 The power to which a base number must be raised to get the desired number.Log10(100)=x: 10^x=100, 10^2=100, x=2
Term
 Log Rules
Definition
 Log(x*y)= Log(x)+Log(y)Log(x/y)= Log(x)-Log(y)
Term
 Logs to Know
Definition
 Log(1)=0 Log(5)=0.7Log(2)=0.3 Log (10)=1.0Log(4)=0.6
Term
 Distance Equation
Definition
 Distance= Rate*time
Term
 Wave
Definition
 A mechanism which transfers energy from one place to another.
Term
 Shock Wave
Definition
 A wave resulting from a sudden impact or impulse of energy.
Term
 Cyclical Wave
Definition
 When a wave is created from a somewhat repetitive source.Ex. ultrasound from a transducer.
Term
 First Classification of WavesHow a Wave Propagates
Definition
 1.Mechanical Waves: need a medium2.Electromagnetical: vacuum or medium
Term
 Electromagnetic Waves
Definition
 A transfer of energy through a varying electromagnetic field. Will travel in a vacuum or medium. Heat,Light,X-ray, Gamma,TV signal
Term
 Mechanical Waves
Definition
 A physical interaction between the wave(energy) and the media which the wave travels through. Must have a medium!Ocean waves, sound
Term
 Propagation of Mechanical Waves
Definition
 Propagation implies a change in location(of energy concentration) per time.
Term
 Transverse Waves
Definition
 Particle moves across or perpendicularto the wave's propagation direction.
Term
 Longitudinal Waves
Definition
 Particle motion is along the direction of the wave propagation.
Term
 Compressions
Definition
 "Close" Areas of high concentration in a longitudinal wave.
Term
 Rarefactions
Definition
 "Spread out" Areas of low concentration in a longitudinal wave.
Term
 Acoustic Variables (4)
Definition
 Changes due to mechanical interactions with the medium.1.Pressure 2.Density 3.Distance 4.Temperature
Term
 Pressure
Definition
 Force per area. P=F/APa(pascals)Atm(atmospheres)mmHg(millimeters of mercury)
Term
 Density
Definition
 p=m/V mass unit/volume unit; g/cm^3Density up-Speed down
Term
 Temperature
Definition
 Some wave energy is lost to heat.Celsius 0-100 freeze-boilFarenheit 32-212 freeze-boil
Term
 Particle Motion (Distance)
Definition
 Particles oscillate about their original location, they DO NOT actually travel, the energy does.
Term
 Acoustic Parameters (7)
Definition
 Describe the features of a particular sound wave. 1.Frequency 2.Period 3.Propagation Velocity 4.Wavelength 5.Amplitude 6.Power 7.Intensity
Term
 Frequency(f)
Definition
 Event/Time: Cycles/SecHertz(Hz)=1/sec the inverse is sec.Determined by source(transducer), not effected by the media, not changed by the sonographer.
Term
 Classification of Sound
Definition
 Infrasonic: 0-20HzAudible: 20-20,000HzUltrasonic: >20kHZDiagnostic: 2-12MHZ
Term
 Period(P)
Definition
 The time needed to complete a single cycle. P=1/fUnits of time.
Term
 Propagation Velocity(C)
Definition
 The rate at which the wave travels through the medium. Based on the medium. Distance/time: m/s
Term
 Propagation Velocities to Know
Definition
 Air: 330 m/sLung: 300-1200 m/sFat: 1450 m/sSoft Tissue: 1540 m/sTendon: 1850 m/sBone: 2000-4000 m/s
Term
 Wavelength (λ)
Definition
 The physical distance from one peak compression to the next peak compression. Units of length.
Term
 Wavelength Formula
Definition
 λ=C/f
Term
 Bigness Parameters
Definition
 The parameters a sonographer can change. Amplitude, Power, Intensity.
Term
 Amplitude
Definition
 The maximum variation of a(acoustic) variable from its mean value. Units are that of the acoustic variables. Amp= Max-Min/2, Mean= Max+Min/2
Term
 Characteristics of a Medium (3)
Definition
 1.Elasticity2.Compressibility3.Stiffness
Term
 Elasticity
Definition
 Jeans vs. Spandex. The ability for a solid object to return to its original shape after distortion by a force.
Term
 Compressibility
Definition
 Foam ball vs. golf ball. A measure of how much the volume of the material changes under a given pressure.
Term
 Stiffness
Definition
 A materiel that cannot be compressed much. The inverse of elasticity or compressibility. Stiffness up-Speed up
Term
 Bulk Modulus
Definition
 The decrease in the ratio of the stress to the strain. High BM=incompressible+inelastic+stiffLow BM=compressible+elastic+not stiffBM up-Speed up
Term
 Axial Resolution
Definition
 Ability to distinguish two structures that are parallel to the sound beam & close together. Depends on spatial pulse length (λ*# of cycles).
Term
 Power
Definition
 The rate at which work is performed, the rate of energy transfer. Determined by the source. Watts.P∝Amp^2
Term
 Intensity
Definition
 The concentration of energy within a sound beam. Determined by source. Watts/cm^2. P∝I∝Amp^2, I=Power/Beam Area
Term
 Decibels(dB)
Definition
 A logarithmic power ratio. Ratio implies division of 2 numbers.
Term
 Power Form of dB Equation
Definition
 dB=10*Log(Pf/Pi)
Term
 Amplitude Form of the dB Equation
Definition
 dB=20*Log(Af/Ai)
Term
 Relationship of f to Amplitude
Definition
 NOT related at all!
Term
 Attenuation
Definition
 A decrease in wave amplitude (or intensity) due to the mechanical wave interaction with the medium. Dependent upon: Pathlength (greater distance traveled,more attenuation) & frequency (higer f more attenuation).
Term
 Components of Attenuation(3)
Definition
 1.Absorption2.Reflection3.Refraction
Term
 Absorption (Attenuation)
Definition
 A conversion of energy from the sound wave into heat within the medium.Dependent upon: Viscosity (higher viscosity,higher absorption) & f (higher f higher absorption).
Term
 Reflection (Attenuation)
Definition
 A change in energy propagation direction such that some of the energy returns in the general direction of the source. The foundation for Diagnostic Ultrasound, we receive and process reflected energy to create images.
Term
 Attenuation Coefficient
Definition
 The amount of attenuation per centimeter. Units: dB/cm.Increase f, we increase the attenuation coefficient.
Term
 Attenuation Coefficients to Know
Definition
 1.Soft Tissue: .5dB/(cm-MHz)2.Muscle: 1.0dB/(cm-MHz)3.Blood: .125dB/(cm-MHz)
Term
 Time of Flight
Definition
 The time needed for an Ultrasound"pulse" to travel to the reflector and return to the transducer. Use: 2d=r*t. Also, go-return time.
Term
 Flight Time for 1cm
Definition
 13μsec (6.5μsec there-6.5μsec back).
Term
 Angle of Incidence
Definition
 The angle formed between the wave front and the interface of the reflecting structure is called the incident angle.The angle formed between the line perpendicular to the reflector and the wave direction.
Term
 Incidence for Specular Reflection.
Definition
 Must be 90°!
Term
 Normal Incidence (PORN)
Definition
 P:PerpindicularO:OrthognalR:Right AngleN:Ninety Degrees
Term
 The Angle of Reflection
Definition
 Equal to the angle of incidence, exceptuse the reflected wave front and direction.
Term
 Types of Reflection (3)
Definition
 1.Specular2.Scattering3.Rayleigh Scattering
Term
 Specular Reflection
Definition
 Mirror like, incident angle ALWAYS equals the reflected angle. Occurs with a smooth surface that is large in comparison to the wavelength.Must have: 1.PORN 2.Impedence Mismatch
Term
 Scattering Reflection
Definition
 Back Scattering. Occurs when the surface reflector is rough with respect to the wavelength.
Term
 Rayleigh Scattering
Definition
 Occurs when the reflecting structures are very small in comparison to the wavelength. Also f dependant, equal f^4. Ex. Blood.
Term
 Impedance
Definition
 Z=Density*C, Units: kg/(m^2*sec)=Rayls
Term
 Conservation of Energy
Definition
 The reflected energy plus the transmitted energy will equal the totalenergy.
Term
 Reflection Equation
Definition
 (Z2-Z1/Z2+Z1)^2= % Reflected energy.If Z2=Z1 then no reflection.If Z2 is much bigger than Z1 then 100% reflection.
Term
 Transmission Equation
Definition
 1-%reflected
Term
 Refraction
Definition
 Is effectively the bending of the wave at an interface of two media. Due to a change in propagation speed when a wave's incident angle is other than 0°.Must have an Oblique incidence and a difference in propagation speeds.
Term
 Snell's Law of Refraction
Definition
 Predicts the amount of refraction that will occur. Ci/Ct=sinθi/sinθt1500m/s/1500m/s=1
Term
 Attenuation Equation
Definition
 Pathlength*Attenuation Coefficient*Frequency
Term
 Continuous Wave
Definition
 "On" all of the time, 2 crystals, can't send and receive at the same time. Range ambiguity: unable to locate the depth of an object.
Term
 Pulsed Wave
Definition
 A pulse is a collection of cycles that travel together. "On & OFF", can send and receive. Range resolution(specificity). Used in all diagnostic ultrasound,except CW Doppler.
Term
 Parameters of a Pulsed Wave (6)
Definition
 1.Pulse Duration 2.Pulse Repetition Period 3.Pulse Repetition Frequency 4.Duty Factor 5.Spatial Pulse Length 6.Axial Resolution.
Term
 Pulse Duration (PD)
Definition
 The amount of time for which a transmit pulse lasts. From the start of one pulse, to the end of that pulse. Does not include listening time.Cannot be changed.
Term
 Pulse Repetition Period (PRP)
Definition
 The time until a transmitted pulse is repeated. From the beginning of one pulse to the beginning of the next pulse, includes listening time. Can be changed by changing listening time.
Term
 PD Equation
Definition
 PD = Period * #of Cycles.
Term
 PRP/PRF Relationship
Definition
 PRP = 1/PRF
Term
 Pulse Repetion Frequency (PRF)
Definition
 The number of pulses that occur in 1 sec. Related to imaging depth. Can be changed.
Term
 Duty Factor (DF)
Definition
 The percentage of time that a system transmits sound. DF=PD/PRPThe largest duty factor would be 100%, always transmitting.
Term
 Spatial Pulse Length (SPL)
Definition
 The length or distance that a pulse occupies in space. The distance of Pulse Duration. Important to axial resolution.
Term
 LARRD Resolution
Definition
Term
 LARRD Resolution Equation
Definition
 LARRD = SPL/2. Compare Axial Resolutionnumber to distance between structures. If the AR# is smaller than the distancewe can see the structures independantly. Short pulse means good Axial Resolution.
Term
 2-D Image
Definition
 Need1.Pulsed Wave:to reduce range ambiguity.2.Acoustic Line:a single beam transmitted in a specific direction.3.Receive Line:returning echoes registered by a system from a single line.
Term
 Diplay Line
Definition
 The data displayed on the screen.
Term
 Image
Definition
 An image is the picture generated by sequentially transmitting many acoustic lines in various directions and then reconstructing the received data (a frame).
Term
 Frame Time
Definition
 The amount of time it takes to complete 1 frame. Frame Time = # Lines*PRP
Term
 Frame Rate
Definition
 The reciprocal of frame time, the amount of frames per second. Hertz.Frame Rate= 1/Frame Time
Term
 Temporal Resolution
Definition
 The ability to accurately locate moving structures at any particular instant in time. Higher the frame rate worse the Temp. Res. Lower the frame rate better the Temp. Res.
Term
 Scan Lines
Definition
 The more scan lines, the longer it would take to create one image, or frame.
Term
 Imaging Depth
Definition
 The shallower the depth, the less amount of time it would take to send and receive an echo.
Term
 Resolution
Definition
 The ability or inability to distinguishbetween two structures or to visualize an activity.
Term
 Scanned Vs. Non-scanned Modalities
Definition
 1.Scanned modalities acquire information over a plane(or volume in 3D), non-scanned modalities acquire information only along a line.2.Temporal Resolution is degraded with scanned modalities.3.The risk of thermal bioeffects is usually much greater with nonscanned modalities.
Term
 Color Scans & Packets
Definition
 Each Color Display Line is comprised of multiple acoustic lines referred to as a packet or ensemble. As a result the frame time is generally greater, degrading temporal resolution.
Term
 Bandwidth
Definition
 The range of fequencies over which a device can operate. Imaging transducers have a Wide Bandwidth due to backing material.
Term
 Bandwidth(BW) Equation
Definition
 BW= Max. freq. - Min. freq.
Term
 Fractional Bandwidth (FBW)
Definition
 FBW= BW/Operating freq.
Term
 Quality Factor (QF)
Definition
 QF=1/FBW = Operating freq./BWRepresents the degree of damping. Imaging transducers are Low-Q, 2-3 pulses.
Term
 PD and BW
Definition
 PD∝1/BW
Term
 Bandwidth and Ultrasound Modes
Definition
 Widest to most narrow: B-mode,color Doppler,spectral PW Doppler, CW spectral Doppler.
Term
 Value of Greater Bandwidth
Definition
 1.Flexibility 2.Dynamic Frequency Tuning
Term
 CW Doppler and Bandwidth
Definition
 CW Doppler requires very little bandwidth. It has greater penetration and sensitivity.
Term
 Flexibility (BW)
Definition
 The ability to operate at different frequencies. Optimizes resolution and penetration. Aka: Multi-Hertz Operationand Frequency Agility.
Term
 Dynamic Frequency Tuning (BW)
Definition
 Transmit over the whole bandwidth, then receive frequency from higher to lower with increasing depth. Aka: Sliding Receive Filters.
Term
 Transducer
Definition
 Any device which converts one form of energy to another form of energy. Ex: nerves,lights,speakers,heaters.
Term
 Piezoelectric Effect
Definition
 Mechanical deformation results when an electric field is applied to certain crystal materials, or a varying electrical signal is produced when the crystal structure is mechanically deformed.
Term
 Pulse Wave Frequency and Crystal Thickness
Definition
 f(o)∝1/thickness
Term
 PW Operating Frequency Equation
Definition
 f(o){MHz}=C{mm/usec}/2t(mm)t=crystal thicknessC=in crystal
Term
 CW Operating Frequency
Definition
 f(o)=Transducer f=Drive Voltage f
Term
 Impulse Response
Definition
 A single pulse produces multiple cycles of ringing.
Term
 Crystal Diameter
Definition
 Larger diameter, larger beamwidth, deeper focus.
Term
 Lateral Resolution
Definition
 The ability to distinguish two structures that are perpindicular to the sound wave and close together.
Term
 Lateral Resolution Equation
Definition
 Lateral Resolution=Lateral BeamwidthHigher frequencies form narrower beams improving lateral resolution.
Term
 Matching Layer Thickness
Definition
 The ideal thickness is a quarter of the wavelength.
Term
 Changing the Focus
Definition
 1.Lenses 2.Curved Elements 3.Electronic Focusing 4.Mirrors
Term
 Piezoelectric Crystals
Definition
 Convert electropotential (voltage) into acoustic waves and acoustic waves back into voltage.
Term
 Backing Material
Definition
 Shortens spatial pulse length improving axial resolution.
Term
 Matching Layer
Definition
 Minimizes the acoustic impedance mismatch from crystal to tissue and tissue back to crystal.
Term
 Wires
Definition
Term
 Lens
Definition
 Helps to focus beam in the elevation plane.
Term
 PZT
Definition
Term
 Poling
Definition
 Heating the crystal and aligning the molecules with an electrical field.Increases the Efficiency.
Term
 Curie Point
Definition
 The temperature at which a material will lose efficiency as a piezoelectric material. 300C (572F) for PZT.
Term
 Near Zone Length (NZL)
Definition
 Aka: Focal Depth, Depth of Focus, Fresnel Zone. Where the beam converges.NZL(mm)=D^2(mm)*f(o){MHz}/6
Term
 NZL & Frequency
Definition
 NZL∝f(o)
Term
 NZL & Crystal Diameter
Definition
 NZL∝D^2
Term
 LAAST Resolution
Definition
 Lateral Angular Azimuthal Side-by-Side Transverse.
Term
 Pedof (Blind) Transducer
Definition
Term
 Sequencing
Definition
 Turning on and off swithches, groups of elements are activated over time (in sequence) to scan across the patient.
Term
 Linear Switched Array Transducer
Definition
 Obsolete. Straight,Sequenced,Multiple Crystals.
Term
 Mechanical Steering
Definition
 Crystal is pointed in different directions over time,via a motor, to produce an image.
Term
 Mechanical Transducers
Definition
 First used in cardiac imaging to get around the ribs.Disadvantage: Fixed Focus.
Term
 Mechanical(Phased) Annular Array Transducer
Definition
 Mechanical Steering, Phased (Electric) Focused, Rings, Multiple Crystals.Disadvantage: Rings were hard and expensive to make.
Term
 Phasing
Definition
 Electronic control is done by using small time(phase) delays between the excitation pulses which drive each element. By changing the delay pattern the beam can be steered and focused.
Term
 Sector Transducer
Definition
 Uses electric steering(Phasing) to create a sector scan. Most often used for cardiac imaging. TEE Transducer is one type.Advantage: Small transducer footprint.Disadvantage: Narrow near field image.
Term
 Phased Array Linear Transducer
Definition
 Phased(Electric) Focus and Steering, Multiple Crystals, Straight.Advantage:Bigger near field image, can be linear(unsteered) or can be somewhat steered and focused.
Term
 Curved Linear Phased Array Transducer
Definition
 Convex, Straight, Phased(Electric) Focus, Multiple Crystals.Mainly used for abdomen.Advantage: Variable FocusDisadvantage: Expensive
Term
 PZT Pro & Cons
Definition
 Pro: Very repeatable characteristics.High Freq. of natural resonance.Highly efficient.Cons: Generally a high impedance compared to tissue (30-40 Mrayls).This means a high amount of impedance mismatch, and reflection.
Term
 Case
Definition
 Protects the patient and sonographer from shock.Protects the crystals from damage.
Term
 Focus
Definition
 The location where the sound beam reaches its minimum diameter.
Term
 Focal Zone
Definition
 The region surrounding the focus.Where the beam is narrow and the picture is relatively good.
Term
 Far Zone
Definition
 Aka: Fraunhofer Zone.The region beyond the focus.Where the beam diverges.
Term
 A-Mode
Definition
 Amplitude ModeVery precise measurement of distance(depth). Shows an upward deflection when the signal returns.
Term
 B-Mode
Definition
 First form of gray scale imaging.Showed depth and intensity of reflection.
Term
 M-Mode
Definition
 Think motion. Displays the changing position of reflectors with the respect to time.
Term
 1.5-D Arrays
Definition
 More elements side by side than up and down. Improved elevation resolution.
Term
 2-D Arrays
Definition
 Performs 3-D scans. Same number of crystals side by side as up and down.
Term
 Volume Equation
Definition
 V=4πr^3/3Volume ∝ D^3
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