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Cardiovascular Principles. Ultrasound Physics and Instrumentation. Wave. Definition: Disturbance or variation that transfers energy progressively form point to point in a medium. Wave. Key words: Disturbance Variation Transfer of Energy. Sound Wave.
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Cardiovascular Principles Ultrasound Physics and Instrumentation
Wave Definition: Disturbance or variation that transfers energy progressively form point to point in a medium.
Wave • Key words: • Disturbance • Variation • Transfer of Energy
Sound Wave Definition: Mechanical radiant energy that is transmitted by longitudinal pressure waves through a medium.
Sound Wave • Variables • Acoustic Variables
Acoustic Variables • Pressure • Density • Temperature • Particle Motion = Displacement
Acoustic Variable Variable versus Time High Low Variable Time
Acoustic Variable Variable versus Time Pressure Time
Acoustic Variable Variable versus Time Pressure T Time Period is the time it takes for a sound wave to complete one cycle of oscillation.
Acoustic Variable The period is inversely proportional to the frequency Period = T Frequency = f T = 1 f Period versus Frequency
Acoustic Variable Variable versus Time Pressure T Time
Acoustic Variable Variable versus Time Pressure T Time
Wavelength Variable versus Distance Pressure l Distance
Wavelength Wavelength is the space or distance over which a complete wave cycle occurs.
Wave Equation V = f l V = velocity f = frequency l = wavelength
Velocity Definition The velocity of sound is the speed with which a particular value of an acoustic variable moves.
Velocity The Velocity is determined by the Bulk Modulus and the density of the medium.
Velocity c = velocity B = Bulk Modulus r = Density
Velocity The Bulk Modulus is a measure of the stiffness of the medium.
Range Equation Distance = velocity x time
Range Equation Velocity = speed of sound in soft tissue. Distance = reflector distance. Time = time it takes the sound wave to reach reflector
Range Equation Time that can be measured is the go – return time The actual time = go-return time 2
Range Equation Reflector distance = velocity x go-return time 2
Amplitude Definition: Maximum variation in an acoustic variable. It is the difference between the resting value and the maximum value of an acoustic variable
Amplitude A Pressure Time
Amplitude • Amplitude decreases as the ultrasound wave travels in tissue. Increasing the amplitude • Increases depth of penetration • Increases the sensitivity
Power • The rate of doing work • Units – Watts • Determine by the Ultrasound System • Power is proportional to amplitude squared.
Intensity Intensity is the concentration of power in a sound beam. Intensity = power area
Pulsed Ultrasound A C A = PRP B = Pulse Duration C= Reception Time B
Pulsed Ultrasound Pulsed Duration = period x cycles per pulse PRP = the time form the beginning of one pulse to the beginning of the next. PRP = 1 PRF
Pulsed Ultrasound • # of pulses per second is determined by • Strength of the excitation voltage. • The damping characteristics
Pulsed Ultrasound PRF = # of pulses per second Duty Factor = PD PRP
Pulsed Ultrasound SPL Distance
Pulse Ultrasound Spatial Pulse Length = SPL SPL = wavelength x cycles per pulse SPL determines the axial resolution
Intensity Values The area of the beam is not uniformed. therefore the Intensity in the sound beam is not uniform. Beam Cross-sectional Profile
Intensity Values Spatial – refers to the space variation Temporal – refers to the time variation
Intensity Values Peak – the maximum value Average – the mean value
Intensity Values Spatial Peak Intensity is measured along the central beam axis where the beam area is narrowest. Spatial Average intensity is the average intensity in the sound beam and is usually measured at the transducer surface.
Intensity Value Temporal Peak Intensity is the maximum intensity when the sound is on. Temporal average is the average intensity during the whole pulse cycle. Pulsed Average Intensity is the average intensity during the duration of the pulse only. TP > PA > TA
Pulsed UltrasoundTemporal Intensities C A A = Temporal peak B = Pulse Average C= Temporal Average B
Intensity Values TP SP PA SA TA
Intensity Value TA Intensity = Pulsed Average Intensity x Duty factor DF = TA/PA For Continuous Wave Ultrasound the DF = 1
Intensity Value The SP/SA factor describes the distribution of intensity in an ultrasound beam in space: SP/SA factor = SP Intensity SA Intensity SP/SA factor = BUR (Beam Uniformity Ratio)
Attenuation Decibel Unit
Logarithm Logarithm to the base 10 of a number is equal to the number of 10 that must be multiplied together to result in that number. Or It is the power to which 10 must be raised to produce that number.