# Ultrasound Physics

 pressure, density, and particle vibration; sound wave quantities that vary in space and time acoustic variables region of low density and pressure in a compressional wave rarefaction reduction in differences between small and large amplitudes. region of high density and pressure in a wave compression wave in which the particle motion is parallel to the direction of wave travel (compressional wave) longitudinal wave number of cycles per second frequency unit of frequency, one cycle per second; unit of pulse repetition frequency, one pulse per second. hertz T/F A wave is a traveling variation of some quantity or quantities. True T/F Sound is a traveling variation of acoustic variables. True T/F Acoustic variables include pressure, density, and particle motion. True T/F A cycle is one complete variation in pressure or other acoustic variable. True T/F Frequency is the number of cycles in a wave that occur in 1 second. True One hertz is one cycle per second. The abbreviation for hertz is Hz. True T/F One kilohertz is 1000 cycles per second. The abbreviation for kilohertz is kHz. True T/F One megahertz is one million cycles per second. The abbreviation for megahertz is MHz. True sound of frequency too low for human hearing (<20 hertz) Infrasound sound of frequency too high for human hearing (>20,000 hertz) Ultrasound imaging depth penetration time per cycle period the common unit for period in ultrasound microsecond (μs) Period = 1/Frequency T (μs) = 1 / f (MHz) If frequency increases, period _______. decreases length of space over which a cycle occurs wavelength T/F Wavelength is commonly expressed in millimeters. True the speed with which a wave moves through a medium propagation speed Wavelength is = propagation speed (c) divided by frequency λ (mm) = c (mm/μs) / f (MHz) If frequency increases, wavelength ______. decreases the resistance of a material to compression stiffness Propagation speeds are highest in ______ and lowest in ______. solids (highest)gases (lowest) Propagation speed values in soft tissue range from _____ to _____. 1.44 to 1.64 mm/μs The average propagation speed of sound in tissue is _____. 1.54 mm/μs progression of travel propagation sound propagation in which the propagation speed depends on pressure causing the wave to shape to change and harmonics to be generated nonlinear propagation the primary frequency in a collection of frequencies that can include odd and even harmonics and subharmonics fundamental frequency frequencies that are even and odd multiples of another, commonly called fundamental or operating frequency harmonics a wave in which cycles repeat indefinitely; not pulsed. continuous wave ultrasound produced in pulsed form by applying electric pulses or voltages of one or a few cycles to the transducer pulsed ultrasound a brief excursion of a quantity from its normal value; a few cycles pulse T/F With continuous wave ultrasound, cycles repeat indefinitely. Pulsed ultrasound consists of pulses separated by gaps in time. A pulse is a few cycles of ultrasound. True number of pulses per second pulse repetition frequency or pulse repetition rate interval of time from the beginning of one pulse to the beginning of the next pulse repetition period PRF is commonly expressed in kilohertz PRP is commonly expressed in milliseconds PRP (ms) = 1 / PRF (kHz) If pulse repetition frequency increases, pulse repetition period ______. decreases Interval of time from beginning to end of a pulse pulse duration T/F Shorter pulses, compared with longer ones, improve the quality of sonographic images. True T/F Sonographic pulses are typically 2 or 3 cycles long. Doppler pulses are typically 5 to 30 cycles long. True Pulse duration = period (time for one cycle) X number of cycles in the pulse (n) PD (μs) = n X T (μs) T/F Pulse duration is the time for a pulse to occur. True T/F If frequency is increased, period is decreased, reducing pulse duration. If the number of cycles in a pulse is reduced, pulse duration is decreased. True fraction of time that pulsed ultrasound is on duty factor T/F Longer pulses increase the duty factor because the sound is on more of the time. True DF = PD (μs) / PRP (μs) DF =( PD (μs) X PRF (kHz) ) / 1000 (kHz / MHz) T/F If pulse duration increases, duty factor ______. increases if PRF increases, pulse repetition period _____ and duty factor ________. decreasesincreases length of space over which a pulse occurs spatial pulse length Spatial pulse length = length of each cycle X the number of cycles in the pulse SPL (mm) = n X λ (mm) T/F Spatial pulse length is the length of space that a pulse takes up. True T/F If the number of cycles in a pulse increases, spatial pulse length increases. If frequency increases wavelength and spatial pulse length decrease. True T/F Shorter pulses improve sonographic image resolution. True range of frequencies contained in an ultrasound pulse; range of frequencies within which a material, device, or system can operate. bandwidth bandwidth divided by operating frequency fractional bandwidth nonspecific term referring to amplitude or intensity strength maximum variation of an acoustic variable or voltage amplitude power divided by area intensity rate at which work is done; rate at which energy is transferred power T/F If beam power increases, intensity increases. If beam area decreases (focusing), intensity increases. True force multiplied by displacement work conversion of sound to heat absorption decrease in amplitude and intensity with distance as a wave travels through a medium attenuation portion of sound returned from a media boundary; echo reflection diffusion or redirection of sound in several directions upon encountering a particle suspension or a rough surface scattering reflection echoes unit of power or intensity ratio; the number of decibels is 10 times the logarithm (to the base 10) of the power or intensity ratio. decibel attenuation per centimeter of wave travel attenuation coefficient time it takes a wave to vibrate a single cycle period Period is determined by the ________ _______. sound source the number of particular events that occur in a specific duration of time. in ultrasound, the number of cycles that occur in one second frequency Diagnostic range of frequency in ultrasound 2 MHz - 10 MHz Frequency is determined by the ______ _______. sound source Frequency and period have what type of relationship inversely proportional and a reciprocal relationship distance or length of one complete cycle wavelength wavelength is determined by the ______ ______ and the _____. sound source and medium shorter wavelengths produce ______ quality images higher frequency and wavelength have a _______ relationship as long as they are in the same medium inverse the distance that a sound wave travels through a medium in 1 second propagation speed propagation speed is determined by the medium order the medium that sound travels the fastest in (normal states of matter) solids liquids gases 2 medium characteristics that affect propagation speed stiffnessdensity propagation speed and stiffness are ______ related directly other name for stiffness bulk modulus propagation speed and density are ______ related inversely the difference in the maximum value and the average or undisturbed value of an acoustic variable may also be the difference between the minimum and the average amplitude amplitude is _______ by the sonographer adjustable the difference between the maximum and minimum values of an acoustic variable peak-to-peak amplitude rate of energy transfer power power is measured in watts power is _____ by the sonographer adjustable power is ______ to the amplitude ______ proportionalsquared concentration of energy in a sound beam intensity intensity = power/cross sectional area Intensity is measured in watts/cm ^2 intensity is _______ by the sonographer adjustable intensity and power are ________ proportional intensity is proportional to the amplitude _______ squared What parameters describe pulsed sound? pulse durationpulse repetition periodpulse repetition frequencyduty factorspatial pulse length the actual time from the start of a pulse to the end of that pulse pulse duration pulse = # cycles X period pulse duration = # cycles / frequency pulse duration is ______ to the number of cycles in the pulse proportional pulse duration is ______ proportional to the period directly Pulse duration is _______ proportional to the frequency directly long pulses have either many cycles individual cycles with long periods short pulses have either few cycles in the pulseindividual cycles with short periods clinical imaging uses pulses that contain how many cycles 2-4 distance from the start of a pulse to the end of that pulse spatial pulse length SPL = # of cycles X λ SPL is ______ proportional to the number of cycles directly SPL is ______ proportional to the wavelength directly SPL is _______ proportional to frequency inversely The major difference between SPL and PD SPL refers to distance PD refers time time from the start of one pulse to the start of the next pulse . includes the pulse duration and the listening time PRP PRP is related to the ____ of view depth PRP and imaging depth are ______ related directly the number of pulses that are transmitted into the body each second Pulse repetition frequency depth of view and PRF are ______ related inversely PRP and PRF are _______ related and ______ inversely related and reciprocals seconds (PRP) go with hertz (PRF) milliseconds (PRP) go with ______ (PRF) kilohertz the percentage of time or fraction of time that the system is transmitting a pulse duty factor duty factor% = (pulse duration / PRP) X 100 a duty factor of 1 would refer to a ______ wave continuous wave a duty factor of 0 means the system is _____ off duty factor is _____ related to imaging depth inversely What are the 7 parameters required to completely characterize a sound wave? periodfrequencywavelengthspeedamplitudepower intensity tissue/material through which the sound waves travel medium 3 parameters describe the size, magnitude, or strength of a sound wave amplitudepower intensity 10^9 giga G billion 10^6 mega M million 10^3 kilo k thousand 10^2 hecto h hundred 10^1 deca da ten 10^-1 deci d tenth 10^-2 centi c hundredth 10^-3 milli m thousandth 10^-6 micro µ millionth 10^-9 nano n billionth AuthorQwizdom100 ID104276 Card SetUltrasound Physics DescriptionNotes Updated2012-08-26T16:27:55Z Show Answers