What factors influence the choice of frequency in ultrasound imaging?
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A trade-off between spatial resolution and penetration depth.
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What factors influence the choice of frequency in ultrasound imaging?
A trade-off between spatial resolution and penetration depth.
What is generally assumed about ultrasound in medical imaging?
It is the safest medical imaging modality.
What is the mechanism similar to scattering in ultrasonic properties?
Specular (mirror-like) reflection.
In which imaging scenarios should contrast agents be avoided?
In fetal imaging.
What is the microscopic mechanism of piezoelectricity?
It can be understood as a collection of randomly oriented electric dipoles.
What is one attractive characteristic of ultrasound in diagnostic radiology?
Relatively low cost.
What are the two main components of an acoustic wave?
Compressions and rarefactions (expansions).
What is the formula for lateral resolution in ultrasonic transduction?
Lateral resolution is obtained by setting the sinc function = 0 in L F LR λ = ( ) ( F Lx x U λ sinc).
What type of wave is discussed in section 12.2 of the IAEA Diagnostic Radiology Physics handbook?
Ultrasonic plane waves.
What is the focus of Chapter 12 in the Diagnostic Radiology Physics handbook?
Ultrasound and its various aspects.
How is the lateral beam pattern computed in ultrasound imaging?
By ignoring the η and y terms.
What is the primary mechanism of attenuation in ultrasound?
Thermal absorption.
What is pulse-echo imaging typically performed with?
The same focused aperture for transmission and reception.
What happens when an applied force deforms a piezoelectric crystal?
It results in a rearrangement of the dipoles that induces a net charge across the crystal.
What happens to the signal received from the range gate when scatterers are moving in Pulsed-Wave Doppler?
The signal changes with each subsequent pulse, creating a staircase signal.
What additional output do Doppler systems provide besides audio?
The time-frequency spectrum of the demodulated signal.
What is the transmission coefficient for plane waves in fluid media at normal incidence?
It is given by the formula involving the acoustic impedances and amplitudes of the waves.
What operation is used to construct the staircase signal in Pulsed-Wave Doppler?
Sample-and-hold operation.
What does the Rayleigh resolution criterion define?
It defines the resolution as the distance from the peak of the beam to the first zero of the beam.
What improves the bandwidth and sensitivity of an ultrasonic transducer?
Sandwiching the piezoelectric crystal between a backing layer and a matching layer.
What is the relationship between PRF and the depth of the range gate?
Maximum PRF is given by c / (2z), where z is the depth.
What is the most commonly used diagnostic imaging modality?
Ultrasound.
What theory is applied to analyze the beam pattern in ultrasonic transduction?
Scalar diffraction theory.
What occurs when a voltage difference is applied across a piezoelectric crystal?
It changes the arrangement of the dipoles, producing a bulk deformation of the crystal.
How does an acoustic wave propagate?
Via transfer of momentum among incremental volumes of the medium.
What is the conventional material used for fabricating transducers in diagnostic imaging?
Ferroelectric ceramic lead zirconate titanate (PZT).
What is the relationship between the amplitudes of incident and reflected waves in ultrasound?
They are related by the reflection coefficient, R.
What happens to the angles of incidence and transmission at normal incidence?
The angles are equal, θ_i = θ_t = 0.
What are Ultrasonic Plane Waves?
A type of wave used in ultrasound imaging.
What are some medical applications of ultrasound?
Cardiac and vascular imaging, imaging of abdominal organs, and in utero imaging of the developing fetus.
What principle is used to analyze the beam pattern produced by an ultrasound transducer?
Huygens-Fresnel principle.
What does the mechanical index (MI) measure?
The relative risk of inducing cavitation.
What is the purpose of high-velocity Doppler mode in pulsed-wave Doppler?
To use a higher PRF than the range-gate depth would ordinarily allow, increasing |v max|.
What physical processes influence the information in an ultrasonic image?
Propagation, reflection, and attenuation of ultrasound waves in tissue.
When does scattering occur in ultrasonic waves?
When the wave encounters a variation in the acoustic impedance of the medium.
How can an aperture be described in the context of ultrasound transduction?
As a collection of point sources.
What is a significant safety advantage of ultrasound waves?
They are non-ionizing.
What is Doppler ultrasound used for?
To image moving blood and estimate blood velocity.
What type of wave does the transmitter emit in Continuous-Wave Doppler?
A continuous sinusoidal wave in the form cos(ω₀t).
What does I SPTA stand for in ultrasound exposure measurement?
Spatial Peak Temporal Average Intensity.
What is the purpose of the backing layer in a transducer?
To absorb ultrasound radiated from the back face of the crystal and dampen reverberations within the crystal.
Which source of attenuation is the most significant in diagnostic ultrasound?
Thermal absorption.
What occurs when c1 < c2 in terms of wave transmission?
The wave is bent away from the normal.
What frequency range is generally used for diagnostic imaging with ultrasound?
From 2 to 15 MHz.
What is an acoustic wave?
A traveling pressure disturbance that produces alternating compressions and rarefactions of the propagation medium.
What is cavitation in the context of ultrasound?
Oscillation in the volume of a gas bubble in response to pressure fluctuations produced by an incident ultrasound wave.
What feature of ultrasound scanners enhances their usability?
Portability.
What increases the risk of inertial cavitation during ultrasound imaging?
The presence of excess gas, particularly significant volumes of gas bubbles.
What is the effect of nonlinear propagation at low acoustic intensities?
It is negligible.
How does Pulsed-Wave Doppler address the limitations of CW Doppler?
By transmitting a sequence of short pulses instead of a continuous sine tone.
What is the formula for the Doppler effect in ultrasound?
c f v f D o D θ cos 2 =.
What is produced by the superposition of spherical wavelets in ultrasound transduction?
The field produced by the aperture.
What capability allows ultrasound to visualize dynamic processes?
The ability to produce real-time images of blood flow and moving structures.
What is the relationship between the amplitudes of incident and transmitted waves in ultrasonic plane waves?
They are related by the transmission coefficient, T.
What are some additional applications of ultrasound mentioned?
Cancer imaging, musculoskeletal imaging, and ophthalmology.
What happens when a high-intensity ultrasound pulse is transmitted through tissue?
A substantial amount of energy can be transferred to the tissue, increasing the risk of adverse effects.
What is the formula for calculating the mechanical index (MI)?
MI = p_max / p_max(−) after correction for attenuation.
What does Snell's law describe in the context of ultrasonic plane waves?
The relationship between the angles of incidence and transmission when a wave crosses an interface between two media.
What does the pixel gray scale in a Doppler spectrum represent?
The magnitude of the short-time Fourier transform of the Doppler signal.
What does the pressure plane wave p(x, t) propagate through?
A homogeneous, non-attenuating fluid medium.
What are the main causes of attenuation of ultrasonic waves in a medium?
Specular reflections, divergence, scattering from inhomogeneities, and thermal absorption.
Who prepared the slide set for the IAEA publication?
E. Okuno from the Institute of Physics of S. Paulo University.
What integral describes the resulting beam in the far field of an unfocused aperture?
The Fraunhofer diffraction integral.
What type of cavitation does low-intensity ultrasound typically produce?
Harmless stable cavitation.
What effect does nonlinearity have on an initially sinusoidal wave?
It distorts it into a sawtooth pattern.
What is a key advantage of using PZT in transducers?
It provides a relatively high electrical-to-mechanical coupling efficiency at low cost.
What is the frequency range of ultrasound?
Greater than 20 kHz, which is the maximum frequency audible to humans.
How is ultrasound technology evolving?
Ongoing technological improvements continue to expand its use for various applications.
What does the lateral point-spread function (PSF) depend on?
The square of the sinc function.
What is the primary shortcoming of Continuous Wave (CW) Doppler?
The lack of spatial resolution due to the large area of overlap between the transmitter and receiver beams.
What limits the pulse-repetition frequency (PRF) in Pulsed-Wave Doppler?
The depth of the range gate.
How can biological effects of ultrasound be utilized beneficially?
By therapeutic ultrasound devices.
How is the lateral resolution (LR) calculated in pulse-echo imaging?
LR = λ / (L_F).
What size features cause scattering in ultrasonic waves?
Features with dimensions similar to or smaller than the wavelength.
What happens in high-velocity mode regarding pulse transmission?
The second (and perhaps third) pulse is transmitted before echoes from the first pulse are received.
What does the sample-and-hold step limit in Doppler measurements?
The maximum Doppler frequency that can be measured without aliasing.
Why is the term p_max(−) used in the MI formula?
It reflects that inertial cavitation is triggered by the overexpansion of a gas bubble.
How do scattered echoes compare to specular reflections?
Scattered echoes are omnidirectional and significantly weaker than specular reflections.
What is the typical range of the f-number for ultrasound imaging systems?
Typically between 2 and at most 6.
What is the effective sampling frequency in Doppler measurements?
The pulse-repetition frequency (PRF) of the transmitted pulses.
How are the acoustic impedances Z related to the transmission and reflection coefficients?
They are used in the formulas to calculate the coefficients for incident and transmitted waves.
What does the equation of continuity represent?
A mass balance for an incremental volume of the medium.
What does the sinc function represent in the context of ultrasound imaging?
The Fourier transform of the rect function.
What can occur in pulsed Doppler techniques due to multiple pulses being transmitted?
Local heating can occur at the focus.
How do higher frequency waves affect ultrasound imaging?
They can be focused more tightly but are attenuated more rapidly by tissue.
What is the maximum blood flow velocity under normal conditions at the entrance to the aorta?
About 1 m/s.
What is the field in a plane at distance z from the aperture represented as?
U(x, y).
What is a typical shape of the pulse-echo lateral point-spread function (PSF)?
A sinc² beam.
What does the measured Doppler spectrum include?
Contributions from all moving scatterers within the area of intersection of the two beams.
What does U(ξ, η) represent?
The field in the aperture plane.
What do most tissues contain that can lead to cavitation?
Small volumes of gas that can coalesce to form cavitation nuclei.
What happens to each incremental volume of the medium in an acoustic wave?
It undergoes small oscillations about its original position but does not travel with the pressure disturbance.
What type of aperture do ultrasound imaging systems typically employ?
A focused rectangular aperture.
What does a pixel in a Doppler spectrum indicate?
The proportion of red blood cells moving at a particular velocity at a specific time.
Who studied the Doppler effect and in what year?
Christian Doppler in 1842.
What form do the received echoes take if the reflectors are moving?
The form cos([ω₀ + ω_D]t), where ω_D = 2πf_D.
What does the Doppler signal consist of in high-velocity mode?
A superposition of echoes from within the range gate due to the first pulse and echoes from shallower depths due to subsequent pulses.
What is the purpose of the spectral display in Doppler systems?
To effectively present the pulsatile characteristics of intra-cardiac and vascular flow.
In the context of Pulsed-Wave Doppler, what does the variable 'z' represent?
The depth at which the range gate is positioned.
What does the vertical dotted line represent in the Doppler signal illustration?
The sample time for obtaining the Doppler signal.
What does the equation involving η, ξ, and λ represent?
It involves a two-dimensional spatial Fourier transformation with effective spatial frequencies.
What is the Doppler equation used to calculate Doppler frequency?
fD = (c / |v|) * fo * cos(θD)
What is introduced into the wave's frequency spectrum when a sinusoidal wave transforms into a sawtooth wave?
Harmonics.
What dimensions are typically treated as separable in medical ultrasound imaging?
Lateral (x) dimension within the image plane and elevation (y) dimension perpendicular to the image plane.
When is cavitation most likely to occur in vivo?
When microbubble contrast agents are employed or if the lungs are exposed to ultrasound.
What does the Doppler equation indicate about MHz transmit frequencies used for diagnostic ultrasound?
They will produce Doppler frequencies of at most a few kHz, which is within the range of audible frequencies.
What formula is used to calculate maximum velocity in high-velocity Doppler mode?
v max = (D o / PRF) * (c / 4 * cos θ).
What does p_max represent in the MI formula?
The peak rarefactional pressure.
What is done to the output of the sample-and-hold operation in Pulsed-Wave Doppler?
It is low-pass filtered to obtain a smoothly varying Doppler signal.
What is the f-number of a transducer?
F / L is called the f-number of the transducer.
What is the effect of a single pulse at diagnostic imaging intensities on tissue temperature?
The local temperature rise is small.
When should caution be exercised when using contrast agents?
In echocardiography of patients with pulmonary hypertension or other unstable cardiopulmonary conditions.
What is the relationship between the smoothed signal frequency and the Doppler frequency?
The frequency of the smoothed signal is equal to the Doppler frequency.
How is ultrasound exposure traditionally quantified?
By measuring the spatial peak temporal average intensity (I SPTA).
What happens as the echo from each successive transmission is received in Pulsed-Wave Doppler?
A single sample at the expected arrival time of echoes from the range gate is acquired and held until the next pulse echo is received.
What is Ultrasonic Transduction?
The process of converting electrical energy into ultrasound waves and vice versa.
What are many modern transducers made of?
Composites of PZT and a non-piezoelectric polymer.
According to Shannon’s sampling theorem, what is the formula for the maximum unaliased frequency of the smoothed Doppler signal?
f max = PRF / 2.
What is the formula for the amplitude of a wave in the presence of attenuation?
P(x, t) = P₀ e^(-αx) cos(ωt - kx), where α is the attenuation coefficient.
How is the attenuation coefficient α related to frequency in soft tissues?
α is proportional to f^m, where 1 < m < 2.
What is the relationship between U(y, x, z) and the spatial frequencies kx and ky?
They are related through the two-dimensional spatial Fourier transformation.
What does a CW Doppler transducer consist of?
Two adjacent piezoelectric elements angled slightly toward one another.
Why does repeated insonation increase the risk of thermal bioeffects?
Because heat may accumulate more quickly than it can be dissipated by blood flow.
What are the angles involved at a planar interface in ultrasound?
Angle of incidence (θᵢ), angle of reflection (θᵣ), and angle of transmission (θᵗ).
Which book discusses Doppler ultrasound physics and instrumentation?
'Doppler Ultrasound: Physics, Instrumentation and Signal Processing' by D.H. Evans and W.N. McDicken.
What is the attenuation coefficient of liver at 1 MHz?
0.96 dB/cm.
How is acoustic impedance (Z) defined for a plane wave?
Z = ρ₀ * c, where ρ₀ is the undisturbed mass density of the medium and c is the speed of sound.
Who is the author of 'Estimation of Blood Velocities Using Ultrasound'?
J.A. Jensen.
What is the attenuation coefficient of muscle at 1 MHz?
1.2 dB/cm.
Since when have most scanners displayed real-time estimates of TI and MI?
Since 1992.
What is the attenuation coefficient of skull bone at 1 MHz?
11.3 dB/cm.
What happens to a wave transmitted into a second medium when c1 > c2?
The wave is bent toward the normal.
What happens near the focus of beams used for diagnostic imaging?
Density variations produced by the wave become significant.
How is the intensity of an ultrasound wave defined?
As the average power per unit cross-sectional area.
What does 'c' represent in the formula for maximum PRF?
The speed of sound in the medium.
How many slides are in the IAEA slide set?
54 slides.
Why are biological effects of ultrasound undesirable during diagnostic imaging?
Because they can pose risks to the patient.
What happens to the frequency of waves in the direction of motion according to the Doppler effect?
The frequency is compressed.
How is a Doppler signal recovered from the received signal?
Via frequency demodulation of the received signal.
What is the general range for lateral resolution in ultrasound?
Generally in the 1-2 mm range.
What is the typical range of peak pressures used in diagnostic imaging?
0.1 – 4.0 MPa.
Why might low-MI scanning not always be feasible?
Some contrast-enhanced imaging protocols require disrupting microbubbles at MI > 1 to obtain diagnostic information.
Which book focuses on diagnostic ultrasound principles and instruments?
Diagnostic Ultrasound: Principles and Instruments, 7th edn. by Kremkau.
How is thermal absorption used in therapeutic ultrasound?
For hyperthermia treatment of cancerous tumors by transmitting high-intensity pulses.
Who authored 'Fundamentals of Physical Acoustics'?
D.T. Blackstock.
What is the focus of 'Foundations of Biomedical Ultrasound'?
Biomedical ultrasound principles.
What is the unit of the frequency-dependent amplitude attenuation coefficient (α)?
Np/m (nepers per meter).
What does the wave number (k) represent?
k = 2π/λ, where λ is the wavelength.
What does ρ₀ represent in the context of acoustic impedance?
The undisturbed mass density of the medium.
What is κ in the context of ultrasound?
The compressibility of the medium.
What is the acoustic impedance of water?
1.48 MRayl.
What is the acoustic impedance range for blood?
1.61-1.65 MRayl.
Where is the lowest sound speed found?
In gases.
What operation is described in the context of Pulsed-Wave Doppler?
Sample-and-hold operation.
What are the two most important mechanisms for biological effects of ultrasound?
Thermal absorption and cavitation.
Which equations are used to formulate a pressure plane wave?
Euler’s equation and the equation of continuity.
What is Euler's equation derived from?
Newton’s second law of motion.
What is the equation for a monochromatic plane wave?
P(t, x) = p₀ cos(kx - ωt), where k is the wave number and ω is the angular frequency.
What is the formula for intensity in terms of pressure amplitude and medium density?
I = P^2 / (2 * ρ * c), where P is pressure amplitude, ρ is undisturbed mass density, and c is the speed of sound.
What is the recommended mechanical index (MI) to avoid inertial cavitation when using contrast agents?
Maintain an MI < 0.3.
What happens to the compressive segments of a wave in nonlinear propagation?
They catch up to the rarefactional segments ahead of them.
What causes nonlinearity in acoustic propagation?
The pressure wave alters the density of the medium.
What is the temperature range produced by the sudden collapse of a bubble during inertial cavitation?
1,000 – 10,000 °C.
What are the simplest Doppler systems typically used?
Continuous-wave (CW) Doppler systems, usually small hand-held devices.
What does a negative value of the reflection coefficient (R) imply?
That the reflected wave is inverted with respect to the incident wave.
What does the variable ω represent in the wave equation?
The radian frequency, calculated as ω = 2πf.
What determines the length of the transmitted pulse in ultrasonic transduction?
The bandwidth of the transducer.
What is the formula for acoustic impedance (Z) in plane waves?
Z = ρo * c, where ρo is the density and c is the speed of sound.
What is the formula for the speed of sound in a medium?
c = √(κ/ρ₀), where κ is the bulk modulus and ρ₀ is the density.
What is the significance of the focal point in ultrasound exposure?
It is where the transmitted signal is measured at the greatest intensity.
What is the significance of the Mechanical Index (MI)?
It reflects the potential for mechanical bioeffects from ultrasound exposure.
What additional factor is considered in the tissue thermal model for TI?
The pulse repetition frequency.
What is the acoustic impedance of air?
0.0004 MRayl.
What is the sound speed in air?
330 m/s.
What is the sound speed range in liver?
1555-1570 m/s.
What are the acoustic impedance characteristics of liquids and soft tissues?
Intermediate values.
What does the acronym PZT stand for?
Lead (Pb), zirconium (Zr), and titanium (Ti).
What does the reflection coefficient (R) indicate in ultrasound?
It indicates the relationship between the incident and reflected wave amplitudes.
What does the reflection coefficient R represent in ultrasonic wave transmission?
It represents the ratio of the amplitude of the reflected wave to the amplitude of the incident wave.
What do Ultrasonic Properties of Biological Tissue refer to?
The characteristics of biological tissues that affect ultrasound propagation.
What is the formula for the lateral beam pattern when letting z = F (focal distance)?
U(x) ∝ sinc(F/Lx).
What is produced when an acoustic wave encounters a difference in acoustic impedance?
A reflection.
What happens during inertial cavitation?
The rarefractional phase of the pressure wave expands the bubble beyond its maximum stable volume, resulting in a sudden collapse.
What is the change in frequency produced by the motion of a reflector called?
Doppler frequency (fD).
What is the title of the book by Kinsler et al. on acoustics?
Fundamentals of Acoustics, 4th edn.
How can an ultrasound image be interpreted?
As a map of the relative variations in acoustic impedance in the tissues.
What happens to the frequency of waves in the opposite direction of motion according to the Doppler effect?
The frequency is expanded.
What can refraction lead to in clinical imaging applications?
It can be an important source of artifacts.
How does sound speed depend on density in acoustic propagation?
Sound speed depends on density according to the relationship ρκ^1 = c.
What does 'c' represent in the Doppler equation?
The speed of sound in the medium.
Who authored 'Acoustics: An Introduction to its Physical Principles and Applications'?
A.D. Pierce.
What does AR stand for in the context of imaging systems?
Axial resolution.
What is the formula for axial resolution in ultrasonic transduction?
AR = (2 * λ) / (N * c), where N is the number of cycles and λ is the wavelength.
When is a Doppler system most sensitive to motion?
When the motion is directly toward or away from the transducer (θD = 0 or θD = π).
What is the attenuation coefficient of blood at 1 MHz?
0.17 dB/cm.
What type of waveform is typically used in diagnostic ultrasound?
Radio-frequency pulse waveform.
What is the acoustic impedance range for muscle?
1.62-1.71 MRayl.
How does the sound speed in soft tissues compare to that in water?
It is similar at body temperature.
What is the purpose of the range-gate cursor in Pulsed-Wave Doppler?
To determine the location from which Doppler data will be acquired within a B-mode image.
How do the simplest Continuous-Wave (CW) Doppler devices work?
They direct the demodulated Doppler signal to a speaker for the physician to interpret audibly.
What is illustrated by the ten consecutive echo signals in the Pulsed-Wave Doppler section?
Echo signals received from a scatterer moving toward the transducer.
What is the significance of the Fraunhofer diffraction integral in ultrasonic transduction?
It describes the beam behavior at and beyond the focus of a focused aperture.
What does ρ₀ represent in the context of ultrasonic waves?
The undisturbed mass density of the medium.
What does the monochromatic plane wave equation represent?
It describes the behavior of ultrasonic waves in a medium.
What does the symbol α represent in the context of ultrasonic plane waves?
The frequency-dependent amplitude attenuation coefficient (in Np/m).
What does an ultrasound image display?
The magnitude (absolute value of amplitude) of ultrasound echoes.
What type of signals are received in Pulsed-Wave Doppler when a scatterer is moving toward the transducer?
Ten consecutive echo signals.
What is the acoustic wave equation obtained from?
Combining Euler's equation and the equation of continuity.
What is the formula for the maximum velocity that can be measured by a pulsed-wave Doppler system?
v max = (c * f D * cos(θ)) / (2 * PRF).
What does the Doppler effect apply to?
Echoes from moving reflectors such as red blood cells and waves radiated from moving sources.
What is the physical basis of the tissue harmonic imaging mode?
The transformation from a sinusoidal to a sawtooth wave.
What does the variable 'c' represent in the Doppler equation?
The speed of sound in the medium.
What is the attenuation coefficient of water at 1 MHz?
0.0022 dB/cm.
What is the attenuation coefficient of fat at 1 MHz?
0.52 dB/cm.
Which book provides insights into diagnostic ultrasound imaging?
Diagnostic Ultrasound Imaging: Inside Out by Szabo.
How is the radian frequency (ω) calculated?
ω = 2πf, where f is the frequency.
What type of resource is 'Diagnostic Radiology Physics: a Handbook for Teachers and Students'?
A handbook that includes various chapters on diagnostic radiology physics.
What is the range of acoustic impedance for fat?
1.34-1.38 MRayl.
What is the acoustic impedance range for skull bone?
6.0-7.8 MRayl.
How does the compressive phase of the wave propagate compared to the rarefactional phase?
The compressive phase propagates at a higher velocity than the rarefactional phase.
How does blood flow affect heat dissipation in B-mode imaging?
Blood flow typically dissipates the heat before the same volume of tissue is insonified again.
How does frequency relate to the likelihood of inertial cavitation?
Inertial cavitation is more likely at lower frequencies, as indicated by the f^(-1/2) term in the MI formula.
What causes the speckle texture in ultrasound images?
Constructive and destructive interference of echoes scattered backward from cellular-scale tissue features.
Where is the transmitted signal measured for I SPTA?
At the point with greatest intensity within the radiated field, usually the focus of the transducer.
Where is the matching layer bonded in an ultrasonic transducer?
To the front face of the piezoelectric crystal.
What is the title of the consensus report by the Bioeffects Committee of the AIUM?
Consensus Report on Potential Bioeffects of Diagnostic Ultrasound: Executive Summary.
What is the significance of the length of the aperture (L) in ultrasound imaging?
It determines the characteristics of the lateral beam pattern.
What is the attenuation coefficient of air at 1 MHz?
12 dB/cm.
What does κ represent in the context of the speed of sound?
The bulk modulus of the medium.
What does the Thermal Index (TI) represent?
The ratio of the acoustic power output by the scanner to the estimated acoustic power needed to raise the temperature of the tissue by 1 °C.
What is the difference in heating between diagnostic imaging and therapeutic ultrasound?
Therapeutic ultrasound uses high-intensity pulses that produce more rapid heating than those used for diagnostic imaging.
What is the primary consequence of frequency-dependent attenuation in ultrasound?
Higher frequency waves are attenuated more rapidly than lower frequency waves, resulting in shallower penetration depths.
What is represented in the schematic of the Doppler effect?
The relative separation of the maxima of consecutive cycles of the radiated wave as a function of the Doppler angle, θ D.
What does the variable 'θ' represent in the Doppler equation?
The angle between the direction of the sound wave and the direction of the moving object.
What is the significance of the Doppler angle (θD) in the Doppler effect?
It is the angle between the direction of motion and a ray pointed from the reflector to the receiver.
What does Z represent in ultrasound physics?
Acoustic impedance.
How do different tissue types affect the calculation of the Thermal Index (TI)?
Different thermal models are used for soft tissue, skeletal bone, and cranial bone.
What is the typical axial resolution achieved in ultrasound imaging?
Finer than 1 mm.
What is the conversion factor between Np and dB?
1 Np ≈ 8.686 dB.
What is the sound speed range in skull bone?
3360-4080 m/s.
How does ultrasound achieve contrast among soft tissue structures?
Without the need for an injected contrast agent.
What does the matching layer do in an ultrasonic transducer?
Reduces the reflection coefficient between the transducer and the tissue, increasing sensitivity to weak echoes.
What is the term for the change in direction of a wave as it passes into a different medium?
Refraction.
What type of Doppler display is mentioned in the text?
Pulsed Doppler spectral display.
What is κ in the context of ultrasonic waves?
The compressibility of the medium, indicating fractional change in volume per unit pressure.
What is the significance of Doppler Physics in ultrasound?
It is used to measure the velocity of moving objects, such as blood flow.
What effect does temporal averaging have on I SPTA measurements?
It results in a greater measured exposure for modalities like pulsed Doppler.
What does u(x, t) represent in the equations for ultrasonic waves?
The particle velocity produced by the wave.
What is the limiting case of refraction?
Occurs when c2 > c1 and θi > arcsin(c1 / c2), resulting in θt being imaginary and total reflection.
What does 'fo' represent in the Doppler equation?
The frequency of the incident wave.
How is intensity related to pressure amplitude for acoustic plane waves?
Intensity is proportional to the square of the pressure amplitude.
What is the main subject of 'Physical Principles of Medical Ultrasonics'?
The physical principles underlying medical ultrasonics.
What is the typical duration of transmitted pulses in diagnostic ultrasound?
1.5-2.0 cycles.
What does FWHM stand for?
Full-width at half maximum.
What is the sound speed in water?
1480 m/s.
What is the sound speed range in muscle?
1550-1600 m/s.
Why is the similarity between water and soft tissue important?
It justifies the use of equations for fluid media to analyze wave propagation in biomedical ultrasound.
What is the formula for maximum Doppler frequency (D_max) in relation to PRF?
D_max = (D_o * PRF * c * v * cos(θ)) / 4.
How do composite materials of PZT and non-piezoelectric polymers benefit transducers?
They have a lower acoustic impedance, improving acoustic coupling into tissue and increasing bandwidth.
How is acoustic intensity expressed in decibels?
I dB = 10 * log10(I / I_ref), where I_ref is the reference intensity.
What is the typical value of m for most applications of diagnostic ultrasound?
m ≈ 1.
What does the variable 't S E I ∆' represent in the context of acoustic intensity?
It is evaluated over a surface perpendicular to the propagation direction.
What is the wave number (k) in the context of ultrasonic waves?
k = 2π/λ, where λ is the wavelength.
What is the focus of Shung's book published in 2006?
Diagnostic Ultrasound: Imaging and Blood Flow Measurements.
What are the two key acoustic output metrics mentioned?
Thermal Index (TI) and Mechanical Index (MI).
What is a monochromatic plane wave solution?
P(x,t) = P₀ cos(kx - ωt), where P₀ is the amplitude, ω is the radian frequency, and k is the wave number.
Why is there a division by 2 in the axial resolution formula?
Because the pulse makes a round trip from the transducer to a reflector and back.
What is the purpose of additional exposure parameters in ultrasound?
To more accurately reflect the risks of producing thermal and mechanical bioeffects.
What is the acoustic impedance of liver?
1.65 MRayl.
Where is the highest sound speed found?
In solids.
Why is understanding acoustic wave reflection important?
It is valuable for interpreting ultrasound images.
What are the Biological Effects of Ultrasound?
The impact of ultrasound on biological tissues and organisms.
What is the relationship between sound speed in two materials?
c₁ is the sound speed in the first material, and c₂ is the sound speed in the second material with a higher speed.
What is the relationship between Neper and decibels?
1 Np ≈ 8.686 dB.
What is the title of the book by Zagzebski on ultrasound physics?
Essentials of Ultrasound Physics.
What type of resource is 'Diagnostic Radiology Physics: a Handbook for Teachers and Students'?
A handbook covering various aspects of diagnostic radiology physics.
What is the range of sound speed in fat?
1450-1460 m/s.
What are the acoustic impedance characteristics of solids?
High values.
How are attenuation coefficients of biological tissues usually reported?
In dB/(cm × MHz).
What is the sound speed range in blood?
1550-1560 m/s.
What are the acoustic impedance characteristics of gases?
Low values.
