Fetal Echocardiography and Ultrasound Physics - Flashcards

A comprehensive set of questions and answers covering basic proportion concepts, ultrasound units, acoustic variables and parameters, wave behavior, and pulsed ultrasound physics relevant to OB/GYN/fetal echocardiography.

What is direct proportion?

Two quantities increase together; their ratio remains constant (y ∝ x).

What is inverse proportion?

Two quantities where one increases as the other decreases; their product is constant (xy = k).

What is a reciprocal relationship? Example: 2 and 1/2.

Their product equals 1 (2 × 0.5 = 1); reciprocals multiply to 1.

How many inches are in a foot?

12 inches.

Name three common length units.

Meter (m), inch, kilometer (km).

What is the unit for time?

Second (s).

What is the unit for mass?

Kilogram (kg).

What does the prefix kilo- mean?

10^3 (one thousand).

What does the prefix mega- mean?

10^6 (one million).

What does the prefix milli- mean?

10^-3 (one thousandth).

What is the speed of sound in soft tissue?

Approximately 1,540 m/s (about 1.54 mm/µs).

True or false: Sound can travel through a vacuum?

False; sound requires a medium.

What are the three acoustic variables?

Pressure, Density, Distance (particle motion).

What are acoustic parameters?

Features of a sound wave such as period, frequency, amplitude, power, speed, and wavelength.

How do acoustic variables differ from acoustic parameters?

Variables describe the instantaneous state; parameters describe waveform characteristics.

What is a longitudinal wave?

Particles move in the same direction as the wave propagation.

Are ultrasound waves longitudinal or transverse?

Longitudinal (mechanical) waves.

What is the reciprocal relationship between period and frequency?

Period = 1/frequency; frequency = 1/period.

What is the wavelength formula?

λ = c/f; in soft tissue, λ(mm) ≈ 1.54 / f(MHz).

What determines propagation speed of sound?

The medium’s properties, especially density and stiffness.

How are speed and density related?

Inverse relationship; higher density generally lowers speed.

How are speed and stiffness related?

Direct relationship; higher stiffness increases speed.

What is the typical propagation speed in bone?

Approximately 2000–4000 m/s.

What is the typical diagnostic ultrasound frequency range?

About 2–10 MHz.

What is the relationship between frequency and wavelength?

Higher frequency yields shorter wavelength.

What is attenuation?

The decrease in intensity as sound propagates due to absorption, scattering, and reflection.

What are the units for pressure in acoustic variables?

Pascals (Pa).

What are the units for density in acoustic variables?

kg/cm^3.

What are the units for particle distance in acoustic variables?

Centimeters or inches; units of distance.

What is the peak-to-peak amplitude?

The difference between the maximum and minimum values of an acoustic variable.

What is the relationship between amplitude and power?

Power is proportional to amplitude^2.

What is the relationship between power and intensity?

Intensity = Power / beam area; power relates to amplitude squared.

What are the units for intensity?

Watts per square centimeter (W/cm^2).

What is the unit for power?

Watt (W).

What is the typical speed of sound in air?

Approximately 330 m/s (often cited as ~343 m/s).

What is the typical speed of sound in fat?

Approximately 1450 m/s.

What is the typical speed of sound in lung?

Approximately 300–1200 m/s.

What is a pulse duration (PD)?

The time from the start to the end of a single pulse; units microseconds; PD = #cycles × period; determined by the source.

What are the two components of pulsed ultrasound?

Transmit (on) time and Receive (off) time.

What is the spatial pulse length (SPL)?

The distance that a pulse occupies in space; SPL = #cycles × wavelength; units mm; determines axial resolution.

What are typical SPL values in soft tissue?

Approximately 0.1–1.0 mm.

What is the relationship between SPL and axial resolution?

Shorter SPL yields better axial resolution.

What is the formula for SPL in terms of wavelength and cycles?

SPL = (# of cycles in the pulse) × (wavelength).

What is pulse repetition period (PRP)?

The time from the start of one pulse to the start of the next; units ms; PRP = 1 / PRF.

What is pulse repetition frequency (PRF)?

The number of pulses emitted per second; units Hz; PRF = 1 / PRP.

What is the duty factor (DF)?

DF = (PD / PRP) × 100; percentage of time the system transmits; DF is adjustable via depth.

How does depth of view affect PRF and PRP?

Deeper imaging lowers PRF and raises PRP; DF decreases with depth.

What does DF do with shallow vs deep imaging?

Shallow imaging: higher DF; deep imaging: lower DF.

What is the spatial pulse length’s typical unit?

Millimeters (mm).

What is the difference between continuous and pulsed ultrasound in terms of on/off time?

Pulsed has transmit (on) and receive (off) times; continuous wave is always on.

What is the ultrasound frequency range considered ultrasound (not audible to humans)?

Frequencies greater than 20 kHz; clinical imaging uses 2–10 MHz.

What is the audible frequency range for humans?

Approximately 20 Hz to 20 kHz.

What is the speed of sound in a given medium determined by?

Medium properties (density and stiffness).

What is the meaning of 'frequency is inversely related to penetration' in ultrasound?

Higher frequency penetrates less; lower frequency penetrates more.

What is the unit for period?

Seconds (s) or microseconds (µs).

What is the unit for frequency?

Hertz (Hz; cycles per second).

What is the relationship freq × period = 1?

They are reciprocals; as one increases, the other decreases accordingly.

What is the unit for wavelength?

Meters or millimeters (mm) depending on context.

What is the meaning of 'axial resolution'?

Resolution along the beam axis; shorter SPL improves axial resolution.

What is the effect of increasing frequency on attenuation?

Higher frequency increases attenuation.

What is the definition of pressure in acoustic terms?

Concentration of force within an area; measured in Pascals (Pa).

What is the definition of density in acoustic terms?

Concentration of mass within a volume; units kg/cm^3.

What is the definition of distance in acoustic terms?

Measure of particle motion; units cm, feet, miles.

What are constructive interference and destructive interference?

Constructive: waves in phase; amplitude increases. Destructive: waves out of phase; amplitude decreases.

Which axis is the horizontal axis on a graph?

X-axis.

Which axis is the vertical axis on a graph?

Y-axis.

What describes a sound wave as a series of compressions and rarefactions?

Compression is high-pressure region; rarefaction is low-pressure region; together describe longitudinal ultrasound waves.

What is the speed of sound in air (typical value)?

Approximately 330 m/s.

What is the speed range for soft tissue (typical)?

Approximately 1,520–1,540 m/s (about 1.54 mm/µs).

What is a wave’s wavelength in soft tissue at 3 MHz roughly?

Approximately 0.5 mm (using λ ≈ 1.54 / f in MHz).

What is the unit for power in ultrasound terms?

Watts (W).

What is the unit for pressure amplitude in clinical ultrasound?

Pascals (Pa) and often reported in dB for relative amplitude.

What is the formula for PRP in terms of PRF?

PRP = 1 / PRF.

What are the two components of pulsed ultrasound in imaging?

Transmit (on) time and Receive (off) time.

What determines SPL?

Number of cycles in the pulse × wavelength.

What is the typical range for SPL in soft tissue?

Approximately 0.1–1.0 mm.

What does 'SPL' influence in imaging?

Axial resolution; shorter SPL improves image accuracy.

What is the relationship between density and speed in a medium?

Inverse relationship; higher density generally lowers speed.

What is the relationship between stiffness and speed in a medium?

Direct relationship; higher stiffness increases speed.

What is the maximum speed range for bone?

Approximately 2000–4000 m/s.

What is the typical range of frequencies used in diagnostic ultrasound?

2–10 MHz.

Which term best describes the time from start to end of a pulse?

Pulse duration (PD).

Which term best describes the distance from the start to the end of one pulse?

Spatial pulse length (SPL).

Which term describes the time from the start of one pulse to the start of the next pulse?

Pulse repetition period (PRP).

Which term describes the number of pulses emitted per second?

Pulse repetition frequency (PRF).

Which term describes the fraction of time the system is transmitting?

Duty factor (DF).

What is the typical unit for speed in tissue?

m/s (e.g., 1540 m/s).

What is the typical unit for wavelength in ultrasound?

mm or meters depending on scale.

What is the typical unit for time in PD and PRP calculations?

Seconds or microseconds (µs).

What is the effect of increasing depth on PRF?

PRF decreases with greater depth.

What is the effect of increasing depth on PRP?

PRP increases with greater depth.

What is the purpose of the duty factor in pulsed ultrasound?

Quantifies the fraction of time the pulser is on; relates to safety and image quality.

What is the relation between frequency and period?

They are reciprocals: period = 1/frequency.

What is the energy unit for ultrasound attenuation due to tissue properties?

Intensity (W/cm^2) and power (W) decrease with attenuation.

What is the definition of wave interference?

Superposition of two or more waves leading to constructive or destructive interference.

What is the ultrasound category based on frequency exceeding 20,000 Hz?

Ultrasound.

What is the relation between wavelength and frequency in a given medium?

Higher frequency yields shorter wavelength; speed is constant for a given medium.

What does a higher frequency do to penetration depth?

Reduces penetration depth; higher frequency attenuates more.

What is the speed of sound in fat?

Approximately 1450 m/s.

What is the speed of sound in air and soft tissue as given in notes?

Air ~330 m/s; Soft tissue ~1540 m/s.