DMS 101 – Physics Exam 1 Review

This flashcard set covers the fundamental principles of ultrasound physics as outlined in the DMS 101 Exam 1 Review, including propagation speeds, wave characteristics, transducers, and attenuation.

What are the propagation speeds in soft tissue, bone, lung, and fat, and what factors affect the speed of sound?

Soft tissue: $1540\,m/s$, bone: $3500\,m/s$, lung: $500\,m/s$, and fat: $1450\,m/s$. Speed is affected by the stiffness (bulk modulus) and density of the medium.

What does sound require in order to travel?

Sound is a mechanical wave that requires a medium (matter) to travel through; it cannot travel in a vacuum.

What image shapes are produced by linear format and curve linear transducers?

A linear format transducer produces a rectangular image shape, while a curve linear transducer produces a blunted sector or curved shape.

What are PRP, PRF, and PD, and how are they related?

PRP (Pulse Repetition Period) is the time from the start of one pulse to the start of the next. PRF (Pulse Repetition Frequency) is the number of pulses per second. PD (Pulse Duration) is the actual time from the start of a pulse to the end of that pulse. PRP and PRF are reciprocals: $PRP \times PRF = 1$.

What is frequency, what unit measures it, what controls it, and how does it relate to period and wavelength?

Frequency is the number of cycles per second, measured in Hertz ($Hz$). It is determined by the sound source. Frequency ($f$) is the reciprocal of period ($T = \frac{1}{f}$) and is inversely proportional to wavelength ($\lambda = \frac{c}{f}$).

Which frequency ranges are classified as infrasonic, audible, and ultrasonic?

Infrasonic is less than $20\,Hz$, audible sound is between $20\,Hz$ and $20,000\,Hz$, and ultrasonic is greater than $20,000\,Hz$ (or $20\,kHz$).

What are the formulas for period ($T$) and wavelength ($\lambda$)?

Period: $T = \frac{1}{f}$. Wavelength: $\lambda = \frac{c}{f}$, where $c$ is propagation speed and $f$ is frequency.

What are the acoustic variables?

The acoustic variables identify sound waves and include pressure ($Pascals$), density ($kg/m^3$), and distance (particle motion).

What is SPL and what factors affect it?

SPL (Spatial Pulse Length) is the distance from the start to the end of a pulse ($SPL = n \times \lambda$). It is affected by the sound source (number of cycles) and the medium (wavelength).

How can you describe the nature of sound?

Sound is a mechanical, longitudinal wave that travels in a straight line through a medium.

Does high frequency or low frequency sound propagate further?

Low frequency sound propagates further because it undergoes less attenuation than high frequency sound.

How is the number $2345$ expressed in scientific notation?

$$2.345 \times 10^3$$

What are compression and rarefaction?

Compression is a region of high pressure and high density in a longitudinal wave, while rarefaction is a region of low pressure and low density.

What are stiffness and density, how do they affect speed, and what is bulk modulus?

Stiffness is the ability of a medium to resist compression; density is the relative weight of a material. Speed is directly proportional to stiffness and inversely proportional to density. Bulk Modulus is another term for stiffness.

What numerical values represent the prefixes Mega and milli?

Mega = $10^6$ (one million) and milli = $10^{-3}$ (one thousandth).

What is impedance, what is its formula, and what scenario creates the greatest reflection?

Impedance ($Z$) is the acoustic resistance to sound in a medium, calculated as $Z = \rho \times c$ ($\rho$ is density, $c$ is speed). The greatest reflection occurs when there is a large impedance mismatch between two media.

Who are Jacque and Pierre Curie, and who is Christian Doppler?

Jacque and Pierre Curie discovered the piezoelectric effect. Christian Doppler discovered the Doppler effect, describing the change in frequency due to motion.

What happens to sound energy when it is absorbed?

When sound is absorbed, it is converted into heat energy.

What are power, intensity, and amplitude, and how are they related?

Power is the rate of energy transfer, intensity is the concentration of energy in a beam ($I = \frac{Power}{Area}$), and amplitude is the wave's magnitude. Intensity and Power are proportional to Amplitude squared ($Intensity \propto Amplitude^2$).

What is Duty Factor, what influences it, can we control it, and how is it measured?

Duty Factor is the percentage of time the system spends transmitting sound ($DF = \frac{PD}{PRP} \times 100$). It is influenced by imaging depth, can be adjusted by the operator via depth controls, and is a unitless ratio.

What does B Mode mean and what influences the brightness of the dots?

B Mode stands for Brightness Mode. The brightness of the dot is influenced by the strength (amplitude) of the returning echo.

What is IRC?

IRC (Intensity Reflection Coefficient) is the percentage of the incident intensity that is reflected back at a boundary between two media.

What is attenuation, what affects it, how is it compensated, and what are its three components?

Attenuation is the weakening of the sound beam as it travels, affected by frequency and path length. It is compensated using Time Gain Compensation (TGC). The three components are absorption, reflection, and scattering.

What is refraction, what principle describes it, and what are its requirements?

Refraction is the bending of a sound beam during transmission. It is mathematically described by Snell's Law and requires oblique incidence and a difference in propagation speeds between two media.

What is required for a reflection to be created at a boundary?

A reflection requires a change or mismatch in acoustic impedance ($Z$) at the boundary of two media.

What are Rayleigh Scatter, scatter, and non-specular reflectors?

Scatter is the redirection of sound in many directions. Rayleigh Scatter occurs when reflections are much smaller than the wavelength (e.g., RBCs) and redirects sound equally in all directions. Non-specular reflectors are caused by rough surfaces.

What is Normal Incidence?

Normal Incidence occurs when the incident sound beam strikes the boundary of two media at exactly $90^{\circ}$.

What is the Attenuation Coefficient and what is its formula in soft tissue?

The Attenuation Coefficient is the amount of attenuation per centimeter of travel ($dB/cm$). The formula in soft tissue is $\text{Attenuation Coefficient} = \frac{\text{Frequency (MHz)}}{2}$.

Does transmission or reflection occur more frequently with an ultrasound wave?

Transmission happens significantly more than reflection; typically, $> 99\%$ of the beam is transmitted at soft tissue boundaries.

What do the decibel values $-3\,dB$, $-6\,dB$, $3\,dB$, and $10\,dB$ signify?

$-3\,dB$ means half the intensity; $-6\,dB$ means one-fourth; $3\,dB$ means double; and $10\,dB$ means ten times the original intensity.