Ultrasound Physics (Midterm Exam Review)

What 2 words are used to describe sound?

Longitudinal & Mechanical

Decreased dynamic range/compression= what type of contrast?

Higher contrast (less shades of grey)

Increased dynamic range/compression= what type of contrast?

Less contrast (more shades of grey)

What are 7 acoustic parameters that describe a sound wave?

1. Period
2. Frequency
3. Amplitude
4. Power
5. Intensity
6. Wavelength
7. Propagation Speed

What are the 3 acoustic variables?

1. Pressure
2. Density
3. Distance

What type of wave moves in a direction that is perpendicular to the direction that the wave propagates?

Transverse Waves

What type of waves moves in the same direction that the wave propagates?

Longitudinal Waves

A pair of waves are considered ______________ when their peaks (maximum value) and troughs (minimum value) occur at the same time and location.

IN-PHASE

A pair of waves are considered________________ when their peaks and troughs occur at different times.

OUT-OF-PHASE

This occurs when the interference of a pair of out-of-phase waves results in the formation of a single wave of lesser amplitude than at least one of its components.

Destructive Interference

This occurs when the interference of a pair of in-phase waves result in the formation of a wave of greater amplitude than either of its components.

Constructive Interference

What is the time it takes a wave to vibrate a single cycle, or the time from the start of one cycle to the start of the next cycle?

Period

What is the number of particle events that occur in a specific duration of time?

Frequency

Infrasound

Sound waves with frequencies below 20 Hz.

audible sound

between 20 Hz and 20 kHz

Ultrasound

Sound waves with frequencies above 20kHz (20,000 Hz).

If frequency increases, the wavelength will...

decrease

If frequency increases, the period.....

decreases

What 3 parameters describe the size, magnitude, or strength of a sound wave?

1. Intensity
2. Power
3. Amplitude
(Also known as the "Bigness Parameters")

What is 2x's the value of amplitude?

peak-to-peak amplitude

What is the measure of the degree of change in an acoustic variable from resting position to the maximum disturbance?

Amplitude

What is the weakening of amplitude?

Attenuation

What is the rate of energy transfer?

Power

What is the parameter energy per unit area of sound beam?

Intensity

Where is the intensity the greatest?

At the focal zone

What is the distance or length of one complete cycle?

Wavelength

What is the rate at which a sound wave travels through a medium?

Propagation Speed

What is the speed of sound in soft tissue?

1,540 m/s

What 2 characteristics of a medium affect speed of sound?

Stiffness & Density

What is the relative weight of a material?

Density

What is it called when compression is resisted?

stiffness

What is the relationship between stiffness and speed?

directly related ( when speed increases than stiffness increases)

What is the relationship between density and speed?

inversely related (when density increases than speed decreases)

What is the opposite of stiffness?

elasticity and compressibility

What is another name for stiffness?

bulk modulus

The doppler effect describes the change in ______________ or _______________

Pitch or Frequency

What type of transducer is ideal for imaging superficial structures? It has better resolution and less penetration, but higher frequency (5-13 MHz).

Linear Transducer

What type of transducer is ideal for imaging intra-abdominal structures? It has deeper penetration and wide depth of field, but lower frequency (2-5MHz).

Curvilinear Transducer

What type of transducer is ideal for imaging the chest, especially between ribs? It has has large depth of field with a small footprint which allows view of deep structures. (2-5MHz)

Phased Array Transducer

What affects the brightness of all echoes in the imaging sector?

Overall Gain

What can be adjusted at increments of depth on the ultrasound machine?

Time Gain Compensation (TGC)

What is the ability to distinguish 2 points as separate in space?

Spatial Resolution

What are the 2 types of spatial resolution?

Axial & Lateral

What type of resolution is affected by the width of the beam and depth of imaging?

Lateral Resolution

What is the ability to detect that an object has moved over time?

Temporal resolution

Adjusting the __________ ___________ improves lateral resolution at the level of the image.

focal zone

What type of zoom "magnifies" the image by TURNING the knob?

Read Zoom

What type of zoom "re-write's" the image in the selected region of interest by PUSHING the knob?

Write Zoom

To improve image quality, what are 2 ways we can increase frame rate?

1. By narrowing the image sector, which decreases the time it takes to scan one frame
2. By decreasing the depth, which decreases pulse repetition period (PRP) thus increasing frame rate as well as improving lateral resolution

What do waves transfer from one location to another?

energy

Sound waves can also be described as....

>series of compressions and rarefaction
>long, pressure waves

If 2 waves are traveling in a medium and arrive at a location at the same time, what event takes place?

interference

What type of waves will exhibit both constructive and destructive interference?

Waves of different frequency

What units are used to report pressure of a sound beam?

Pressure= Pascals

True or False:
Acoustic variables allow us to determine which waves are sound waves and which one's are not?

TRUE

True or False:
Acoustic parameters are used to describe the features of sound wave?

TRUE

Parameters and their units:

Wavelength= millimeters
Frequency= Herts
Intensity= watts/cm2
Propagation speed= meters/sec
Period= seconds
Power= Watts

What is a common unit for measuring electric signals?

decibels (dB)

What type of decibel reports signals that are increasing in strength or getting larger?

Positive Decibels

What type of decibel reports signals that are decreasing in strength or getting smaller?

Negative Decibels

What occurs when sound strikes a boundary and the portion of the waves energy is redirected?

reflection

What type of echogenicity describes brighter/ greater reflection of sound?

hyperechoic (EX. bone)

What type of echogenicity describes darker/ lesser reflection of sound?

hypoechoic (EX. fat)

What type of echogenicity describes black/ no reflection?

anechoic (EX. blood/water)

What type of echogenicty describes 2 areas of similar brightness?

isoechoic (EX. muscle)

What type of echogenicity describes uniform structure/ composition?

homogenous

What type of echogenicity describes nonuniform structure/ composition?

heterogenous

What 2 factors is attenuation determined by?

path length & frequency of sound

What is the relationship between distance and attenuation?

Directly related

What is the relationship between frequency and attenuation?

Directly related

What 3 processes contribute to attenuation?

1. Reflection
2. Scattering
3. Absorption

More Attenuation=

longer distance & higher frequency

Less Attenuation=

shorter distances & lower frequencies

What type of reflection is when the boundary is smooth and the sound is reflected in only one direction in an organized manner?

Specular reflection (EX. mirror)

What type of reflection is when the wave reflects off of an irregular surface and it radiates in more than one direction?

Diffuse Reflection (EX. Backscatter)

What type of reflection is random and redirection of sound in many directions?

Scattering

What occurs when the structure's dimensions are much smaller than the beam's wavelength?

Rayleigh Scattering

What occurs when ultrasonic energy is converted into another energy form, such as heat?

Absorption

What is the number of decibels of attenuation that occurs when sound travels 1cm?

Attenuation coefficient

From high to low, what is the correct order of a medium's relationship to attenuation?

Highest

Air
bone & lung
muscle
soft tissue
fat
blood, urine, biologic fluid
water

Lowest

What is the distance sound travels in a tissue that reduces the intensity of sound to one-half its original value?

Half-value layer thickness

What does half-value layer thickness depend on?

Medium & frequency of sound

What is influenced by the acoustic impedance?

Reflection

What is the acoustic resistance to sound traveling in a medium?

impedance

What is critical to ultrasound's ability to image structure located deep in the body?

Transmission

What is the unit of Impedance?

rayls

Medium, sound source, or both:

What is associated with impedance?

Medium only

What is the angle at which the waves strike a boundary and determines the behavior of the pulse?

incidece

What angle has measurements other than 90*?

oblique

What angle is less than 90 degrees?

acute angle

What angle is exactly 90 degrees?

right angle

What angle is more than 90 degrees?

obtuse angle

What type of incidence strikes a boundary at exactly 90 degrees?

normal incidence

What type of incidence strikes a boundary at any angle other than 90 degrees?

Oblique incidence

What is a sound wave's intensity immediately before it strikes a boundary?

incident intensity

What is the intensity of the portion of incident sound beam that, after striking a boundary, returns back from where it came?

reflected intensity

What is the intensity of at the portion incident sound beam that, after striking a boundary, continues forward in the same direction that it was traveling?

transmitted intensity

reflected intensity + transmitted intensity=

incident intensity

What is the percentage of the intensity that bounces back when a sound beam strikes the boundary between two media?

Intensity Reflection Coefficient (IRC) {1% or less}

What is the percentage of intensity that passes in the forward direction then the beam strikes an interface between two media?

Intensity Transmission Coefficient (ITC) {99% or more}