Physics Exam 1 chapter 1 and 2

The _________ is formally defined as the decrease in the ratio of the stress to the strain, where the stress is defined as the change in pressure applied, and the strain is defined as the percent change in volume which occurs as a result of the stress.

Bulk Modulus

Identify the symbol that designates "one millionth of"

μ

The symbol for the spatial length of a single cycle is:

λ

a linear image will produce a ___ display

rectangular

What is the distance in millimeters to the reflector in soft tissue with a round trip of 52 μs?

40mm

Anatomic imaging with ultrasound is accomplished by the __________ ________ technique

pulse-echo

Sonography requires knowledge of the ________ of origin and the _____ of returning echoes

location; strength

3D imaging requires scanning the ultrasound through many adjacent tissue _____ to build a 3D volume of echo information

cross sections

A region of low pressure in a wave is a region of

none of the above (out of refraction, compressibility, and compression)

A region of rarefaction along the path of sound propagation is a region of high pressure

False

Specular reflectors, also known as a scatterers, usually produces low amplitude reflections

False

Acoustic impedance is a characteristic of the sound as it passes through the tissue

False

Acoustic speckle is caused by:

Scatters moving into and out of the beam which cause interference patterns to alternate between constructive and destructive and result in a displayed dot pattern

Acoustic variables include all of the following, except?

Stiffness

Arrange the following symbols in order to form the equation for the fraction of the time of the pulse repetition period that the sound is on.

1 DF

2 =

3 PD

4 /

5 PRP

As density increases, propagation speed increases as well

False

As pulse round trip time increases, reflector distance decreases

False

A decrease in the intensity of sound is known as ______

attenuation

Attenuation is defined as the progressive weakening of the sound beam as it passes through the tissues

True

Attenuation is higher in lung than in other soft tissues

True

In soft tissue, if it were possible to image with 4 different probes simultaneously, which of the following would arrive back to the system first :

A.) the sound emitted from a 2MHz probe

B.) the sound emitted from a 3MHz probe

C.) the sound emitted from a 5MHz probe

D.) the sound emitted from a 7MHz probe

E.) none of the above

F.) not enough information to determine

E because all sound, regardless of the frequency, travels at the same speed through any specific medium

The best example of of a Rayleigh scatter is

the red blood cell

Both period and wavelength are directly proportional to frequency

False

Diagnostic ultrasound uses short bursts of ultrasound, these bursts are referred to as:

pulses

For PW ultrasound, the DF will always be:

When rarefactions travel faster that compressions, harmonics are created

False

If 3MHz ultrasound with an intensity of 10mW/cm^2 is applied to soft tissue, what is the intensity at a depth of 2cm?

Use HID 3/(frequency*(1/2)

Answer half of the initial intensity and 5 mW/cm^2

If beam power increases by a factor of 2, intensity will _____

double

If the frequency in soft tissue is doubled, the propagation speed is:

unchanged (determined by the medium)

All of the following are true concerning acoustic impedance, except:

It is a property of the sound beam as it passes through the tissue

The frequency range of audible sound:

20 Hz to 20 kHz

If the spatial pulse length for a four-cycle pulse is 2 mm, the wavelength is ____

0.5mm

If you switch to a lower frequency for penetration, the wavelength of the transducer ________.

Increases

Impedance determines how much of an incident sound wave is reflected back into the first medium and how much is transmitted into the second medium

True

Impedance increases if density or propagation speed increase

True

Z= ρ x c

In the following equation, the unit for "Z" are:

None of these responses (out of μ, m/s, kg/cm^3)

Z= ρ x c

In the following equation, the units for the parameter represented by the symbol "rho" are:

g/cm^3

Z= ρ x c

In the following equation, the symbol "Z" represents:

Acoustic impedance

Intensity=Power^2

False

Is the reflected angle ALWAYS equal to the transmission angle

False

The period for a 4MHz transmit frequency is .25 milliseconds

False

Turning this knob increases or decreases the transmit voltage used to drive the transducer to create the sound wave which penetrate the body

Transmit Power

Knowledge and understanding of acoustic physics is no longer essential for ultrasonographers because of the technological advances made by the equipment manufacturers

False

Liquid suspensions that can be injected into the circulation intravenously to increase echogenicity are known as:

Contrast agents

Match the following definitions and terms:

__2__ # of pulses/second 1.Pulse repetition period

__1__ time from the beginning 2.Pulse Repetition Frequency

of one pulse to the beginning

of the next 3.Duty Factor

__4__ time it takes for a single 4.Pulse Duration

pulse to occur

__3__ fraction of time that

pulsed ultrasound is on

Match the following definitions and terms:

__4__ speed with which a wave 1.Frequency

moves through a medium

__2__ unitless. 2.Duty Factor

__1__ number of wave cycles

period second 3.Amplitude

__3__ maximum variation that

occurs in an acoustic variable. 4.None of these

Period and wavelength are directly proportional

False

Propagation speed in soft tissue is

1540 m/s or 1.54mm/μs

Propagation speed is higher in ___ than soft tissue

bone

Pulse duration will increase with all of the following except:

frequency

Reflection and scattering give rise to echoes that form the basis of the diagnostic process

True

Refraction is the region of low pressure and low density within the wave

False

Refraction will never occurs if...

There is is perpendicular incidence and oblique incident with identical propagation speeds

Scatter Reflectors (non-specular reflectors) are high angle dependent

False

Scatterers are:

Smaller than 1 wavelength, typically rough surfaced, angle independent

Snell's law:

Predicts the amount of refraction

Sound can travel in a vacuum

False

Sound is form of ______________________ energy.

Mechanical

Sound is a form of energy consisting of mechanically produced waves

True

Sound is a:

Longitudinal, mechanical, compression wave with traveling variation of acoustic variables

Sound is described as a longitudinal, compression wave

True

Specular reflectors:

Cause high amplitude reflections

The angle of incidence is usually greater than the angle of reflection

False

The brightness of the dot on the display corresponds to the echo:

strength

The even harmonics of 7MHz are ___ MHz

14, 28, 42

The following are all ultrasound frequencies except:

18.0 KHz

The higher the SPL, the better the axial resolution

False

The length of 1 cycle in space is known as:

Wavelength

The metric prefix milli means 1/1,000,000

False

The rate at which energy passes through a unit area is called ___

intensity

The symbol used to represent the speed of sound in soft tissue is:

c

The term "acoustic" pertains to:

Sound

The units for intensity:

mW/cm^2

Three phenomena which contribute to attenuation are reflection, scattering and most importantly ____, which is the dominant contributing factor to the attenuation of sound in soft tissue

absorption

To calculate total attenuation, one must multiply the path length by _____

attenuation coefficient, 1/2*frequency, f/2 (all mean the same)

Ultrasound for diagnostic purposes falls in the range of:

2-20MHz

Ultrasound imaging involves the sonographer, patient, ____, instrument, and somologist

Transducer

Ultrasound pulses contain a range of frequencies called the ____

bandwidth

Units for duty factor are:

None of the above (out of decibels, rayls, hertz)

Wavelength= propagation speed*frequency

False

What does -3dB mean?

one half the original intensity

What is the duty factor for continuous wave ultrasound?

100% or 1

What is the attenuation coefficient of a 5MHz transducer?

2.5dB/cm

When density in a medium increases, propagation speed will:

decrease

When echoes arrive at the transducer in such a way that they reinforce one another, it is known as destructive interference

False (it's constructive interference)

When scanning the liver, a 4MHz transducer is used. what is the half intensity depth?

1.5cm use equation 3/[(frequency*(1/2)]

Which of the following equations would be used to calculate intensity reflection coefficient?

A.) IRC={z2 - z1/z2 + z1)^2

Which of the following statements is untrue concerning scatterers?

They cause high amplitude reflections

Which of the following would constitute a definition for pressure?

A. Concentration of mass

B. Concentration of force

C. Concentration of heat

D. Mass per unit volume

B (concentration of force)

With an angle of incidence=80 degrees, refraction will occur

Not enough information given to determine

Which of the following would constitute a definition for density?

A and D (concentration of mass, mass per unit volume)

With a wavelength of 0.2mm in soft tissue, the frequency is approximately ___ and the period is ___

7.7MHz; 0.13μs

With an incidence angle of 85 degrees, what is the reflected angle if the impedance values of two media are 38 rayls and 45 rayls?

85 degrees

With harmonics, the wave progressively becomes more sinusoidal

False

___ are the even and odd multiples of the fundamental frequency

harmonics

Frequency and period are

Both b and c (reciprocal to one another and inversely proportional)

Wavelength:

A and b only ( is determined by the source and is determined by the medium)

3/[frequency*(1/2)]=?

HID

Sonographers should begin every exam with the lowest frequency, increasing only as needed for depth of penetration

False

An increase in frequency will result in:

A decrease in T, an increase in the numeric value for resolution, and an increase in depth of penetration

False