ultrasound physics: final exam

the pulser of an instrument automatically reduces the PRF for deeper imaging to avoid the ___ artifact.

range ambiguity

if an echo arrives 143 microseconds after the pulse that produced was emitted, it should be located at a depth of ____ cm. if a second pulse was emitted 13 microseconds before the arrival of this echo, it will be placed incorrectly at a depth of ___ cm.

11 cm, 1 cm

if the propagation speed in a soft tissue path is 1.60 mm/microsecond, a diagnostic instrument assumes a propagation speed too ____ and will show reflectors too ____ the transducer.

low, close to

true or false? mirror image can occur with only one reflector.

false

the most common artifact encountered in Doppler ultrasound is ___.

aliasing

which of the following can reduce or eliminate aliasing?

-increased PRF

-increased doppler angle

-increased operating frequency

-use of continuous wave mode

increased PRF, increased doppler angle, use of continuous wave mode

true or false? the fine texture in soft tissue indicates the excellent resolution that actually exists there.

false

the fact that a beam, as it scans through tissue, has some nonzero width perpendicular to the scan plane results in the ____ _____ artifact.

slice thickness

which of the following can cause improper location of objects on a display?

-shadowing

-enhancement

-speed error

-mirror image

-refraction

-grating lobe

speed error, mirror image, refraction, grating lobe

true or false? refraction can cause shadowing.

true

unreal structure displayed

reverberation

structure displayed with improper brightness

shadowing, enhancement

structure improperly positioned

propagation speed error, refraction

structure improperly shaped

propagation speed error, refraction

reverberation results in added reflectors being imaged with equal ___.

separation

in reverberation, subsequent reflections are ____ than previous ones.

weaker

enhancement is caused by a ____.

weakly attenuating structure

which of the following can correct or eliminate aliasing?

-decreased PRF

-decreased doppler angle

-increased operating frequency

-baseline shifting

baseline shifting

true or false? shadowing results in a decreased echo amplitudes.

true

propagation speed error results in improper ____ position of a reflector on the display.

axial

to avoid aliasing, a signal voltage must be sampled at least ____ time(s) per cycle.

2

if the highest doppler shift frequency present in a signal exceeds ____ the PRF, aliasing will occur.

one half

when doppler gain is set too high, which artifact is likely to occur?

spectrum mirror image

which artifact should be suspected if one observes twin gestational sacs when scanning through the rectus abdominis muscle?

refraction

range ambiguity can occur in which of the following?

-imaging instruments

-duplex instruments

-pulsed wave doppler instruments

-color flow instruments

-all of the above

all of the above

if the PRF is 4 kHz, which of the following doppler shifts will cause aliasing?

• 1 kHz

• 2 kHz

• 3 kHz

• 4 kHz

3 kHz, 4 kHz

if the PRF is 10 kHz, which of the following doppler shifts will cause aliasing?

• 1 kHz

• 2 kHz

• 3 kHz

• 4 kHz

• none of the above

none of the above

there is no problem with aliasing as long as the doppler shifts are ____ half the PRF.

less than

true or false? if doppler shift is 2.6 kHz, no aliasing would result with a PRF of 10 kHz.

true

if there were a problem in question 27 (true: if doppler shift is 2.6 kHz, no aliasing would result with a PRF of 10 kHz.), ____ could be used to avoid it.

continous-wave, power

if red represents a positive doppler shift and blue represents a negative one, what color is seen for normal flow toward the transducer? what color is seen for aliasing flow toward the transducer? what colors are seen for normal flow away and for aliasing flow away from the transducer?

red, blue, blue, red

when a pulse is emitted before all the echoes from the previous pulse have been received, which artifact occurs?

range ambiguity

when a strong reflector is located in the scan plane, which of the following artifactsi s likely to occur?

-aliasing

-range ambiguity

-spectrum mirror image

-location mirror image

-speckle

location mirror image (in class, he said the answer was “mirror image”)

increasing PRF to avoid aliasing can cause which of the following?

-baseline shift

-range ambiguity

-spectrum mirror image

-location mirror image

-speckle

range ambiguity

which of the following decreases the likelihood of range-ambiguity artifact?

-decreasing operating frequency

-decreasing PRF

-decreasing doppler angle

-baseline shift

-increasing pulser output

decreasing PRF

range ambiguity produces which error in spectral doppler studies?

incorrect gate location

range ambiguity produces which error in anatomic imaging?

range too short

if the maximum imaging depth is 5 cm, the frequency is 2 MHz, and the doppler angle is zero, what is the maximum flow speed that will avoid aliasing and range ambiguity?

300 cm/s

true or false? solving aliasing by decreasing operating frequency increases the possibility of range ambiguity artifact.

true

true or false? if operating frequency is increased to decrease the possibility of range ambiguity (by increasing attenuation), the possibility of aliasing increases.

true

if a pulsed wave Doppler sample volume is located at a depth of 8 cm, the sampled echoes arrive at what time following the emission of the pulse?

104 microseconds

a tissue equivalent ____ has an attenuation of approximately 0.5 dB/cm-MHz and a propagation speed of 1.54 mm/microsecond. a ____ does not mimic tissue but provides a means for measuring some aspect of instrument performance.

phantom, test object

match the parameters measured with the items used.

1. nylon fibers

2. attenuating scattering material

3. simulated cysts

4. hyperechoic and hypoechoic simulated lesions

5. thin scattering layer

axial resolution =

nylon fibers, simulated cysts

match the parameters measured with the items used.

1. nylon fibers

2. attenuating scattering material

3. simulated cysts

4. hyperechoic and hypoechoic simulated lesions

5. thin scattering layer

lateral resolution =

nylon fibers, simulated cysts

match the parameters measured with the items used.

1. nylon fibers

2. attenuating scattering material

3. simulated cysts

4. hyperechoic and hypoechoic simulated lesions

5. thin scattering layer

range accuracy =

nylon fibers

match the parameters measured with the items used.

1. nylon fibers

2. attenuating scattering material

3. simulated cysts

4. hyperechoic and hypoechoic simulated lesions

5. thin scattering layer

caliper accuracy =

nylon fibers

match the parameters measured with the items used.

1. nylon fibers

2. attenuating scattering material

3. simulated cysts

4. hyperechoic and hypoechoic simulated lesions

5. thin scattering layer

contrast resolution =

hyperechoic/hypoechoic lesions, simulated cysts

match the parameters measured with the items used.

1. nylon fibers

2. attenuating scattering material

3. simulated cysts

4. hyperechoic and hypoechoic simulated lesions

5. thin scattering layer

compensation=

attenuating scattering material

match the parameters measured with the items used.

1. nylon fibers

2. attenuating scattering material

3. simulated cysts

4. hyperechoic and hypoechoic simulated lesions

5. thin scattering layer

sensitivity =

attenuating scattering material

match the parameters measured with the items used.

1. nylon fibers

2. attenuating scattering material

3. simulated cysts

4. hyperechoic and hypoechoic simulated lesions

5. thin scattering layer

beam profile =

thin scattering layer

match the parameters measured with the items used.

1. nylon fibers

2. attenuating scattering material

3. simulated cysts

4. hyperechoic and hypoechoic simulated lesions

5. thin scattering layer

section thickness =

thin scattering layer

match the parameters measured with the correlating types of observation modes.

gain settings =

compensation, dynamic range

match the parameters measured with the correlating types of observation modes.

deepest scattering material imaged =

compensation, sensitivity, dynamic range

match the parameters measured with the correlating types of observation modes.

fiber distances from the transducer or from each other on the display

range accuracy, caliper accuracy

match the parameters measured with the correlating types of observation modes.

minimum spacing of separately displayed fibers

axial resolution

match the parameters measured with the correlating types of observation modes.

lateral smearing of fibers =

lateral resolution

true or false? test objects and phantoms can be used by the instrument operator.

true

a moving ___ test object is useful in checking the accuracy of doppler spectral displays.

string

a ___ phantom is useful in simulating physiologic _____ conditions for a doppler instrument.

flow, flow

which of the following is used for doppler sensitivity measurements?

-cyst phantom

-profile test object

-string test object

-contrast phantom

-none of the above

none of the above

tissue equivalent phantoms attempt to represent some acoustic property of ____.

tissues

true or false? the string test object measures volumetric flow rate.

false

with the use of a hydrophone, which of the following can be measured or calculated?

-impedance

-amplitude

-period

-pulse duration

-pulse repetition period

amplitude, period, pulse duration, pulse repetition period

true or false? all hydrophones consist of a small element mounted on the end of a needle.

false

a needle hydrophone contains a small ____ element.

transducer, piezoelectric

true or false? because of its small size, a hydrophone can measure spatial details of a sound beam.

true

a hydrophone ____.

produces a voltage

heating depends most directly on ____.

SATA intensity

conditions under which cavitation may occur are best described by ____.

peak rarefactional pressure

bioeffects have been observed in experimental animals with intensities greater than ___.

100 mW/cm² SPTA

bioeffects have been observed in experimental animals with focused intensities greater than ____.

1 W/cm² SPTA

focal lesions have been observed in experimental animals with intensities greater than ____.

10 W/cm² SPTA

true or false? the available epidemiologic data are sufficient to make a final judgement on the safety of diagnostic ultrasound.

false

exposure is minimized by using ultrasound _____.

only when indicated, with minimum intensity, with minimum time

which of the following is (are) used currently to indicate output on the display?
-percent

-decibel

-SPTA intensity

-mechanical index

-all of the above

all of the above

which of the following affect(s) exposure of a fetus?

-intensity at the transducer

-distance to the fetus

-frequency

-gain

intensity at the transducer, distance to the fetus, frequency

true or false? there is no possible hazard involved in the use of diagnostic ultrasound.

false

true or false? ultrasound should not be used as a diagnostic tool because of the bioeffects it can produce.

false

no independently confirmed, significant bioeffects in mammalian tissues have been reported at intensities below ____.

100 mW/cm² SPTA

yes or no? is there any known risk with the current use of diagnostic ultrasound?

no

yes or no? are there any bioeffects that ultrasound produces in small animals under experimental conditions?

yes

which of the following are mechanisms by which ultrasound can produce bioeffects?

-direction ionization

-absorption

-photoelectric effect

-cavitation

-compton effect

absorption, cavitation

which of the following relates to heating?

-impedance

-sound speed

-absorption

-refraction

-diffraction

absorption

which of the following endpoints is documented well enough in the scientific literature to allow a risk assessment for diagnostic ultrasound to be based on it?

-fetal weight

-sister chromatid exchange

-fetal abnormalities

-carcinogenesis

-none

none

on which of the following endpoints has more than one epidemiologic study shown a statistically significant effect of ultrasound exposure?

-fetal activity

-birth weight

-fetal abnormalities

-dyslexia

-none

none

which of the following acoustic parameters has (have) been documented in ultrasound epidemiologic studies published thus far?

-frequency

-exposure time

-intenstiy and pulsing conditions

-scanning patterns

-none

none

a device commonly used to measure the output of diagnostic ultrasound instruments is a(n) ____

hydrophone

a typical output intensity (SPTA) for an ultrasound imaging instrument is ____.

1 mW.cm²

which of the following typically has the highest output intensity?

-fetal monitor doppler

-duplex pulsed doppler

-color doppler shift

-color power doppler

-phase array, gray scale

duplex pulsed doppler

as far as we know now, which of the following is the most correct and informative response to a patient’s question, “Will this hurt me or my baby?”

-No.

-Yes.

-We don’t know.

-The risks are well understood, but the benefits always outweigh them.

-There is no known risk with ultrasound imaging as it is applied currently.

There is no known risk with ultrasound imaging as it is applied currently.

to minimize whatever risk there may be with ultrasound imaging, which of the following should be done?

-scan to produce pictures for the family album

-scan to determine fetal sex

-minimize exposure time

-scan for medical indications only

-minimize exposure intensity

minimize exposure time, scan for medical indications only, minimize exposure intensity

which of the following controls affect instrument output intensity?

-dynamic range, compression

-transmit, output

-near gain, far gain

-overall gain

-slope, TGC

transmit, output

which of the following are correct for a duplex, pulsed wave doppler instrument?

-tissue anywhere in the doppler beam is exposed to ultrasound

-tissue anywhere in the imaging plane is exposed to ultrasound

-imaging intensities are higher than for conventional gray scale instruments

-doppler intensities are higher than for continuous wave fetal monitoring

tissue anywhere in the doppler beam is exposed to ultrasound, tissue anywhere in the imaging plane is exposed to ultrasound, tdoppler intensities are higher than for continuous wave fetal monitoring

the tissue of greatest concern regarding bioeffects in an abdominal scan is the ___.

fetus

would it be wise to substitute a duplex, pulsed wave doppler device for an inoperative fetal monitor for long term (e.g. 24 hour) monitoring in labor?

no

which of the following is (are) likely to be exposed to ultrasound during a diagnostic study?

-patient

-sonographer

-sonologist

-observers in the room

patient

no bioeffects have been observed in nonhuman mammalian tissues at thermal index values of less than ___.

2

no bioeffects have been observed in nonhuman mammalian tissues at mechanical index values of less than ___

0.4

no bioeffects have been observed in nonhuman mammalian tissues at peak rarefactional pressure values (megapascals) of less than ___.

0.4