Midterm Questions

Which best describes the elements in a linear sequential array transducer?

Rectangular, 1 wavelength wide

Which of the following will improve a system's temporal resolution?

Increased PRF

Which of the following is preferable for diagnostic imaging?

High signal-to-noise ratio

What is most likely to occur if the diameter of a single, disc-shaped, unfocused transducer is increased?

The beam width in the far field is reduced

What is axial resolution determined by?

Pulse Length

If medium A has a higher attenuation rate than medium B, which medium has the thickest half value layer?

Medium B

A pulse's Time-of-flight is 39 microseconds. What is the total distance the pulse wave traveled?

6 cm

What is the shape of the elements in an annular phased array transducer?

Circles or rings

Which of the following explains why a sound beam created by a disc-shaped crystal is hourglass shaped?

Huygens' Principle

Two ultrasound systems have near zone lengths of 8cm. At the focus, System G's lateral resolution is 3.0 mm, whereas System P's is 5.0 mm. Which system will produce higher quality pictures at their foci?

System G

Why is decreased sensitivity an undesirable consequence related to the use of the backing material?

It limits reception of weak reflected echoes

What is the actual time that an US machine is creating a pulse?

Pulse Duration

The focus of an ultrasound system is the location where the ______.

optimum transverse resolution is

Which of these intensities is the smallest?

SATA

What determines the frequency of a sound beam from a pulsed transducer?

PZT Thickness

Which type of transducer utilizes time-delay beam steering as the primary method to direct the beam throughout the field of view?

Phased Array

Which two controls determine a system's temporal resolution?

depth of view and pulses per image

What operator control alters image contrast?

Dynamic Range

Two ultrasound systems are identical except for the diameter of the transducer's piezoelectric crystal. Which system has the deepest focus?

the one with the larger diameter crystal

What function is used to reduce lobe artifacts?

Apodization

True or False: One way for a sonographer can alter the axial resolution achieved during an exam is to adjust the maximum imaging depth.

False

Which of the following lists orders the impedance from highest to lowest?

PZT, matching layer, gel, skin

If the incident angle of a sound beam is 60 degrees, what will the reflection angle be?

60 degrees

While scanning in a water tank, what location in a sound beam has the highest intensity?

Focal point

Which of the following intensity measurements will have the greatest value?

SPTP

A sound wave strikes a boundary with an orthogonal incidence. What is another name for this?

Perpendicular

At what location is the sound beam diameter three times greater than the transducer diameter?

At the depth equal to four focal lengths

What part of the ultrasound system determines the firing patterns for phased array focusing?

Beam former

Slice thickness is measuring the sound beam in what direction?

Top to Bottom

What happens when the active element in a mechanical transducer is damaged?

The entire image is lost

Which of the following is different from the others?

Dynamic Range

The diameter of a disc-shaped, unfocused pzt crystal is 1.2cm. The near zone length is 8cm. What is the best estimate for the lateral resolution at a depth of 16cm?

1.2 cm

All of these decrease temporal resolution except:

Narrower sector

Which of the following actions will improve the signal-to-noise ratio?

increase output power

What is the impedance of a medium with a density of 2 (kg/m3) and a propagation speed of 300 (m/s)?

600 Rayls

A sonographer increases the line density from 1 line per degree of sector to 3 lines per degree of sector. What is the most likely consequence of the action?

Temporal resolution decreases

The lateral resolution of an ultrasound system is primarily determined by the _____.

width of the sound pulse

When exposed to strong electrical currents while being heated to a substantial temperature, certain types of material will become ___________?

Polarized

All of the following describe dynamic receive focusing except:

May be used by single crystal transducers

With regard to ALARA, what is the best way to image deeper?

Decrease transducer frequency

What is the result of decreasing the PZT thickness?

An increase in the frequency of the transducer

What part of the transducer is used to decrease reflection at the PZT/skin boundary?

Matching Layer

Which type of transducer utilizes time delay beam steering as the primary method to direct the beam throughout the field of view?

Phased array

True or False: The backing material helps to decrease the duty cycle at the particular PRF.

True

What happens to the beam when it is focused?

Beam diameter in the near field and focal zone is reduced

True or False: The acoustic impedance of the skin is greater than that acoustic impedances of both the matching layer and the piezoelectric element.

False

The region between the transducer element and the point at which the sound beam is narrowest is called the:

Near zone length

The sonographer reduced the sector size from 90 degrees to 30 degrees. Frame rate, however, did not change. What else happened?

multi-focus was turned on

-10dB means that the intensity is reduced to ________ of its original value.

one-tenth

Which of the following measurements describes the beam's intensity at the instant in time of its maximum value?

Temporal Peak Velocity

The minimum number of active elements in a mechanical transducer is:

1

True or False: The higher the frequency of the cycles within a pulse, the lower the numerical value of the axial resolution.

True

Which of these means adjustable focusing or multi-focusing?

Phased array

In which region of a sound beam is focusing most effective?

The end of the near zone

Which of the following actions would cause a PZT crystal to lose its special properties?

exposing it to high temperatures

The Y-axis for A-mode ultrasound represents what?

Amplitude

An ultrasonic pulse is traveling in soft tissue. Which of the following is most important in the determination of the frequency of sound?

the propagation speed of the ultrasound transducer's matching layer

What is the time needed to make a single image if the frame rate of ultrasound system is 20 Hz?

0.05 s

Which PZT crystal would have the lowest possible frequency?

8 mm thick, 2cm diameter, 2.0 mm/µs propagation speed

Huygens' Principle is based on_______

interference

What is the rationale for ALARA principle?

Patient exposure

In which of the following would refraction occur?

Oblique incidence - Medium 1 speed is less than Medium 2 speed

Which of the following transducers has the best axial resolution?

2.7 MHz and 2 cycles/pulse

A sonographer, using a phased array ultrasound system, turns off the multi-focus feature. What is the most likely consequence of this action?

Temporal resolution improves

The lateral resolution of an ultrasound system is 4mm. Two structures are separated by 3mm and lie side by side in relation to the sound beam's main axis. What will most likely appear on the system's display?

one echo

What is the thickness of the matching layer of a 2MHz pulsed wave transducer?

one-quarter the wavelength of sound in the matching layer

A sonographer reduced the sector size from 90 degrees to 30 degrees. Frame rate, however, didn't change. What else happened?

Multi-focus was turned on

A sound beam travels through the body, reflects off a surface at a depth of 2cm and returns to the transducer. What is the time-of-flight?

26 microseconds

What is the point or location where a beam reaches its smallest dimension?

focus

What are the 3 types of attenuation?

Scattering, Reflection, Absorption

Which transducer has the narrowest bandwidth?

Continuous wave

What is NOT true about multi-focusing?

Temporal resolution will be improved

What type of focusing can be adjusted by the sonographer?

Phased array

Which of the following results in the least attenuation?

4 MHz sound, path length 2cm

What is the relationship between the thickness of the PZT and frequency?

Inversely related

A pulsed-wave transducer has a resonant frequency of 4MHz. The lowest frequency in the pulse is 2MHz and the highest is 7MHz. What is the bandwidth?

5 MHz

What is the advantage of using a 1 1/2 Dimensional array transducer?

improved elevational resolution

Which type of transducer may produce grating lobes?

Multi-element

What is the result of reducing the thickness of the PZT crystal?

Increase in the frequency of the transducer

What determines elevation resolution?

Shape of active crystal

A channel is comprised of an active element, the____________, and the wire that connects them.

Beam former

Which of the following will result in a minimum beam divergence deep in the far zone?

high frequency, large diameter

A sonographer adjusts an ultrasound scan to double the depth of view from 5cm to 10 cm. If the frame rate remains the same, which one of the following also occurs?

Narrower sector

A sound beam has increased from its initial intensity by a factor of 1000. How is this described in decibel notation?

30 dB change

The average intensity across the beam's entire cross-sectional area is termed:

Spatial average intensity

All of the following occur with focusing except:

Lower intensity at the focus

The Intensity Reflection Coefficient of a particular sound beam is 20%. What is the Intensity Transmission Coefficient?

80%

Two ultrasound systems produce pulses. One pulse is 0.4 µsec in duration and the other is 0.2 µsec long. Which pulse is most likely to provide the best radial resolution?

0.2µsec system

A sonographer adjusts an ultrasound scan to decrease the depth of view from 12cm to 4cm. What happens to the frame rate?

It increases

Which of the following focusing techniques is different from the others?

phased

A sound beam with an intensity of 8 w/cm2 has undergone a -6 dB change. What is the final intensity?

2 w/cm²

Which resolution is considered improved when the numerical value goes down?

Axial Resolution

Which of the following results in the most attenuation?

6MHz sound, path length 8cm

Which of the following forms of resolution improve when frame rate increases?

Temporal

Which has the greatest amount of attenuation?

Bone

Which of the following crystals will produce sound with the highest frequency?

Thin and with a high speed

What is the lowest of all the temporal intensities?

temporal average intensity

With B-mode, on which axis is the strength of the reflection input?

z-axis

The ability of a system to display two structures that are very close together when the structures are parallel to the sound beam's main axis is measured by?

Axial Resolution

During ____________ electrical energy from the system is converted into sound .

Transmission