Exam 2

Which statement best defines a transducer?

a device that converts one form of energy into another

During ultrasound transmission, the transducer converts:

electrical energy into sound energy

During receptio, returning echos are converted from:

sound energy into electrical energy

Which event describes the reverse piezoelectric effect

Electrical energy is converted into ultrasound (sound) energy

Which event describes the direct piezoelectric effect?

echos press the crystal and generate an electriacal signal

What is the most common synthetic ferroelectric material in modern transducers?

lead zirconate titanate (PZT)

Which transducer component is active and performs the energy conversion?

piezoelectric element

Where is the backing (damping) material located?

directly behind the piezoelectric element

What is a primary function of backing material?

absorb backward sound and reduce ringing

What is diffraction?

the spreading out of sound into a pie shape from a small source

According to Huygen’s Principle, what causes the ultrasound beam to form its typical hourglass shape?

overlapping and interference of wavelets

What is the focus of an ultrasound beam?

the point where the beam reaches its minimum diameter

Which TWO factors affect near zone length?

frequency and transducer diameter

Axial resolution describes the ability to distinguish two structures that are:

front to back and parallel to the beam

Which action improves axial resolution?

using a higher-frequency transducer

Lateral resolution is equal to:

beam diameter

Which component of the transducer converts electrical energy into sound energy and returning echoes into electrical energy?

piezoelectric element

What is A-mode?

a display mode that shows echo amplitude as spikes

What is electronic curvature?

creating a curved beam by electronically controlling the timing of elements

What is Huygen’s Principle?

each point on a wavefront acts as a source of a new wavelet

Which of the following are the three types of spatial resolution?

axial, lateral, and elevational

What are grating lobes?

unwanted off-axis sound beams produced by array transducers

What is bandwidth?

the range of frequencies produced by a transducer

What is axial resolution?

the ability to distinguish two structures that are front-to-back and parallel to the sound beam

Which equation is used to calculate axial resolution?

spatial pulse length ÷ 2

What is lateral resolution?

the ability to distinguish two structures that are side-by-side and perpendicular to the sound beam

What is lateral resolution equal to?

beam diameter

Where is lateral resolution BEST?

at the focus

What is the focal point?

the point where the beam reaches its minimum diameter

What is the near zone also called?

fresnel zone

What is the far zone also called?

fraunhofer zone

Which two factors affect near zone length?

transducer diameter and frequency

Which type of transducer is absorbed more in the body?

higher-frequency transducer

What is the purpose of coupling gel?

to remove air between the transducer and skin and improve sound transmission

What is the piezoelectric effect?

the conversion between electrical energy and mechanical energy

What is constructive interference?

when waves combine and produce a greater amplitude

What is apodization?

varying the amplitude of excitation across elements of an array transducer

What is subdicing

dividing a transducer element into smaller pieces to reduce grating lobes

Which spatial resolution is BEST in diagnostic ultrasound?

axial resolution

Which spatial resolution is WORST in diagnostic ultrasound?

elevational resolution

How can axial resolution be improved?

use a higher-frequency transducer

Which combination correctly describes increased damping?

broader bandwidth; lower sensitivity and amplitude

Increasing damping mostly directly produces which result?

shorter pulses and improved axial resolution

What is the main purpose of the matching layer?

reduce impedance mismatch and improve sound transmission

What do electrodes and electrical wires do?

apply voltage and carry signlas toand from the system

Each active element in a transducer requires:

its own electrical connection

what is the correct response to a transducer with cracked housing?

do not use it because of shock and infection risk

Bandwidth is best defined as:

the range of frequencies in the ultrasound pulse

Which set of fetures decribes a broad-bandwidth transducer?

many frequencies, short pulses, low Q

Which equation correctly calculates quality factor (Q)?

Q = operating frequency / bandwidth

A transducer has an operating frequency of 6MHz and a bandwidth of 3 MHz. What is its Q factor?

2

If operating frequency stays constant and Q increases, bandwidth will:

narrow

Electronic curvature relates to:

a firing pattern that focuses and ultrasound beam

How does an annular-array transducer steer the ultrasound beam?

mechanically

If one element in a linear switched-array transducer is damaged, how will the image be affected?

there will be an area of vertical droput

Lateral resoultion is approximatly equal to:

beam diameter

More absorbtion of ultrasound energy occurs when using a transducer with:

a higher frequency

The best thickness for a matching layer is:

one-quarter wavelength

The most common piexoelectric material used in ultrasound imaging is:

lead zirconate titanate (PZT-5)

The purpose of coupling gel is to:

eliminate reflection at the skin surface caused by air

Axial resolution will be most affected by changes in:

beam frequency. and pulse damping

Focusing the ultrasound beam will reduce beam diameter at all distances from the transducer face

false

A transducer has an impeadence of 2,000,000 Rayls and skin has 800,00 Rayls. The best matching-layer choice is:

1,250,000 Rayls

If transducer frequency changes from 12.0 MHz to 6.0 MHz, the near-zone length will:

be halved

For a single-element transducer, a 16cm scan with 100 image lines contains 1,600 pulses.

false

Assuming a fixed frequency, what