Transducers (Chapter 3--Physics)

For a particular transducer element material, if a thickness of 0.4 mm yields an operating frequency of 5 MHz, the thickness required for an operating frequency of 10 MHz is _________ mm.

0.2

An unfocused 3.5-MHz, 13-mm transducer produces three-cycle pulses. The axial resolution in soft tissue is _______ mm.

0.7 (size not needed)

Because diagnostic ultrasound pulses are usually two or three cycles long, axial resolution is usually equal to ________ to _________ wavelengths.

1, 1.5

For pulses traveling through soft tissue in which the frequency is 3 MHz and there are four cycles per pulse, the axial resolution is ________ mm.

1.0

If there are three cycles of a 1-mm wavelength in a pulse, the axial resolution is ________ mm.

1.5

Which of the following transducer frequencies would have the thinnest elements?

10 MHz

The PRF is ___________ Hz if 30 frames (40 lines each) are displayed per second (single focus).

1200

If frequencies less than __________ MHz are used, axial resolution is not sufficient.

2

The range of frequencies useful for most applications of diagnostic ultrasound is ________ to ________ MHz.

2, 20

If frequencies higher than _________ MHz are used, penetration is not sufficient.

20 (less than 20 MHz in many applications)

What are the axial resolutions in Figure 3-35, A-B?

3 mm, 2 mm

At what depth is the best lateral resolution in Figure 3-14, C?

4 cm

If the PRF of an instrument is 1 kHz and it displays (single focus) 25 frames per second, there are ________ lines per frame.

40

An unfocused 3.5-MHz, 13-mm transducer will yield a minimum beam width (best lateral resolution) of _______ mm.

6.5 (frequency not needed)

Which transducer element has the longest near zone?

8 mm, 7 MHz

The maximum frame rate permitted for 15-cm penetration, three foci, and 200 scan lines per frame is ______.

8.5

A 5-MHz unfocused transducer with an element thickness of 0.4 mm, an element width of 13 mm, and a near-zone length of 14 cm produces two-cycle pulses. Determine the following: a. operating frequency if thickness is reduced to 0.2 mm: ________ MHz b. axial resolution in the case of (a): _______ mm at 5 MHz c. depth at which lateral resolution is best: ________ cm d. lateral resolution at 14 cm: _________ mm e. lateral resolution at 28 cm: _________ mm f. this transducer can be focused at depths less than _______ cm

a. 10 b. 0.15 c. 14 d. 6.5 e. 13 f. 14

Match each transducer characteristic with the sound beam characteristic it determines (answers may be used more than once): a. element thickness: ______, _______, and _______ b. element width: __________ c. element shape (flat or curved): _______ d. damping: ________

a. axial resolution, lateral resolution, operating frequency b. lateral resolution c. lateral resolution d. axial resolution

Match the following transducer assembly parts with their functions: a. cable: _________ b. damping material: _________ c. piezoelectric element: ____________ d. matching layer: ____________

a. conducts voltage pulses b. reduces pulse duration c. converts voltage pulses to sound pulses d. reduces reflection at transducer surface

Match the following (answer may be used more than once): a. linear array ________ b. phased array ________ c. convex array _________

a. voltage pulses are applied in succession to groups of elements across the face of a transducer b. voltage pulses are applied to most or all elements as a group, but with small time differences c. voltage pulses are applied in succession to groups of elements across the face of a transducer

A coupling medium on the skin surface eliminates reflection caused by _______.

air

Transducer size is also called __________.

aperture

Near-zone length increases with increasing source __________ and _________.

aperture, frequency

Increasing frequency decreases penetration because _________ is increased.

attenuation

Which of the following transducer(s) can focus at 6 cm?

b and c 4 MHz, near-zone length of 6 cm; 4 MHz, near-zone length of 10 cm

The damping layer is in front/back of the element.

back

Lateral resolution is equal to _________ _________.

beam width

To operate a transducer at more than one frequency requires _______ ________.

broad bandwidth

Mixtures of a piezoelectric ceramic and a nonpiezoelectric polymer are called ___________.

composites

In __________ and _________ arrays, pulses travel out in different directions from different starting points on the transducer face.

convex, vector

Focusing in section thickness can be accomplished with __________ elements or a _________.

curved, lens

The addition of damping material to a transducer reduces the number of _________ in the pulse, this improving _________ __________. It increases ________.

cycles, axial resolution, bandwidth

Lateral resolution does not depend on __________.

damping

Operating frequency _________ when transducer element thickness is increased.

decreases

A sector image is a result of sector steering of the beam. This means that pulses travel in ________ direction(s) from a common ________ at the transducer face.

different, origin

Single-element transducers are in the form of ________.

disks

Doubling the number of cycles per pulse causes axial resolution to be ____________.

doubled

Damping material reduces the ________ of the transducer and _______ of the diagnostic system.

efficiency, sensitivity

Ultrasound transducers convert __________ energy into ________ energy, and vice versa.

electric, ultrasound

A transducer ________ is part of a transducer _________.

element, assembly

The term transducer is used to refer to a transducer _________ or to a transducer _________.

element, assembly

Electronic focusing in section thickness requires multiple rows of _________.

elements

Transducer arrays are transducer assemblies with several transducer________.

elements

A transducer converts one form of ________ to another.

energy

A transducer with a near-zone length of 10 cm can be focused at 12 cm. True or false?

false

Axial resolution is often not as good as lateral resolution in diagnostic ultrasound. True or false?

false

Beam diameter may be reduced in the far zone by focusing. True or false?

false

Damping increases efficiency. True or false?

false

Damping lengthens the pulse. True or false?

false

Focusing reduces the beam diameter at all distances fro the transducer. True or false?

false

For a given frequency, a smaller aperture always yields improved lateral resolution. True or false?

false

If better resolution is desired, a lower frequency will help. True or false?

false

When studying an obese subject, a higher frequency likely will be required. True or false?

false

For focused transducer, the best lateral resolution (minimum beam width) is found in the ________ region.

focal

The two resolutions may be comparable in the ________ region of a strongly focused beam.

focal

If the elements of a phased array are pulsed in rapid succession from outside in, the resulting beam is __________.

focused

Lateral resolution is improved by _________.

focusing

Which three things determine beam diameter for a disk transducer?

frequency, aperture, distance from disk face

Lateral resolution is determined by ____________. (There is more than one correct answer to the question.)

frequency, aperture, distance from the transducer, focusing

The matching layer is in front/back of the element.

front

For an unfocused transducer, the best lateral resolution (minimum beam width) is _________ the transducer width. This value of lateral resolution is found at a distance from the transducer face that is equal to the ________ ________ length.

half, near zone

Doubling the frequency causes axial resolution to be _______.

halved

The matching layer has __________ impedance.

intermediate

The distance from a transducer to the location of the narrowest beam width produced by a focused transducer is called focal __________.

length

Shorter time delays between elements fired from outside in result in _______ curvature in the emitted pulse and a _______ focus.

less, deeper

__________ and ________ describe how arrays are constructed.

linear, convex

A higher-frequency transducer producers a ________ near-zone length.

longer

Which of the following improve sound transmission from the transducer element into the tissue? (more than one correct answer)

matching layer, coupling medium

Sound may be focused by using a ________.

more than one of the above (curved element, lens, phased array)

Transducer assemblies are also called __________.

more than one of the above (transducers, probes, scanheads)

The dividing point between the two regions referred to in Exercise 30 is at a distance from the transducer equal to _________ ________ length.

near zone

A beam is divided into two regions, called the _________ zone and the ________ zone.

near, far

Is it practical to attempt to operate a 5-MHz transducer with a bandwidth of 2.5 at 3 and 7 MHz?

no [because these frequencies are outside the 2.5 MHz bandwidth (3.75-6.25 MHz)]

Is it practical to attempt to operate a 5-MHz transducer with a bandwidth of 1 MHz at 6 MHz?

no [because these frequencies are outside the bandwidth (4.5-5.5 MHz)]

_________, __________, and _________ describe how arrays are operated.

phased, sequenced (he said he didn't like vector)

Phased arrays scan beams by _________ element groups.

phasing

Ultrasound transducers operate on the ________ principle.

piezoelectric

The principle on which ultrasound transducers operate is the ________.

piezoelectric effect

An electric voltage pulse, when applied to a transducer, produces an ultrasound ________ of a(n) _________ that is equal to that of the voltage pulse.

pulse, frequency

Elements in linear arrays are in the form of ___________.

rectangles

The matching layer on the transducer surface reduces ________ caused by impedance differences.

reflection

Which of the following is not decreased by damping?

refraction

The lower and upper limits of the frequency range useful in diagnostic ultrasound are determined by ________ and _________ requirements, respectively.

resolution, penetration

Operating frequency is also called ________ _________.

resonance frequency

Axial resolution is the minimum reflector separation required along the direction of the _________ ________ to produce separate ________.

scan lines, echoes

Lateral resolution is the minimum _________ between two reflectors at the same depth such that when a beam is scanned across them, two separate ________ are produced.

separation, echoes

A smaller aperture produces a(n) _________ near-zone length.

shorter

Axial resolution depends directly on _________ _________ __________.

spatial pulse length

If the elements of a phased array are pulsed in rapid succession from right to left, the resulting beam is ________.

steered left

A rectangular image is a result of linear scanning of the beam. This means that pulses travel in ________ ________ direction(s) from _________ starting point(s) across the transducer face.

the same, different

The ________ of a transducer element changes when voltage is applied to its faces.

thickness

The resonance frequency of an element is determined by its _________.

thickness

Beam diameter may be reduced in the near zone by focusing. True or false?

true

For an aperture of a given size, increasing frequency improves lateral resolution. True or false?

true

Imaging involving 10-cm penetration, a single focus, 100 scan lines per frame, and 30 frames per second can be accomplished without range ambiguity. True or false?

true

In Exercise 83 and 84 (two prior), axial resolution is better than lateral resolution. True or false?

true

Lateral resolution varies with distance from the transducer. True or false?

true

Smaller axial resolution is better. True or false?

true

A two-cycle pulse of 5-MHz ultrasound produces separate echoes from reflectors in soft tissue separated by 1 mm. True or false?

true (axial resolution 0.3 mm)

A phased linear array with a single line of elements can focus in ________ dimension(s).

two (he says)

Ultrasound transducers typically generate pulses of _________ or _________ cycles.

two, three

If there are two cycles per pulse, the axial resolution is equal to the ___________. At 5 MHz in soft tissue, this is ________ mm.

wavelength, 0.3

Increasing frequency improves resolution because ________ is reduced, thus reducing __________ ________ __________.

wavelength, spatial pulse length