UNIT 12 TRANSDUCERS

Which transducer type is least commonly used today due to mechanical wear?

Mechanical

Which statement best describes beam steering in a mechanical transducer?

Physical motor movement of the transducer element

Beam focusing in a mechanical transducer is achieved primarily by:

Fixed acoustic lens or crystal curvature

Which image shape is produced by a mechanical transducer?

Sector

Crystal failure in a mechanical transducer most commonly results in:

Complete loss of image

Beam focusing in a linear array is achieved by:

Electronic transmit and dynamic receive

What is the typical image shape of a linear array?

Rectangular

Linear array transducers are MOST commonly used for:

Vascular and small parts

Elevational resolution in a linear array is:

Fixed and mechanically focused (moderate)

Crystal failure in a linear array causes:

Vertical dropout line

Beam steering in a convex array is:

Electronic steering

Beam focusing in a convex array is achieved by:

Electronic delays and lens

What image shape does a convex array produce?

Blunted sector

Convex array transducers are MOST commonly used for:

Abdominal and OB/GYN

Crystal failure in a convex array causes:

Curved or arc shape line dropout

Beam steering in a phased array is accomplished by:

Electronic timing delays

Beam focusing in a phased array is achieved by:

Electronic delays

Phased arrays produce what image shape?

Sector

Phased array transducers are BEST suited for:

Cardiac imaging

Elevational resolution in phased arrays is typically:

Poor to moderate

Crystal failure in a phased array causes:

Horizontal line dropout

Beam steering in an annular array is:

Mechanical

Beam focusing in an annular array is achieved by:

Electronic delays to concentric rings

Annular arrays are known for having:

Excellent elevational resolution

Which statement best describes elevational resolution in a mechanical transducer?

Fixed by an acoustic lens and moderate

A mechanical transducer most commonly contains:

One crystals

Lateral resolution in a linear array is BEST described as:

excellent near field and at focus

Which transducer has the best overall lateral and elevational resolution?

Annular

Crystal failure in an annular array results in:

Ring-shaped loss

What is the purpose of dynamic aperture in array transducers?

To improve lateral resolution at varying depths

A key advantage of phased array transducers is:

Small footprint allowing imaging between ribs

Compared to phased arrays, linear arrays have:

Better near-field resolution

Why do phased arrays have poorer near-field resolution?

Small aperture

Electronic steering in phased arrays is accomplished by:

Varying timing delays

Electronic steering affects which resolution?

Lateral

Side lobes are:

Weak off-axis beams

Side lobes most commonly cause artifacts in:

Fluid-filled structures

Which reduces side lobes?

Apodization

Compared to side lobes, grating lobes are:

Stronger and predictable

Which technique reduces grating lobes?

Subdicing

Apodization works by:

Reducing voltage to outer elements

Primary purpose of apodization:

Reduce side and grating lobes

Subdicing is used to:

Reduce element spacing

Subdicing primarily reduces:

Grating lobes

Subdicing works by:

Dividing elements into smaller units

Vector arrays differ from linear arrays because they:

Use electronic steering

Which design feature MOST directly prevents grating lobes?

Smaller element spacing

Elevational resolution refers to the ability to distinguish objects that are:

Above and below the imaging plane

Poor elevational resolution most commonly causes which artifact?

Section thickness artifact

Which transducer typically has the BEST elevational resolution?

Annular array

Which adjustment improves elevational resolution?

Increasing frequency

Elevational resolution improves when slice thickness is:

Decreased

Grating lobes are most commonly associated with which transducer type?

Array transducers

A structure located in a grating lobe will appear:

Duplicated or displaced

Grating lobes primarily degrade which type of resolution?

Lateral

Which combination of techniques reduces grating lobes?

Apodization, subdicing, higher frequency

Which adjustment would increase grating lobe artifacts?

Increasing steering angle

Side lobes are produced by which type of transducer?

Mechanical transducers

Which of the following MOST reduces side lobe artifacts?

Harmonic imaging

Which method reduces grating lobes by weighting center elements

more heavily than outer elements?

Apodization

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

1

How are the piezoelectric crystals of a linear phased array transducer fired?

At almost exactly the same time

The pattern of electrical signals exciting the piezoelectric crystals of a linear phased array transducer ____

Typically changes from one acoustic pulse to the next

All of the following describe dynamic receive focusing except:

Automatically performed by system

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

Circles

What is true of the electric pulses that excite the active elements of an annular phased array transducer?

They arrive at each PZT crystal at different times, microseconds apart

What transducer steer the beam with a motor and focus the beam with an acoustic lens or a curved PZT element?

Mechanical

What transducer typically produce an image, that throughout its entire depth, is approximately as wide as the ultrasound transducer itself?

Linear sequential array

When looking at images, produced by these transducer systems, which one can be distinguished from all of the others?

Linear sequential array

What is the advantage of using 1 ½ dimensional array transducer?

Improved elevational resolution

Which transducer possesses the best slice thickness resolution?

1 ½ dimensional array

What is the use of a greater number of channels to receive echoes from ever increasing depths called?

Dynamic aperture

The excitation of array elements with dissimilar voltages is called ____ and is used to ____

Apodization, reduce lobe artifact

For a linear array transducer consisting of a single row of elements, what method is most used to focus the beam in the elevational resolution?

Mechanical focusing

What benefit would you obtain by choosing a transducer having a large diameter compared to one having a small diameter?

It can focus at greater depths

Dynamic receive focusing uses:

Time delay before echo signals from array elements are combined

Which of the following minimizes the degree to which beam width varies with depth?

Dynamic aperture

For a single transducer to offer multiple frequency selections for scanning, it must have:

Wide bandwidth

What is an advantage of single crystal or pure wave crystal transducer?

Wide bandwidth

What type of resolution is most affected by the mechanical focus on a linear array transducer?

Elevational resolution

What type of resolution is affected most by electronic focusing?

Lateral resolution

A transducer with a small footprint has the following disadvantage:

Resolution is degraded at large distances

What type of transducer has the same measurement for elevational and lateral resolution?

Linear sequential array

What array transducer fires all of the elements for each acoustic scan line, using small time delays to steer the beam?

Phased array

How is a trapezoidal shape created with a linear array transducer?

Electric beam steering

What advantage does a trapezoidal shaped image of steered linear array transducer have?

Improved field of view

What disadvantage is related to a tightly curved array?

Lateral resolution degrades with depth

What best describes the difference between the ultrasound frequencies used for Doppler and for B-mode imaging with a given transducer?

The frequency for Doppler is usually lower than the imaging

Which transducer will exhibit the LEAST amount of volume averaging?

1.5D or multirow array

Which of the following helps to improve the elevational resolution in a B-mode image?

Focusing with an acoustic lens

What is the main advantage you will have by choosing a transducer that produces a thin slice over the image plane?

Decreased volume averaging