UNIT 12

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)

Lateral resolution in a mechanical transducer is generally:

Moderate and depth-dependent

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

Lateral resolution in a mechanical transducer is:

Best at the focal zone

A mechanical transducer most commonly contains:

One crystals

Lateral resolution in a linear array is BEST described as:

excellent near field and at focus

Lateral resolution in a convex array is best:

At the focal zone

Which transducer has poor elevational resolution but good focal-zone lateral resolution for cardiac imaging?

Phased array

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