Chapter Twelve - Two Dimensional Imaging

What is the shape of the active element in a mechanical transducer?

Single, circular, disc-shaped (coin)

The active element in a mechanical transducer is _____________ moved.

Physically

When the active element is moved in a mechanical transducer, what is created?

A scanning plane

How does sound travel?

In a straight line

______________ sound beams optimize lateral resolution.

Narrow

What is the process of creating two-dimensional images?

Multiple pulses sent at slightly different directions and times

How is a 2-D image/frame created?

The process is repeated many times

If there are 16 scan lines, it means…

There are 16 pulses required to create 1 frame

Each frame of an image is made up of many scan lines created by…

A pulse from the transducer

What are the transducer characteristics?

• “Active element” array

• Acoustic footprint

• Image shape

• Focus

• Steering technique

• Crystal Malfunction

How many crystals are in a mechanical transducer?

Only one

What is the shape of the image created by a mechanical transducer?

Fan or sector shaped

What kind of steering is used while using a mechanical transducer?

Mechanical steering

What is mechanical steering?

The crystal is rotating with the help of a motor, sound beams are emitted as the crystal moves

What kind of focusing is used while using a mechanical transducer?

Fixed focusing or conventional mechanical (has a fixed focal depth)

What are two examples of fixed focusing?

• Internal focusing - curved active element

• External focusing - acoustic lens

Since the focusing in a mechanical transducer is fixed, how would I change my focus?

It would require you to change out the entire transducer

Why does focusing occur in both horizontal and vertical planes?

Because of the hourglass shape of the sound beam

When the PZT crystal is damaged in a mechanical transducer, what happens to the overall image?

The entire image is destroyed

Modern transducers are called

Arrays, containing multiple active elements in a single transducer

What are elements?

An array comprised of a single slab of PZT cut into a collection of separate pieces

Each active element has its own… and is….

Electrical circuitry in the ultrasound system, acoustically isolated from its neighbor

What is a channel?

Combination of the active element, wire, and system electronics

The system has the ability to…

Ring a single element or groups of elements in various ways

How are the elements arranged in a (linear) array transducer?

In a line

How are the elements arranged in a (convex, curved, or curvilinear) array transducer?

In an arc

How are the elements arranged in a (annular) array transducer?

In ringed shaped elements

What is the footprint?

Face of transducer that comes in contact with skin

A linear phased array transducer has a __________ acoustic footprint.

Small

How many crystals are in a linear phased array transducer?

100-300, width of each element ¼ to ½ of the sound’s wavelength

What is the shape of the image created by a linear phased array transducer?

Fan or sector shaped

Electronic steering process called

Phasing

What kind of steering is used while using a linear phased array transducer?

Phasing

What happens during electronic steering (phasing)?

Sound beams are electronically transmitted in different directions without the use of moving parts

What kind of focusing is used while using a linear phased array transducer?

Electronic

What happens during electronic focusing?

There are controls that allow the sonographer to modify the depth and amount of focusing of the sound beam

What is the advantage of phased array systems?

Availability of electronically controlled, adjustable focusing.

Electronic focusing allows the sonographer to appropriately…

Match the beam’s characteristics to the clinical requirements

What does it mean to have multi-focusing capability?

Transmitting multiple beams down the same scan line, each with a different focal depth

Phased array always means…

Adjustable or multi focus

When the PZT crystal is damaged in a linear phased array transducer, what happens to the overall image?

Inconsistent or erratic beam steering and focusing

While using a linear phased array transducer, electronic signals….

Excite multiple crystals to create only one sound pulse

How are crystals fired in a linear phased array transducer?

Simultaneously (small time delays to beam, will affect steering and focusing)

When steering with a linear phased array transducer, signals are nanoseconds apart, meaning

There are phase delays that are creating a slope that will steer the beam

What will focus a linear phased array beam?

Electronic curvature

Slope =

Steer

Curvature =

Focus

What is Dynamic Receive Focusing?

Returning echoes have time delays too, creates receive zone focus with optimal image quality

What is another name for Dynamic receive focusing?

Dynamic focusing

What is the shape of the active element in an Annular Phased Array transducer?

Disc-like

How many crystals are in a Annular Phased Array transducer?

Multiple ring-shaped elements with a common center

What kind of steering is used while using a Annular Phased Array transducer?

Mechanical Steering

What kind of focusing is used while using a Annular Phased Array transducer?

Multiple focusing from different focal depths

Smaller PZT diameter =

Creates shallow focus beam

Larger PZT diameter =

Creates deeper focus beam

The inter rings of an Annular phased array transducer are responsible for _________ imaging

Shallow

The outer rings of an Annular phased array transducer are responsible for _________ imaging

Deep

How can we describe the focusing process on an Annular Phased Array Transducer?

Each crystal is fired down the same scan line, but information is only stored from the respective focal zone

What is the shape of the image created by an Annular phase array transducer?

Fan or sector shaped

When the PZT crystal is damaged in an Annular phased array transducer, what happens to the overall image?

Horizontal or side-to-side band of dropout at a particular depth

A linear sequential array transducer has a __________ acoustic footprint.

Large

What is the shape of the image created by a Linear Sequential Array transducer?

Rectangular image

How many crystals are in a Linear Sequential Array transducer?

120-250 rectangular-shaped strips

What kind of steering is used while using a Linear Sequential Array transducer?

A small group of the crystals are fired simultaneously

What kind of focusing is used while using a Linear Sequential Array transducer?

Both transmit and receive focusing using electronic phase delays

What is electronic transmit focusinig?

A curved pattern of the active elements (outer elements are fired earlier than the inner elements)

What is receive focusing?

Introducing electrical delays in the signals returning from the transducer (phase delays change continuously during reception)

When the PZT crystal is damaged in a Linear Sequential Array transducer, what happens to the overall image?

Only the image extending directly below the damaged element is affected

What kind of scan lines do Linear Sequential Array Transducers create?

Parallel

Beam steering by sloped delays in electrical spikes create what shape of image?

Parallelogram-shaped image

What are other names for Convex Array Transducers?

Convex Sequential or Curvilinear

How are the active elements arranged in a convex array transducer?

In an arc

A convex array transducer has a __________ acoustic footprint.

Large

What is the shape of the image created by a convex array transducer?

Blunted sector shape

What kind of focusing is used while using a mechanical transducer?

Electronic, curved spike pattern

What kind of steering is used while using a Convex transducer?

Electronic, due to shape the sound beams are not parallel

How many crystals are in a convex transducer?

120-250 rectangular shaped strips shaped in an arc

What is transmit focusing in relation to convex array transducers?

Curved spike pattern of phased excitation of crystals with delays

What is dynamic receive focusing in relation to convex array transducer?

Electrical delays in the returning signals

When the PZT crystal is damaged in a convex array transducer, what happens to the overall image?

Drop out of the image directly under the affected crystal, vertical line

What is the shape of an endovaginal transducer?

Blunted sector

An endovagainal transducer has a __________ acoustic footprint.

Small, fortunately

What kind of focusing and steering is used while using an endovaginal transducer?

Electronic

When the PZT crystal is damaged in an endovaginal transducer, what happens to the overall image?

Steering and focusing mayhem, may impact image

Vector array transducers is a…

Combination of linear sequential and linear phased array technology

What kind of focusing and steering is used while using a vector array transducer?

Electronic

What is the shape of the image created by a vector array transducer?

Trapezoidal, flat-topped sector

Volume imaging

Three-Dimensional (3-D)

What is a 2-D array?

Thousands of elements arranged in a checkerboard pattern, creating 3-D image

What is 4-D imaging?

Real-time 3-D

What is rendering?

Data constructs a 3-D image, creates an image from three-dimensional data acquired during the ultrasound exam

Real time acquisition of data displayed in _____ planes

3

3-D pixel is a ________

Vaxel

What is resolution?

Accuracy in imaging

What is another name for axial resolution?

Depth, range, radial, longitudinal

What is another name for Lateral Resolution?

Azimuthal, angular, and transverse

What is another word for elevation resolution?

Slice thickness

How is slice thickness resolution?

Imaging plane thickness

How is slice thickness resolution measured?

Perpendicular, or above-below imaging plane

We assume imaging plane is thin, but not always, beam thickness varies with ______.

Depth