Ultrasound Physics Chapter 12

Whenever the crystal in any single crystal transducer breaks, _____________________________.

The entire image is lost

Linear: active elements are arranged ________________________________.

In a straight line

Annular: elements are arranged _______________________________________.

As circular rings with a common center

Convex: active elements are arranged in a __________________________________. The transducer may also be called a __________________ or _________________ _______________.

Arched (bowed) line, curved, curvilinear

Phased array means:

Adjustable or electronic

The sound beam is _________________ ___________________ when the spike line is horizontal. The sound is ___________________ if the spike line has a slope. The sound beam is _______________ if the spike pattern is curved.

Directed downward, steered, focused

The linear phased array transducer is compact & has no moving parts. The beam is steered and focused using an ______________ technique called ___________.

Electrical, phasing

Elements in a linear phased array are __________.

Rectangular

Slope -> _____________________

Steering

Curvature-> ________________

Transmit focusing

Active element malfunction: mechanical transducer

Loss of entire image

Active element malfunction: linear and convex arrays

Dropout of image information from top to bottom

Active element malfunction: phased arrays

Erratic steering and focusing, image affected is variable

Active element malfunction: annular phased arrays

Horizontal dropout (at a particular depth)

Mechanical: shape, steering & focusing?

Sector, mechanical, fixed

Linear sequential: shape, steering & focusing?

Rectangular, electronic, electronic

Phased array: shape, steering & focusing?

Sector, electronic, electronic

Annular phased: shape, steering & focusing?

Sector, mechanical, electronic

Convex: shape, steering & focusing?

Blunted sector, electronic, electronic

Vector: shape, steering & focusing?

Trapezoidal, electronic, electronic

The mechanical transducer contains a ____________, _______________, _________________ active element that is _______________ ___________.

Singular,circular, disk shaped, physically moved

The mechanical transducer contains a ___________________ active element.

Single

Mechanical transducers have a fixed focal depth or __________________, ____________________ or ___________________ focusing.

Conventional, mechanical, fixed

___________________ __________________ with the use of a curved active element.

Internal focusing

___________________ ___________________ with the use of an acoustic lens.

External focusing

Modern ultrasound transducers are called ______________ , comprised of a single slab of PZT cut into pieces called _________________.

Arrays, elements

A ____________________ is the combination of the active element, wire and systems electronics.

Channel

Linear phased array transducers are focused _________________, unlike mechanical transducers, which have a __________ __________ focus.

Electronically, single fixed

Advantage of linear array transducers:

Adjustable focusing (multi-focusing)

In linear array, the sonographer can adjust the ______________ _____________.

Focal depth

Damage to one of the elements of a phased array transducer results in:

Inconsistent, erratic beam steering and focusing

In linear phased array, the overall pattern of the ______________ _______________ from the ultrasound system determines the sound beam's direction and focus.

Electrical signals

In linear phased array, the time differences between the electrical signals are called __________ ____________.

Phase delays

In linear phased array, the sound beam is __________________ if the line spike has a ___________.

Steered, Slope

In linear phased array, the electronics within the ultrasound system that create patterns is called the ___________ ______________.

Beam former

When a spike pattern is a straight line, an __________________ ______________ _______________ is created.

Unfocused sound beam

Linear phased array: A curved pattern of electrical spikes creates a ______________ ______________ _______________ during transmission.

Focused sound beam

Linear phased array: the sound beam is _____________ if the spike pattern is curved.

Focused

Linear phased array: to determine beam steering, draw a line from the far _________ to the far ___________ spike. The direction of steering is __________________ to this line.

Left, right, perpendicular

Linear phased array: electronic pattern - slope, sound beam - _______________

Steering

Linear phased array: electronic pattern - curvature, sound beam - _______________

Transmit focusing

A sound beam only has one focus. To create an image with multiple transmit foci at different depths, the ultrasound system must send _______________ ________________ _________________ down each scan line

Multiple sound beams

Focusing can occur during _________________ and __________________.

Transmission, reception

A more accurate image can be created when the ultrasound receiver introduces ____________ ____________ _____________ to some electrical signals during reception.

Variable time delays

The delay patterns during receive-focusing ______________ ________________ as the transducer listens for reflections.

Change continuously

Sound beams created by _____________ ________________ transducers are hourglass shape.

Single element

Off axis sound beams are called _____________________.

Side lobes

Reflections arising from within the side lobes _______________ ______________ _______________.

Degrade lateral resolution

Grating lobes are created by _______________ transducers.

Array

Off axis sound beams (grating lobes) _____________ lateral resolution, _____________ image quality and create ____________.

Degrade, reduce, artifacts

Reducing the strength of side and grating lobes can be achieved through a process called _________________.

Apodization

____________________ of each element in a linear array transducer reduces grating lobes.

Subdicing

Dividing a crystal into a group of smaller crystals (sub-elements) that act as a single crystal is called _____________.

Subdicing

Another term for elevational resolution:

Slice thickness

Slice thickness is measured in a direction __________________ to the imaging plane or _____________________ the imaging plane.

Perpendicular, above to below

When the slice is thick, structures above and beneath the plane create _________________ that appear in the image.

Reflections

Active elements that are ________ shaped provide the thinnest ultrasound slices.

Disc

Disc shaped crystals are found in _________________ and _____________ _______________ array transducers.

Mechanical, annular phased

With phasing, the beam is focused/narrowed only _______________________ in the imaging plane, but not _______________________. Narrowing improves _________________, but does not affect ___________________.

Side by side, above and below, lateral resolution, slice thickness

Limitation of linear arrays?

Inability to create thin slices

Create thinner beams with improved slice thickness:

1 1/2 dimensional array

1 and 1/2 D array have multiple crystals in the __________________________ direction.

Up and down

Mechanical scanning and linear phased arrays create _________________ images.

Sector shaped

Many active elements fire at almost the same time in a __________________ scanner.

Phased array

A mechanical transducer steers the sound beam ______________.

Mechanically

___________________ __________________ _____________ transducers steer the sound beams mechanically. They are multi-focused.

Annular phased array

_____________________ _____________________ array transducers create a rectangular shaped images.

Linear sequential

A linear phased array transducer has 128 crystals. How many of these crystals are fired to create a single sound beam?

All active elements are fired

A linear sequential array transducer has 128 crystals. How many of these crystals are fired to create a single sound beam?

A small group

In a linear phased array, what is the firing pattern that steers a beam to the left or right?

Electronic slope

In a linear phased array, what is the firing pattern that focuses a sound beam?

Electronic curvature

There are _________ time delays in the firing pattern of a linear phased array.

Tiny

A machine that displays Doppler and 2 dimensional images is called a ________________________.

Duplex scanner

_____________________ transducer creates a ____________ slice and improves _____________________.

1 and 1/2 dimensional array, elevational resolution

Type of transducer that contains a single, circular, disc-shaped active element that is physically moved?

Mechanical

The focusing technique using electrical steering and focusing?

Phased

With linear phased arrays, sounds beam are focused _______________.

Electronically

The term phased array means ____________ or ______________.

Electronic or adjustable

Which type of transducer has a single element that physically moves back and forth?

Mechanical

Which transducer has round elements?

Annular phased array

What are two methods employed to reduce grating lobes?

Apodization, subdicing

Beam steering in vector arrays combine ____________ and __________ __________ technologies. Some, but not all of the crystals are fired simultaneously to create a ___________ _________ ________.

Linear, phased array, single sound beam.

Axial resolution =

Front to back

Lateral resolution =

Side to side

Elevational resolution =

Above to below

What transducer types have the best elevational resolution?

Mechanical and annular phased

At all depths, the beam is much ___________ than it is __________.

Thicker, wide

______________ creates an image from 3D data.

Rendering

True or false: mechanical scanning produces pictures that are similar in shape to linear phased array images

true

true or false: many active elements fire at almost the same time in a mechanical scanner

false - only one PZT

Which transducer is best described as mechanically steered and fixed, single focus?

mechanical

Which transducer is best described as mechanically steered and multi-focus?

annular phased array transducer

Which transducer creates a rectangular shaped image?

linear sequential array

a linear phased array transducer has 128 crystals. how many of these crystals are fired to create a single sound beam?

128

A linear sequential array transducer has 128 crystals. How many of these crystals are fired to create a single sound beam?

a small group

In a linear phased array, what is the firing pattern that steers a beam to the left or right?

sloped

In linear phased arrays, what is the firing pattern that focuses a sound beam?

curved

True or false: there are large time delays in the firing pattern of a linear phased array transducer

false - there are tiny delays

True or false: a machine that displays A-mode and 2D images is called a duplex scanner

false - doppler and 2D

What improves elevational resolution?

one and one half dimensional array - it creates a thin slice