Chapter 10: Axial and Lateral Resolution

____ is the ability to create accurate images

resolution

measures the ability of a system to display two structures that are very close together when the structures are parallel to the sound beam’s main axis

axial resolution

axial resolution is measured in ____

mm or any unit of distance

____ resolution is related to the spatial pulse length and pulse duration

axial

shorter pulses improve ____ resolution

axial

for axial resolution, use the mnemonic LARRD:

• Longitudinal

• Axial

• Range

• Radial

• Depth

is axial resolution adjustable

no

axial resolution ranges from __ to __ mm

0.1 to 1.0 mm

a short pulse is created in two ways:

• less ringing

• higher frequency

a pulse is short if there are few cycles in the pulse; this is known as ____

less ringing

one way to reduce ringing is to ____ the crystal after it has been excited by an electrical signal from the system

dampen

pulses made of higher frequency cycles have superior ____ resolution

axial

the ability to distinctly identify two structures that are very close together when they are side by side, or perpendicular to the sound beam’s main axis

lateral resolution

lateral resolution is determined by ____

the width of the sound beam

for lateral resolution, use the mnemonic LATA:

• Lateral

• Angular

• Transverse

• Azimuthal

lateral resolution is best at the ____

focus

lateral resolution is good within the ____

focal zone

lateral resolution = ____

beam diameter

which type of resolution is better in clinical imaging: lateral or axial

axial

focusing concentrates the sound energy into a narrower beam and thus improves ____ resolution

lateral

the three methods of focusing are:

• external

• internal

• phased array

focusing with a lens

external

focusing with a curved active element

internal

focusing with the electronics of the ultrasound system

phased array

fixed focusing is also called ____ or ____

conventional or mechanical

with ____ focusing, the focal depth and the extent of focusing are determined when the transducer is fabricated, and cannot be changed

fixed

with ____ focusing, a lens is placed in front of the piezoelectric material

external

with ____ focusing, a curved piezoelectric crystal concentrates the sound energy into a narrower or tighter beam

internal

____ focusing is the most common form of fixed focusing

internal

effects of focusing:

• beam diameter in near field and focal zone is ____

• focal depth is ____

• beam diameter in the far zone ____

• focal zone is ____

reduced; shallower; increases; smaller