Ch 10 Axial and Lateral Resolution

Resolution

the ability to create accurate images. (image quality)

Axial resolution

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

its units are mm

Axial resolution is related to

Spatial pulse length

Shorter pulses improve

axial resolution

Other names for axial resolution

LAARD- Longitudinal, Axial, Range, Radial, Depth

formula for axial resolution

AR(mm) = SPL (mm) / 2

two ways that a short pulse is created

less ringing (damping), higher frequency

6 things associated with better axial resolution

shorter SPL

shorter PD

higher frequencies (shorter wavelength)

fewer cycles per pulse (less ringing/ damping)

lower numerical values

wide bandwidth & low Q factor

Lateral resolution

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

units are mm

what is lateral resolution determined by?

the width of the sound beam

Names for lateral resolution

LATA; Lateral, Angular, Transverse, Azithumal

formula for lateral resolution

lateral resolution (mm) = beam diameter (mm)

what specific reason is axial resolution improved in the image

shorter pulses (they are associated with high frequency sound)

what specifically improves lateral resolution in the far field?

smaller beam diameter (focusing)- (higher frequency sound beams are narrower than lower frequency beams)

aperture

diameter of the transducer

three methods of focusing

external (with a lens), internal (curved active element), phased array ( w/ electronics of the US system)

F # is

a type of focusing

formula : focal length / aperture

fixed focusing is also called

conventional or mechanical focusing

lens

external focusing; type of focus is fixed, conventional, mechanical

curved active element

internal focusing; focus type is fixed, conventional, or mechanical

electronic

phased array (time delays); focus type is adjustable