Ultrasound Physics - chap 10+11

Resolution

Ability to accurately image structures

What are the two characteristics of a pulse that improves image quality

• shorter pulses

• narrower pulses

axial resolution

ability of a system to display two structures that are close to each other front to back/ parallel to the sound beam

is axial resolution the most precious type?

yes

What is axial resolution also called?

• longitudinal

• axial

• range

• radial

• depth

LARRD

What is axial resolution determined by?

spatial pulse length

• sound source and the medium

Relationship between SPL and axial resolution

inversely related

can axial resolution can be adjusted by the sonographer?

no

units for axial resolution?

mm, any units of distance

in order to improve image accuracy what do we want?

• lower number values = shorter pulses therefore we increase our image accuracy

relationship between freq and numerical value of LARRD

inverse

• freq increases, the numerical value of LARRD decreases

what are the equations for axial resolution

axial res (mm) = spatial pulse length (mm) /2

axial res (mm) = WL (mm) * # of cycles/pulse /2

LARRD resolution improves with what two things

• less ringing

• higher frequencies

Lateral Resolution

ability to distinctly identify two structures that are SIDE BY SIDE or PERPENDICULAR to the sound beam

lateral resolution measures what?

the detail on an image

lateral resolution is also known as what?

• Lateral

• angular

• transverse

• azimuthal

LATA

What is lateral resolution determined by?

• width of the sound beam

( narrow beams have better resolution)

what is the equation for lateral resolution

lateral resolution (mm) = beam diameter (mm)

which type of resolution is better in clinical imaging system and why?

axial bc the sound pulse is shorter than wide

when we have high frequencies do they improve both axial and lateral resolution?

yes both

axial: shorter pulses are associated with high frequency sound

lateral: high freq sound beams diverge less in the far field making them narrower

to create an image with better lateral resolution what do we do?

focusing by concentrates the sound energy into a narrower beam and improves lateral resolution

focusing

narrows the waist of the sound beam resulting in improved lateral resolution

two types of focusing

1. fixed: internal or external

2. adjustable