Define:

Resolution

The ability to create accurate images.

Define:

 Axial Resolution

Units?

Changed by sonographer?

Typical values?

Equation

 The ability to distinguish two structures that are close to each other front to back, parallel to, or along the beam's main axis.

mm, cm--all units of distance

No, a pulse is a pulse is a pulse

0.05 - 0.5 mm

LARRD resolution (mm) = SPL (mm)/2

remember SPL = λ x #cycles per pulse

What are some synonyms for axial resolution?

LARRD resolution

Longitudinal

Axial

Range

Radial

Depth

What element in the transducer helps with axial resolution?

The backing material is designed to dampen the pulse ring to shorten the pulse duration in order to achieve a better axial resolution.

What two factors help improve LARRD resolution?

Less ringing, fewer cycles in pulse

Higher frequency sound, shorter wavelength

note: As frequency increases, the numerical value of the LARRD resolution decreases. This means that we have improved LARRD resolution and more accurate images with high frequency.

Define:

Lateral Resolution

Units?

The ability to distinctly indentify two structures that are very close together when they are side by side or perpendicular to the sound beam's main axis.

mm, all units of length. A smaller number creates a more accurate image

What are some synonyms for lateral resolution?

LATA resolution

Lateral

Angular

Transverse

Azimuthal

What determines lateral resolution?

Lateral resolution is determined by the beam diameter; narrower beams have better resolution. Beam diameter varies with depth; lateral resolution changes with depth.

Define:

Focusing

What are the three methods of focusing?

Focusing concentrates the sound energy into a narrower beam and thus improves lateral resolution.

external focusing (lens)

internal focusing (curved active element)

phased array focusing (electronic)