Resolution- Prep and Edel.

Resolution

the ability to create accurate images

Axial resolution (LARRD)

measures the ability of a system to display 2 structures that are very close together when the structures are parallel to sound beams axis (one on top of the other)

other names for axial resolution

longitudinal, axial, range, radial ,depth

acronym for axial resolution 

LARRD 

Formula for axial resolution:

axial res. (mm)= SPL/2

axial re. (mm)= wavelength x # cycles / 2

axial res. (mm)= 0.77 x # of cycles/ freq.

shorter pulses =

increased axial resolution

If poor axial resolution reflectors will appear as ___ 

one structure not two 

How do we enhance image resolution?

• backing material (shortens pulses)

• Purpose of the short pulses are to improve image accuracy and enhance axial resolution

Lateral resolution

the ability to distinctively identify two structures that are very close together when they are side by side or perpendicular to thee beams axis

LAT resolution is determined by 

width of the sound beam 

the more narrow a beam the _____ the lateral resolution

better

LAT resolution changes with _____

depth (best at the focus)

LAT resolution is best at _____

the focus

Acronym for LAT. resolution

LATA

Other names for lateral resolution

lateral, angular, transverse, azimuthal

If poor lat resolution two reflectors positioned nearer than the width of the beam would be demonstrated as _____

a single oval reflector

_____ freq. improves both axial and lateral resolution (spatial resolution)

high

_____ resolution is improved over the entire image 

axial 

_____ resolution improved in the far field because higher freq. (less divergence optimal to improve LAT. resolution in the far field)

lateral

Less far field beam divergence occurs with ____ diameter, and _____ freq. active element transducer

large, high

Focusing

concentrates the energy into a narrower beam thus improving lateral resolution

mechanical transducers are focused by 

using a curved internal element or external lens 

Array transducers are focused by

way of electronic delays

What is needed to optimize lateral resolution

focusing

Spatial resolution 

detail of the displayed image, ability of the system to differentiate and display adjacent structures as separate “overall detail” 

what resolutions make up spatial resolution

axial, lateral and elevational

Elevational resolution

slice thickness plane

• improved as thickness of elevational plane decreases

spatial resolution of an analog display is described in _____ 

line pairs per millimeter (lp/mm) 

Spatial resolution of a digital display is defined by _____

pixel density

Increased pixel density, _____ spatial resolution

increased

Contrast resolution

ability of the US system to detect discrete differences btwn greyscale intensities (echo amplitude)

constrast resolution ____ with more bits per pixel

increases

• allows system to display more shades of grey

_____ display describes contrast resolution 

greyscale 

Temporal resolution

time required for acquisition of one imaging frame.

• systems ability to differentiate btwn rapid events

• “choppyness of the flip book”

increased frame rate, ____ temporal resolution

increased

Slow down frame rate but give more detail: 

• adding more focal zones

• increasing # scan lines or fill interpolation 

• increase Doppler packet size

• increase depth

• increase FOV (sector size) 

increased spatial resolution, _____ temporal resolution

decreased

Axial and parallel are both shorter words so they go together

how to remember parallel to beam and axial resolution

How do we optimize axial resolution 

shorten pulse (increase freq, and use of backing material) 

How do we optimize lateral resolution

narrow beam (beam focusing, decrease beam divergence)

Decrease in frame rate yields poor ____ resolution

temporal

What would enhance temporal resolution 

decreased imaging depth