US registry review: image resolution

electronic focusing can be

adjusted by tech and allows multiple focusing points

low FR allows

an increased number of acoustic lines and improves image quality (spatial res) with increased line density

what do some transducer arrays allow that will improve elevational resolution

additional focusing along the axis of the beam width

why is the speed of sound in tissue a limitation of temporal resolution>?

bc it cant be altered to improve TR

why is signal to noise ratio not changed by gain adjustments(amplification)

bc the signal and noise are both amplified

value of LR =

beam diameter

what does LR vary with

beam width and imaging depth

smaller numerical value for AR indicate

better AR

thinner slices=

better elevational resolution

high signal to noise ratios produce

better image quality

smaller spatial resolution numbers=

better resolution

contrast resolution depends on

# of bits per pixel in the image memory

contrast resolution =

DR/number of shades

acoustic lines=

PRF/ FR

how much of the image does axial resolution improve

entire image

depth decrease also =

increase resolution

decreasing depth = ______ = _______

increased PRF = increased FR and improved TR

reducing the size of field of view = ________ = ________

increased PRF = increased FR and improved TR

a very black and white image demonstrates

increased contrast, but reduced CR

axial resolution improves entire image with

increased freq and damping (shorter pulse length)

signal to noise ratio improves with

increased output power

increased signal with constant noise levels=

increased ratio

poor STR=

increased slice thickness= inability to demonstrate small structures correctly

what all degrades TR?

- activating harmonic imaging or spatial compounding - increasing imaging depth - increasing size of the FOV -adding focal zones

Changes in the beam with focusing at the focal zone

-decreases the beam diameter

decreased FR may cause

-visible delay in display of information -time delay between transducer movement and anatomy displayed

average axial resolution for US

0.1-1mm

time (per frame) x FR =

1

axial resolution=

1/2 SPL

what functions will improve CR

B color or colorize

TR is limited by

FR of the system, monitor, storage device and human eye

TR is determined by

FR, lines per frame, and image depth

acronym for synonyms of axial resolution

LARRD: longitudinal axial range radial depth

Synonyms for lateral resolution

LATA lateral, angular, transverse, azimuthal

what has the best TR

M mode

what has to decrease to improve AR?

SPL

spatial resolution varies with what physical parameters of the beam

SPL and beam width

what determines axial resolution

SPL and pulse duration (set by transducer)

AR improves when

SPL decreases

A low FR improves

Spatial resolution

what offers the best TR?

single focus, narrow sector, and low line density

elevational resolution

a measure of the beam width perpendicular to the image plane

Poor Contrast Resolution refers to

a more black and white image

when does spatial resolution improve

as the minimum required reflector separation decreases

where is LR best?

at the narrowest portion of the beam (focal Point)

less cycles in pulse improves what

axial

What does spatial resolution refer to?

axial and lateral resolution collectively

how can sono adjust contrast res

by changing the DR, rejection and contrast setting on monitor

how does sonographer adjust LR

by using focusing and changing sector width

signal to noise ratio also improves with

coded excitation

what has the worst TR

color doppler

contrast resolution is defined as

decibels per shade

increased frame time leads to

decreased FR and TR

as the # of focal zones increases, the FR

decreases

as the # of imaging depth increases, the FR

decreases

as the # scan lines increases, frame rate ________

decreases

as the time to produce a single frame increases, the FR

decreases (vice versa)

changes in the beam with focusing in the near field

decreases the beam diameter

as frequency increases, the numerical value for AR ___ and AR ____

decreases, improves

temporal resolution decreases with

deeper imaging depths multiple focal zone increases # of pulses per scan line wider sector angle increased line density

AR doesnt vary with

depth, same across whole image

contrast resolution provides the ability to

differentiate a hyper-echoic hemangioma within the hyper-echoic liver tissue

what allows the best elevational resolution

disc shaped elements allow thinnest slices

higher frame rate must be used for

echocardiography

mechanical focusing:

external- lens, fixed internal- curved element, fixed focal point

what place is LR the best

focal point

SNR is unchanged by

gain adjustments (amplification)

far field resolution improves with

high frequency (narrow) probes

TR is better with

higher FR

higher FR =

higher temporal resolution

best STR=

identical to the lateral resolution on mechanical and annular transducers due to disk shape of the element

what does contrast resolution vary with

impedance mismatch of the tissues

increasing the number of bits per pixel will

improve contrast res

depth decrease=

increase PRF and # of acoustic lines

changes in the beam with focusing at the far field

increases the beam diameter

LR improves with

increasing the number of scan lines per image

better axial res=

less cycles in pulse

what has the poorest elevational resolution

linear transducers

elevational resolution is set by

manufacturer

what can be used to reduce slice thickness and improve resolution

mechanical focusing with lens

lateral resolution

minimum distance between reflectors that is required for the system to identify structures perpendicular to the axis of the beam (side by side)

contrast resolution improves with

more bits per pixel more shades of grey on the image

high FR used for echocardiography due to

movement of cardiac structures in the heart

focal point is

narrowest portion of the beam

can AR be changed by sono?

no unless transducer is changed

low FR is good for

non mobile structures

if two structures that are side by side are closer together than the width of the beam then

only 1 wide reflection is displayed on the image

electronic focusing:

phased- electronic

what does parallel processing refer to

processing multiple lines of signals at the same time

temporal resolution in M mode is = to

pulse repetition period (PRP)

higher FR cause

reduced line density and image quality

AR is ____ across entire image

same

temporal resolution increases with

shallow imaging depth single focal zone decreased # of pulses per scan line narrower sector angle decreased line density applying fill in interpolation

better AR=

shorter SPL and PD

elevational resolution is also called

slice thickness resolution (STR)

numerical values of AR are smaller than ___ bc

smaller than LR bc US pulses are shorter than they are wide

Signal to noise ratio improves with what else

spatial and frequency compounding and increased persistence

higher FR reduces image quality which is

spatial resolution

slowest component determines

temporal resolution

frame time

the amount of time required to produce a single frame

Focusing improves the resolution in

the area of focusing

FR can be improved by?

the use of parallel processing

Frame time=

time to create a single scan line X # of scan lines

Frame rates that vary change with

transducer frequency, display depth, and focal zone settings

can contrast resolution be adjusted by sono?

yes