SPI BOARD RETAKE

Axial resolution describes:

one measure of detail found in an image.

Axial resolution measures:

the ability of a system to display two structures that are very close together when the structures are parallel to the sound beams main axis.

Axial resolution answers the question:

what is the minimum distance that two structures are positioned front-to-back (parallel to the sound beam) can be apart and still produce two distinct echoes on an ultrasound.

Axial resolution is measured in:

mm, or any other unit of distance

Axial resolution is related to:

spatial pulse length

Spatial pulse length is determined by:

sound source and medium

Shorter pulses:

improve axial resolution

Axial resolution is also related to:

pulse duration

In a particular medium:

short pulses also have a short length

Axial resolution synonyms:

LAARD (longitudinal, axial range, radial, and depth)

Is axial resolution adjustable?

no

Axial resolution =

spatial pulse length / 2

Axial resolution is also =

wavelength x #cycles in a pulse / 2

A short pulse is created in two ways:

-less ringing

-higher frequency

Better axial resolution is associated with:

shorter spatial pulse length

Better axial resolution is associated with:

shorter pulse duration

Better axial resolution is associated with:

higher frequencies (short wavelengths)

Better axial resolution is associated with:

fewer cycles per pulse (less ringing)

Better axial resolution is associated with:

lower numerical values

Lateral resolution:

is the ability to distinctly identify two structures that are very close together when they are side by sided, or perpendicular to the sound beams main axis.

Lateral resolution answers the question:

what is the minimum distance that two structures side by side, can be apart and still produce two distinct echoes on an ultrasound image.

Lateral resolution units:

mm, cm, or any distance

Lateral resolution is determined by the:

width of the sound beam

Lateral resolution will:

vary with depth

Lateral resolution is also called:

LATA (lateral, angular, transverse, or azimuthal)

Lateral resolution =

beam diameter

Lateral resolution is best at:

focus

Axial resolution is:

better, because ultrasound pulses are shorter than they are wide.

Higher frequency transducers improve:

both axial and lateral resolution

Axial resolution is:

improved in the entire image because shorter pulses are associated with high frequency sound

Lateral resolution is:

improved in the far field only because high frequency pulses diverge less in the far field than low frequency pulses.

Higher frequency sound beams are:

narrower than lower frequency beams.

Spatial compounding:

is a method of using sonographic information from several direct imaging angles to produce a single image

Spatial compounding will:

reduce speckle and minimize shadowing artifacts.

Spatial compounding will result in:

reduced frame rates and reduced temporal resolution.

Frequency compounding:

reduced speckle artifact and noise in ultrasound image

In frequency compounding:

the reflected signal is divided in sub-bands of limited frequencies, and an image is created from each sub-band.

Persistence is also known as:

temporal compounding, or temporal average

Persistence:

continues to display information from older images

With persistance:

a number of previous frames are superimposed on the most current frame.

Persistence means:

the displayed image contains history from earlier frames

Advantages of persistence:

a smoother image with reduced noise, higher singal-to-noise ratio, and improved image quality is produced.

The limitation of persistence:

a reduction in the displaced frame rate, which reduces temporal resolution.

Persistence is most effective in:

slowly moving structures.

Temporal resolution:

the most important operation parameter associated with an ultrasound move is the systems ability to create numerous frames each second

Frame rate is determined by:

-sounds speed in the medium

-the depth of imaging

Frame rates units:

hertz, or per second

One factor that affects frame rate is:

speed of sound in the medium

Another factor that affects frame rate is:

imaging depth

Temporal resolution:

pertains to the accuracy in times

Temporal resolution will describe:

the ability to precisely position moving structures from instant to instant

Temporal resolution is excellent:

when a system produces many frames per second.

Temporal resolution is substandard when:

when it produces few frames per second.

Temporal resolution is determined by:

frame rate

Displaying a high number of images per second (high frame rate):

improves temporal resolution

Temporal resolution is reduced when:

few images are displayed per second (low frame rate)

Tempirak resolution units:

hertz, or per second

System settings affecting frame rate:

-imaging depth

-number of pulses per frame

Imaging depth and frame rate:

inversely related

Shallow imaging:

-short go-return time

-shorter Tframe

-higher frame rate

-superior temporal resolution

Deep imaging:

- long go return time

- longer Tframe

- lower frame rate

- inferior temporal resolution

Pulses per frame and frame rate are,

inversely related

Factors determine number of pulses per frame:

number of focal points

sector size

line density

When the sonographer expands the sector size:

more pulses are required to create an image, therefore decreasing temporal resolution

Line density:

ultrasound systems can alter the spacing between sound beams

Low line density:

lines may be spaced far apart

High line density:

lines are tightly packed

When line density is low:

few pulses create each image

Low line density will have a:

high frame rate

In low line density:

temporal resolution is high

High line density will have:

low frame rate

High line density consists of:

more pulses per image

In high line density:

temporal resolution is low

High line density will:

have smaller gaps between the lines

High line density will then:

improve the accuracy of the individual image

With high line density, each image contains more detail known as:

improved spatial(detail) resolution

Better- higher frame rate:

-shallower imaging

-single focus

-narrow sector

-low line density

Worse- lower frame rate:

-deeper imaging

-multiple focal points (improves lateral resolution)

-wide sector

-high line density (improves spatial resolution)

Output power:

affects the image brightness by altering the strength of the sound pulse that the transducer sends into the body

Output power improves:

the signal to noise ratio

Receiver gain:

alters the strength of the voltages in the receiver that the transducer created during receptions

Bernoullis principle describes:

the relationship between velocity and pressure in a moving fluid.

Doppler shift and the velocity of the blood cells, are:

directly related

Doppler shift and frequency of the transmitted sound, are:

directly related

Continuous wave duty factor:

100%

Continuous wave lacks:

range ambiguity

Pulsed wave doppler:

range resolution

Pulsed wave disadvantage:

aliasing

Nyquist limit:

PRF/2

Nyquist frequency:

the highest doppler frequency of velocity that can be measured without the appearance of aliasing

Less aliasing:

-slower blood velocity

-lower freq transducer

-shallow gate (high PRF)

More aliasing:

-faster blood velocity

-higher frequency transducer

-deep gate (low PRF)

Variance map:

left-laminar

right-turbulent

Doppler packets:

multiple ultrasound pulses used to accurately determine blood velocities

Packets:

composed of a larger number of pulses

Larger packets advantages:

-more accurate velocity measurement

-increased sensitivity to low flow

Larger packets disadvantage:

-more time needed to acquire data

-reduced frame rate

-decreased temporal reoslution

Wall filter:

used to eliminate low frequency doppler shifts from moving anatomy rather than from moving blood cells.

Wall filter serves as a:

reject

Crosstalk:

a mirror image artifact that appears on a spectral doppler display