Ultrasound Physics Chapter 13

Static scanning

When images are displayed one frame at a time.

Frame Rate

The systems ability to create numerous frames each second.

Frame rate is determined by?

-Sound's speed in the medium.

-the depth of imaging

Frame rate unit?

Hz

Temporal resolution?

Pertains to "accuracy in time," describes the ability to precisely position moving structures from instant to instant.

Temporal resolution is determined by?

Frame rate

Temporal resolutions units?

Hz

T-frame?

Time it takes to make one frame.

20 frames per second. How much time will it take to make 1 frame?

1/20th of a second.

Frame rate and T-frame are ______ related?

Inversely. (Reciprocals)

What determines the ultrasound systems frame rate?

-imaging depth

-# of pulses per frame.

Shallow imaging _____ frame rate and ______ temporal resolution.

Increases; improves

Deeper imaging ____ frame rate and _____ temporal resolution.

Decreases;degrades

I'm aging depth and frame rate are ______ related.

Inversely

T frame's equation?

# pulses x PRP

Frame rate unit?

Hz

T frames unit?

Seconds

If a sound pulse has a PRP of 0.01 seconds. What will be the frame time if 10 sound pulses are used to construct a frame?

0.01 x 10

1/10

(Take reciprocal)

10 Hz.

Pulses per frame and frame rate are _____ related.

Inversely

3 Factors determining number of pulses per frame?

-number of focal points

-sector size

-line density

Single focus has __ temp res and __ lateral res

better, poor

Multi-focus has?

Diminished temporal resolution and improved layers resolution.

Line density

Altering the space between sound beams.

When line density is low, few pulses create each image and the frame rate is______?

High

When line density is high, the number of pulses per image ____ , frame rate _____ and temporal resolution ______.

Increases; drops; decreases

If temporal resolution increases then image detail ______.

Decreases.

Image detail is also known as?

Spatial resolution.

Temporal resolution is the same thing as ?

Frame rate

With stationary structures, frame rate ___, image quality ____ and temporal resolution _____.

Decreases;increases;decreases.

Moving structures have ____ frame rate, ____ image quality and ____ temporal resolution.

Increases;decreases;increases

Better temporal resolution has ____ frame rate.

Higher

Lateral resolution improves with?

Multi focusing

Spatial resolution improves with ?

High line density

A sonographer adjusts an ultrasound scan to double the depth of view from 5 cm to 10 cm. if the frame rate remains the same, what happens to the sector?

Narrows.

A sonographer reduces the sector angle from 90 degrees to 30 degrees. At the same time, the ultrasound system automatically increases the line density from 1 line per degree to 2 lines per degree. No other changes are made. What will happen to the frame rate?

Increases.

What is the most important in determining the frame rate of a system?

Speed of sound in the medium.

What is the time needed to make a single image if the frame rate of an ultrasound system is 20 Hz?

0.05 seconds.

If you increase the PRF and leave all other controls unchanged, what will happen?

Frame rate will increase

Which of the following characteristic(s) of a transducer’s components determine the spread of the sound beam in the Fraunhofer zone? 1. thickness of the active element and frequency of the transducer 2. thickness of the matching layer only 3. diameter of the active element and frequency of the transducer 4.thickness of the active element only

diameter of PZT and frequency of the transducer determine divergence

With regards to temporal resolution, which of the following terms does not fit with the others? lower line density, higher frame rate, improved temporal resolution, deeper imaging

deeper imaging - decreases temporal resolution

Which of the following is consistent with increased or improved temporal resolution? more detailed image, more gray shade, color doppler, higher frame rate

higher frame rate

All of the following changes will improve temporal resolution except - decreasing the number of focal zones in the image, increasing the spacing between adjacent scan lines in the image, increasing frame rate, changing to a lower frequency transducer

changing to a lower frequency transducer

A sonographer adjusts an ultrasound scan to double the depth of view from 5 - 10 cm. If the frame rate remains the same, which one the the following also occurs?

narrow sector

How is temporal resolution measured?

frame rate

Which of the following has the greatest effect upon temporal resolution? speed of sound in the medium, frequency of sound, transducer dampening, pulse duration

speed of sound in the medium

A sonographer alters the size of the sector produced by an ultrasound system from 45 degrees to 90 degrees. At the same time, the ultrasound system automatically alters the line density. It is decreased from 4 lines/degree to 2 lines/degree.. No other changes are made. Which of the following statements is true?

-spatial resolution increases

-temporal resolution increases

-temporal resolution decreases

-spatial resolution decreases

spatial resolution decreases

A sonographer increases the number of foci in an image from 1 to 4. Which of the following statements is most correct?

-axial resolution increases and temporal resolution increases

-lateral resolution increases and temporal resolution increases

-lateral resolution increases and temporal resolution decreases

-axial resolution increases and temporal resolution decreases

lateral resolution increases and temporal resolution decreases

A monographer adjusts an ultrasound scan to double the depth of view from 5 to 10cm. What happens to the frame rate?

frame rate will be halved

A sonographer, using a phased array ultrasound system, turns off the multi-focus feature. What is the most likely consequence of this action?

temporal resolution increases

Which of the following factors is related to temporal resolution?

-line density

-wavelegth

-frequency

-period

line density

What else may occur when temporal resolution improves?

image quality degrades

When changed, which of the following factors with have no effect upon frame rate?

-sector size

-line density

-PRP

-spatial pulse length

spatial pulse length

All of these decrease temporal resolution except:

-narrower sector

-multi focus imaging

-deeper imaging

-lower frame rate

narrower sector

A sonographer increases the line density from 2 line per degree of sector to 5 lines per degree of sector. What is the consequence of this action?

temporal resolution decreases

A sonographer adjusts an image to change the sector size from 90 to 45 degrees. Nothing else changes. The frame rate is…

doubled

Which of the following will have no effect upon temporal resolution?

-increasing transducer frequency

-increasing imaging depth

-decreasing sector size

-increasing # of foci

increasing transducer frequency

Multiple focal points improves what?

lateral resolution

Sector size is reduced from 90 deg to 30 deg and line destiny is increased from 1 to 2 lines per degree. No other changes are made, what will happen to frame rate?

increase (90 total pulses to 60 total pulses)

Sector size is reduced from 90 deg to 30 deg and line destiny is increased from 1 to 2 lines per degree. No other changes are made, what will happen to temporal resolution?

remains unchanged

which of the following is most important in determining the frame rate of a system?

-depth of view

-dynamic range of the receiver

-transducer frequency

-transmitter output

depth of view

What is the frame rate is each image of the US system is created in 0.02 seconds (1/50 second)?

50Hz

What is the time needed to make a single image if the frame rate of an ultrasound system is 20Hz?

0.05s

T/F: the critical factor in determining frame rate, line density, and imaging depth is transducer style

false

T/F: the number of lines per frame and the frame rate determine frequency

false

T/F: the number of lines per frame and the frame rate determine the PRF

true

T/F: if the imaging depth of a scan is 15cm and there are 100 lines in the image, then the umber of pulses making uo the scan is 1500

false

T/F: if the imaging depth of a scan is 15cm and there are 100 lines in the image, then the number of pulses making up the scan is 100

true

T/F: if 100 scan lines makes up an image and the frame rate is 30 per second, then the transducers frequency is 1000Hz

false

T/F: if 100 scan lines makes up an image and the frame rate is 30 per second, then the systems PRF is 1000Hz

true

When the frame rate us 30Hz, how long does it take to create a frame?

1/30 sec

Under certain conditions, an US system creates each image in 0.01 sec. What is the frame rate

100Hz

what is the fundamental limitation of temporal resolution?

speed of sound in the medium

Which of the following will improve temporal resolution:

-inc sector angle

-inc line density

-inc PRF

-inc frequency

inc PRF

T/F: an US system with a longer pulse duration will generally have better temporal resolution

false

T/F: the length of a pulse does not directly influence the temporal resolution

true - factors that affect temp res: max imaging depth, sector angle, line density, and number of foci per scan line

Two imaging system produce acoustic pulses: one pulse is 0.4 microseconds long and the other is 0.2 microseconds long, which is most likely to provide the best temporal resolution

cannot be determined - bc temp res is not related to pulse length

Which two factors determine temporal resolution?

speed of sound and depth of view - fr increases and depth decreases, fr increases as speed inc

Which two controls determine a systems temporal resolution?

depth of view and pulses per image

T/F: an US system with a shorter PRP will have better temp res than a system with a longer PRP

True - shorter prp = more pulses therefore inc frame rate and temp res

What is the primary disadvantage of multiple focal zones along each scan line of a 2D image?

dec temp res

What is the primary advantage of multiple focal zones along each scan line of a 2D image?

improved lateral res

T/F: with sector scanning, images with greater detail (spatial res) are created when the number of acoustic pulses per degree of sector is increased

true - ie more scan lines = better spatial res

An ultrasound system with a 4.0MHz transducer is used to image structures as deep as 15cm. Twenty images are produced each second, each requiring 100 acoustic pulses. What is the PRF of the system?

2000Hz - 20 images/sec x 100 pulses/image

Which of the following sector imaging systems will have the best image detail if all other parameters are identical?

90 deg w/ 100 pulses/image

80 deg w/ 40 pulses/image

70 deg w/ 84 pulses/image

60 deg w/ 60 pulses/image

70 deg w/ 84 pulses/image - 70/84 = 1.2 = highest value

Of the following, which imaging modality has the poorest temporal resolution?

2d, real time

a-mode

color flow imaging

m-mode

color for imaging

Which US imaging modality had the best temp res?

b-scanning

duplex imaging

color flow imaging

m-mode

m-mode

All of the following reduce temporal res by increasing the number if pulses per image except:

-inc number of foci

-inc line density

-inc field of view

-inc depth of view

increasing depth of view changed PRP not the number of pulses per image

A sonographer reduces the sector size from 90 deg to 30 deg. Frame rate, however, did not change. What else happened?

-imaging depth dec

-pulse duration inc

-multifocus turned on

-PRF inc

multifocus was turned on