ASN Ultrasound Course

Question 1

What determines lateral resolution

Answer 1

diameter of beams, narrower better lateral resolution

Question 2

Why is high frequency better in terms of resolution?

Answer 2

Axial resolution improved because shorter pulses associated w/ high freq sound. Lat res improved b because high freq pulses diverge less from field.

Question 3

How does axial resolution vary w/ depth

Answer 3

It doesn’t its same at all depth

Question 4

How does lateral resolution vary w/ depth

Answer 4

Best resolution in the focus

Question 5

What are 3 ways to focus ultrasound beam?

Answer 5

external focusing (with lens), internal focusing (with curved active element), phased array focusing (with electronics in ultrasound system).

Question 6

What are effects associated with focusing

Answer 6

decreased size of focal zone, beam beyond focal zone widening.

Question 7

What are two determinants of divergence?

Answer 7

High frequency and wider probe decrease divergence

Question 8

What does A mode stand for?

Answer 8

amplitude mode

Question 9

What creates large vs smaller spike on A mode

Answer 9

strong reflection creates tall spikes

Question 10

Who uses A mode?

Answer 10

ophthalmology - where depth or structure thickness important

Question 11

What are displayed on axis of B m mode?

Answer 11

Z amplitude, X depth, Y none

Question 12

What are display mode axes with M-mode

Answer 12

x time, y depth, z none.

Question 13

Describe mechanical transducor

Answer 13

single circular disc-shaped active element that is physically moved creating s can plane. Fixed focus adjustable only w/ internal or external focusing.

Question 14

Describe transducor arrays

Answer 14

Single slab of PZT cut into collection of separate pieces called elements.

Question 15

Describe linear phased arrays

Answer 15

Rectangular elements side by side width 1/4-1/2 wavelength. Beam steering occurs via electronic process called phasing.

Question 16

How do you get a focused beam with a linear phased array?

Answer 16

With dome shaped arrival of electrical signal at transducer.

Question 17

Where is focus of smaller diameter PZT crystal vs bigger deeper or more shallow?

Answer 17

Smaller diameter = shallower

Question 18

What can annular phased array do?

Answer 18

It can focus at multiple depths simulataneously - inner core focuses more shallow and outer deeper.

Question 19

Describe linear sequential arrays?

Answer 19

Box with a bunch of rectangular arrays 120-250. Small group fired simulataneously

Question 20

How does beam focusing occure w/ linear sequential?

Answer 20

electronic focusing

Question 21

Image shape and size w/ linear sequential arrays?

Answer 21

rectangular. Never wider than the transducer.

Question 22

Why are multipole transducers fired at once?

Answer 22

To cancel out huygens wavelet theory (spherical shape) -take advantage of interference

Question 23

Can linear phased arrays be steered electronically?

Answer 23

Yes leading to parallelogram shaped images

Question 24

Can a curved version of linear array probes be made?

Answer 24

Oh yeah!

Question 25

Can linear and curvilinear array probes use dynamic receive focusing?

Answer 25

Yes

Question 26

What is elevational resolution?

Answer 26

Slice thickness

Question 27

What type of transducer has the best elevational resolution? And what is the elevation

Answer 27

disc shaped crystals such as those found in mechanical or annular phased array tranducers

Question 28

What are side lobes in ultrasound? What thype of transducer creates them?

Answer 28

Off axis sound beams. Can degrade lateral resolution. Single element transducer.

Question 29

What are grating lobes?

Answer 29

Similar to side lobes but create dby array tranducers. AAgain degrade lateral res and reduce image quality.

Question 30

How does apodization eliminate grating lobes?

Answer 30

By using lower voltage at edges of probe.

Question 31

How does subdicing reduce grating lobes?

Answer 31

By splitting up an element of linear array transducer into multiple sub elements acting together

Question 32

What technique is used to keep US beam narrow of substantial depth range? How does it work?

Answer 32

Dynamic aperature. Optimizes lateral resolution. Varies the number of crystals producing sound and narrowing element changing focus.

Question 33

What is name of firing pattern that steers and what is name of firing pattern that focuses linear phased array

Answer 33

electronic slope, electronic curvature

Question 34

What improves elevational resolution of linear array

Answer 34

one and a half dimensiional array

Question 35

What are two factors that determine temporal resolutio or frame rate n

Answer 35

sounds speed in medium and depth of imaging

Question 36

How does number of pulses affect temporal resolution

Answer 36

Pulses per frame and frame rate are inversely related. Lower number of pulses per image greater frame rate

Question 37

How do multiple foci affect the temporal resolution?

Answer 37

They improve lateral resolution, but worsen frame rate and worsen temporal resolution.

Question 38

What four parameters lead to higher frame rate (depth, focus, sector width, line density)

Answer 38

shallower, single focus, narrow sector, low line density