Test #1 (Unit 2)

Name the three spatial categories of resolution

1. Axial

2. Lateral

3. Elevational

What does spatial resolution give us the ability to see?

Detail on an image

What is spatial resolution related to?

1. Directly related to # of scan lines

2. Related to # of pixels in a monitor

What size resolution is always better?

1. Smaller

2. Less distance between reflectors to be displayed as separate objects

What is axial resolution?

The minimum reflector separation necessary to resolve reflectors parallel to sound beam

What is axial resolution determined by?

SPL

What does LARD stand for? (Has to do with AR)

Longitudinal, Axial, Range, Depth

To improve AR, SPL must be _____

Reduced

As SPL decreases, AR ____

Decreases

As frequency increases, AR _____

Decreases

Does axial resolution change with depth? Why?

1. No

2. AR is constant along beam path

What is lateral resolution?

Minimum reflector separation necessary to resolve reflectors perpendicular to beam

What is lateral resolution determined by?

Beam width

Does lateral resolution vary with depth? Why?

1. Yes

2. Because of sound beam shape

What does LATA stand for? (Has to do with LR)

Lateral, Angular, Transverse, Azimuthal

Where is LR the best?

At the focus

What is elevational resolution?

1. Minimum reflector separation necessary to resolve reflectors in thickness of beam

2. Slice thickness or section thickness

What is elevational resolution determined by?

Beam thickness

Where is the best ER at?

At the focus

ER varies with ____ because of the shape of the sound beam

Depth

ER is improved by…

1. Focusing

2. Harmonics

How is ER improved by focusing?

1. Only in near field (increase diameter or frequency)

2. Mechanically (lens or curved elements)

3. Electronically with 2D arrays (phasing)

When does a slice thickness artifact occur? How do they appear?

1. When adjacent structures are displayed overlapping structures in scanning plane

2. Appears as echoes within a fluid-filled structure

What is contrast resolution?

The ability of gray-scale display to distinguish subtle differences in echogenicity, or brightness, of adjacent tissues

What is contrast resolution determined by?

1. Number of pixels in an image

2. Number of shades of gray displayed in each pixel

What is contrast resolution controlled by?

1. System’s memory

2. Dynamic range settings

What is temporal resolution?

Ability to follow moving structures in temporal detail

What is frame rate?

Number of images displayed per second

Faster FR = _____ temporal resolution

Improved

Frame Rate is dependent on… (5 things)

1. Line density

2. Lines per frame

3. Depth & PRF

4. Sector Width

5. Number of foci

To avoid ______, the machine waits the time needed for all echoes to return from the selected depth before the next pulse

Range Ambiguity

What is line density?

1. # of scan lines per degree of sector

2. # of scan lines per centimeter

What is lines per frame?

# of lines in each frame

More lines = ____ spatial resolution

Improved

How are line density and lines per frame related to FR?

Inversely

Low LD or LPF = ___ time

Less

High LD or LPF = ____ time

More

Sector Width is _____ related to FR

Inversely

High sector width = ____ FR

Low

Low sector width = ____ FR

High

____ sector width improves image quaility

Low

Why does a low sector width improve image quaility?

1. Less tissue interrogated

2. Less artifacts

3. Improved signal to noise ratio

What does the ultrasound machine automatically do to avoid range ambiguity?

Adjusts PRF based on depth selected

Depth and PRF are ____ related

Inversely

Depth is ____ related to FR

Inversely

PRF is ____ related to FR

Directly

Each pulse can have ____ focus

One

Multiple foci improves _____

Lateral Resolution

Multiple foci requires ____ per scan line

More than 1 pulse

Multiple Foci are _____ related to FR

Inversely

What saves time?

1. Decrease depth

2. Decrease sector width

3. Decrease # of scan lines

4. Decrease Line Density

5. Use one focus