Physics 2 lecture 3

What functions after the receiver?

The image processor

What functions before the scan converter?

The image processor

When do many image optimization features occur?

After echoes return but before display

Where does the scan converter store image data?

System memory

What does the scan converter organize data into?

A pixel matrix

What does freezing the image stop?

Writing new image data

Which adjustments can still be made after freeze?

Postprocessing adjustments

What does a pixel represent?

A specific location within the image

What does pixel brightness depend on?

Echo amplitude

How do strong echoes appear?

Brighter

How do weak echoes appear?

Darker

What does dynamic range affect?

Number of gray shades

When does preprocessing occur?

Before image storage

When does postprocessing occur?

After image storage

What does preprocessing change?

Acquired image data

What does postprocessing change?

Displayed image appearance

When is preprocessing usually performed?

During live scanning

When can postprocessing often be adjusted?

After freeze

What is frequency selection a form of?

Preprocessing

What is harmonic imaging a form of?

Preprocessing

What is output power a form of?

Preprocessing

What is write zoom a form of?

Preprocessing

What are gray maps a form of?

Postprocessing

What is colorization a form of?

Postprocessing

What is read zoom a form of?

Postprocessing

What does write zoom improve?

True image detail

What does write zoom acquire?

Additional image data

Can write zoom usually be changed after freeze?

No

What does read zoom enlarge?

Existing stored pixels

Does read zoom improve true resolution?

No

Can read zoom be adjusted after freeze?

Yes

Which zoom rescans the ROI?

Write zoom

Which zoom only magnifies stored information?

Read zoom

What does fundamental imaging use?

Echoes at the transmitted frequency

What does harmonic imaging use?

Echoes at harmonic frequencies

Where are harmonic frequencies generated?

In tissue

Are harmonic frequencies generated at the transducer?

No

What is the most commonly used harmonic?

The second harmonic

What second harmonic is produced by a 2 MHz transmitted frequency?

4 MHz

What third harmonic is produced by a 2 MHz transmitted frequency?

6 MHz

What results from nonlinear propagation?

Harmonics

Does linear propagation generate harmonics?

No

Does nonlinear propagation generate harmonics?

Yes

Where are harmonic signals weakest?

Near field

Where are harmonic signals strongest?

Mid field

What does harmonic imaging reduce?

Near field clutter

What does harmonic imaging improve?

Contrast resolution

What may harmonic imaging decrease?

Penetration

How do harmonic beams compare to fundamental beams?

Narrower

What is best improved by harmonic imaging?

Poor border definition

What does pulse inversion transmit?

Two pulses per scan line

How is the second pulse transmitted in pulse inversion?

180 degrees out of phase

What does pulse inversion cause fundamental signals to do?

Cancel

What does pulse inversion cause harmonic signals to do?

Strengthen

What may pulse inversion reduce?

Frame rate

What are contrast harmonics produced by?

Microbubble contrast agents

What are tissue harmonics produced by?

Nonlinear propagation through tissue

How do microbubbles generate harmonics?

Through nonlinear oscillation

What does spatial compounding combine?

Images from different beam angles

What does spatial compounding use?

Beam steering

What does spatial compounding reduce?

Speckle noise

What does spatial compounding improve?

Border definition

What does spatial compounding create?

A smoother image

What may spatial compounding reduce?

Shadowing artifacts

What does spatial compounding decrease?

Temporal resolution

What is temporal compounding also called?

Persistence

What does temporal compounding average?

Frames from different times

What does temporal compounding improve?

Signal-to-noise ratio

What does temporal compounding reduce?

Image noise

What does temporal compounding create?

A smoother image

What does increased persistence cause?

Motion blur

What does increased persistence cause temporal resolution to do?

Decrease

When is persistence best used?

For slow moving structures

Where is persistence commonly used?

Color Doppler imaging

What will increasing persistence MOST likely do?

Blur rapidly moving structures

What does frequency compounding combine?

Information from different frequency bands

What does frequency compounding reduce?

Speckle noise

What does frequency compounding improve?

Image smoothness

Does frequency compounding use multiple beam angles?

No

Does frequency compounding average images over time?

No

What is frequency compounding best for reducing?

Speckle noise

What should be used to improve smoothness without multiple beam angles?

Frequency compounding

What does edge enhancement improve?

Border definition

What does edge enhancement increase?

Local contrast

Does edge enhancement improve true spatial resolution?

No

Does sharper image appearance always mean better resolution?

No

What is best improved by edge enhancement?

Poor vessel border definition

What does fill-in interpolation fill?

Gaps between scan lines

What does fill-in interpolation use?

Estimated data

Does fill-in interpolation acquire new information?

No

What does fill-in interpolation improve?

Image continuity

What does fill-in interpolation increase?

Perceived line density

What is best corrected with fill-in interpolation?

Visible scan line gaps

What is the tradeoff of harmonic imaging?

Reduced penetration

What is the tradeoff of spatial compounding?

Reduced temporal resolution

What is the tradeoff of persistence?

Motion blur

What is the tradeoff of frequency compounding?

Increased processing complexity

What is the tradeoff of edge enhancement?

No true resolution improvement

What is the tradeoff of fill-in interpolation?

Uses estimated data

What is an artifact?

An image that does not accurately represent anatomy