Displays and Image Processing ch. 15

What is contrast?

The range of brilliance within the display image.

What is brightness?

Determines the brilliance of the displayed image.

What is display and image processing in ultrasound?

The conversion of received echo signals into a visible grayscale image through amplification, processing, and mapping.

Which display mode is used for grayscale imaging?

B-mode (brightness mode).

What determines pixel brightness in B-mode imaging?

Echo amplitude.

What is real-time imaging?

The rapid display of sequential B-mode frames creating the appearance of motion.

What does overall gain control?

The amplification of all received echoes equally.

What is the primary effect of increasing overall gain?

Increased image brightness without improving resolution.

What is time gain compensation (TGC)?

Depth-dependent gain adjustment used to compensate for attenuation.

Why is TGC necessary?

Deeper echoes experience greater attenuation and require more amplification.

What is dynamic range?

The range of echo amplitudes displayed as shades of gray.

How does increasing dynamic range affect image appearance?

Produces a low-contrast image with many shades of gray.

How does decreasing dynamic range affect image appearance?

Produces a high-contrast image with fewer shades of gray.

What is contrast resolution?

The ability to distinguish differences in echo amplitude.

What is the purpose of a scan converter?

The scan converted translates the information from the penetration patten into a horizontal line pattern.

What is compression?

The reduction of a wide range of echo amplitudes into a smaller displayable range.

Why is compression necessary?

The human eye cannot perceive the full range of returning echo amplitudes.

What is gray-scale mapping?

Assignment of specific shades of gray to echo amplitudes.

Does gray-scale mapping change echo information?

No, it changes the visual presentation only.

What is rejection (threshold)?

A control that eliminates low-amplitude echoes from display.

What is a disadvantage of excessive rejection?

Loss of diagnostically useful low-level echoes.

What is sensitivity in ultrasound imaging?

The ability to detect low-amplitude echoes.

What is persistence?

Frame averaging that reduces noise but decreases temporal resolution.

What is the primary trade-off of persistence?

Reduced temporal resolution and motion blur.

What is frame rate?

The number of complete images displayed per second.

What is spatial compounding?

The combination of images acquired from multiple angles into a single image.

What are the benefits of spatial compounding?

Reduced speckle and improved contrast resolution.

What is the primary disadvantage of spatial compounding?

Decreased frame rate.

What is speckle?

A granular noise pattern caused by constructive and destructive interference.

Which processing techniques reduce speckle?

Spatial compounding and persistence.

What is tissue harmonic imaging?

Imaging using harmonic frequencies generated within tissue.

What are advantages of harmonic imaging?

Improved lateral resolution, reduced clutter, and improved contrast resolution.

What is a disadvantage of harmonic imaging?

Reduced penetration.

What is pre-processing?

Signal processing performed before image storage.

What is post-processing?

Image manipulation performed after data acquisition.

Can pre-processing effects be reversed?

No

Can post-processing effects be reversed?

Yes

Which controls change image appearance without affecting resolution?

Gain, gray-scale mapping, and post-processing.

What is the limitations of analog scan converters?

Image fades, flicker, instability, and deterioration

What are the advantages of digital scan converters?

Uniformity, stability, durability, speed, and accuracy.

What is pixel density?

The number of picture elements per inch.

What is the term for 8 bits of computer memory?

Byte.

What is the term of computer memory that consists of two bytes of 16 bits?

Word

Fewer shades of gray, and degraded contrast resolution is

Fewer bits per pixel.

More shades of gray and improved contrast resolution is

More bits per pixel.

What are characteristics of preprocessing?

TGC

Log compression

Write magnification

Persistence

Spatial compounding

Edge enhancement

Fill-in interpolation.

What are characteristics of post processing

Any change after freeze frame.

Black/ white inversion

Read magnification

Contrast variation

3-D rendering

Does read or write magnification use old data?

Read- old data

Write- new data

Does read or write magnification use post or pre processing?

Read- post processing

Write- pre processing

What is the pixel size of read and write magnification?

Read- larger pixel size- same # of pixels

Write- identical pixel size- more pixels

What is read and write magnification of spatial resolution?

Read- unchanged spatial compound

Write- improved spatial resolution

What is the effect of read and write magnification?

Read- unchanged temporal resolution

Write- may improve temporal resolution

What does coded excitation provide?

Higher signal-to- noise ratio, improved axial, spatial, contrast and deeper penetration.

What is frequency compounding?

Frequency compounding is an advanced technique that reduces speckle artifact and noise in ultrasound images.

What is edge enhancement?

An image processing method that makes pictures look sharper.

What is temporal compounding?

Averages multiple frames over time; reduces noise, more effective for slow motion imaging.

What is fill-In Interpolation

Estimates missing data between scan lines; smooths image, improves detail.

What is elastography?

Based on differing stiffness of the tissue results from the force of the sound beam.

What does PACS stand for?

Picture archiving and communication system.

What is DICOM?

Digital imaging and computers in medicine.