Ch 15 and 16 Displays and Image Processing

Sono Physics

Cathode Ray Tube (CRT)

Older, bulky “TV-style” monitor

◦ Electron gun fires a beam of electrons

Beam strikes phosphor coating ◦ Phosphor glows to form image

CRT Displays – Interlaced Imaging

◦ Image built from 525 horizontal lines

◦ Timing: ◦ 1/60th sec per field ◦ 1/30th sec per frame – 30 frames/sec (30 Hz)

Disadvantages of CRT’s

◦ Lower overall resolution

◦ Bulky & heavy

◦ Uses more electricity

◦ Flicker (Rolling Line)

Liquid Crystal Display (LCD)

Standard display used on modern ultrasound systems

Flat-panel display that uses a backlight

Liquid crystals control how much light passes through the display

LCDs Advantages:

◦ Better resolution & sharper images

◦ Thinner, lighter, & more compact

◦ Energy efficient

◦ Durable

LCD Disadvantages

◦ Requires constant backlight → cannot produce true blacks

◦ Viewing angle limitations (color or brightness may shift)

◦ Can show image “ghosting” with fast movement

Light Emitting Diode (LED) Backlighting

Modern LCD displays commonly use LEDs as the backlight

◦ Replaced fluorescent backlighting in most modern LCDs

◦ Provides bright, uniform illumination

◦ More energy efficient

◦ Common in modern ultrasound system displays

Organic Light Emitting Diode (OLED)

• Each pixel produces its own light

• No backlight required

• Pixels can turn completely off – true blacks

• Excellent contrast

• Fast response time

• Wide viewing angle

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OLED Pros

Excellent contrast and true blacks

◦ Excellent grayscale and color reproduction

◦ Fast response time → minimal motion blur

◦ Wide viewing angle

◦ Thin and lightweight

OLED Cons

◦ Higher cost

◦ Potential for burn-in/image retention

◦ Organic materials can degrade over time

Bistable

2 Brightness levels

High Contrast:

◦ Narrow dynamic range

◦ Few shades of gray

◦ Poor contrast resolution

Gray Scale

Many brightness levels.

What 2 key monitor settings affect how the image appears to the eye?

1. Contrast

2. Brightness

Contrast

The range of brightness levels (brilliances) within a displayed image

Determines how different light & dark areas appear

Brightness

Overall light intensity of the displayed image

◦ Determines how bright or dark the entire image appears

◦ Affects visibility, not the signal strength or anatomy itself

Scan Converters

The Bridge Between Image Creation & Display

Purpose:

◦ Makes gray scale imaging possible ◦ Stores image data between signal processing and final display

The 2 main Processes of Scan Converters

1. Writing (Storage)

2. Reading (Display)

Why are scan converters needed?

To change the format of Image data.

Analog Scan Converter:

Early technology; stored image information as electrical charge/continuous signals.

Digital Scan Converter

Stores image information as numerical values in computer memory.

Binary data: 0s & 1s