Understanding Ultrasound Physics, Edelman: Chapter 15- Displays and Image Processing

what are scan converters?

Store information via "writing" then display it via "reading" creating a display video made up of horizontal lines from converted spokes

what are analog numbers

real world numbers with continuous range of values

what are digital numbers

Numbers associated with computer devices and have discrete values

what was the first type of scan converter?

analog scan converter

how did an analog scan converter work?

funnel shaped vacuum tube with electron gun on smaller end where electrons came out. the larger end of the tube contained a dielectric matrix or silicon wafer

what is spatial resolution?

image detail

why is the spatial resolution good in an analog scan converter?

large number of storage elements within the matrix

what are 4 reasons that analog scan converters are now obsolete?

1. image fade

2. image flicker

3. instability

4. deterioration

what is digitizing?

converting images into numbers

what are 4 advantages of digital scan converters?

1. uniformity

2. stability

3. durability

4. speed

5. accuracy

what are the 2 important elements of the digital scan converters?

1. pixel

2. bits

what is a pixel?

smallest building block of a digital picture

what is pixel density?

number of pixels per inch

low pixel density

1. few pixels per inch

2. larger pixels

3. less detailed image

4. lower spatial resolution

high pixel density

1. many pixels per inch

2. smaller pixels

3. more detailed image

4. higher spatial resolution

what type of pixel density increases spatial resolution

high pixel density

what is a bit

smallest amount of computer memory

what is a binary number

series of zeros and ones

what is a byte?

a group of 8 bits

what is a word of computer memory

2 bytes (16 bits)

fewer bits per pixel: _______ shades of gray, _____ contrast resolution

fewer shades of gray, degraded contrast resolution

More bits per pixel: ___________ shades of gray, ______________ contrast resolution

more shades of gray, improved contrast resolution

how to calculate the number of gray shades

2^number of bits

what is the 5 step process for translating image info from the real world to the computer world and back?

Analog ----> A to D converter ---> digital memory ---> D to A converter ----> analog

what is preprocessing

The manipulation of image data before storage in the scan converter.

what is post processing

The manipulation of image data after storage in the scan converter.

pre processing

- TGC

- Log compression

- write magnification

- persistence

- spatial compounding

- edge enhancement

- fill in interpolation

post processing

- any change after freeze frame

- black/white inversion

- read magnification

- contrast variation

- 3-D rendering

what is read magnification

zooming during post processing

how does post processing zooming effect pixels of the image

it just enlarges them

what is write magnification

zooming during pre processing, chooses the part and completely rescans it

read magnification

-Uses old data

-Post-processing

-Larger pixel size

-Same # of pixels as original ROI

-Unchanged spatial resolution

-Unchanged temporal resolution

write magnification

- Acquires new data

- Pre-processing (before image is stored)

- Identical pixel size

- More pixels in ROI

- Improved spatial resolution

- Improved temporal resolution

what is coded excitation

traditional imaging uses a very short pulse to create each image.

~icoded excitation creates long sound pulses that contain a wide range of frequencies.

coded excitation provides

1. Higher signal-to-noise ratio

2. Improved axial resolution

3. Improved spatial resolution

4. Improved contrast resolution

5. Deeper penetration

what is spatial compounding?

method of using sonographic information from several different imaging angles to produce a single image

what is frequency compounding

Creating an image by averaging frames obtained from different frequency sub-bands, reducing noise

how does edge enhancement work?

by increasing the image contrast in the area immediately around the edge

what is temporal compounding?

is an image processing technique that continues to display info from older images

what is another name for temporal compounding?

persistence or temporal averaging

what is the benefit of temporal compounding?

helps with slow moving structures, like color dopplering

what is fill in interpolation?

a filling in technique of missing pixels

is fill-in interpolation pre or post processing?

preprocessing