Ch 8 Signal Processor + Image Processor

Question 1

What is the signal processor?

Answer 1

-Receives digital signals from beam former
-After processing, it sends digital signals to the image processor

Question 2

List 3 functions of the signal processor that occur in order after the beam former?

Answer 2

-Bandpass filtering
-Amplitude detection
-Compression (dynamic range reduction)

Question 3

What is a bandpass filter?

Answer 3

-A filter that rejects frequencies above + below the accepted bandwidth
-The filter eliminates frequencies outside the echo bandwidth + only retains the accepted most useful frequencies

Question 4

What is amplitude detection?

Answer 4

-Aka demodulation
-Is the conversion of echo voltages from radio frequency form to video form, where it retains amplitudes of echo voltages

Question 5

What is compression + dynamic range?

Answer 5

Compression:
-Process of decreasing the smallest + largest echo amplitudes to a usable range

Dynamic range (dB):
-Ratio of the largest to smallest echo amplitudes from the pt
-Display DR is much higher than visual DR (which is range of signals visual to human eye)

Question 6

Why is compression needed?

Answer 6

B/c display dynamic range is much higher than the visual dynamic range of the human eye

Question 7

Is compression changeable by the sonographer?

Answer 7

-Some is done by the receiver (not our control)
-Video compression is controlled by us, as a post processing technique

Question 8

Is compression + dynamic range directly or inversely related?

Answer 8

Inversely related

High compression = less DR of signals
(meaning now high contrast as signals are black/white)

Low compression = high DR of signals
(meaning low contrast as signals are more shades of grey)

Question 9

Which setting gives us the highest level of contrast resolution?

Answer 9

High compression, low dynamic range

(images will make anechoic structures stand out + grey structures stand out - big contrast)

Question 10

Why is compression important?

Answer 10

-When imaging for thrombi + masses
-If the compression settings are incorrect it can lead to misinterpretation of pathology
-Be mindful of the compression when imaging tissue parenchyma as well (ex. liver, kidneys)

Question 11

What type of resolution is compression important for?

Answer 11

Contrast resolution

Question 12

What is the image processor?

Answer 12

-Converts digitized, filter, detected + compressed scan line data that is stored in image memory
-Locates each series of echoes to each scan line for each pulse, filling up the memory with echo info
-Is accomplished in a fraction of a second

Question 13

List functions of the image processor?

Answer 13

-Preprocessing + postprocessing
-Persistence
-3D acquisitions
-Storing image frames
-Cine loops
-Gray scale
-Color scale
-3D presentation
-Digital to analog conversion

Question 14

What is scan conversion?

Answer 14

-Signals from the beam former + image processor are still in A-mode
-Scan conversion is the process of converting A-mode signals into B-mode signals
-It assists grayscale values to pixel locations on the screen, resulting in an image

(in B-mode each amplitude is mapped to a grayscale level/brightness)

Question 15

List the 2 roles of scan conversion?

Answer 15

-To convert A-mode lines into B-mode lines
-To organize the lines of data into a formatted image

Question 16

Explain image memory?

Answer 16

-After the echo signal converts from A-mode into B-mode, it gets stored in the image memory
-Numbers correspond to the level of brightness from the location of the echo along the matrix

Question 17

Differentiate frame vs FR?

Answer 17

Frame: single image produced by 1 complete scan of the sound beam

FR: # of frames stored per second

Question 18

What gets stored in image memory?

Answer 18

Frames (either a freeze frame or cineloop)

Question 19

Define pixels + bits?

Answer 19

Pixels:
-2D image is divided into squares called pixels in a matrix
-each pixel is represented by multiple layers of brightness
-these layers can be renamed bits (which describes the total # of grayscale levels possible)

Bits:
-digital representation of the shade of grey
-binary digits consist of only 0 or 1

Question 20

The greater the matrix size, the more or less pixels in the matrix?

Answer 20

More (this improves detail resolution)

Question 21

The smaller the matrix size, the more or less pixels in the matrix?

Answer 21

Less (this creates poor resolution)

Question 22

What does 1 + 2 mean in regards to bits?

Answer 22

1: bright display
2: dark display

Question 23

The human eye can see how many shades of grey?

Answer 23

<64 shades

(u/s shows 256 shades)

Question 24

How can we calculate bit depth?

Answer 24

2^n

(ex. 2^8 = 256 shades)

Question 25

Differentiate acoustic vs non-acoustic zoom?

Answer 25

Acoustic (write):
-places zoom box over ROI
-new beams used to display the zoomed image
-preprocessing
-not applied to frozen images
-pixels not enlarged
-improves detail resolution

Non-Acoustic (read):
-no new beams used to generate larger image displays
-stretches data to fit new display size
-postprocessing
-applied to frozen images
-pixels enlarged
-no change to detail resolution

Question 26

Explain acoustic write zoom?

Answer 26

-Not applied to frozen images
-Preprocessing function
-New lines incorporated
-Pixels not enlarged
-Improves detail resolution
-Scan line density increases

Question 27

Explain non-acoustic read zoom?

Answer 27

-Postprocessing function
-Applied to already stored frozen images
-Increases pixel size (stretches image)
-No change to detail resolution

Question 28

What is preprocessing?

Answer 28

Image processing that must be done BEFORE echo data is stores in memory, such as:

-acoustic write zoom
-persistence
-pixel interpolation
-edge enhancement
-3D acquisition
-panoramic imaging
-spatial compounding

Question 29

What is postprocessing?

Answer 29

Image processing that are performed AFTER the echoes are stored in memory, such as:

-non acoustic read zoom
-gray scale maps
-B color
-3D presentation

Question 30

What is persistence?

Answer 30

-Frame averaging (ex. 3 frames averaged into 1)
-It reduces noise + smooths image
-Higher levels are best for slow moving structures

Question 31

Does persistence (frame averaging) increase or decrease the FR?

Answer 31

Decreases it

Question 32

What is pixel interpolation?

Answer 32

-Filling in of missing pixels
-M/c in sector scans
-Assigns brightness value to a missed pixel based on the average brightness of adjacent pixels

(NOT needed for linear scans)

Question 33

Explain the digital-to-analog converter?

Answer 33

Converts the digital data received from the image memory to analog voltages that determine the brightness of the echoes on the display

Question 34

Put the beam former, display, image processor + signal processor in order from which occurs first to last?

Answer 34

-Beam former
-Signal processor
-Image processor
-Display

Question 35

What is the display?

Answer 35

-Presents a visual image derived from voltages received from the image processor
-Is a real time display (meaning several frames are acquired + presented every second)

Question 36

What is proportional to the echo strength?

Answer 36

Brightness (grayscale)

Question 37

List the different ways image display can be presented in?

Answer 37

-A mode
-B mode (aka grayscale or B scan)
-B color
-M mode

Question 38

List 2 image display devices?

Answer 38

-Flat panel display
-Output devices

Question 39

What is A-mode?

Answer 39

-Amplitude mode
-Displays amplitudes of echoes
-No 2D image
-M/c in opthalamologic scans

(depth = x-axis, amplitude = y-axis)

Question 40

What is M-mode?

Answer 40

-Motion mode
-Single scan line is repeatedly transmitted in same direction
-M/c in cardiac scanning (tracks motion)

(depth = y-axis, time = x-axis)

Question 41

What is B-color?

Answer 41

-Chroma maps!!
-Postprocessing function
-Our eyes can differentiate more color tints than grey shades
-Color scale gets added to our image to help compare varying levels of brightness