1. Chapter 10 Digital Signal and Image Processing

2. Data Manipulation
Signal processing is the manipulation of echo-induced radiofrequency signals before their input to the scan converter.

3. Signal and Image Processing

4. Signal Processing Time Gain Compensation
Adaptive Time Gain Compensation
Selective Enhancement
Gain
Reject Control
Logarithmic Compression
Edge Enhancement

5. Time Gain Compensation
Exponential amplification as a function of elapsed time from the transmitted pulse is used to correct the received signals for attenuation.
The reduction in signal level caused by the increased depth at which echoes are generated is compensated by applying time-dependent amplification.

6. Adaptive Time Gain Compensation
Is used for two weakness of TGC which are:
The same variable depth gain is applied to each scan line without consideration of the no uniformity of tissue along the path.
The operator must continually make manual adjustments as the scan plane is changed.

7. Selective Enhancement
In this technique the amplification is applied as a function of depth.
The operator uses a series of slide control keys to set depth, each key corresponding to a certain depth, the displacement of a key denotes the amount of amplification.

8. Gain
Receiver gain increases the amplitude of signals during signal processing and provides the necessary signal strength for analog-to-digital conversion.

9. Reject Control
Reject, by passing signals greater than a prescribed amplitude, removes weak signals and noise.

10. Logarithmic Compression
The dynamic range must be reduced by this technique.
Signals must be combined in groups before display and image recording.

11. Logarithmic Compression
Signal levels over four (left) and three (right) orders of magnitude are assigned values between 0 and 255 for an 8-bit scanner.

12. Logarithmic Compression
Sonogram of the liver with different levels of compression.
A, 75 dB.
B, 40 dB.

13. Edge Enhancement
It is a filtering technique that can be applied to the line-of-sight data to emphasize further a change in signal levels across an interface.

14. Edge Enhancement
The original change in signal level detected along a particular line of sight is manipulated mathematically to produce a more dramatic different at the boundary.

15. Scan Conversion
The angle and depth information (polar coordinates) must be converted to the matrix format (rectangular coordinate) for display.

16. Scan Conversion
Line of sight superimposed on the matrix to demonstrated that not all pixels are sampled by the sound beam.

17. Fill-In Interpolation
A synthetic scan line through the pixel of interest is calculate by interpolating between sampling points (1,2,3and 4) on adjacent scan line.

18. Fill-In Interpolation
Additional axial values are calculated by interpolation along each scan line.
The pixel value is calculated by angular interpolation between these new axial points.

19. Preprocessing
Image Updating
Write Zoom
Panning

20. Image Updating
The ultrasound beam sweeps repeatedly though the patient, new information is constantly becoming available.
The most recent scan data are held in the buffer for updating the image data in memory.
Most simply, the old value at a particular location stored in memory is replaced by the current value for the pixel location.

21. Image Updating A – old matrix data.
B – last-value mode or most recent matrix data.
C – pixel-by-pixel average of these two matrices.

22. Write Zoom
Regional expansion
Reduced field of view (FOV)
Zooming

23. Write Zoom A, original sampled region.
B, central portion of the original region scanned in write-zoom mode.

24. Panning
Panning is an image-acquisition technique that allows the operator to shift the expanded region to a new anatomic location during scanning.

25. Image output component of a real-time scanner

26. Post processing
The image data stored in memory after further processing are converted into a video signal (digital to analog conversion) and sent to a video monitor to display.

27. Post processing Display Gray-Scale Mapping Black and White Inversion
Freeze Frame
Frame Averaging or Persistence
Adaptive Frame Averaging
Read Zoom

28. Gray-Scale Mapping Display of pixels.
Each pixel is assigned a value representing a signal level. each pixel is depicted on the monitor as a uniform shade of gray based on the pixel value.

29. Gray-Scale Mapping
A gray- scale map provides the translation of stored pixel values to different brightness levels.

30. Black and White Inversion
The brightness levels on a gray-scale map are inverted to extend from white (at the low signal amplitude) to black (at the high signal amplitude).

31. Black and White Inversion
The brightness levels on the gray-scale map are inverted. High pixel values such as 240 are displayed as near black.

32. Black and White Inversion
Sonogram of the breast with a mass, A.
And with black / white inversion, B.

33. Freeze Frame
The freeze frame option allows the operator to select an image of interest for prolonged viewing.

34. Frame Averaging or Persistence
Frame Averaging (Persistence) allows successive frames (as many as four or more) to be held in a buffer and then added together to increase the signal-to-noise ratio (SNR).

35. Frame Averaging
Four sampling of scanned area are temporarily held in a buffer.
The displayed image is a pixel-by-pixel average of the samplings
( =12, Which, divided by the four banks equals 3).

36. Adaptive Frame Averaging
Frame averaging is designed to reduce noise, but it can create blurring of fast moving structures.

37. Read Zoom
Read zoom is a display magnification technique applied to the scan data after image storage.

38. Read Zoom
In read- zoom mode the original displayed image, A, is presented in a larger format, B.

39. Read Zoom
Portrait of Abraham Lincoln in normal-size mode, A, and in read zoom mode, B.
The central portion of the image has been magnified by a factor of 2.

40. Read Zoom
Matrix interpolation. Each original pixel is replaced by four smaller pixel. The values assigned to the originals are calculated from values in the surrounding pixels.

41. Read Zoom
A 2x2 portion of the original data matrix, A, is expanded to contain more pixels (16) by linear interpolation, B.

42. Post processing Data Manipulation Contrast Enhancement
Image Equalization
Smoothing
Edge Enhancement

43. Contrast Enhancement
It is an especially powerful technique to increase image contrast.

44. Contrast Enhancement
A linear gray- scale map in which pixel values near are displayed as intermediate shades of gray.

45. Contrast Enhancement
The range of brightness levels for pixel values near is wider .

46. Contrast Enhancement
Types of gray-scale mapping. Linear, logarithm, and threshold linear gray- scale maps.

47. Contrast Enhancement
Sonogram of the liver displayed with different gray- scale maps in A,B, and C.
The gray-scale map for each image is presented in the lower right.

48. Image Equalization
Image equalization is a method to automatically adjust brightness levels throughout the image enhance contrast.

49. Smoothing
Smoothing is an image-processing technique for the reduction of noise.

50. Smoothing
A kernel is applied to the original matrix data to generate the smoothed matrix data.

51. Edge Enhancement
Edge enhancement (also called sharpness) is a filtering technique that can be applied to the matrix image data to increase the visibility of small high- contrast structures.

52. Image Analysis
Region of Interest
Distance Calculation

53. Region of Interest
The boundary of the region of interest is marked with the mouse.
Pixels within this boundary denoted in gray are included in the region of interest.

54. Distance Calculation
The size of the cyst in a breast is determined by making the boundary of the cyst with cursors in two directions.