Display Modes

1. Display Modes

2. Display Mode • A mode • M mode • B mode

3. A mode • First form of echo display. • Echoes displayed as vertical deflection. • Horizontal axis represents distance or depth. • The vertical axis represents the amplitude of the echoes.

4. A mode The horizontal position of the A-mode on the CRT display depends on the transducer- reflector time relationship. • The electronic beam is swept horizontally by the horizontal sweep generator at a speed of 1540 m/s from left to right. • The CRT electron beam is synchronized to start the sweeping action with the application of the transmit pulse voltage.

5. A-mode The vertical position of the trace is determined by the voltage signal amplitude from the video amplifier. The height of the vertical deflection depends on the amplitude of the echoes and receiver function such as the gain and TGC settings.

6. A-mode Amplitude (y-axes) Distance (x-axis)

7. B-mode B-mode means Brightness mode. • Echoes are displayed brightened dots. • The strength of the echoes determines the brightness. • The position of the B-mode dot on the screen represents the reflector distance and is determine by the transducer-reflector time relationship.

8. M-MODE • B mode echoes form an interface that changes position will be seen as echoes moving towards and away from the transducer. • If a trace line is place on this interface and the resulting trace is made to drift across the face of a CRT screen a motion pattern is obtained.

9. M-MODE • The resulting display shows motion of a reflector over distance and time – a distance time graph. • The change in distance (dy) over a period of time dt is represented by the slope of the reflector line of motion. • dy/dt = slope = velocity

10. M-MODE • If this motion pattern is obtained on moving cardiac structures then the resulting images constitute M-mode echocardiography. • M-mode echocardiography is use to evaluate the morphology, movement and velocity of cardiac valves and walls.

11. M-mode Tracing Distance Time

12. M-mode Evaluation • Amplitude • Velocity • Morphology

13. Amplitude Measurement Y2 Amplitude = Y2 –Y1 Y1

14. Slope Measurement Y2 dy = Y2 –Y1 Y1 Slope = dy/dt T1 T2 dt = T2 – T1

15. Real Time Scanner RT describe an ultrasound system that • Acquires • Processes • Displays Images without storing the echo data.

16. Static B Scanner versus RT Scanner

17. Frame Rate • Each sweep of the ultrasound beam produces a frame. • The frame is made up of scan lines • Each can line is produce by a ultrasound pulse • The frame rate depends on the rate of pulse production (pulse repetition frequency) and the number of scan lines in that frame.

18. Frame Rate Frame Scan lines Frame rate = PRF/lines per frame

19. Frame Rate Increase Frame Rate by Increasing PRF • Decreasing image depth Decreasing # of lines per frame • Decrease frame width • Decrease Scan line density -

20. Frame Rate Frame Scan lines Frame rate = PRF/lines per frame

21. Increasing Frame RateDecreasing Image Depth Frame Scan lines Frame rate = PRF/lines per frame

22. Increasing Frame RateDecreasing Scan Line Density Frame Scan lines Frame rate = PRF/lines per frame

23. Increasing Frame RateDecreasing Frame Width Frame Scan lines Frame rate = PRF/lines per frame

24. Frame Rate Decrease Frame Rate by Decreasing PRF • Increasing image depth Increasing # of lines per frame • Increase frame width • Increase Scan line density • Increase # of pulses per scan line - Multiple focal zones - Color Doppler

25. Frame Rate Frame Scan lines Frame rate = PRF/lines per frame

26. Decreasing Frame RateIncrease Image Depth Frame Scan lines Frame rate = PRF/lines per frame

27. Decreasing Frame RateIncreasing Scan Line Density Frame Scan lines Frame rate = PRF/lines per frame

28. Decrease Frame RateMultiple Focal Zones Frame Focal Zones Frame rate = PRF/lines per frame

29. Decrease Frame RateColor Doppler Frame Scan lines Frame rate = PRF/lines per frame

30. Frame Rate The faster the moving reflector the higher the frame required in order to display continuous motion

31. Frame Rate • Frame rate – 15 and 60 f/s • Can be adjusted by the operator • Automatically adjusted as a function of depth and or field of view.

32. Temporal Resolution Temporal resolution is a measure of the ability to separate events in time. The frame rate determines the ability to capture motion accurately. The higher the frame rate the better the temporal resolution.

33. Temporal Resolution The following factors affect the frame rate and thus the temporal resolution. • Image depth • Wide field of view • Multiple transmit focal zones • Color Doppler • Scan line density

34. Beam Steering RT scanners sound beam is steered rapidly and repeatedly.

35. Beam Steering Steering Mechanism Mechanical Electronic Linear Switched Linear Phase Oscillating Mirror Rotating

36. Oscillating Transducer

37. Rotating Transducer Flexible Cable Rotation Point Crystal Membrane

38. Oscillating Transducer Oscillating membrane Annular array Coupling membrane

39. Array Transducer Linear array Phased array Annular array

40. Beam SteeringLinear Phase

41. Beam SteeringLinear Phase

42. Beam SteeringLinear Phase

43. Beam SteeringLinear Switched

44. Beam SteeringLinear Switched

45. Beam SteeringLinear Switched

46. Beam SteeringLinear Switched

47. Transmit Focus

48. Received Focus

49. Received Focus

50. Arrays