1. welcome

2. ULTRASOUND BASIC FACTS
DR TAUSEEF QAMAR BSc ,MBBS (K.E),DMRD ,MTIDU, MUSP, ICEAF(USA) MEMBER AMERICAN INSTITUTE OF ULTRASOUND IN MEDICINE, VICE PRESIDENT PUNJAB ULTRASOUND SOCIETY OF PAKISTAN.
ASSISTANT PROFESSOR RADIOLOGY DEPT: THE UNIVERSITY OF LAHORE.

3. Ultrasound Basic Idea History
– Send waves into body which are reflected at the interfaces between tissue
– Return time of the waves tells us of the depth of the reflecting surface
History
– First practical application, 1912 unsuccessful search for Titanic
– WW II brought massive military research - SONAR (SOund Navigation And Ranging)
– Mid-century used for non-destructive testing of materials
– First used as diagnostic tool in 1942 for localizing brain tumors
– 1950’s 2D gray scale images
– 1965 or so real-time imaging

4. Ultrasound ranges? Human sensitivity: 20 - 20,000Hz
Ultrasound: > 20,000Hz
Diagnostic Ultrasound: MHz

5. Sound waves
• Sound wave propagate by longitudinal motion(compression/expansion), but not transverse motion(side-to-side)
• Can be modelled as weights connected by springs

6. Specular - echoes originating from relatively large, regularly shaped objects with smooth surfaces. These echoes are relatively intense and angle dependent. (i.e.valves) - Reflection from large surfaces
Scattered - echoes originating from relatively small, weakly reflective, irregularly shaped objects are less angle dependant and less intense. (i.e.. blood cells) -Reflection from small surfaces

7. Along each line we transmit a pulse and plot the
reflections that come back vs time

8. Variation in speed

9. Propagation of ultrasound waves in tissue
• Ultrasound imaging systems
commonly operate at 3.5
MHz, which corresponds to a
wavelength of 0.44 mm
when c = 1540 m/s.
Refraction
• When a wave passes from
one medium to another the
frequency is constant, and
since c changes then so
must the wavelength

10. Propagation of ultrasound waves in tissue
Bending of waves from one
medium to another is 'refraction'
• Follows Snell’s Law
sin theta/c1
since λ2 < λ1
we have c2 <c1
and θ2 < θ1

11. Definition/ Terminology
Cycle
Frequency: cycles per second
Wave length
Period
Amplitude
Compression - area of high density
Rarefication - area of low density
velocity = l x ƒ= constant for a given medium

12. A, Initial observation.
B, After a short time, regions of high & low density are displaced to the right

13. Ultrasound Production
Piezoelectric effect:
– Crystals vibrate at given frequency when an alternating current is applied
– Crystal acts as speaker and microphone
Continuous mode:
– continuous-wave Doppler (CW)
Pulsed-echo mode:

14. Continuous-wave output

15. there is no information about the time interval from the signal to the reflection, and, hence, no information about the depth of the received signal; the signal may come from any depth. The continuous Doppler has no Nykvist limit, and can measure maximal velocities. It is used for measuring high velocities.

16. Pulsed Echo Signal generation = only ~1% of the entire pulse cycle
On times; off times
Time of signal return proportional to distance travelled

17. if the PRF = 5 kHz and the time between pulses is 0
if the PRF = 5 kHz and the time between pulses is 0.2 msec, it will take 0.1 msec to reach the target and 0.1 msec to return to the transducer. This means the pulse will travel 15.4 cm before the next pulse is emitted (1,540 m/sec x 0.1 msec = m in 0.1 msec = 15.4 cm). 

19. Pulsed wave output

20. Pulsed Echo PRF: pulse repetition frequency
– Very important in Color Doppler
SPL: spatial pulse length
= wavelength x no. of cycles
Maximal resolution = 0.5 SPL
– The smallest distance between 2 points that
USG can delineate

21. SPL with maximal resolution. Two objects (vertical lines) are
separated by 0.5 SPL. The echo from each interface is shown
by dashed lines. The objects are just resolvable.

22. Pulse length shortened by increasing the frequency.
A The four-cycle pulse from a low-frequency transducer includes both objects within the SPL.
B The four-cycle pulse from a high-frequency transducer has a shorter spatial pulse length and can resolve objects located more closely
together.

23. Doppler shift

24. V never go beyond c…means max shift is twice ft.

26. Tissue Doppler…

27. the main principle is that blood has high velocity (Typically above 50 cm/s, although also all velocities down to zero), but low density, resulting in low intensity (amplitude) reflected signals. Tissue has high density, resulting in high intensity signals, but low velocity (typically below 20 cm/s).

28. The pulsed modus results in a practical limit on the maximum velocity that can be measured. In order to measure velocity at a certain depth, the next pulse cannot be sent out before the signal is returned.  The Doppler shift is thus sampled once for every pulse that is transmitted, and the sampling frequency is thus equal to the pulse repetition frequency (PRF). Frequency aliasing occurs at a Doppler shift that is equal to half of the PRF. fD = ½ * PRF

29. Sampling from increasing depth will  increase the time for the pulse returning, thus increasing the sampling interval and decrease the sampling  frequency.  The Nykvist limit thus decreases with depth. This means that pulsed Doppler has depth resolution, but this leads to a limit to the velocities that can be measured.

30. Ultrasound Transmission
1540 m/s– Velocity assumed the same for all tissue in calculation (which is not totally true)
Acoustic impedance
Attenuation
Reflection
Refraction
Scatter: objects irregular or smaller than the
ultrasound beam

31. Resolution Ability to delineate between two different objects
Axial resolution:
– high frequency
= shorter SPL
= better axial resolution but lower penetration

32. Resolution Lateral Resolution – Sound beam: width of the crystal
– Near field
– Focal zone: best lateral resolution
– Far field
– Dead zone: distance between the transducer
face and the first identifiable echo

33. Resolution Temporal Resolution – Frame per second
– Multiple focal zones
• decreases frame rate
• decrease temporal resolution

34. Diagram illustrating Axial Resolution

35. Modes A mode: amplitude B mode: brightness Real time (frames/sec)
M mode: motion

36. A-Scan Presentation.
The A-scan presentation displays the amount of received ultrasonic energy as a
function of time. The relative amount of received energy is plotted along the
vertical axis and the elapsed time (which may be related to the sound energy
travel time within the material) is displayed along the horizontal axis

37. B-Scan Presentation.
The B-scan presentation is a profile (cross-sectional) view of the test specimen.
In the B-scan, the time-of-flight (travel time) of the sound energy is displayed
along the vertical axis and the linear position of the transducer is displayed along
the horizontal axis

38. Doppler Ultrasound Continuous wave (CW)
– Seldom used, not a/v in most AED machines
Pulsed wave (PW)
Color Doppler
Duplex Doppler:– Putting Color Doppler on top of Grey-scale Bmode
Power Doppler

39. Transducers Formats – linear - rectangular field of view
– sector - pie-shaped field of view

40. In sector scanning, the resolution becomes poorer at increasing depth.

41. Transducers Mechanical Probe: seldom used now Electronic Probe:
– Linear array transducers
• piezoelectric elements linearly arranged
• sequentially activated to produce an image
– Phased array transducers
• smaller scanning surface (foot print)
• good for echocardiography
• more expensive
• elements are activated with phase differences to allow steering of the ultrasound signal

42. sonosite

43. Available transducers
C60/5-2 Convex Array Abdominal
C11/7-4 Microconvex Array
L38/10-5 Linear Array Vascular
C15e/2-4 Microconvex Array Cardiac
ICT/7-4 Endocavity

44. Imaging Modes on the Titan
Split screen
Zoom
Color power Doppler
M-Mode: 3 sweep speeds 1/2:1/2, 1/3:2/3 or full screen options
Pulsed wave (PW) Doppler
Continuous wave (CW) Doppler
Velocity based color flow Doppler
Duplex imaging
3 sweep speeds 1/2:1/2, 1/3:2/3 or full screen options
Tissue Harmonic Imaging (THI)

45. Logiq 100

46. The Logiq 100 PRO's five main probes:
5.0 MHz Convex-Array probe, 40 mm radius, 68° field of view
3.5 MHz Convex-Array probe, 50 mm radius, 68° field of view
7.5 MHz Linear-Array probe, 60 mm field of view
3.5 MHz Micro convex Cardiac probe, 13 mm radius, 82° field of view
6.5 MHz Endocavity probe, 10 mm radius, 120° field of view

47. probes
C36
C55
L76
E72

48. Contd..
Operating modes: B-Mode, Dual B-Image (B/B-Mode), B/M Mode, M-Mode
Dimensions: 276 mm x 244 mm x 405 mm, Weight: 9.8 kg (without probes)

49. Thank u

50. reference http://www.prioritymedical.com/ultrasoundtransducers.html

51. End……..
queries