Ultrasound

1. Design of Ultrasound Probe
Presented by
Prajakta P. Mhatre
Under The Guidance of
Dr. Uttam Chaskar

2. Sr. No. Topics
1. Introduction
2. Working of Ultrasound Transducer
3. Components of Ultrasound Transducer
4. Parameters related to crystals
5. Factors for Ultrasound Selection
6. Types of Scan
Table of Contents

3. 7. Interactions of Ultrasound in tissue
8. Display Modes
9. Resolution
10. Linear array Transducer crystal arrangement
11. Ultrasound Transducer construction
12. Design of Linear Ultrasound Transducer
13. Reverberation Effect

4. 1. Introduction
 Ultrasonic transducers are used to convert electric signal
to ultrasonic energy thar can be transmitted in tissues.
 Relationship between velocity and frequency is:
c=*
The speed of velocity in soft tissue is 1540m/s.
 The most important component is Piezoelectric crystal.
 Reflected echoes are important.
Ultrasound frequency: <20KHz
Medical Ultrasound frequency: 1-16MHz

5. Ultrasound Transducer

6. 2. Working of Ultrasound transducer

7. Piezoelectricity
Electrical
Energy
Mechanical
Energy
Physical deformation
of crystal structure

8. Time of Flight (TOF) =
2 ∗ 𝑑
𝑐

9. 3. Components of Ultrasound Transducer
Piezoelectric crystal
Electrodes
o Live Electrode
o Ground Electrode
 Backing block
 Acoustic insulator
 Plastic housing
 Insulated cover

10. Ultrasonic Motor
 An ultrasonic motor rotates a rotor by using ultrasonic waves with
high frequencies more than 20,000Hz which a human cannot hear.
 The ultrasonic motor generates ultrasonic waves using
piezoelectric elements, while conventional motors use permanent
magnets or coils to rotate a rotor.
 Fast scanning

11. Piezoelectric crystals
 Natural Piezoelectric crystal
o Quartz
 Artificial Piezoelectric crystals(Ferroelectrics)
o Lead Zirconate Titanate(PZT)
o Barium Titanate
o PZT-4
o PZT-5A

12. 4. Parameters related to crystals
a. Parameters related to crystals
b. Modes of vibration
c. Transducer Q factor
d. Ultrasonic beam separation
e. Quarter-wave matching

13. a. Parameters related to Frequency
Parameters Low Frequency High Frequency
Wavelength High Low
Thickness High High
Imaging structures Deeper structures Superficial body
structures
Depth of
Penetration
High Less
Resolution Low High

14. b. Modes of Vibration
Thickness mode
 Most commonly used.
 Used in medical crystals.

15. c. Transducer Q factor
 Q-factor refers two characteristics of Piezoelectric crystals:
o Purity of sound
o Length of time sound permits
Type of Q Frequency
range
Ring down
time
Spatial Pulse
Length
Application
High Q Narrow (Pure
sound)
More Long Organ
Imaging
Low Q Wide Less Short Doppler

16.  Q-factor =
𝑓0
𝐵𝑊
where, 𝑓0 = Resonance frequency
 Q-factor of piezoelectric materials can be controlled by
altering characteristics of Backing block of transducer.
Piezoelectric material Q-factor
Quartz >25000
PZT-4 >500
PZT-5A 75

17. d. Ultrasonic beam separation
𝑋′  Length of Fresnel zone(𝑋′
)
𝑿′
=
𝒓𝟐

=
𝑫𝟐
𝟒
where, r = radius of transducer
 Dispersion angle of far zone()
sin =
𝟏.𝟐𝟐
𝑫

18. e. Quarter Wave Matching
 Improve energy transfer.
 Matching layer
o suitable thickness
o characteristic impedance
is placed on front surface of transducer.
 Thickness of Matching layer =
𝟏
𝟒
* 
 𝒁𝒎𝒂𝒕𝒄𝒉𝒊𝒏𝒈 𝒍𝒂𝒚𝒆𝒓 = 𝒁𝒕𝒓𝒂𝒏𝒔𝒅𝒖𝒄𝒆𝒓 ∗ 𝒁𝒔𝒐𝒇𝒕 𝒕𝒊𝒔𝒔𝒖𝒆

19. 5. Factors for Transducer selection
 Transducer selection is ultimately determined factors:
o Frequency
o Footprint
o Crystal Thickness(t)
t = 0.5*
o Crystals arrangement
 Selection is often determined by the depth of the
structures to be imaged.

20. Crystal is said to resonate at frequency() determined by
thickness(t).
e.g. PZT-4 crystal
 Thickness= 0.001m = 1mm
 Velocity = 4000m/sec
t = 0.5*
 = 2t = 2*0.001 = 0.002m
Velocity = *
 =
4000
0.002
= 2𝑀𝐻𝑧

21. 6. Interactions of Ultrasound with Tissue
a. Reflection
b. Refraction
c. Transmission
d. Attenuation

22. Reflection
o Acoustic Impedance
Z = v
Refection(%) = (
𝑍2 −𝑍1
𝑍2+𝑍1
)^2 *100
o Beam angle of incidence
Refraction
Transmission
Transmission (%) =
4∗𝑍1∗𝑍2
(𝑍1+𝑍2)^2
* 100

23.  Attenuation
o Absorption: 80%
 Viscosity of medium
 Relaxation time of medium
 Frequency of ultrasound
o Beam Divergence: 20%

24. Parameters A-mode B-mode TM-mode
Stands for Amplitude Brightness Time-motion
Scanning 1D 2D 2D
Output result
obtained in
Spikes Dots Moving wave
Type of transducer
used
Pencil type transducer
(single)
Array of transducer
(Linear Array)
Sector and single one
Complexity Simple Complex Complex
Frequency 2 to 7.5 MHz 2 to 18 MHz 4 to 7 MHz
Applications • Brain Injury
• Calcification
• Ophthalmology
• Abdominal
• Foetal
• Liver
• Gall Bladder
• Cardiac
7. Display Modes

26. 8. Types of Scan
a. Linear Array
b. Linear Phased Array
c. Phase Steered Array

27. B Sector Array Probe

28. Parameters Linear Array
Probe
Phased Array
Probe
Sector Array
Probe
Frequency High Low Low
Aperture Linear Narrow Wide
Depth of
Penetration
Less than 8cm Deep Deep

29. Linear Array Linear Phased Array

30. Phased (steered) Array

31. Applications Linear Array Sector Array Linear Phased
Array
General
Imaging
Yes (Small
parts, breast,
etc.)
Yes (abdominal) Yes (abdominal)
Cardiac No No Yes
Vascular Yes Yes No
OB/GYN No Yes No

32. Features (Linear
Ultrasound Probe)
GE-9L
(GE Healthcare)
EL18-4
(Philips)
12L3
(Siemens)
Frequency Range 3-10MHz 2-22MHz 2.9-11.5MHz
Number of Piezoelectric
elements
190 1920 192
Foot Print 14*53mm 14*50mm 12*13mm
Field of View 44mm 45mm 133mm
Depth of Field 12cm 15cm 16cm
Imaging Mode 2D Imaging, 3D Imaging
& B-Mode
PW, Color Doppler,
Microflow Imaging,
Harmonic Imaging contrast
2D Imaging, Color
Doppler, PW Doppler
Applications • Vascular
• Small Parts
• Pediatric
• Abdomen
• Neonatal
• Obstretrics
• Thyroid
• Vascular Imaging
• Breast
• Musculoskeletal
Imaging
• Pediatric
• Fetal Imaging
• Lung
• Abdomen
• Pelvis
• Renal
• Spine
• Fetal Echo
Cost (Rs.) 2,90,000 2,73,000 1,00,000

33. Features (Sector
Ultrasound Transducer)
GE C1-6
(GE Healthcare)
S4-2
(Philips)
5C1
(Siemens)
Frequency Range 1-6 MHz 2-4 MHz 1.4-5 MHz
Number of Piezoelectric
elements
192 80 128
Foot Print 15*26mm 16*30mm 14*15mm
Field of View 80 degree 90 degree 70 degree
Depth of Field 35cm 30cm 30cm
Imaging Mode 2D Imaging, 3D Imaging &
Pulsed wave Doppler
2D Imaging, CW, PW, Color
Doppler, Tissue Doppler
2D Imaging, Color Doppler,
PW Doppler
Applications • Abdominal
• Obstretrics
• Gynecology Applications
• Abdominal
• Pediatric
• Lung
• Spine
• Thyroid
Cost (Rs.) 75,000 2,69,500 1,20,300

34. Features (Phase
Ultrasound Array)
GE 3Sc-RS
(GE Healthcare)
S4-1
(Philips)
P4-2
(Seimens)
Frequency Range 1.3-4 MHz 1-4 MHz 1.3-4.4 MHz
Number of Piezoelectric
elements
192 85 64
Foot Print 18*24mm 18*20mm 14*17mm
Field of View 90 degree 120 degree 88 degree
Depth of Field 30cm 16cm 30cm
Imaging Mode 2D Imaging, 3D Imaging,
M-Mode, CW & PW Mode
2D Imaging, M-Mode, PW,
CW, Tissue Harmonic
Imaging, Angio-Imaging
2D Imaging, 3D Imaging
Color Doppler, PW
Doppler
Applications • Abdomen
• Renal
• Adult Cardiac
• Pediatric
• Transcranial
Applications
• Cardiac
• Abdominal
• Obstetrics
• Abdomen
• Cardiac
• Emergency
medicine(cardiac)
Cost (Rs.) 1,00,00 3,00,000 2,50,000

35. 9. Resolution
a. Axial Resolution
b. Lateral Resolution
c. Temporal Resolution
d. Contrast Resolution

37. Low Axial Resolution High Axial Resolution
Low frequency High frequency
Long Spatial Pulse Length (SPL) Short Spatial Pulse Length (SPL)
High Amplitude Low Amplitude
Attenuation (in dB) = 0.5 * 2 * depth of reflector (in cm) * frequency
(in MHz)
a. Axial Resolution

38. Axial Resolution =
𝑆𝑃𝐿
2
SPL = number of cycles in a pulse * 

39. b. Lateral Resolution
High Lateral Resolution Low Lateral Resolution
Near zone length is long Near zone length is short
Low wavelength High wavelength
High frequency Low frequency
Large Aperture (wide element
width)
Small Aperture (wide element
width)
Low focal length High focal length
Width of focused beam =
𝑓𝑜𝑐𝑎𝑙 𝑙𝑒𝑛𝑔𝑡ℎ ∗
𝑎𝑝𝑒𝑟𝑡𝑢𝑟𝑒

40. c. Temporal Resolution
 Frame rate   Temporal Resolution
Frame rate can be increased by:
• Reduce depth of penetration
• Reduce number of focal point
• Reduce scan lines per frame
Pulse Repetition Frequency (PRF) = Frame rate * number of foci
* number of scan lines per frame

41. Frame rate =
154000 (
𝑐𝑚
𝑠
)
2 ∗𝑝𝑒𝑛𝑒𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑑𝑒𝑝𝑡ℎ ∗𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑓𝑜𝑐𝑖 ∗𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑠𝑐𝑎𝑛 𝑙𝑖𝑛𝑒𝑠
Depth of Penetration =
𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 ∗𝑡𝑖𝑚𝑒
2
 Depth of Penetration   Frame rate  PRF   Temporal
Resolution
Also, Depth of Penetration   time  fast scanning

42. Narrow BW  High Q  Good Penetration  Poor temporal
Resolution
Narrow BW  Low Q  not Good Penetration  Good
temporal Resolution

43. Dynamic range ( in dB) = 10 * 𝑙𝑜𝑔10(
ℎ𝑖𝑔ℎ𝑒𝑠𝑡 𝑝𝑜𝑤𝑒𝑟
𝑙𝑜𝑤𝑒𝑠𝑡 𝑝𝑜𝑤𝑒𝑟
)
d. Contrast Resolution
Narrow dynamic range   compression   Contrast Resolution
Wide dynamic range   compression   Contrast Resolution

44.  Axial Resolution   SPL
 Lateral Resolution   Near zone length
 Temporal Resolution   Frame Rate
 Contrast Resolution   Narrow dynamic range

45. 10. Linear array Transducer crystal arrangement
E
W
g
p
A
E = Elevation , W = Element width, A = Active aperture, p = centre
to centre distance between elements, g = internal element spacing
Active Aperture(A) = n * p
Precise active aperture(A) = (n – 1) * p + W
n = 6

46. 11. Ultrasound Transducer construction
 Frequency
 Frequency  Short SPL   Axial Resolution
Frequency    wide aperture  long near zone length
  Lateral Resolution
 Aperture
Wide Aperture   Lateral Resolution
 Piezoelectric crystal arrangement

47. 12. Design of Linear Ultrasound Transducer
Parameters Available Transducer Proposed Prototype
1. Crystal Thickness 2mm to 5mm 0.5mm (PZT-5A)
So, high frequency
would be obtained
from thinner crystal.
2. Depth of
Penetration
12 to 16 cm 12 to 14cm
So, Faster Scanning
3. Aperture Wide More wide
So,  Lateral
Resolution

48. 4. Number of
Piezoelectric
crystals
90 – 192
For 64 elements, we
obtain 61 lines/ frame
• 256 elements arranged
as 128-128 elements in
one row
• Approx. 125 lines/frame
• So, Frame rate 
Temporal Resolution
5. Frequency 2 - 12MHz 10 * 15 MHz
High Frequency
So,
 Axial Resolution
 Lateral Resolution

49. Active Aperture
n = 128
Thickness of crystal = 0.5mm
g = 0.1mm
p = 0.6mm
Active Aperture = n * p
= 128 * 0.6mm
= 76.8mm
Active Aperture = 76.8 * 22mm approx.

50. 1 2 3 4 5 6 7 8 9 . . . . . . . . . . . . . . . . . . . . 128
Available Transducer
Proposed Prototype

51. 13. Reverberation effect
 Ultrasound beam are produced by an ultrasound beam
repeatedly bouncing back and forth between two highly
reflective interfaces or between the transducer and a
strong reflector.
 Low reflectivity and acoustic impedance value close to
skin generates reverberations.
 Multiple copies of anatomical structure:
o Degrades image quality
o Decrease accuracy

52.  Depth of penetration TOF Reverberation effect

53.  The image brightness on the US system monitor is strongly related
to the amplitude of the peaks.
 The signal contributes not related to the reflections of the upper and
lower target surfaces are potential sources of reverberations.
 They can be shown in light gray in US system.

54. Thank You