SONOGRAPHIC PHYSICS,
INSTRUMENTATION & DOPPLER
REVIEW
2012
Part 1
1
Review of Ultrasound
Physical Principles
2
ENGINEERING
&
SCIENTIFIC NOTATION
Prefix
Factor Decimal
Symbol
pico
nano
micro
milli
centi
deci
(trillionth)
(billionth)
(millionth)
(thousandth)
(hundredth)
(tenth)
10-12
10-9
10-6
10-3
10-2
10-1
0.000000000001
0.000000001
0.000001
0.001
0.01
0.1
p
n

m
c
d
deca
hecta
kilo
mega
giga
tera
(ten)
(hundred)
(thousand)
(million)
(billion)
(trillion)
101
102
103
106
109
1012
10
100
1000
1000000
1000000000
1000000000000
D
h
k
M
G
T
3
8 BIT BINARY NUMBERS
Binary
128 64 32 16
8
Decimal
4
2
1
00000000
00000001
00001010
00001111
00100000
01000000
10000000
11111111
100 10
1
=
0
=
1
= 10
= 15
= 32
= 64
= 128
= 255
4
DECIBELS
dB
Power or Intensity ratio
(Amplitude ratio) 2
-9
-6
-3
0
+3
+6
+9
+10
+20
+30
+40
+50
+60
+70
+80
0.125
0.25
0.5
1
2
4
8
10
100
1000
10000
100000
1000000
10000000
100000000
Amplitude ratio
(Power or Intensity ratio)½
0.354
0. 5
0.707
1
1.414
2
2.83
3.16
10
31.6
100
316
1000
3160
10000
5
CATEGORIES OF SOUND
• INFRASOUND = below 20 Hz
• AUDIBLE SOUND = 20 Hz to 20 kHz
• ULTRASOUND = above 20 kHz
o Medical Diagnostic Ultrasound = above 1 MHz
6
SOUND VELOCITY
STIFFNESS
OF MEDIUM
DENSITY OF
MEDIUM
SOUND
VELOCITY
Increase
———————
Increase
Decrease
———————
Decrease
———————
Increase
Decrease
———————
Decrease
Increase
7
SOUND VELOCITIES
Material
Air
Meters per second
330
Pure Water
Fat
Soft Tissue
Muscle
1430
1450
1540
1585
Bone
4080
8
PIEZOELECTRIC
EFFECT
•TRANSMIT – Electrical energy to mechanical energy
•RECEIVE – Mechanical energy to electrical energy
9
RESONANT FREQUENCY
•The fundamental frequency of a transducer
PIEZOELECTRIC
ELEMENT THICKNESS
RESONANT FREQUENCY
Increase
Decrease
Decrease
Increase
10
PIEZOELECTRIC EFFECT
Electrical
energy
Mechanical
energy
11
LONGITUDINAL WAVE PROPAGATION
12
WAVE PARAMETERS AND EXAMPLES
Period = 1  Frequency
Wavelength = Velocity  Frequency
Pulse Duration = Period x Number of Cycles
Spatial Pulse Length = Wavelength x Number of Cycles
DAMPING FREQUENCY
PERIOD
WAVELENGTH NUMBER OF
CYCLES
PULSE
DURATION
SPATIAL
PULSE LENGTH
————
Increase
Decrease
Decrease
————
Decrease
Decrease
————
Decrease
Increase
Increase
————
Increase
Increase
Increase
————
————
————
Decrease
Decrease
Decrease
Decrease
————
————
————
Increase
Increase
Increase
13
SAME DAMPING & AMPLITUDE
DIFFERENT FREQUENCY & PHASE
Frequency = 5.0 MHz
Number of Cycles = 3
Period = 0.2 µs
Pulse Duration = 0.6 µs
Wavelength = 0.308 mm
Spatial Pulse Length = 0.924 mm
Frequency = 2.5 MHz
Number of Cycles = 3
Period = 0.4 µs
Pulse Duration = 1.2 µs
Wavelength = 0.616 mm
Spatial Pulse Length = 1.848 mm
3-cycle pulse
3-cycle pulse
shorter periods
longer periods
shorter wavelengths
longer wavelengths
shorter pulse duration
longer pulse duration
shorter spatial pulse length
longer spatial pulse length
14
SAME FREQUENCY, AMPLITUDE, & PHASE
DIFFERENT DAMPING
Frequency = 5.0 MHz
Number of Cycles = 3
Period = 0.2 µs
Pulse Duration = 0.6 µs
Wavelength = 0.308 mm
Spatial Pulse Length = 0.924 mm
Frequency = 5.0 MHz
Number of Cycles = 4
Period = 0.2 µs
Pulse Duration = 0.8 µs
Wavelength = 0.308 mm,
Spatial Pulse Length = 1.232 mm
3-cycle pulse
4-cycle pulse
same periods
same periods
same wavelengths
same wavelengths
shorter pulse duration
longer pulse duration
shorter spatial pulse length
longer spatial pulse length
15
SAME FREQUENCY & DAMPING
DIFFERENT AMPLITUDE & PHASE
Frequency = 5.0 MHz
Number of Cycles = 4
Period = 0.2 µs
Pulse Duration = 0.8 µs
Wavelength = 0.308 mm
Spatial Pulse Length = 1.232 mm
Frequency = 5.0 MHz
Number of Cycles = 4
Period = 0.2 µs
Pulse Duration = 0.8 µs
Wavelength = 0.308 mm
Spatial Pulse Length = 1.232 mm
4-cycle pulse
4-cycle pulse
same periods
same periods
same wavelengths
same wavelengths
same pulse duration
same pulse duration
same spatial pulse length
same spatial pulse length
16
DAMPING vs. BANDWIDTH
DAMPING
BANDWIDTH
Increase
Increase
Decrease
Decrease
17
HIGH DAMPING vs. NO DAMPING
SAME FREQUENCY. DIFFERENT DAMPING
Center frequency = 5.0 MHz
Range = 3.75 MHz to 6.25 MHz
Number of Cycles = 2
Bandwidth = 2.5 MHz
Center frequency = 5.0 MHz
Range = 4.9 MHz to 5.1 MHz
Continuous Wave
Bandwidth = 0.2 MHz
Pulse-echo
CW
Damped
Not damped
Wide Bandwidth
Narrow Bandwidth
18
RANGE EQUATION:
(in tissue)
Distance to the reflector
= 0.77 x round trip time
TIME TO THE
REFLECTOR
(ONE WAY)
DISTANCE TO THE
REFLECTOR
(ONE WAY)
ROUND TRIP
TIME
ROUND TRIP
DISTANCE
6.5 µs
10 mm (1 cm)
13 µs
20 mm (2 cm)
5 µs
7.7 mm (0.77 cm)
10 µs
15.4 mm (1.54 cm)
19
PULSE-ECHO EQUATIONS
Pulse Repetition Period = 1  Pulse Repetition Frequency
Duty Factor = Pulse Duration  Pulse Repetition Period
PRF
PRP
1000 Hz
1/1000 sec (0.001 sec)
2000 Hz
1/2000 sec (0.0005 sec)
4000 Hz
1/4000 sec (0.00025 sec)
20
PULSE-ECHO EQUATIONS
Duty Factor = Pulse Duration  Pulse Repetition Period
PRF
PRP
PULSE
DURATION
DUTY
FACTOR
Increase
Decrease
————
Increase
Decrease
Increase
————
Decrease
————
————
Increase
Increase
————
————
Decrease
Decrease
21
ACOUSTIC IMPEDANCE:
z = r
x
c
(density x velocity)
DENSITY
VELOCITY
ACOUSTIC
IMPEDANCE
Increase
————
Increase
Decrease
————
Decrease
————
Increase
Increase
————
Decrease
Decrease
22
ACOUSTIC IMPEDANCE
(Rayls)
Air
Fat
Water
Soft Tissue
Muscle
Bone
400
1,380,000
1,430,000
1,630,000
1,700,000
7,800,000
23
INTERFACE MATERIALS & ECHO STRENGTH
Soft Tissue to Muscle - Weak (1%)
Fat to Soft Tissue – Weak (1%)
Soft Tissue to Bone - Medium (50%)
Blood to Plaque – Medium (50%)
Soft Tissue to Air - Very Strong (100%)
24
SAGITTAL - LIVER, RIGHT KIDNEY
Acoustic shadow – the result of a strong reflection from a gallstone
25
ACOUSTIC COUPLANT
26
TRANSDUCER MATCHING LAYERS
Assuming a transducer has two matching layers between the
element and the transducer face, an example of matching could be:
Piezoelectric element - acoustic impedance = 30,000,000 rayls
First matching layer - acoustic impedance = 16,000,000 rayls
Second matching layer - acoustic impedance = 7,000,000 rayls
Transducer face material - acoustic impedance = 3,600,000 rayls
Acoustic couplant - acoustic impedance = 1,800,000 rayls
Skin - acoustic impedance = 1,700,000 rayls
27
RESOLUTION
Interfaces not closely spaced
GOOD
Closely spaced
GOOD
Closely spaced
POOR
28
AXIAL RESOLUTION
SCANNED STRUCTURE
DISPLAYED IMAGE
29
AXIAL RESOLUTION
SPATIAL PULSE LENGTH
AXIAL RESOLUTION
4 mm
2 mm
3 mm
1.5 mm
2 mm
1 mm
30
LATERAL RESOLUTION
SCANNED STRUCTURE
DISPLAYED IMAGE
31
LATERAL RESOLUTION
BEAM-WIDTH
BEAM-WIDTH
LATERAL RESOLUTION
4 mm
4 mm
3 mm
3 mm
2 mm
2 mm
32
LATERAL RESOLUTION
33
LATERAL RESOLUTION
34
RESOLUTION vs. PENETRATION
HIGH-FREQUENCY TRANSDUCERS
BETTER RESOLUTION
GREATER ATTENUATION
POORER PENETRATION
LOW-FREQUENCY TRANSDUCERS
POORER RESOLUTION
LESS ATTENUATION
BETTER PENETRATION
35
TRANSDUCER FREQUENCIES
2 MHz
2.25 MHz
2.5 MHz
3 MHz
3.5 MHz
4 MHz
5 MHz
10 MHz
7 MHz
12 MHz
7.5 MHz
15 MHz
TRANSDUCER FREQUENCY
ATTENUATION
PENETRATION
HALF INTENSITY DEPTH
Increase
Increase
Decrease
Decrease
Decrease
Decrease
Increase
Increase
36
IN TISSUE:
Attenuation = 0.5 dB per cm per MHz
H.I.D. = 6 ÷ Frequency
Frequency
2 MHz
2.25 MHz
2.5 MHz
3 MHz
3.5 MHz
4 MHz
5 MHz
7 MHz
7.5 MHz
10 MHz
15 MHz
-dB per cm
1
1.125
1.25
1.5
1.75
2
2.5
3.5
3.75
5
7.5
Half-Intensity-Depth
3 cm
2.67 cm
2.4 cm
2 cm
1.71 cm
1.5 cm
1.2 cm
0.86 cm
0.8 cm
0.6 cm
0.4 cm
37
SAGITTAL - LIVER
2.5 MHz
4 MHz
38
SAGITTAL - LIVER, RIGHT KIDNEY
3.5 MHz
5 MHz
39
BREAST
THYROID
7 MHz
7 MHz
VASCULAR
7.5 MHz
OPHTHALMIC
10 MHz
40