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ultrasound
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Cachard ESMP 2013 Archamps 1
Basic principles of ultrasound
Christian CACHARD [email protected]
CREATIS www.creatis.insa-lyon.fr
Université Lyon 1
Teresa Robinson Consultant Clinical Scientist
Head of the Vascular Studies Unit, United Bristol Healthcare NHS Trust
2
Université de Lyon
Cachard ESMP 2013 Archamps 3
CREATIS is a key european laboratory
for biological and medical imaging
3D modelling of human heart based on MRI
Simulation of dose distribution for radiotherapy
at the interface between
engineering, computer sciences
and living sciences
Elastography
About 200 persons
Cachard ESMP 2013 Archamps 4
Development of
imaging methods,
new algorithms,
and instrumental systems to answer medical questions
3D augmented reality
3D imaging of cardiac muscular fibers
4
In vivo quantification of metabolite concentration (MR spectroscopy at 4.7T)
5
1 - Imaging of the Heart-Vessels-Lungs
2 - Images et models
3 – Ultrasound Imaging
4 - Tomographic imaging and therapy with radiation
5 - MRI and Optics : Methods and Systems
6 – Brain imaging
5
MR spectroscopy
Multi-organs segmentation Dynamic model of the heart
Diffusion Tensor Imaging of the brain
Microarchitecture and micro-vasculature of trabecular bone(1 voxel=1,4µm)
6 research teams
Segmentation and tracking of carotid artery wall in US
Cachard ESMP 2013 Archamps 6
Ultrasound imaging platform
6
3 research ultrasound scanners, motorized and automated acquisition system Imaging biological deformation in vivo
2D ultrasound elastography ultrasonore Breast cancer, Coll. HCL and
Institute of Cancer Research, Londres
Cachard ESMP 2013 Archamps 7
Medical applications
Cardio-vascular: atherosclerosis and ischemia
3D dynamic model of the heart including fiber orientation. Coll. Auckland Bioengineering Institute
3D tomographic reconstruction of a stent, Coll. GEHealthcare
MRI sequences for cardiac function quantification
Real-time quantification of Carotide wall movement Coll. HCL et Hopital Univ. Sydney Clinical protocol SARD
High resolution simulation of diffusion tensor imaging Coll. Harbin Institute of Technology
7
Cachard ESMP 2013 Archamps 9
Basic principles of ultrasound
1: Overview
2: Sound waves
3: Ultrasound generation
4: Ultrasound in tissue
Cachard ESMP 2013 Archamps 11
Ultrasound scanning
Scanner
Probe Ultrasound imaging is Non Destructive Testing
Cachard ESMP 2013 Archamps 12
Cachard ESMP 2013 Archamps 13
The place of ultrasound in medical imaging
Public Hospitals in Lyon (2012)
– 9 MRI
– 11 scanners
– 8 gamma (scintillation) cameras
– 1 PET (Positron Emission Tomographie)
– More than 100 ultrasound scanners
Cachard ESMP 2013 Archamps 14
Real time imaging
10 to 60 frames/s
Cachard ESMP 2013 Archamps 15
The place of ultrasound in medical imaging
Ultrasound has the last ten years been the fastest growing imaging modality for non-invasive medical diagnosis.
Of all the various kinds of diagnostic produced in the world, one of four is an ultrasound scan.
Reasons for this are the ability to image soft tissue and blood flow • the real time imaging capabilities,
• the harmlessness for the patient and the physician (no radiation)
• the low cost of the equipment.
• no special building requirements as for X-ray, Nuclear, and Magnetic Resonance imaging.
Limitations are that ultrasound imaging cannot be done through bone or air (limitations on chest imaging).
Cachard ESMP 2013 Archamps 16
Mechanical wave
Sound is a mechanical wave
Created by a vibrating object
Propagated through a medium
Vacuum chamber
Knocking the bell inside the vacuum chamber
no sound propagates
Cachard ESMP 2013 Archamps 17
The acoustic pressure
The acoustic pressure is the change of pressure around the
static (ambient) pressure
Acoustic pressure amplitude
t
p (Pa)
105 Ambient pressure
• Ultrasound energy is exactly like
sound energy, it is a variation in the
pressure within a medium.
• Sound is a pressure wave
Cachard ESMP 2013 Archamps 18
Ultrasound
Frequency of Sound
20 Hz
20 000 000 Hz
2 000 000 Hz
20 000 Hz Audible Sound
Diagnostic Medical
Ultrasound
(3-7 MHz)
Infrasound (earthquake) 20 Hz
20 MHz
2 MHz
20 kHz
Cachard ESMP 2013 Archamps 19
The probe: transmitter and receiver
• The same probe is used first as transmitter,
second as receiver
• Probe Loudspeaker + Microphone
Cachard ESMP 2013 Archamps 20
Ultrasound scanner and sonar
• Ultrasound scanner works as sonar
Cachard ESMP 2013 Archamps 21
Diagnostic Ultrasound
Echoes
return
Processed into
picture
Pictures
analysed
Sound waves
directed into
patient
Which pulse(s)?
Which processing?
22
2
tcd
d = ?
c= 1500 m/s
Depth
or time
Probe Time
tf time of flight
Range of depth and time of flight
0.75 cm < depth < 15 cm
10 µs < tf: time of flight < 200 µs
Target
(sound velocity in water)
Cachard ESMP 2013 Archamps 23
Reflection and transmission
One transmitted pulse gives rise to a train of
received echoes. Time
Depth
We can calculate where the echoes have come
from by timing how long they take to get back.
24
The probe includes
128 to 512
transducer elements
… … … ....
25
Depth /
time
Time of frame acquisition
Width
Amplitude
… … … ....
TPRF
128 to 512
transducer
elements
26
Depth /
time
0.75 cm < depth < 15 cm
10 µs < time of flight < 200 µs
TPRF
TPRF >> maximum time of flight
PRF: Pulse Repetition Frequency
PRF = 1/ TPRF
TPRF > 5 x (maximum time of flight)
1 kHZ < PRF < 20 kHZ
Cachard ESMP 2013 Archamps 27
Range
Frequency 1 MHz < frequency< 10 MHz
Time of flight 10 µs < time of flight < 200 µs
Pulse Repetion Frequency 1 kHZ < PRF < 20 kHZ
Cachard ESMP 2013 Archamps 28
Echoes from ONE pulse
The echo
amplitudes are
converted to
shades of grey
A-Mode
(amplitude)
B-Mode
(brightness)
Amplitude
Cachard ESMP 2013 Archamps 29
One
Frame
B (Brightness) Mode Image
64 to 512
transducer elements
10 to 60 frames/s
Cachard ESMP 2013 Archamps 30
Visible scan
lines (48)
1970’
B mode image 1970’
Cachard ESMP 2013 Archamps 31
Range
Frequency 1 MHz < frequency< 10 MHz
Time of flight 10 µs < time of flight < 200 µs
Pulse Repetion Frequency 1 kHZ < PRF < 20 kHZ
Number of elements 64 <Nelt < 512
Frame acquisition (PRF = 5kHz) 10 frame/s < Nframe <80 frame/s
Cachard ESMP 2013 Archamps 32
Shapes of the images: linear or sectorial
32 Thyroid mass
B (Brightness) Mode Images
Ovarian Cyst
Popliteal artery
Gall bladder & stone
Cachard ESMP 2013 Archamps 33
Linear probe Sectorial probe
Shapes of the images: linear or sectorial
34
Scanning of pressure beam with
a sectorial probe
Cachard ESMP 2013 Archamps 35
B mode and M mode
B-mode
M-mode
(or TM mode,
Time Motion)
time
t1 t2 t3
Cachard ESMP 2013 Archamps 36
Imaging modes
A mode
TM mode B mode
Envelope Signal
Time (s)
Scan plane Distance (cm)
Dep
th (cm
)
Dep
th (cm
)
One frame: 20 to 50 ms One continuous image of 5 s
Cachard ESMP 2013 Archamps 37
Doppler modes: velocity measurements
37 Spectral Doppler
“Ultrasonic Doppler Modes”
Piero Tortoli
Colour Doppler
Cachard ESMP 2013 Archamps 38
1: Overview
2: Sound Waves
3: Ultrasound generation
4: Ultrasound in Tissue
Basic Principles of Ultrasound
Cachard ESMP 2013 Archamps 39
Wave Motion: transverse wave
Up and down
Particle movement
Wave propagation
Cachard ESMP 2013 Archamps 40
Wave Motion: transverse wave
40
Stadium wave
Direction of energy transport
Cachard ESMP 2013 Archamps 41
Wave motion: Longitudinal Wave
Direction of energy transport
Cachard ESMP 2013 Archamps 42
Transverse Wave Longitudinal Wave
Particle movement
Wave propagation
Particle movement
Wave propagation
Wave motion in tissue
Direction of energy transport Direction of energy transport
Cachard ESMP 2013 Archamps 43
Elastic deformable medium
– gas, liquid or solid.
Molecules do not travel from one
end of the medium to the other.
No flow of particles
Pressure amplitude
Depth
rare
fact
ion
com
pre
ssio
n
wave velocity c
44
At each spatial position , the material points are oscillating around their
equilibrium position with a particle velocity v
if u is the displacement of the material point, v = du/dt
Molecules do not travel from one end of the medium to the other.
Depth
wave velocity c
Valeur de u pour une pression donnée
Cachard ESMP 2013 Archamps 45
Sound is a mechanical wave
• Created by a vibrating object
• Propagated through a medium
Sound is a pressure wave
• Consists of repeating pattern of high and low pressure regions
Sound is a longitudinal wave
• Motion of particles is in a direction parallel to direction of energy transport
The Nature of a Sound Wave in tissue (liquids)
Cachard ESMP 2013 Archamps 46
The Frequency of a wave
T = 1 / f
Peak excess pressure
=
amplitude A0 of wave
ftAA 2sin0
Wave equation
Cachard ESMP 2013 Archamps 47
Wavelength and frequency of the wave
Wavelength, = c T = c / f
Wavelength,
Spatial periodicity
Time
Period, T=1/f
Temporal periodicity
Depends on source
Depends on velocity of sound, c
(depends on material)
Distance
Pressure rare
fact
ion
com
pre
ssio
n
Cachard ESMP 2013 Archamps 48
Velocity of the wave
48
Air c = 330 m/s
Water c = 1500 m/s
If source is 3 MHz frequency
= 1500/ 3 .106 = 0.5mm
= 330/ 3.3 .103 = 0.5 m
If source is 3.3 kHz frequency
Cachard ESMP 2013 Archamps 49
On ultrasound scanner the ultrasound wave is emitted as pulses (not a continuous sine )
Ultrasound Pulse
Pressure
Time
Length of pulse is about 3 to 5 periods
f = 3 MHz
1 µs < Tp < 1.66 µs
Cachard ESMP 2013 Archamps 50
Range
Frequency 1 MHz < frequency< 10 MHz
Time of pulse (length 3 periods) 0.3 µs < TP< 3 µs
Time of flight 10 µs < time of flight < 200 µs
Pulse Repetion Frequency 1 kHZ < PRF < 20 kHZ
Number of elements 64 <Nelt < 512
Frame rate (PRF = 5kHz) 10 frame/s < Nframe <80 frame/s
Time of frame(PRF = 5kHz) 12 ms < Time of frame< 100 ms
Cachard ESMP 2013 Archamps 51
Range Equation
It is possible to predict the distance (d) of a reflecting surface from the transducer if the time (t) between transmission and reception of the pulse is measured and the velocity (c) of the ultrasound along the path is known
t . c
2 d =
d
c
t
Pulse Echo
Cachard ESMP 2013 Archamps 52
Intensity
The intensity associated with the wave is
defined as the power flowing through a
unit area (measured in W/m2 or mW/cm2 )
Power
1m
1m
Ii (t,r) p (t,r) 2
c r
Cachard ESMP 2013 Archamps 53
c
PI
r2
2
0
Intensity for a sinusoidal wave
• Time averaged intensity (I) for
a sinusoidal wave (where P0 is
the peak-pressure amplitude)
Ii (t,r) p (t,r) 2
c r
P0
Pressure
Intensity
Cachard ESMP 2013 Archamps 54
Intensity for a pulsed wave
PRFsppa
spta
TI
I
Ispta (Temporal
Average)
TPRF
Isptp (Temporal
Peak)
Isppa (Pulse
Average)
≈ 1/200
Intensity Pressure
time
Intensity
Cachard ESMP 2013 Archamps 55
Isptp
Ispta
Isppa
True time axis
Cachard ESMP 2013 Archamps 56
1: Overview and History
2: Sound Waves
3: Ultrasound Generation
4: Ultrasound in Tissue
Basic Principles of Ultrasound
Cachard ESMP 2013 Archamps 57
Sources of Sound Waves
Sound production requires
a vibrating object
Vocal chords
Collision!
Audio speaker system
Piezoelectric element
Cachard ESMP 2013 Archamps 58
Ultrasound generation and detection
Pierre and Jacques Currie
Piezoelectric effect discovered in 1880
• Piezoelectric materials
• Quartz
• PZT (Lead, Zirconate,Titanate- PbZrTi)
Cachard ESMP 2013 Archamps 59
Quartz
+
- Expansion
+
- Contraction
• Apply a voltage between the two faces of a piezoelectric material: result is deformation (inverse piezoelectric effect)
Ultrasound generation
Cachard ESMP 2013 Archamps 60
Ultrasound detection
Apply force to piezoelectric material: result is electrical charge proportional to force (direct piezoelectric effect)
The frequency of the force applied will affect the frequency with which a voltage is generated
Force
Force
Cachard ESMP 2013 Archamps 61
Piezoelectric materials and transducers
“Ultrasound transducers”
Hervé Liebgott
Cachard ESMP 2013 Archamps 62
Beam Shape
Beam width lateral resolution
Cachard ESMP 2013 Archamps 63
Beam Shape
w
λ
W>>λ
w
λ
W<<λ Small point source
Diffraction
directional
Spherical wave Plane wave
Cachard ESMP 2013 Archamps 64
Plane Disc Source: Intensity of the field
Near field Far field
Non-uniform beam Uniform beam
Intensity
Distance from probe
Near field Far field
Intensity on axis
propagation
Avoid measurements in the near field
Cachard ESMP 2013 Archamps 65
Ultrasound beam from a plane disc source
Intensity
Distance from probe
Near field Far field
Cachard ESMP 2013 Archamps 66
Spatial Resolution
Temporal Resolution
Contrast Resolution
Imaging Resolution
Cachard ESMP 2013 Archamps 67
Spatial Resolution
Spatial (in space)
axial (along the beam)
lateral (across the beam)
• azimuth (in the scan plane)
• elevation or slice thickness (perpendicular to the scan plane)
Cachard ESMP 2013 Archamps 68
Axial Resolution
The minimum reflector spacing along the axis of the ultrasound beam that results in separate, distinguishable echoes on the display.
Cachard ESMP 2013 Archamps 69
Axial Resolution
Example 10 MHz transducer
mmHz
sm
f
c5.0
000,000,3
/1540
mmHz
sm
f
c15.0
000,000,10
/1540
ra = number of cycles of the transmitted pulse x 3
ra =3 x 0.5 = 1.5 mm
ra =3 x 0.15 = 0.45 mm
Example 3 MHz transducer
First definition
Resolution is length at half size
Second definition
Cachard ESMP 2013 Archamps 70
Lateral Resolution
The ability to distinguish two closely spaced reflectors that are positioned perpendicular to the axis of the ultrasound beam.
Cachard ESMP 2013 Archamps 71
Elevational Resolution (slice thickness)
Works in a direction perpendicular to the image plane.
Dictates the thickness of the section of tissue that contributes to echoes visualized on the image.
Cachard ESMP 2013 Archamps 72
The time interval between pulses
• limits the temporal resolution
• it is usually set so that there is sufficient time for the most distant echo to return to the transducer before the next pulse is launched
Temporal Resolution
Cachard ESMP 2013 Archamps 73
Temporal Resolution
Interval to allow
echoes to return
Sequence of pulses from transducer
Typical PRF = 5kHz
TPRF = 0.2 ms
Time
TPRF can be chosen as the delay of five times the maximum
observed distance
TPRF
Cachard ESMP 2013 Archamps 74
Contrast Resolution
The ability to display regions of differing echo size
Low
High
Cachard ESMP 2013 Archamps 75 75
“Q-assurance of US equipment”
Jean Martial Mari
Cachard ESMP 2013 Archamps 76
1: Overview and History
2: Sound Waves
3: Ultrasound Generation
4: Ultrasound in Tissue
Basic Principles of Ultrasound
77
Cachard ESMP 2013 Archamps 78
Speed of Sound
78
Cachard ESMP 2013 Archamps 79
Speed of Sound
r
kc
Bulk modulus
Density
Cachard ESMP 2013 Archamps 80
Air 330m/s
Water 1480m/s
Fat 1460m/s
Blood 1560m/s
Muscle 1600m/s
Bone 4060m/s
Speed of Sound
Average soft tissue
value = 1540m/s
Programme the
ultrasound
machine with...
This can lead to small errors in the estimated distance travelled because of the
variation in the speed of sound in different tissues.
81
Cachard ESMP 2013 Archamps 82
kz r
Acoustic Impedance
82
Bulk modulus Density x
Cachard ESMP 2013 Archamps 83
Acoustic Impedance
Acoustic impedance analogous to electrical impedance
P = local pressure
v = local particle velocity
v
Pz
U : Potential
I : Intensity
I
Uz
Cachard ESMP 2013 Archamps 84
Similar Values
Air 0.0004 x 106 rayls
Lung 0.18 x 106
Fat 1.34 x 106
Water 1.48 x 106
Blood 1.65 x 106
Muscle 1.71 x 106
Skull Bone 7.80 x 106
Acoustic Impedance
85
Cachard ESMP 2013 Archamps 86
Reflection at boundaries
At the boundary between tissues ultrasound is partially reflected
The relative proportions of the energy reflected and transmitted depend on the acoustic impedance between the two materials
Incident
wave
Transmitted wave
Reflected
wave
The laws of optics apply to ultrasound
Cachard ESMP 2013 Archamps 87
Reflection at interface perpendicular to the wave
rit
rit
vvv
PPP
Z1
Z2
Pi , vi
Pt , vt
Pr , vr Replace v with P/z, the
reflexion coefficient is obtained
12
12
zz
zz
P
P
i
r
Cachard ESMP 2013 Archamps 88
Reflection at interface perpendicular to the wave
z2 z1
12
12
zz
zz
P
P
i
r
Z1
Z2
Pi , vi
Pt , vt
Pr , vr
0r
i
P
P
• z2 z1 1r
i
P
P
complete transmission
complete reflexion
Cachard ESMP 2013 Archamps 89
Specular Reflection
Non-perpendicular
Incidence
Perpendicular
Incidence
Reflected beam
travels off at an angle.
No wave go back to
the probe Strong orientation dependence
Cachard ESMP 2013 Archamps 90
Diffuse Reflection
Reflected waves
travel in various
directions away
from the interface
Cachard ESMP 2013 Archamps 91
Diffuse Reflection
Reflected waves travel in
various directions away from
the interface
Some orientation dependence
Cachard ESMP 2013 Archamps 92
Rayleigh Scattering
Particles size <<
Waves are scattered and
travel off in all directions
Energy loss f 4
Cachard ESMP 2013 Archamps 93
Rayleigh Scattering
Particles size <<
Little orientation dependence
Waves are scattered and
travel off in all directions
Energy loss f 4
Cachard ESMP 2013 Archamps 94
The amplitude of the echoes (image grey level)
does not have a simple relationship with the tissue (unlike X-ray CT [Hounsfield numbers]).
Echo size depends on
• size of structure compared with λ
• relative acoustic impedances across boundary
• shape and orientation of boundary
Echo Amplitude - Beware!
Cachard ESMP 2013 Archamps 95
In tissue: Specular Reflection, Diffuse Reflection or Rayleigh Scattering?
Particles size <<
Specular reflection from large flat boundaries
Diffuse reflection
from small structures
Rayleigh Scattering from very small structures
Strong Weak Very weak
Reflection or scattering?
Cachard ESMP 2013 Archamps 96
Coupling gel
Cachard ESMP 2013 Archamps 97
Strong
Reflection
Weak
Reflection
Very weak
Reflection
Cachard ESMP 2013 Archamps 98
Calcification
99
Cachard ESMP 2013 Archamps 100
Attenuation
The energy of the ultrasound beam is reduced with distance
Energy is lost from the beam by:
Absorption (conversion into heat)
Scattering (reflection out of beam confines,
refraction, divergence)
Cachard ESMP 2013 Archamps 101
Attenuation in an image
Bright deep to the cyst Dark
deep to
the defect
in the
phantom!
Dark deep to the cyst
Cachard ESMP 2013 Archamps 102
Attenuation Coefficient
z
z eII 0
The intensity, Iz, of an ultrasound beam is related
to distance from the source, z, thus:
Where I0 is the intensity at z = 0, the transducer face.
Iz
z
Cachard ESMP 2013 Archamps 103
Attenuation Coefficient
Attenuation is approximately exponential,
the slope of the logarithmic graph is constant.
Attenuation coefficient is quoted in dB/cm
In addition, for soft tissue,
attenuation is proportional to frequency.
The attenuation coefficient for soft tissue is
0.5 - 0.7 dB/cm/MHz
Cachard ESMP 2013 Archamps 104
Attenuation – compensation: TGC
Average echo
Amplification
factor
Echo train
after compensation
Time
(distance)
For deeper distance noisy is amplified
Cachard ESMP 2013 Archamps 105
TGC: Time Gain Compensation
depth
gain
Cachard ESMP 2013 Archamps 106
Cachard ESMP 2013 Archamps 107
Nonlinear propagation
Nonlinear coefficient
Nonlinear parameter
𝜌𝜕𝑣
𝜕𝑡+ 𝛻𝑝 = 0 The motion equation
The pressure is expanded using the Taylor series
The celerity
linear
Cachard ESMP 2013 Archamps 108
Nonlinear propagation: celerity
Nonlinear coefficient
Nonlinear parameter
f0 + 2 f0+ 3 f0 + .... f0
After propagation
𝑣 =𝑝
𝜌 𝑐
Cachard ESMP 2013 Archamps 109
Non-Linear propagation
Under conditions of relatively high pressure amplitude the speed of
sound is NOT CONSTANT but varies over the propagation path (z)
Material B/A
water (30°C) 5.2
blood 6.3
liver 7.6
spleen 7.8
fat 11.1
𝑐 𝑧 = 𝑐0 + 1 + 𝐵
2 𝐴𝑣(𝑧)
Cachard ESMP 2013 Archamps 110
After a sufficient distance, the faster
moving high-pressure parts of the wave
catch up to the slower low-pressure parts.
The result is a
sawtooth wave
The distorted wave has many harmonic frequencies
Higher
speed
Higher
speed
Lower
speed
Lower
speed
Cachard ESMP 2013 Archamps 111
Higher
speed
Higher
speed
Lower
speed
Lower
speed
Cachard ESMP 2013 Archamps 113
Harmonics
f0
Fundamental
2f0
2nd
3rd
3f0
Frequency
Amplitude
The amplitude decreases is about 20 dB per harmonic
Cachard ESMP 2013 Archamps 114
Harmonic Imaging
A relatively recent innovation in
diagnostic ultrasound imaging is
Tissue Harmonic Imaging
Discovered by accident it uses the
effects of non-linear propagation.
Cachard ESMP 2013 Archamps 115
Ultrasound contrast agent
“Contrast agents in US”
Thierry Bettinger
Cachard ESMP 2013 Archamps 116
Native harmonic frequencies are used to improve images
How?
• By tuning the receiver to the harmonic frequency (2Fo) rather than the transmitted frequency Fo
Benefits
• Reduces clutter (noise), increases resolution at depth, improves sensitivity
117 117
118
Cachard ESMP 2013 Archamps 119
Thermal
• tissue heating, cell death for T > 42oC
Mechanical
• cavitation bubbles for pressures > threshold o unfortunately threshold is frequency dependent
Safety
Possible damage from ultrasound:
Cachard ESMP 2013 Archamps 120
• Thermal index
– relates to temperature
– potential for heating effects (metabolic rate)
• Mechanical Index
– relates to pressure
– potential for bubble effects (cavitation)
Mechanical and Thermal Indices
Cachard ESMP 2013 Archamps 121
Thermal Index
• TI is the ratio between:
– the power exposing the tissue, W
– the power required to cause a 1oC temperature
rise, Wdeg
TI =
Wdeg
W
Cachard ESMP 2013 Archamps 122
• MI describes the likelihood of the negative
pressure causing bubble activity
MI P-d
f
=
P-d is the ‘derated’ pressure at the site in the body
f is the frequency of the pulse
megapascals
(megahertz) 1/2
Mechanical Index
Cachard ESMP 2013 Archamps 123
Medical Index (MI)
f
p MI
MPa
MHz
Ultrasound medical scanner: 0.01 < MI < 2
The transmitted pressure amplitude (Pascal) and
Medical Index (MI)
Example: f = 2 MHz
P (MPa) 0,0 0,1 0,1 0,2 0,5 1,0
MI 0,01 0,04 0,07 0,14 0,35 0,71
Cachard ESMP 2013 Archamps 124
MI > 3 Possibility of minor damage to neonatal lung or intestine
MI 2 Limitation of medical scanner
MI >0.7 Theoretical risk of cavitation.
TI>0.7 Restrict exposure time of a fetus
TI>1.0 Eye scanning not recommended
TI>3.0 Fetal scanning not recommeded
Guidelines
Cachard ESMP 2013 Archamps 125 125
“Therapeutic US principles”
Jean Martial Mari
126
Cachard ESMP 2013 Archamps 127
Scanner settings
•Fixed settings : MI, TCG, gain
•Adjustement: focus, sector
size
Cachard ESMP 2013 Archamps 128
PHILIPS
Cachard ESMP 2013 Archamps 129
Ultrasound Imaging, Bjorn A. J. Angelsen, ISBN 82-995811-0-9, Emantec AS, Trondheim, Norway, www.ultrasoundbook.com
Ultrasound in Medecine, Institute of Physics, Publishing Bristol and Philadelphia
References