alpha_7_instruction_manual_safety_instruction_volum.pdf
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ULTRASOUND DIAGNOSTIC
INSTRUMENT
Instruction Manual
Safety Instruction
(volume 2/2)
Instruction manuals consist of this
manual, How to Use and
Measurement.
Before using this instrument, please
read Safety Instruction.
MN1-5368 rev.10
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ProSound logo is registered mark of Hitachi Aloka Medical, Ltd. in Japan and other countries.
Copyright©Hitachi Aloka Medical, Ltd. All rights reserved.
Microsoft and Windows Media player is registered trademark of Microsoft Corporations in United States and/or other
countries. All brand name and product name are trademarks or registered trademarks of their respective companies. In
this manual, ® and ™ are omitted.
VS-FlexGrid Pro copyright©1999-2000 Videosoft Corporation. Portions of this software are based in part on the work
of the Independent JPEG Group.
Real-time Tissue Elastography is a registered trademark of Hitachi Medical Corporation.
MN1-5368 rev.10
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Introduction
Introduction
This is an instruction manual for model ProSound α7, an ultrasound diagnostic instrument.
Read the manual carefully before using the instrument. Take special note of the items in Chapter
1, "Safety Precautions."
Keep this manual securely for future reference.
Symbols Used in this Document
The following items are important in preventing harm or injury to equipment operator or patient.
There are four levels of harm/damage that can be caused by ignoring instructions/displays or
using the equipment incorrectly: "Danger," "Warning," "Caution," and "Note."
These types are indicated by the following symbols.
Indicates an imminently hazardous situation that will result in the death of or
serious injury to the equipment operator.
Indicates a hazardous situation that could result in death or serious injury.
Indicates a hazardous situation that may result in slight or moderate injury, or
property damage.
Indicates a request concerning an item that must be observed in order to
prevent damage or deterioration to the equipment and also to ensure effective
use.
Contents of cautions shows the following graphics.
This mark indicates and alert, additional information.
This mark indicates that the action is not allowed.
This mark indicates that the action is required.
Conventions used in this manual.
NOTE:
Notes containing additional information.
IMPORTANT:
Information that is considered especially important.
Input, output and screen-messages are presented in the following font: message.
Menus and switches are written as Menu. Submenus are indicated by the use of angle brackets:
Menu > sub-menu > sub-menu.
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Introduction
About the model “ProSound α7”
The ProSound α7 is intended to be used by doctors and other qualified personnel in fracture
diagnostics and hemodynamic diagnostics.
However, this equipment is not designed to be used in ophthalmic ultrasound diagnosis, as its
sound intensity is not compliant with ophthalmic restrictions established by the FDA.
Only physicians and other qualified personnel should operate this equipment for diagnostic
purposes. Read section 1-1 of the Safety Instruction.
1)
PRECAUTIONS Concerning the Use/Management of the ProSound α7
•
Do not disassemble, repair or remodel this equipment or optional features without our
consent.
NOTE:
Disassemble means to remove the parts or options from the equipment
using tools.
NOTE:
Remodel means to install or connect unauthorized parts or equipment
including the power cord.
•
Assembly of the equipment or optional accessories shall be performed by our third party
certified. Please contact one of our offices listed on back cover.
NOTE:
Assemble means to install or connect parts or optional accessories in/to the
device using tools.
2)
•
Transporting this equipment (via automobile/ship) shall be performed by a third party
certified by the manufacturer. Please contact one of our offices listed on back cover.
•
Please conduct routine cleaning and inspection of the equipment. Refer to Chapter 5 of the
Safety Instruction for details.
•
Ensure that the output level of the scan conforms to the required duration of diagnosis.
•
If any malfunction or abnormality is discovered during operation of the equipment, remove
the probe from the patient immediately and discontinue use. If any abnormality is observed
in the patient, provide proper care as quickly as possible. Refer to Chapter 4 of the Safety
Instructions for more information on dealing with the equipment appropriately. If the
malfunction is not listed in Chapter 4 of the Safety Instruction manual, contact one of our
offices listed on back cover.
PRECAUTIONS for the ProSound α7 Installation
This equipment is a electrical medical device that intended for use in hospitals and
research facilities. The device should be installed in accordance with the following
guidelines.
•
Install in accordance with Chapter 3 of the Safety Instructions.
•
Install in an environment that conforms to the operating environments indicated in section
2-2-2 of the Safety Instruction manual.
•
Install in an environment that ensures electromagnetic compatibility, in accordance with
section 1-2-6 of the Safety Instruction manual, "Precautions Concerning the Maintenance
of Electromagnetic Compatibility," and Item 1-3, "Guidelines for Electromagnetic
compatibility."
NOTE:
The electromagnetic compatibility (EMC) is the ability of device to function
satisfactorily in its electromagnetic environment without introducing intolerable
electromagnetic disturbance to anything in that environment.
4
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Introduction
Classification of ProSound α7
• Protection against electric shock (ME equipment): class I • ME equipment
• Protection Against Electric Shock (Applied Parts): Type BF Applied Parts
–
Probe/scanner applied parts and parts treated as applied parts:
Refer to the following diagram (Probe/Scanner Pattern Diagram) and table.
Figure: Probe/Scanner Pattern Diagram
Above illustrates a surface/intraoperative probe. Below shows a coelomic probe.
B
C
A
connector
D
connector
Applicable part
of body
C
Applied part
A
parts treated as applied
parts
B - C length
surface of body
Ultrasonic irradiation area (D)
A to B
100 cm
Intraoperative
Ultrasonic irradiation area (D)
A to B
20 cm
A to C
A to C
N/A
Endocavity
–
Physiological signal applied part: ECG electrodes
Part treated as applied part: 2m from the ECG electrode of the ECG patient cable (consult
following diagram)
2 meters
ECG electrodes
connector
ECG patient lead
• Protection against electric shock (Defibrillation-proof applied parts): Not suitable
• Protection against harmful ingress of water or particulate matter
–
equipment: IPX0 (Ordinary equipment)
–
Probe applied part: IPX7 (Watertight equipment)
• Suitability for use in an oxygen rich environment: Not suitable
• Method(s) of sterilization: Not suitable for sterilization/disinfection with medicinal
solution, gas or radiation.
• Mode of operation: Continuous operation
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CONTENTS
1 Safety Precaution
1-1
Purpose of Use ...................................................................................................................... 1-1
1-2
Precautions for Use ............................................................................................................... 1-2
1-2-1
1-2-2
1-2-3
1-2-4
1-2-5
1-2-6
1-3
Electromagnetic compatibility .............................................................................................. 1-15
1-3-1
1-3-2
1-3-3
1-3-4
1-3-5
1-4
Warnings and Safety Notice .................................................................................................... 1-3
Labels ...................................................................................................................................... 1-6
Precautions concerning acoustic power ................................................................................ 1-11
Precautions for Use in Conjunction with Drugs ..................................................................... 1-12
Precautions for Use in Conjunction with Other Medical Devices........................................... 1-13
Guideline for Electromagnetic Compatibility.......................................................................... 1-14
Guidance and manufacturer’s declaration –electromagnetic emissions ............................... 1-15
Essential performance........................................................................................................... 1-16
Guidance and manufacturer’s declaration – electromagnetic immunity ................................ 1-17
Guidance and manufacturer’s declaration – electromagnetic immunity ................................ 1-18
Recommended separation distances between portable and mobile RF communications
equipment and the ProSound α7 ...........................................................................................1-19
Electrostatic Discharge (ESD) Guidelines ........................................................................... 1-20
2 Specification and Parts Name
2-1
Principle of Operation ............................................................................................................ 2-1
2-2
Specifications ......................................................................................................................... 2-3
2-2-1
2-2-2
2-2-3
2-3
Power Requirements ............................................................................................................... 2-6
Environmental Conditions ....................................................................................................... 2-6
Classification of ProSound α7 ................................................................................................. 2-7
Name of Each Parts ............................................................................................................... 2-8
2-3-1
2-3-2
Name of Each Part .................................................................................................................. 2-8
Operation Panel .................................................................................................................... 2-12
3 Preparations for Use
3-1
Installing the equipment ......................................................................................................... 3-1
3-2
Connecting the Peripheral Instrument ................................................................................... 3-3
3-2-1
3-2-2
3-2-3
3-3
Moving the equipment .......................................................................................................... 3-10
3-3-1
3-3-2
3-4
6
Connecting a Probe to the Instrument..................................................................................... 3-4
Connect the Physiological Signal Connector .......................................................................... 3-6
Connecting with Other Instrument ........................................................................................... 3-8
Isolate from the supply main ................................................................................................. 3-10
Moving the Instrument ........................................................................................................... 3-10
Storing the Instrument .......................................................................................................... 3-13
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3-5
Inspection Before Using ....................................................................................................... 3-14
3-5-1
3-5-2
3-6
Screen Display ..................................................................................................................... 3-16
3-6-1
3-6-2
3-6-3
3-7
Character Display .................................................................................................................. 3-16
Graphic Display ..................................................................................................................... 3-17
Color display.......................................................................................................................... 3-18
Adjusting the Operation Panel ............................................................................................. 3-19
3-7-1
3-7-2
3-7-3
3-7-4
3-8
External Inspection ................................................................................................................ 3-14
Operation Check ................................................................................................................... 3-15
Adjust the Height of the Operation Panel .............................................................................. 3-19
Adjust the Angle of the Operation Panel ............................................................................... 3-20
Adjusting the Brightness of the Touch Panel ........................................................................ 3-21
Adjust the Brightness of the Operation Panel Switch ............................................................ 3-21
Adjusting the Monitor ........................................................................................................... 3-22
3-8-1
3-8-2
3-8-3
Adjust the Angle and Position of the Monitor ........................................................................ 3-22
Adjust the Brightness of the Monitor ..................................................................................... 3-25
Setting combinations of Brightness ....................................................................................... 3-29
4 Troubleshootings
4-1
Messages ............................................................................................................................... 4-1
4-2
Message List .......................................................................................................................... 4-2
4-3
Assistance Messages ............................................................................................................ 4-9
4-4
Other troubles ...................................................................................................................... 4-11
4-4-1
Image Display and Image Degradation ................................................................................. 4-11
5 Maintenance
5-1
After Using the Instrument ..................................................................................................... 5-1
5-1-1
5-2
Cleaning ................................................................................................................................. 5-3
5-2-1
5-2-2
5-2-3
5-2-4
5-3
State of the Instrument and Accessories................................................................................. 5-2
Clean the Instrument ...............................................................................................................
Clean the Trackball .................................................................................................................
Clean the Air Filter...................................................................................................................
Cleaning the Endo-cavity Probe Holder (Horizontal)...............................................................
5-4
5-5
5-6
5-7
Maintenance .......................................................................................................................... 5-9
5-3-1
5-3-2
5-3-3
Daily check: For Using the Instrument for a Long Period ...................................................... 5-10
Checking the Measurement Accuracy................................................................................... 5-11
Safety Inspection................................................................................................................... 5-18
6 Composition
6-1
Standard composition ............................................................................................................ 6-1
6-2
Options ................................................................................................................................... 6-2
6-2-1
6-2-2
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Recording instruments ............................................................................................................ 6-2
Functional expansion instruments ........................................................................................... 6-3
7
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6-2-3
6-2-4
Other accessories ................................................................................................................... 6-3
Software .................................................................................................................................. 6-4
7 Probes
7-1
Caution in the Handling of Probes ......................................................................................... 7-1
7-1-1
7-1-2
7-2
Probe specifications ............................................................................................................... 7-6
7-2-1
7-2-2
7-2-3
7-2-4
7-2-5
7-2-6
7-3
Caution about Handling of Probes .......................................................................................... 7-1
Cautions about Cleaning and Storage .................................................................................... 7-4
Convex Sector Probes ............................................................................................................ 7-7
Linear Probes ........................................................................................................................ 7-11
Phased Array Sector Probes ................................................................................................. 7-15
Biplane Probes ...................................................................................................................... 7-18
3D Scanners.......................................................................................................................... 7-19
Independent Probes .............................................................................................................. 7-20
Clinical Measurement Range ............................................................................................... 7-21
8 Acoustic Output Safety Information
8-1
Acoustic output index ............................................................................................................. 8-1
8-2
Interaction between ultrasound and tissues ........................................................................... 8-3
8-2-1
8-3
Possible Biological Effects ...................................................................................................... 8-4
Derivation and Meaning of MI / TI .......................................................................................... 8-6
8-3-1
8-3-2
Mechanical Index (MI) ............................................................................................................. 8-7
Thermal Index (TI) ................................................................................................................... 8-7
8-4
Setting condition influencing device output ............................................................................ 8-9
8-5
Recommendation on ALARA principle ................................................................................. 8-10
8-6
Default Setting ..................................................................................................................... 8-11
8-7
Acoustic output limits ........................................................................................................... 8-11
8-8
Measurement uncertainties .................................................................................................. 8-12
8-8-1
8-8-2
8-9
Protocol for calculating the measurement uncertainties........................................................ 8-12
Results of measurement uncertainties .................................................................................. 8-14
References ........................................................................................................................... 8-21
9 Acoustic Output Tables
9-1
Acoustic power measurement value ...................................................................................... 9-1
9-2
Display accuracy of MI/TI ....................................................................................................... 9-2
9-3
Acoustic Output Tables .......................................................................................................... 9-2
9-3-1
9-3-2
9-3-3
9-3-4
9-3-5
9-3-6
8
List of symbols for Acoustic Output Tables ............................................................................. 9-2
Convex Sector Probes ............................................................................................................ 9-4
Linear Probes ...................................................................................................................... 9-100
Phased ArraySector Probes ................................................................................................ 9-196
Biplane Probes .................................................................................................................... 9-268
3D Probes ........................................................................................................................... 9-292
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9-3-7
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Independent Probes ............................................................................................................ 9-310
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8 Acoustic Output Safety Information
8-1 Acoustic output index
8
Acoustic Output Safety Information
8-1
Acoustic output index
With this device, output indices about the potential for ultrasound induced biological effect to
the tissue are displayed. The displayed indices are the four forms. Of these, mechanical index,
MI shows the mechanical bioeffect in tissue, and thermal indices, TIs show the thermal
bioeffect in tissue provided three forms according to tissue models.
• Mechanical index: MI
Mechanical index (MI) provides an on-screen indication of the relative potential for
ultrasound to induce an adverse bioeffect by a non-thermal mechanism such as
cavitation.
The mechanical bioeffect is caused by the motion of tissue induced when ultrasound
pressure waves pass through or near a gaseous body. The majority of the mechanical
interactions relate to the generation, growth, vibration and possible collapse of
microbubbles within the tissue. This behavior is referred to as cavitation.
Because the thermal bioeffect is not so significant in the mode of B, B/M, and M
respectively, the mechanical index becomes important.
The mechanical index is displayed on all modes.
In other imaging modes, the thermal bioeffect is also important.
• Thermal index: TI
–
Soft tissue Thermal Index : TIS
The soft tissue thermal index provides information on temperature increase within soft
homogeneous tissue (heart, first trimester fetal and abdominal scans). TIS can be displayed
on all modes.
–
Bone Thermal index: TIB
The bone thermal index (TIB) provides information on temperature increase of bone at or
near the focus when the beam passes through soft tissue (second and third trimester fetal
and neonatal cephalic through the fontanels scans).
TIB can be displayed on all modes and at the time of transducer use. In addition, with scan
modes including B mode imaging, the value of TIB becomes equal to the value of TIS.
–
Cranial Bone Thermal index : TIC
The cranial bone thermal index (TIC) provides information on temperature increase of bone
at or near the surface, such as may occur during pediatric and adult cranial scan, in which
the ultrasound beam passes through bone near the beam entrance into the body.
TIC can be displayed on all modes.
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8 Acoustic Output Safety Information
8-1 Acoustic output index
The demarcation between safe levels and levels that the potential for biological effects exist is
important for the operators. The WFUMB (World Federation for Ultrasound in Medicine and
Biology) gives some guidelines.
For example, "Embryonic and fetal in situ temperature above 41 ℃ (4 ℃ above normal
temperature) for 5 min or more should be considered potentially hazardous.", etc.
On the other hand, the indices provide us an indication of the conditions which are more likely
than others to produce thermal and/or mechanical bioeffect in comparison with other physical
quantities such as the peak rarefactional acoustic pressure or its intensity.
For example, TI values above a certain upper level of the range (more than 1.0) might be better
to avoid in obstetric applications. Such a restriction allows a reasonable safety margin
considering the WFUMB recommendation that a temperature increase of 4 ℃ for 5 min or more
should be considered as potentially hazardous to embryonic and fetal tissue.
However if particular clinical results cannot be obtained with lower values, increased output
may be warranted, but particular attention to limit the exposure time should be made. Any extra
thermal load to the fetus when the mother has a fever is also unwise, and again note should be
made to avoid high TI values.
The following list shows an indication of importance of maintaining low values of MI/TI in
clinical use by IEC 60601-2-37.
Table: Relative importance of maintaining low exposure indices in various scanning
situations
Of greater importance
MI
• With contrast agents
• Cardiac scanning (lung exposure)
Of less importance
• In the absence of gas bodies:
i.e. in most tissue imaging
• Abdominal scanning (bowel gas)
TI
• First trimester scanning
• Fetal skull and spine
• In well-perfused tissue:
For example, Liver and spleen
• Patient with fever
• In Cardiac scanning
• In any poorly perfused tissue
• In vascular scanning
• If ribs or bones are exposed: TIB
CAUTION:
It has been thought that cavitation is hard to occur with the diagnostic ultrasound
because it contains as high as several MHz to several dozen MHz frequencies.
However, according to the animal experiments, it is reported that the tissues where originally air
bubbles exist such as lung and bowel are easy to receive the damage of petechia in low acoustic
pressure.
Also according to the animal experiments, ultrasonically induced lung damage in the fluid-filled
lungs of fetuses is not to be expected.
From these facts, it is requested to be careful for using contrast agent to inject air bubbles
intentionally.
8-2
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8 Acoustic Output Safety Information
8-2 Interaction between ultrasound and tissues
8-2
Interaction between ultrasound and tissues
When ultrasound propagates through human tissue, there is a potential for tissue damage.
During an exam, though ultrasound images are produced with "receiving" a part of the energy
of the transmitted ultrasound wave by the transducer, which energy is reflected from the
irradiated tissue, much of the ultrasound energy is absorbed by body tissue. Ultrasound
generated by the transducer is a physical pressure wave with typical frequencies range from 2
MHz (megahertz, or millions of cycles per second) to 10 MHz. In ultrasound irradiation, the
energy absorbed in the tissue may cause some biological effects.
These mechanisms are classified as mechanical action and thermal action, respectively.
Mechanical bioeffects are due to the pressure waves causing mechanical or physical movement
of the tissues and tissue components. These components such as cells, fluids, etc., oscillate. If
conditions are met, it is possible that these oscillations may affect the structure or function of
living tissues. At present, mechanical effects are thought to be instantaneous in nature, and
closely relate to the peak-rarefactional (peak-negative) acoustic pressure of the ultrasound
pulse.
An extreme example of the mechanical effects of ultrasound is shock - wave lithotripsy, where
focused ultrasound waves are used to break apart kidney stones.
The second type of bioeffect, the thermal bioeffect, is due to the tissues absorbing the energy of
the ultrasound beam. When an acoustic wave transmits through the body tissue, the energy of a
sound wave is attenuated. There are two main causes for attenuation: Absorption and scattering.
Absorption is the conversion of ultrasonic energy into heat; whereas, scattering is the
redirection of the ultrasound away from the direction it was originally traveling. Absorption of
acoustic energy by tissue results in the generation of heat in the tissue. This is what is referred
to as the thermal mechanism. Unlike mechanical bioeffect, thermal bioeffect is thought to be
temporal in nature, and relate to a tissue volume, perfusion rate, exposure time, and duty factor
(ratio of the duration of transmitting pulse to the pulse repetition period).
Among the physiological effects known to occur due to tissue heating are abnormalities in cell
physiology or the low rate of DNA synthesis and increased possibility for the retardation of
growth of systems such as the heart, brain and skeleton of the fetus.
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8 Acoustic Output Safety Information
8-2 Interaction between ultrasound and tissues
8-2-1
Possible Biological Effects
Mechanical bioeffect
Mechanical bioeffect is occurred by the oscillation of a pressure wave when ultrasound wave is
transmitted to the body system. This pressure wave acts on microscopic gas bubbles and other
"nucleation sites" in tissue.
These nucleation sites, although presently poorly understood, are believed to serve as starting
points for the development of gas bubbles. Because gas is much more compressible than fluid,
the microscopic gas bubbles can expand and contract greatly in comparison to the immediately
surrounding tissues and fluid. The large change in size may damage tissues.
Though mechanical bioeffect contain cavitation (ultrasonically activated behavior of micro
bubbles and other "nucleation sites" in tissue), acoustic radiation force and microstreaming, etc,
cavitation is thought to be most important.
There are two categories of cavitation: Non-inertial (once termed Steady-state) cavitation and
Inertial (once termed Transient) cavitation.
Non-inertial cavitation arises from the repeated expansion and contraction of the micro bubbles
in response to the varying pressures in ultrasound pulses. This oscillation can lead to a
phenomenon known as "micro streaming", where the oscillation of gas bubbles in tissue leads
to motion in the fluid around the gas bubbles. This phenomenon has shown that micro streaming
has the possibility of causing disruption of cell membranes.
During inertial cavitation, pre-existing bubbles or cavitation nuclei expand from the pressure of
the ultrasonic field and then collapse in a violent implosion. Although this phenomenon occurs
on the microscopic level, it has been demonstrated to produce extremely high temperatures and
pressures in the immediate vicinity, which can lead to cell death.
The potential for mechanical bioeffects is related to the peak negative (rarefactional) pressure
of the ultrasound wave and its frequency. Higher values of negative pressure (if amplitude wave
becomes large) increase the potential for mechanical bioeffect. Higher frequencies decrease the
potential for mechanical bioeffect.
At this time, there is no solid evidence that cavitation occurs in human tissue with the output
intensities available on current ultrasound diagnostic systems. However, mechanical effects are
theoretically possible.
8-4
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8 Acoustic Output Safety Information
8-2 Interaction between ultrasound and tissues
Thermal bioeffect
Thermal bioeffect occurs over longer periods of time, where absorption of the ultrasound energy
results is heating of tissues. Excessive heating can lead to disruptions in cellular processes and
structures, especially in developing fetal tissues. As stated above, the energy which is producing
image by receiving reflected energy from the body's internal tissues by the transducer is very
limited out of the total energy transmitted to the body system. The residual energy must be
absorbed by the tissues. With this absorption, heat is developed mainly in two areas such as at
the surface of the body where ultrasound beam enters and in the vicinity of the focus of the
beam.
Because of difference in their physical properties, different tissues absorb ultrasound energy at
different rates. Absorption coefficient is affected by the ultrasonic power (energy per unit of
time), the volume of tissues involved and its perfusion rate, or the amount of blood flow through
the target tissues. Bone tissue, with its higher density and lower perfusion rate than those of soft
tissues, absorbs more ultrasound energy.
Bone tissue at the surface will absorb the largest portion, and has the highest susceptibility to
heating from ultrasound exposure. Bone tissue not at the surface, but at the focus point of the
beam, will also absorb a higher portion of energy. Soft tissues absorb the least. Because tissue
absorbs ultrasound energy at different rates, a single model to describe all of the different
properties of different tissues is not available. Currently, there are three different models to
describe thermal bioeffects in tissue. The three models are
• Soft tissues
• Bone at focus and
• Bone at the surface.
The type of ultrasound beam also influences the potential for thermal bioeffect. In non-scanning
mode (example: D-mode), as the position and direction of an ultrasound beam converging
energy are fixed, the ultrasound energy of high-density occurs for a comparatively small tissue
volume. This tends to increase the thermal bioeffects in the tissue.
In addition, in B mode, as the position and direction of ultrasound beam are variable, the energy
of ultrasound is scattered in a comparatively large volume of tissues so that the perfusion rate
becomes high and the process of heat becomes not so significant.
At this time, there is no solid evidence that the temperature elevation with currently available
ultrasound diagnostic systems is harmful to the human body.
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8 Acoustic Output Safety Information
8-3 Derivation and Meaning of MI / TI
8-3
Derivation and Meaning of MI / TI
In 1992, AIUM (The American Institute of Ultrasound in Medicine) and NEMA (National
Electrical Manufacturers Association) published the voluntary standard "TI/MI output display
standard" (AIUM/NEMA: Standard for real-time display of thermal and mechanical acoustic
output indices on diagnostic ultrasound equipment). This standard has established the method
calculating and displaying indices relatively indicating the possibility of mechanical and
thermal bioeffect. IEC 60601-2-37 "Particular requirements for the basic safety and essential
performance of ultrasonic medical diagnostic and monitoring equipment" employs the same
indices. Therefore the user can control the acoustic output while confirming the indices are
real-time displayed on the majority of modern diagnostic ultrasound equipment.
These indices, the thermal index (TI) and the mechanical index (MI), provide unitless numbers
giving information on the likelihood of an adverse biological effect resulting from the current
ultrasound examination. The indices were designed so that if either index exceeded a predefined
value, there was a potential for harm. When the value of index exceeds 1.0, the user should
assess if the examination could be performed with a lower acoustic output, or consider
mitigating factors in reevaluating the risk-benefit analysis. Mitigating factors include the
absence of gas-containing structures, anatomical sites that would be particularly invulnerable to
damage and the perfusion rate in the region being examined. Also, the duration of the
examination should be kept to a minimum to avoid any unnecessary exposure. However there
is another risk that must be considered: the risk of not doing the ultrasound exam and either not
having the enough information necessary to diagnose. It is also important to recognize that the
potential harm from misdiagnosis can have greater consequences than that of
ultrasound-induced bioeffect.
8-6
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8 Acoustic Output Safety Information
8-3 Derivation and Meaning of MI / TI
8-3-1
Mechanical Index (MI)
Scientific evidence suggests that mechanical or nonthermal bioeffect, like cavitation, are a
threshold phenomenon, occurring only when a certain level of output is exceeded. However the
threshold level varies depending on the tissue. The potential for mechanical effects is thought
to increase as peak-rarefactional acoustic pressure increases, but to decrease as the ultrasound
frequency increases.
Therefore the mechanical index MI is defined as:
CMI = 1 MPa MHz-1/2
MI =
pr, α fawf-1/2
CMI
pr : attenuated peak-rarefactional acoustic pressure (MPa)
fawf: acoustic working frequency (MHz)
CMI is a standardization coefficient, and it is 1 [MPa MHz-1/2]. Therefore, MI is unitless.
The MI becomes important at a gas/soft tissue interface, for example in cardiac scanning where
the lung surface may be exposed. Most critically, however, is with the use of contrast materials
containing gas bubbles when most attention should be paid to limit MI.
As the ultrasound goes through the fluid such as amniotic fluid or bladder with very little
decrease, the sound pressure received by the tissues might be high even if the value of MI is low.
8-3-2
Thermal Index (TI)
TI is defined that the ratio of attenuated acoustic power at a specified point, Pα [mW] to the
attenuated acoustic power required to raise the temperature at that point in a specific tissue
model by 1 ℃ , Pdeg [mW].
TI =
Pα
Pdeg
Pα: attenuated output power
TI is unitless as well as MI.
There are three thermal indices are used for different combinations of soft tissue and bone in the
area to be examined, namely, TIS (soft tissue), TIB (bone) and TIC (cranial bone). The purpose
of the thermal indices is to keep users aware of conditions that may lead to a temperature rise
whether at the surface, within the tissues, or at the point where the ultrasound is focusing on
bone. Each thermal index estimates temperature rise under certain assumptions.
• For scanning mode, the position of the maximum heating is assumed to be at the surface
of the probe for all tissue models.
• For non-scanning mode, if bone is not present, the maximum heating is likely to occur
between the surface of the probe and the focus of the ultrasonic beam.
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8 Acoustic Output Safety Information
8-3 Derivation and Meaning of MI / TI
• For non-scanning mode, if bone is present and located near the focus of the ultrasonic
beam, the maximum heating is likely to occur at the surface of the bone. When doing
diagnoses of the fetus that are developing neural tissues, such as the brain and spinal
cord, that may be in a region of heated bone, it is recommended to display TIB and pay
attention to its value.
When you are undecided which TI should be displayed, it is preferable to refer the following
chart to decide where the bones are located in the region at which is irradiated by ultrasound.
Table: Thermal Index categories and models
Scanning mode
Non-scanning mode
TIS:
Soft tissue thermal index
Probe
Tissue surface
Probe
Soft tissue
Before a focus
TIB:
Bone thermal index
Tissue surface
Probe
Soft tissue
Soft tissue
Bone surface
Bone
TIC:
Cranial-bone thermal index
Probe
Probe
Bone
Bone surface
Bone
Bone surface
Soft tissue
8-8
Soft tissue
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8 Acoustic Output Safety Information
8-4 Setting condition influencing device output
8-4
Setting condition influencing device output
It is necessary to understand the setting condition of the ultrasonic diagnostic equipment
influencing MI/TI to use the indicated information of MI/TI more effectively. MI is calculated
using the peak rarefactional (negative) acoustic pressure. TI is proportional to the time averaged
value whereas MI is proportional to instantaneous value. The following table shows diagnosis
device control settings to influence MI/TI.
Some parameters such as the pulse repetition frequency are not displayed on a screen of the
device. Therefore it is recommended to read carefully the instruction manual (User’s Guide) in
use.
Table: Ultrasound Diagnostic System setting condition to influence MI/TI
*1
Settings condition to influence MI/TI in continuous wave doppler (CWD) are only drive
voltage and electric focus.
*2
Gain do not influence MI/TI for processing gain after receiving.
System Control Settings*1
COMMON Drive Voltage
B
M
PW
Mflow
MN1-5368 rev.10
Switch or function
MI
TI
―
Acoustic Power
Electric focus
Focus
Gain*2
Gain
―
Pulse repetition frequency
Depth/Range
―
PRF limit
―
Drive frequency
Image/Freq
Number of scanning lines
Framerate
―
Beam Process
―
ScanArea
―
Imaging mode (wave)
ExPHD, PHD
Pulse repetition frequency
Depth/Range
Drive frequency
Image/Freq
Imaging mode (wave)
ExPHD, PHD
Pulse repetition frequency
Velocity Range
―
High PRF
―
―
Drive frequency
Image/Freq
Pulse duration
IP Select
Imaging mode (wave)
TDI
Pulse repetition frequency
Velocity Range
―
High PRF
―
Drive frequency
Image/Freq
Pulse duration
IP Select
Imaging mode (wave)
TDI
―
―
8-9
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8 Acoustic Output Safety Information
8-5 Recommendation on ALARA principle
System Control Settings*1
Flow
8-5
Pulse repetition frequency
Switch or function
MI
Depth/Range
―
Velocity Range
―
Drive frequency
Image/Freq
Number of scanning lines
Framerate
―
Beam Process
―
Flow Area
―
Average (Flow)
―
Pulse duration
IP Select
―
Imaging mode (wave)
eFlow, Power, TDI
TI
Recommendation on ALARA principle
ALARA stands for "As Low As Reasonably Achievable". Following the ALARA principle
means that total acoustic output is kept as low as reasonably achievable, while diagnostic
information being optimized. This guiding philosophy is the same as in the use of X-ray
equipment.
For example, when the mechanical index (MI) is considered,
• Selection of appropriate probe
• Selection of drive frequency (higher frequency is lower in MI value)
• Selection of electronic focus
• Lower Drive voltage
• Adjust Gain (Higher Gain)
Keep in mind these points during examination. In addition, be more careful before using a
contrast agent.
When Thermal Index(TI) is considered,
• Selection of appropriate TI
• Appropriate image adjustment (raise the gain, etc.)
• Reduction of TI value (reduce transmission voltage, lowering pulse repetition frequency,
widen the scan width in the case of scan mode)
• Shorten exposure time
Keep in mind these points during examination.
8-10
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8 Acoustic Output Safety Information
8-6 Default Setting
8-6
Default Setting
In order to avoid unintentional high acoustic output, the acoustic output is limited by default
setting in the following cases (it becomes a low value):
• Power On
• Select the type of examination (Application) with the preset feature
• Switching the probe
• New Patient Function Operation (ID input)
Default setting (Low value) limits the acoustic output less than DVA% = 70%, Ispta, α < 94
mW/cm2, MI<1.0, or TI<3.0 whichever less.
8-7
Acoustic output limits
The values of spatial peak temporal average intensity (Ispta, α), mechanical index (MI) and
thermal indices (TIs) do not exceed 720 mW/cm2, 1.9 and 6 respectively for other than fetal
examination.
There are cases that the mechanical index (MI) and the thermal index (TI) are more than 1 by
the type of probe and the mode of image display. At that time, it displays the value in real time.
For fetal examination, the mechanical index (MI) and thermal indices (TIs) do not exceed 1.0
and 3.0 respectively.
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8 Acoustic Output Safety Information
8-8 Measurement uncertainties
8-8
Measurement uncertainties
8-8-1
Protocol for calculating the measurement uncertainties
The protocol for calculating the measurement uncertainties follows the methods used in NEMA
UD 2-2004.
The reporting of an acoustic output quantity requires the specification of the measurement mean
and a quantitative estimate of the uncertainty associated with the measurement. Uncertainty is
expressed in terms of confidence limits or tolerance limits. A 95% confidence limit defines a
range of values that will contain the true mean (or some other specified quantity) 95% of the
time. A 95% tolerance limit defines a range of values that will contain a specified percentage of
all values 95% of the time.
An important feature of this approach is the incorporation of the Type A and Type B
terminology in classifying the components of measurement uncertainty, as recommended by the
International Organization for Standardization (ISO, 1993), and adopted by the American
National Standards Institute (ANSI/NCSL, 1997). These new terms replace the previous terms:
"random uncertainty" and "systematic uncertainty". Type A and Type B uncertainties are
distinguished on the basis by which their numerical values are estimated.
Type A uncertainties are those that are evaluated by statistical treatment of repeated
measurements, and Type B are those that are evaluated by other means. An important reason
for the new classification is to provide an internationally accepted procedure for mathematically
combining individual components of uncertainty into a single total uncertainty regardless of
whether arising from random or systematic effects.
Basic to this approach is representing each component of uncertainty by an estimated standard
deviation, termed standard uncertainty. Its symbol is ui and is equal to the positive square root
of the estimated variance ui2 .
For a Type A uncertainty component, ui equals the statistically estimated standard deviation.
Statistical methods involve the analysis of multiple replications to estimate population
parameters, such as the mean and the standard deviation.
Type B evaluations are based on scientific judgment using all of the relevant information, which
may include:
1)
previous measurement data,
2)
experience with the relevant materials and instruments,
3)
manufacturer's specifications,
4)
data provided national standards laboratories,
5)
uncertainty data taken from handbooks.
It should be noted that Type A evaluations of uncertainty based on limited data are not
necessarily more reliable than soundly based Type B evaluations (Taylor and Kuyatt, 1994).
8-12
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8 Acoustic Output Safety Information
8-8 Measurement uncertainties
Type A Evaluated Uncertainty
A Type A standard uncertainty, uA, of a measured quantity is equal to the standard deviation of
the sample mean, which is commonly called the standard error. It is given by,
u A=
Sx
√n
(1)
where Sx is the sample standard deviation and n is the number of repetitions. As indicated in
equation(1), a Type A uncertainty is reduced by performing additional measurements. This
results from the increase in the size of the denominator. Ideally, the measurements should be
repeated a sufficient number of times to yield a reliable estimate of the standard error.
Type B Evaluated Uncertainty
A Type B evaluation of uncertainty is performed after all adjustments for correctable systematic
errors have been made. The statistical distributions of all remaining systematic errors are
combined to produce an overall statistical distribution. Unless there is information to the
contrary, the individual probability distributions are considered independent rectangular
distributions, each possessing a variance equal to ai2/3, where ai is the semi-range limit for the
ith uncertainty component. Because of the independence of the individual distributions, the
total variance equals the sum of the individual variances. Thus, for n rectangularly distributed
uncertainty components, the total variance, σ2, is given by
σ 2 = σ 12+ σ 22 + … + σ n2
(2)
and the Type B standard uncertainty, uB, is then
uB = √σ2 =
√
a12 + a22 + ... + an2
3
(3)
Combined Uncertainty
The combined or total uncertainty of a measured quantity includes both Type A and Type B
evaluated components of uncertainty. It is computed after all blunders have been removed from
the data base, and after all possible systematic corrections have been made. The combined
uncertainty, uC, of a measured quantity is given by
uC = √uA2 + uB2
(4)
The ISO (1993) advocates using the combined standard uncertainty as the parameter for
expressing quantitatively the uncertainty of the result of a measurement and in giving the results
MN1-5368 rev.10
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8 Acoustic Output Safety Information
8-8 Measurement uncertainties
for all international comparisons of measurements. Although uC can be universally used to
express the uncertainty of a measurement result, in many commercial, industrial, and regulatory
applications, and when health and safety are concerned, it is often desirable to provide a
measure of uncertainty that includes a larger proportion of the distribution of values that could
be reasonable attributed to the measurand. This is provided by multiplying the combined
standard uncertainty by a coverage factor k to yield the expanded uncertainty U. That is,
U = k • uC
(5)
The result of a measurement is then conveniently expressed as
x=x±U
(6)
The value of the coverage factor k is chosen based on the level of confidence required for any
given application. In general, k will be in the range of 2 to 3. NIST has adopted a policy of
setting k = 2, unless stated otherwise (Taylor and Kuyatt, 1994). In ultrasonic exposimetry, k is
usually set to the value of t.975, at the appropriate number of degrees of freedom, in order to
provide a 95% level of confidence about the expected value of the measurand. Whatever the
value of k chosen, it must be clearly stated in the final specification of the uncertainty.
8-8-2
Results of measurement uncertainties
Now we would like to offer the results of measurement uncertainties of our products. 4 units of
ALOKA SSD-4000 and 6 units of UST-9123 for 4 times repeated acoustic output
measurements (e.g. total power (P), pulse-intensity integral (Ipi), peak-rarefactional acoustic
pressure (pr), acoustic working frequency (fawf)). Though this product model may be different
from the model specified in this manual, we believe we can obtain the similar results from
different set of console and probes. The results were analyzed using a two-way crossed analysis
of variance with repeated measurements.
In this analysis it is assumed that the consoles and transducers are independent and that all
repeated measurements are independent. It is also assumed that all preliminary steps, such as
correcting for systematic errors, have been performed.
There are six transducers (p = 6), four consoles (q = 4) and four times (r = 4) repeated
measurements.
8-14
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8 Acoustic Output Safety Information
8-8 Measurement uncertainties
p : transducers
q : consoles
r : repetetions
COMPUTATIONAL SET UP FOR
transducers (i =1, 2,..., p)
consoles (j =1, 2,..., q)
1
2
...
q
1
m11, s11
m12, s12
...
m1q, s1q
m1 .
2
m21, s21
m22, s22
...
m2q, s2q
m2 .
..
.
..
.
..
.
..
.
..
.
p
mp1, sp1
mp2, sp2
...
mpq, spq
mp .
m. 1
m. 2
...
m. q
m
Si .
S. j
ijth cell mean
r
1
mij = r 3 xijk
k=1
(7)
ith transducer mean
q
1
mi• = q 3 mij
j=1
(8)
jth console mean
p
1
m•j = p 3 mij
i =1
(9)
overall mean
1
m = pq
p
q
33 mij
(10)
i =1 j =1
standard deviation of ijth cell
S ij =
r
x ijk - m ij) 2/ (r - 1)
√3
(11)
k =1
standard deviation of transducer
S i• =
p
m i - m) 2/ (p - 1)
√3 •
(12)
i =1
standard deviation of console
S •j =
q
- m ) 2/ (q - 1)
√ 3 m •j
(13)
ij=1
Using equation (8), (9) and (10), transducer mean, console mean and overall mean are calculated
respectively. The standard deviation calculated using equation (11) is expressed in percentage to overall
mean value.
The variability inherent in the measurement technique is quantified by Smeas, the square root of the
variance attributed solely to the measurement technique. That is,
MN1-5368 rev.10
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