1 Safety
6 Basic User Manual
1.3.1 Biological Safety
Diagnostic ultrasound is recognized as being safe, but the possibility of biological effects
exists when using it in high exposure levels and long exposure times. Thus ultrasound
should be used in a prudent manner to provide medical benefit to the patient.
1.3.2 ALARA
It is required to practice ALARA when using ultrasound energy. Practicing ALARA
ensures that the total energy level is controlled below a low enough level at which
bioeffects are not generated while diagnostic information is being accumulated. The total
energy is controlled by output intensity and total radiation time. The output intensity
necessary for examinations differs depending on the patient and the clinical case.
Not all examinations can be performed with an extremely low level of acoustic energy.
Controlling the acoustic level at an extremely low level leads to low-quality images or
insufficient Doppler signals, adversely affecting the reliability of the diagnosis. However,
increasing the acoustic power more than necessary does not always contribute to an
increase in quality of information required for diagnosis, rather increasing the risk of
generating bioeffects.
The operator must take responsibility for the safety of the patients and utilize the
ultrasound deliberately. Deliberate use of the ultrasound means that output power of the
ultrasound must be selected based on ALARA. Additional information regarding the
concept of ALARA and the possible bioeffects of Ultrasound is available in a document
from the AIUM (American Institute of Ultrasound Medicine) title “Medical Ultrasound
Safety”.
1.3.3 Mechanical and Thermal Indices
The display of the system consists of two parts: Thermal Index (TI) and Mechanical Index
(MI).
■ MI/TI Explanation
In October 1987, the American Institute of Ultrasound in Medicine (AIUM) ratified a
report prepared by its Bioeffects Committee (Bioeffects Considerations for the Safety
of Diagnostic Ultrasound, J Ultrasound Med.,Sept. 1988: Vol. 7, No. 9 Supplement),
sometimes referred to as the StoweReport, which reviewed available data on possible
effects of ultrasound exposure. Another report “Bioeffects and Safety of Diagnostic
Ultrasound” dated January28, 1993, provides more current information.
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Mechanical Index (MI)
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